JD Supply HVAC, Heating & Cooling Outlet - New York JD Supply HVAC, Heating & Cooling Outlet - New York
JD Supply HVAC, Heating & Cooling Outlet - New York JD Supply HVAC, Heating & Cooling Outlet - New York JD Supply HVAC, Heating & Cooling Outlet - New York JD Supply HVAC, Heating & Cooling Outlet - New York JD Supply HVAC, Heating & Cooling Outlet - New York JD Supply HVAC, Heating & Cooling Outlet - New York JD Supply HVAC, Heating & Cooling Outlet - New York
JD Supply HVAC, Heating & Cooling Outlet - New York
JD Supply HVAC, Heating & Cooling Outlet - New York
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HVAC / Heating / Cooling Systems Equipment Guide

Glossary Of Definitions For Heating Systems Equipment, Cooling Systems Equipment,  & HVAC Systems Equipment

1. Heating System Guide

  • Residential Heating Systems
  • Commercial Heating Systems

  • 2. Cooling System Guide
  • Residential Cooling Systems
  • Commercial Cooling Systems

  • 3. Heating & Cooling Guide
  • Residential Heating & Cooling
  • Commercial Heating & Cooling

  • 4. Hot Water Heater Guide
  • Storage Water Heaters
  • Tankless Water Heaters

  • 5. Thermostat Control Guide
  • DIY Thermostats
  • Professional Thermostats

  • 6. Humidity Control Guide
  • Humidifiers Guide
  • Dehumidifiers Guide

  • 7. Air Filters Guide
    8. Air Cleaners Guide
    9. HEPA Filters Guide
  • Medical HEPA Filters
  • Industrial HEPA Filters
  • Residential HEPA Filters
  • Cleanroom HEPA Filters
  • HEPA Filter Replacement

  • 10. Pumps & Valves Guide
  • Sump Pumps
  • Backup Sump Pumps
  • Effluent Pumps

  • HVAC / Heating / Cooling
    Discount Equipment And
    OEM Parts Catalog

    JD Supply Discount Heating & Cooling Equipment Outlet - New York

    Heating Equipment
    Equipment, OEM Parts & Supplies:

  • Boilers
  • Furnaces
  • Humidifiers
  • Water Heaters
  • Heat Pumps
  • Heat Exchangers
  • Cooling Equipment
    Equipment, OEM Parts & Supplies:

  • Air Conditioning Systems
  • Chillers
  • Cooling Towers
  • Air Filters & Air Cleaners
    OEM Parts & Supplies:

  • Residential Air Cleaners
  • Furnace Air Filters
  • HVAC Air Filters
  • Pumps & Valves
    Equipment, OEM Parts & Supplies:

  • Pumps
  • Valves

  • JD Supply - Discount HVAC Heating & Cooling Outlet - New York
    Glossary Of Terms & Definitions

    This Glossary Of Terms & Definitions Is Intended For Use In Context With HVAC, Heating & Cooling Systems. Other Definitions For These Terms May Also Be Relevant When Used In A Different Context.

    JD Supply - HVAC Heating & Cooling Term Definitions:

    0-9  A  B  C  D  E  F  G  H  I  J  K  L 
    M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z 

    0-9 - No terms


    Absolute Humidity Definition: - the weight of water vapor in a given amount of air. Measured in grains/ft3 (grains/ft3 x 2.28835191x10-6 = g/cm3).

    Absolute Pressure Definition: - generally taken as gauge pressure + atmospheric pressure, but more precisely the total pressure measured relative to absolute zero pressure (the pressure that would occur in a pure vacuum). Measured in lb/in2 (psi x0.689475729 = N/cm2).

    Absolute Temperature Definition: - the temperature measured on a scale with zero set at absolute zero, such as the Rankin (°R=°F+459.69) or Kelvin (°K=°C+273.15) absolute temperature scales.

    Absolute Zero Definition: - the lowest possible temperature, where all molecular activity theoretically ceases. -456.69°F or -273.15°C.

    Accumulator Definition: - (steam) a pressure vessel containing water and/or steam, which is used to store the heat of steam for use at a later time, at some lower pressure.

    Acid Cleaning Definition: - the process of cleaning the interior surfaces of steam generating units by filling the unit with dilute acid accompanied by an inhibitor to prevent corrosion, and subsequently draining, washing and neutralizing the acid by a further wash of alkaline water.

    Acidity Definition: - represents the amount of free carbon dioxide, mineral acids, and salts (especially sulphates of iron and aluminum) which hydrolyze to give hydrogen ions in water. Reported as milliequivalents per liter of acid, or ppm acidity as calcium carbonate, or PH (the measure of hydrogen ion concentration).

    Adiabatic Flame Temperature Definition: - the theoretical temperature that would be attained by the products of combustion provided the entire chemical energy of the fuel, the sensible heat content of the fuel and combustion above the datum temperature were transferred to the products of combustion. This assumes: no heat loss to surroundings and no dissociation.

    AGA Definition: - American Gas Association - this organization has been replaced by CSA who purchased rights to the AGA name and standards.

    Air Definition: - the mixture of oxygen, nitrogen, and other gases, which with varying amounts of water vapor, forms the atmosphere of the earth.

    Air Atomizing Oil Burner Definition: - a burner for firing oil in which the oil is atomized by compressed air, which is forced into and through one or more streams of oil which results in the breaking of the oil into a fine spray.

    Air Conditioning Definition: - the process of controlling the temperature, humidity, cleanliness and distribution of the air.

    Air Deficiency Definition: - insufficient air, in an air-fuel mixture, to supply the oxygen required for complete oxidation of the fuel.

    Air-Free Definition: - the descriptive characteristic of a substance from which air has been removed.

    Air-Fuel Ratio Definition: - the ratio of the weight, or volume, of air to fuel.

    Air Infiltration Definition: - the leakage of air into a setting or duct.

    Air Saturated Definition: - air, which contains the maximum amount of water vapor that it can hold at its temperature and pressure.

    Air Standard Conditions Definition: - conditions at which Btu ratings for summer air conditioning equipment is rated. 95°F dry bulb, 75°F wet bulb at the condenser inlet and 80°F dry bulb, 67°F -wet bulb at the evaporator inlet.

    Air Vent Definition: - a valve opening in the top of the highest drum of a boiler or pressure vessel for venting air. Alkalinity - represents the amount of carbonates, bicarbonates, hydroxides and silicates or phosphates in the water and is reported as grains per gallon, or ppm as calcium carbonate.

    Ambient Definition: - refers to the temperature surrounding a body or unit under test.

    Ambient Air Definition: - the air that surrounds the equipment. The standard ambient air for performance calculations is air at 80°F, 60% relative humidity, and a barometric pressure of 29.921 in. Hg, giving a specific humidity of 0.013 lb of water vapor per lb of dry air.

    Ambient Temperature Definition: - the temperature of the air surrounding the equipment.

    Ammonia Definition: - NH3 commonly found as a gas, terms like liquid ammonia and anhydrous ammonia are also in common use. In systems where ammonia is as a refrigerant (r717), brass or bronze valves should not be used. Carbon steel valves are more commonly used in ammonia refrigeration systems.

    Analysis Definition: - quantitative determination of the constituent parts.

    Analysis Ultimate Definition: - chemical analysis of solid, liquid or gaseous fuels. In the case of coal or coke, determination of carbon, hydrogen, sulfur, nitrogen, oxygen, and ash.

    ANSI Definition: - American National Standards Institute, publishes the rules for design of piping system components.

    API Definition: - American Petroleum Institute sets standards for products used in the petroleum and refining industry, as well as serving as the information and public relations arm of the industry.

    Aquastat Definition: - water limit temperature control, a safety device often used on boilers.

    Arrester Definition: - a device to impede the flow of large dust particles or sparks from a stack, usually screening at the top.

    As-Fired Fuel Definition: - fuel in the condition as fed to the fuel burning equipment.

    Ash Definition: - the incombustible inorganic matter in the fuel.

    Ash-Free Basis Definition: - the method of reporting fuel analysis, whereby ash is deducted and other constituents are recalculated to total 100%.

    Ash Pit Definition: - a pit or hopper located below a furnace where refuse is accumulated and from which refuse is removed at intervals.

    ASME Definition: - American Society of Mechanical Engineers.

    Aspirating Burner Definition: - a burner in which the fuel in a gaseous or finely divided form is burned in suspension, the air for combustion being supplied by bringing into contact with the fuel, air drawn through one or more openings by the lower static pressure created by the velocity of the fuel stream.

    As-Received Fuel Definition: - fuel in the condition as received at the plant.

    ASSE Definition: - American Society of Sanitary Engineering

    ASTM Definition: - American Society for Testing and Materials is concerned with specifying materials and test procedures for the materials that are used in valves.

    Atmospheric Air Definition: - air under the prevailing atmospheric conditions.

    Atmospheric Pressure Definition: - the weight of a 1 square inch column of the earth’s atmosphere. At sea level this pressure is 14.696 pounds per square inch.

    Atmospheric Vacuum Breaker (AVB) Definition: - a backflow prevention device used in plumbing to prevent backflow of non-potable liquids into the potable (drinking water) system. It is usually constructed of brass and resembles a 90-degree elbow with a hood on its top to allow air to enter the water system if a siphon attempts to form. Inside this elbow is a poppet valve that is held "up" by the water pressure found in the system, closing the air entrance to the device. If the pressure in the "upstream side" is reduced to atmospheric pressure or below, the poppet valve drops and allows air to enter the system, breaking the siphon.

    Atomizer Definition: - a device by means of which a liquid is reduced to a very fine spray.

    Auto-Drain (Valve) Definition: - More appropriately, this valve option should be called "automatic-venting". For JD Supply’s apollo ball valve, auto drain availability is limited to bronze valves only. The valve is intended to vent the down stream pressure on a closed valve equipped with this option. It should be used only on either water or compressed non-hazardous gases, such as air or nitrogen. Valves with this option have limited service temperature and pressure ranges of +50F to +250F and 0psig to 125psig. These valves are subject to damage from dirt and debris in the piping system making them prone to leaks.

    Available Draft Definition: - the draft, which may be utilized to cause the flow of air for combustion or the flow of products of combustion.

    Availability Factor Definition: - the fraction of time during which the unit is in operable condition.

    Axial Fan Definition: - consists of a propeller or disc type of wheel within a cylinder that discharges air parallel to the axis of the wheel.


    Backflow Prevention Device Definition: - a device, a valve, used to protect water supplies from contamination. Many types of backflow devices also have ports so that they can be tested or examined to ensure that they are functioning properly. A check valve is a common form of backflow preventer. Backflow prevention protects the potable water system from minor, moderate, and severe hazards. There are over 10,000 reported cases of backflow contamination each year. Some cases can be fatal. Backflow devices are required by law where needed and must be installed in accordance with plumbing code. A backflow assembly has test cocks and shut-off valves and must be tested each year, if relocated or repaired, and when installed.

    Baffle Definition: - a plate or wall for deflecting gases or liquids.

    Baffle Tile Definition: - a tile for deflecting gases.

    Baffle-Type Collector Definition: - a device in gas paths utilizing baffles so arranged as to deflect dust particles out of the gas stream.

    Ball Valve Definition: - the ball valve is similar in concept to the plug valve but uses a rotating ball with a hole through it that allows straight-through flow in the open position and shuts off flow when the ball is rotated 90 degrees to block the flow passage. It is used for on-off and some throttling services.

    Barometric Pressure Definition: - atmospheric pressure as determined by a barometer usually expressed in inches of mercury.

    Base Load Definition: - base load is the term applied to that portion of a station or boiler load that is practically constant for long periods.

    Beaded Tube End Definition: - the rounded exposed end of a rolled tube when the tube metal is formed over against the sheet in which the tube is rolled.

    Bimetallic Strip Definition: - two metal strips with different rates of expansion fastened together. When heated or cooled the strip will warp, and can be made to open or close a switch or valve.

    Black Liquor Definition: - highly alkaline black to dark brown liquid. Thick like molasses. Contains the dreggs of the pulp making process including lime, dirt, gravel, etc. Typically very high solids content and very hot.

    Bleach Definition: - see sodium hypochlorite. Household bleach has a typical concentration of less than 20%.

    Blind Nipple Definition: - a nipple, or a short piece of pipe or tube, closed at one end.

    Blowdown Definition: - boiler water that is removed from the boiler in order to maintain the desired concentration levels of suspended and dissolved solids in the boiler and removal of sludge.

    Blowdown Safety Valve Definition: - the difference between the pressure at which a safety valve opens and at which it closes.

    Blowdown Valve Definition: - a valve generally used to continuously regulate concentration of solids in the boiler, not a drain valve. (often called continuous blowdown.)

    Blow-Off Valve Definition: - a specially designed, manually operated, valve that connects to the boiler for the purpose of reducing the concentration of solids in the boiler or for draining purposes. (often called bottom blowdown.)

    Blower Definition: - a fan used to force air under pressure.

    Boiler Definition: - a closed vessel in which water is heated, steam is generated, steam is superheated, or any combination thereof, under pressure or vacuum by the application of heat from combustible fuels, electricity or nuclear energy.

    Boiler Efficiency Definition: - the term boiler efficiency is often substituted for combustion or thermal efficiency. True boiler efficiency is the measure of fuel-to-steam efficiency.

    Boiler and Pressure Vessel Code Definition: - a series of standards produced and distributed by the American society of mechanical engineers (asme), which defines requirements associated with pressure containing systems.

    Boiler Horsepower Definition: - the evaporation of 34-1/2 lbs of water per hour from a temperature of 212°F into dry saturated steam at the same temperature. Equivalent to 33,475 btu/hr.

    Boiling Point Definition: - the temperature at which the addition of any heat will begin a change of state from a liquid to a vapor.

    Boiler Rating Definition: - the heating capacity of a boiler expressed in boiler horsepower, btu/hour, or pounds of steam/hour.

    Boiler Shell Definition: - the outer cylindrical portion of a pressure vessel.

    Boiler Water Definition: - a term construed to mean a representative sample of the circulating boiler water, after the generated steam has been separated and before the incoming feed water or added chemical becomes mixed with it so that its composition is affected.

    Boiling Definition: - the conversion of a liquid into vapor with the formation of bubbles.

    Boiling Out Definition: - the boiling of highly alkaline water in boiler pressure parts for the removal of oils, greases, etc.

    Bonnet Definition: - a bonnet basically acts as a cover on the valve body. It is commonly semi-permanently screwed into the valve body. During manufacture of the valve, the internal parts were put into the body and then the bonnet was attached to hold everything together inside. To access internal parts of a valve, a user would take off the bonnet, usually for maintenance. Many valves do not have bonnets; for example, plug valves usually do not have bonnets.

    Booster Fan Definition: - a device for increasing the pressure or flow of a gas.

    Breeching Definition: - a duct that transports the products of combustion between parts of a steam generating unit or to the stack.

    Bridgewall Definition: - a wall in a furnace over which the products of combustion pass.

    British Thermal Unit (BTU) Definition: - the mean British thermal unit is 1/180 of the heat required to raise the temperature of 1 lb of water from 32 °f to 212 °f at a constant atmospheric pressure. A btu is essentially 252 calories.

    Buckstay Definition: - a structural member placed against a furnace or boiler wall to restrain the motion of the wall.

    Bunker Coil Definition: - residual fuel oil of high viscosity commonly used in marine and stationary steam power plants. (No. 6 fuel oil)

    Burner Definition: - a device for the introduction of fuel and air into a furnace at the desired velocities, turbulence and concentration.

    Burner Windbox Definition: - a plenum chamber around a burner that maintains an air pressure sufficient for proper distribution and discharge of secondary air.

    Burner Windbox Pressure Definition: - the air pressure maintained in the windbox or plenum chamber measured above atmospheric pressure.

    Butterfly Valve Definition: - the butterfly valve controls flow by using a circular disc or vane with its pivot axis at right angles to the direction of flow in the pipe. A butterfly valve requires a minimum of space and can be used both for on off and throttling services.

    By-Pass Definition: - a passage for a fluid, permitting a portion of the fluid to flow around its normal pass flow channel.


    CaCO3 Definition: - Calcium Carbonate (Limestone).

    Calorie Definition: - the mean calorie is 1/100 of the heat required to raise the temperature of 1 gram of water from zero c to 100°C at a constant atmospheric pressure. It is about equal to the quantity of heat required to raise one gram of water 1°C. Another definition is: a calorie is 3600/860 joules.

    Calorimeter Definition: - apparatus for determining the calorific value of a fuel.

    Capacity Factor Definition: - the ratio of the average load carried to the maximum design capacity.

    Capillary Tube Definition: - a refrigerant control consisting of a small diameter tube which controls flow by restriction. They are carefully sized by inside diameter and length for each particular application.

    Carbon Definition: - element. The principal combustible constituent of all fuels.

    Carryover Definition: - the chemical solids and liquid entrained with the steam from a boiler.

    Casing Definition: - a covering of sheets of metal or other material such as fire resistant composition board used to enclose all or a portion of a steam generating unit.

    Caustic Definition: - caustic is an entire family of chemicals characterized by the hydroxyl radical. The family includes such common products as calcium hydroxide, potassium hydroxide (potash) and sodium hydroxide (caustic soda). Glass reinforced PTFE should not be used with these chemicals.

    Centigrade (Celsius) Definition: - a temperature scale with the freezing point of water 0oC and the boiling point 100oC at sea level.

    Central Station Definition: - a power plant or steam heating plant that generates power or steam.

    Centrifugal Fan Definition: - consists of a fan rotor or wheel within a housing that discharges air at a right angle to the axis of the wheel.

    CGA Definition: - Canadian Gas Association. This organization has been replaced by CSA who purchased rights to the CGA name and standards.

    Check Valve Definition: - a mechanical device, a valve, that normally allows fluid (liquid or gas) to flow through it in only one direction. Check valves are two-port valves, meaning they have two openings in the body, one for fluid to enter and the other for fluid to leave. There are various types of check valves used in a wide variety of applications. Check valves are often part of common household items. Although they are available in a wide range of sizes and costs, many check valves are very small, simple, and/or cheap. Check valves work automatically and most are not controlled by a person or any external control; accordingly, most do not have any valve handle or stem. The bodies (external shells) of most check valves are made of plastic or metal.

    Chemical Analysis Definition: - determination of the principal chemical constituents.

    Chemical Feed Pipe Definition: - a pipe inside a boiler drum through which chemicals for treating the boiler water are introduced.

    Chimney Definition: - a brick, metal or concrete stack.

    Circulation Definition: - the movement of water and steam within a steam-generating unit.

    Circulation Ratio Definition: - the ratio of water entering a circuit to the steam generated by that passes that circuit in a unit of time.

    Circulator Definition: - a pipe or tube to pass steam or water between upper boiler drums usually located where the heat absorption is low. Also used to apply to tubes connecting headers of horizontal water tube boilers with drums.

    Class IV Leakage Definition: - Class IV leakage rates are based on tests conducted with water or air at pressures up to 60 psig. Hard seated ball valves, such as those with metal to metal, peek or graphite are commonly promoted as having at least a class iv rating. Allowable leakage is expressed as 0.01% of the valves rated flow capacity. For ball valves, we assume this "capacity" to be equal to the valve’s cv. For a 1" full port valve that allowable leakage rate would be 0.68 gallons per minute or 2574 ml per minute.

    Class V Leakage Definition: - Class V leakage rates are based on tests conducted with water at any agreed pressure up to the valve’s maximum rating. Hard seated ball valves, such as those with metal to metal, peek or graphite seats may achieve a class v rating with special preparation, but most commonly are promoted as having a class iv rating. Assuming a 1" full port valve closed against 100 psig of water pressure, the allowable leakage rate under this classification would be 0.05 ml/minute.

    Class VI Leakage Definition: - Class VI leakage rates are based on tests conducted with air or nitrogen at no more than 50 psig. Any new "soft seated" ball valve should achieve a class vi rating. Assuming a 1" full port valve closed against 50 psig of air pressure, the allowable leakage rate under this classification would be 0.15 ml/minute.

    Cleanout Door Definition: - a door placed so that accumulated refuse may be removed room a boiler setting.

    CMTR Definition: - Certified Material Test Report documents the compliance of a material to specific published standards by the original material producer. All MTR’s issued by JS Supply for our castings are in fact cmtr’s. An mtr for bar stock or forged material issued on the original manufacturer’s letterhead is a CMTR’s. Should those results be reproduced and distributed on JS Supply letterhead they would be referred to as MTR’s.

    CO Definition: - Carbon Monoxide.

    CO2 Definition: - Carbon Dioxide is a colorless, odorless gas. A common product of combustion.

    Collector Definition: - a device used for removing gas borne solids from flue gas.

    Colloid Definition: - a finely divided organic substance which tends to inhibit the formation of dense scale and results in the deposition of sludge, or causes it to remain in suspension, so that it may be blown from the boiler.

    Combustible Loss Definition: - the loss representing the unliberated thermal energy occasioned by failure to oxidize completely some of the combustible matter in the fuel.

    Combustibles Definition: - the heat-producing constituents of a fuel.

    Combustion Definition: - the rapid chemical combination of oxygen with the combustible elements of a fuel resulting in the release of heat.

    Combustion Air Definition: - air used in the combustion process. Air contains oxygen, which is required to combust fuel.

    Combustion Efficiency - the effectiveness of the burner to completely burn the fuel. A well-designed burner will operate with as little as 10 to 20% excess air, while converting all combustibles in the fuel to useful energy.

    Complete Combustion Definition: - the complete oxidation of all the combustible constituents of a fuel.

    Compression Definition: - the reduction of volume of a vapor or gas by mechanical means.

    Compression Ratio Definition: - the ratio determined by dividing the discharge pressure, in psi, by the suction pressure in psi.

    Compressor Definition: - a mechanical device used to compress gases. Three main types are: reciprocating, centrifugal and rotary.

    Concentration Definition: - (1) the weight of solids contained in a unit weight of boiler or feed water. (2) The number of times that the dissolved solids have increased from the original amount in the feedwater to that in the boiler water due to evaporation in generating steam.

    Condensate Definition: - condensed water resulting from the removal of latent heat from steam.

    Condensing Medium Definition: - the substance, usually air or water, to which the heat in a condenser is transferred.

    Condensation Point Definition: - the temperature at which the removal of any heat will begin a change of state from a vapor to a liquid.

    Condensing Unit Definition: - the portion of a refrigeration system where the compression and condensation of refrigerant is accomplished. Sometimes referred to as the ’high side’.

    Conduction (Heat) Definition: - the transfer of energy, in the form of heat (thermal vibrations), from molecule to molecule within a substance.

    Conductivity (Thermal) Definition: - (1) a material property relating heat flux (heat transferred per unit area per unit time) to a temperature difference. In American units, it is typically defined as the amount of heat (btu) transmitted in one hour through one square foot of material 1 inch thick, with a temperature difference of 1°f between the two surfaces of the material. (2) The property of a water sample to transmit electric current under a set of standard conditions. Usually expressed as microhms conductance.

    Contactor Definition: - an electromagnetic actuated relay. Usually used to refer to the relay, which closes the circuit to a compressor.

    Continuous Blowdown Definition: - the uninterrupted removal of concentrated boiler water from a boiler to control total solids concentration in the remaining water.

    Control Definition: - any manual or automatic device for the regulation of a machine to keep it at normal operation. If automatic, the device is motivated by variations in temperature, pressure, water level, time, light, or other influences.

    Control Valves Definition: - valves used within industrial plants and elsewhere to control operating conditions such as temperature, pressure, flow, and liquid level by fully or partially opening or closing in response to signals received from controllers that compare a "set point" to a "process variable" whose value is provided by sensors that monitor changes in such conditions. The opening or closing of control valves is done by means of electric, hydraulic or pneumatic systems.

    CSA Definition: - Canadian Standards Association. Replaced the former AGA and CGA organizations.

    Convection Definition: - the transfer of heat by a moving fluid.

    Cooling Anticipator Definition: - a resistance heater (usually not adjustable) in parallel with the cooling circuit. It is ’on’ when the current is ’off", adding heat to shorten the off cycle.

    Cooling Efficiency Definition: - is measured as an Energy Efficiency Ratio (EER). The higher the EER, the more efficient the system. EER is dependent on many factors, and that high-efficiency equipment comes with a higher price tag - but the energy savings can pay back in the difference in just a few years.

    COP Definition: - Coefficient of Performance, the ratio of work performed or accomplished as compared to the energy used.

    Corrosion Definition: - the wasting away of metal due to chemical action. In a boiler, usually caused by the presence of O2, CO2, or an acid.

    Crankcase Heater Definition: - electric heating element that is used to heat the compressor crankcase to prevent migrating refrigerant from condensing and diluting the crankcase oil during the off-cycle.

    Crown Sheet Definition: - in a firebox boiler, the plate forming the top of the furnace.

    Crude Oil Definition: - unrefined petroleum.

    Cubic Feet Per Minute Definition: - a common means of assigning quantitative values to volumes of air in transit, usually abbreviated cfm.

    Cycle Definition: - the complete course of operation of a refrigerant back to a selected starting point in a system. Also used to describe alternating current through 360 space degrees.


    Damper Definition: - a device for introducing a variable pressure drop in a system used for regulating the volumetric flow of a gas, such as air.

    Davit Definition: - the structure on large firetube boilers from which the front and rear doors are suspended when opened.

    Deaeration Definition: - removal of air and gases from boiler feed water prior to its introduction to a boiler.

    Degasification Definition: - removal of gases from samples of steam taken for purity test. Removal of CO2 from water as in the ion exchange method of softening.

    Delayed Combustion Definition: - a continuation of combustion beyond the furnace.

    Density Definition: - mass or weight per unit of volume. For example, standard air = .075 pounds per cubic foot.

    Design Load Definition: - the load for which a steam-generating unit is designed, considered the maximum load to be carried.

    Design Pressure Definition: - the pressure used in the design of a boiler for the purpose of calculating the minimum permissible thickness or physical characteristics of the different parts of the boiler.

    Design Steam Temperature Definition: - the temperature of steam for which a boiler is designed.

    Dew Point Definition: - the temperature at which condensation starts.

    Diaphragm Valve Definition: - the diaphragm valve effects closure by means of a flexible diaphragm attached to a compressor. When the compressor is lowered by the valve stem onto a weir, the diaphragm seals and cuts off flow. The diaphragm valve handles corrosive, erosive and dirty services. It is an easily maintained valve.

    Dielectric Union Definition: - dielectric unions are required in some applications by code. In particular on water heaters, in the transition from black pipe to copper. The basis for their use is to prevent galvanic corrosion of the black iron pipe. Whether or not they are technically necessary depends largely on water chemistry. In applications with dissolved electrolytes their use would be beneficial.

    Discharge Line Definition: - a tube used to convey the compressed refrigerant vapor from the compressor to the condenser inlet.

    Discharge Pressure Definition: - the pressure read at the compressor outlet. Also called head pressure or high side pressure.

    Disengaging Surface Definition: - the surface of the boiler water from which steam is released.

    Dissociation Definition: - the pro Definition:cess by which a chemical compound breaks down into simpler constituents, as do co2 and h2o at high temperature.

    Dissolved Solid Definition: - those solids in water, which are in solution.

    Distillate Fuels Definition: - liquid fuels distilled usually from crude petroleum.

    Distillation Definition: - vaporization of a substance with subsequent recovery of the vapor by condensation. Often used in less precise sense to refer to vaporization of volatile constituents of a fuel without subsequent condensation.

    Distilled Water Definition: - water produced by vaporization and condensation with a resulting higher purity.

    Double Check Valve or Double Check Valve Assembly (DCVA) Definition: - a backflow prevention device designed to protect water supplies from contamination. It consists of two check valves assembled in series usually with a ball or gate valve installed at each end for isolation and testing. Often, test cocks (very small ball valves) are in place to attach test equipment for evaluating whether the double check assembly is still functional. The double check valve assembly is suitable for prevention of back pressure and back siphonage, but is not suitable for high hazard applications. It is commonly used on lawn irrigation and fire sprinkler systems.

    Downcomer Definition: - a tube or pipe in a boiler or waterwall circulating system through which fluid flows downward.

    Drain Definition: - a valved connection at the lowest point for the removal of all water from the pressure parts.

    Draft Definition: - the difference between atmospheric pressure and some lower pressure existing in the furnace stack or gas passages of a steam-generating unit.

    Draft Differential Definition: - the difference in static pressure between two points in a system.

    Draft Gauge Definition: - a device for measuring draft, usually in inches of water.

    Dry Air Definition: - air, which contains no moisture vapor.

    Dryback Boiler Definition: - firetube boiler with a refractory lined back door. Door opens to allow maintenance and/or inspection.

    Dry Bulb Temperature Definition: - temperature read with an ordinary thermometer.

    Dry Gas Definition: - gas containing no water vapor.

    Dry-Gas Loss Definition: - the loss representing the difference between the heat content of the dry exhaust gases and their heat content at the temperature of ambient air.

    Dry Steam Definition: - steam containing no moisture. Commercially dry steam containing not more than one half of one percent moisture.

    Duct Definition: - a passage for air or gas flow.


    Economizer Definition: - utilizes waste heat by transferring heat from flue gases to warm incoming feedwater.

    EDR Definition: - Equivalent Direct Radiation is the rate of heat transfer from a radiator or convector. It is equivalent to the square feet of surface area necessary to transfer heat at the same rate at which it is produced by a generator. A single boiler horsepower equals 140-ft2 EDR.

    Efficiency Definition: - the ratio of output to input. See also combustion, fuel-to-steam and thermal efficiency.

    Effective Temperature Definition: - an arbitrary concept, which combines into a single value the effect of temperature, humidity, and air movement as, sensed by the human body.

    Ejector Definition: - a device, which utilizes the kinetic energy in a jet of water or other fluid to remove a fluid or fluent material from tanks or hoppers.

    Electric Boiler Definition: - a boiler in which electric energy is used as the source of heat.

    Electrostatic Precipitator Definition: - a device for collecting dust, mist or fume from a gas stream, by placing an electrical charge on the particle and removing that particle onto a collecting electrode.

    Energy Efficiency Ratio Definition: - EER is a measure of how efficiently a cooling system will operate when the outdoor temperature is at a specific level (95°F). In technical terms, EER is the steady-state rate of heat energy removal (i.e. cooling capacity) by the product measured in Btuh divided by the steady-state rate of energy input to the product measured in watts. This ratio is expressed in Btuh/watt. The higher the EER, the more efficient the air conditioner

    Enthalpy Definition: - total amount of heat in one pound of a substance calculated from accepted temperature base, expressed in btu’s per pound mass.

    Entrainment Definition: - the conveying of particles of water or solids from the boiler water by the steam.

    Equalizer Definition: - connections between parts of a boiler to equalize pressures.

    Equivalent Evaporation Definition: - evaporation expressed in pounds of water evaporated from a temperature of 212°F to dry saturated steam at 212°F.

    Equivalent Length Definition: - that length of straight tubing which has the same pressure drop as the fitting, valve or accessory (of the same nominal size) being considered.

    Evaporation Definition: - the change of state from a liquid to a vapor.

    Evaporation Rate Definition: - the number of pounds of water that is evaporated in a unit of time.

    Evaporative Cooling Definition: - the cooling effect of vaporization of a liquid in a moving air stream.

    Evaporator Definition: - a device in which a liquid refrigerant is vaporized. Some superheating usually takes place.

    Evaporator Superheat Definition: - the actual temperature of the refrigerant vapor at the evaporator exit as compared to the saturated vapor temperature indicated by the suction pressure.

    Excess Air Definition: - air supplied for combustion in excess of that theoretically required for complete oxidation.

    Expansion Joint Definition: - the joint to permit movement due to expansion without undue stress.

    Explosion Door Definition: - a door in a furnace or boiler setting that is designed to be opened by a pre-determined gas pressure.

    External Static Pressure Definition: - the sum of the static and velocity pressures of a moving air system at the point of measurement.

    External Treatment Definition: - treatment of boiler feed water prior to its introduction into the boiler.


    Fahrenheit Definition: - a temperature scale with the freezing point of water 32oF and the boiling point 212oF at sea level.

    Fan Definition: - a machine consisting of a rotor and housing for moving air or gases at relatively low pressure differentials.

    Fan Performance Definition: - a measure of fan operation in terms of volume, total pressures, static pressures, speed, power input, mechanical and static efficiency, at a stated air density.

    Fan Performance Curves Definition: - the graphical presentation of total pressure, static pressure, power input, mechanical and static efficiency as ordinates and the range of volumes as abscissa, all at constant speed and air density.

    Feed Pump Definition: - a pump that supplies water to a boiler.

    Feedwater Definition: - water introduced into a boiler during operation. It includes make-up and return condensate.

    Feedwater Treatment Definition: - the treatment of boiler feed water by the addition of chemicals to prevent the formation of scale or to eliminate other objectionable characteristics.

    Feet Per Minute Definition: - a term assigned to a velocity of a moving air stream, usually express fpm.

    FGR Definition: - Flue Gas Recirculation or the recirculation of flue gas with combustion air to reduce nox emissions.

    Filter Definition: - porous material through which fluids or fluid - and solid mixtures are passed to separate matter held in suspension.

    Filter-Drier Definition: - a device that removes moisture, acid and foreign matter from the refrigerant.

    Fin v - a fin is an extended surface, a solid, experiencing energy transfer by conduction within its boundaries, as well as energy transfer with its surroundings by convection and/or radiation, used to enhance heat transfer by increasing surface area.

    Fin Tube Definition: - a tube with one or more fins.

    Fire Safe Definition: - See fire tested. By itself the term has no agreed meaning. Should be accompanied by reference to a specific standard.

    Fire Tested Definition: - the term should be used with reference to a specific standard. Several series of apollo ball valves are available as fire tested to API 607, 4th edition. This is always an optional feature.

    Fired Pressure Vessel Definition: - a vessel containing a fluid under pressure exposed to heat from the combustion of fuel.

    Firetube Definition: - a type of boiler design in which combustion gases flow inside the tubes and water flows outside the tubes.

    Firing Rate Control Definition: - a pressure temperature or flow controller, which controls the firing rate of a burner according to the deviation from pressure or temperature set point. The system may be arranged to operate the burner on-off, high-low or in proportion to load demand.

    Fixed Carbon Definition: - the carbonaceous residue less the ash remaining in the test container after the volatile matter has been driven off in making the proximate analysis of a solid fuel.

    Flame Definition: - a luminous body of burning gas or vapor.

    Flame Detector Definition: - a device which indicates if a fuel (liquid, gaseous, or pulverized) is burning, or if ignition has been lost. The indication may be transmitted to a signal or to a control system.

    Flame Propagation Rate Definition: - speed of travel of ignition through a combustible mixture.

    Flame Safeguard Definition: - a control that sequences the burner through several stages of operation to provide proper air purge, ignition, normal operation, and shutdown for safe operation.

    Flammability Definition: - susceptibility to combustion.

    Flashing Definition: - the process of producing steam by discharging water into a region of pressure lower than the saturation pressure that corresponds to the water temperature

    Flash Gas Definition: - instantaneous evaporation of some liquid refrigerant at the metering device due to pressure drop, which cools the remaining liquid refrigerant to, desired evaporation temperature.

    Flash Point Definition: - the lowest temperature at which, under specified conditions, fuel oil gives off enough vapor to flash into a momentary flame when ignited.

    Flue Definition: - a passage for products of combustion.

    Flue Gas Definition: - the gaseous product of combustion in the flue to the stack.

    Floating Ball Definition: - JS Supply manufactures only "floating ball" ball valves. The term "floating ball" comes from the feature that the ball is suspended in the assembly by the valve seats. There are no other supporting structures, like trunnions. The ball literally "floats" between the valve seats. Floating ball valves are intended to seal on the down stream seat.

    Foaming Definition: - the continuous formation of bubbles which have sufficiently high surface tension to remain as bubbles beyond the disengaging surface.

    Forced Circulation Definition: - the circulation of water in a boiler by mechanical means external to the boiler.

    Forced-Draft Fan Definition: - a fan supplying air under pressure to the fuel burning equipment.

    Fouling Definition: - the accumulation of refuse in gas passages or on heat absorbing surfaces which results in undesirable restriction to the flow of gas or heat.

    Free Ash Definition: - ash which is not included in the fixed ash.

    Freezing Point Definition: - the temperature at which the removal of any heat will begin a change of state from a liquid to a solid.

    Freon Definition: - the word Freon® is a registered trademark of Dupont. A family of refrigerants characterized by their fluorine content. Commonly referred to as R12, R22, R134a, etc. There are now "Freons" that are blends of the basic gases.

    Fuel Definition: - a substance containing one or more combustible components, used for generating heat.

    Fuel-Air Mixture Definition: - mixture of fuel and air.

    Fuel-Air Ratio Definition: - the ratio of the weight, or volume, of fuel to air.

    Fuel Gas Definition: - any one of many hydrocarbon based gases used for fuel. These include refined or purified grades like methane, propane and butane, but may be mixtures like lp or natural gas.

    Fuel Oil Definition: - a liquid fuel derived from petroleum or coal.

    Fuel-To-Steam Efficiency Definition: - the ratio of heat added to boiler feedwater to produce the output steam to the amount of energy inputted with fuel.

    Furnace Definition: - an enclosed space provided for the combustion of fuel.

    Furnace Pressure Definition: - pressure occurring inside the combustion chamber; positive if greater than atmospheric, negative if less than atmospheric, and neutral if equal to atmospheric.

    Furnace Volume Definition: - the cubic contents of the furnace or combustion chamber.

    Fusible Plug Definition: - a hollowed threaded plug having the hollowed portion filled with a low melting point material.


    Gas Analysis Definition: - the determination of the constituents of a gaseous mixture.

    Gas Burner Definition: - a burner that uses gas or fuel.

    Gas Pressure Regulator Definition: - a spring loaded, dead weighted or pressure balanced device, which will maintain the gas pressure to the burner supply line.

    Gate Valve Definition: - the gate valve is a general service valve used primarily for on off, non-throttling service. The valve is closed by a flat face, vertical disc or gate that slides down through the valve to block the flow.

    Gauge Cock Definition: - a valve attached to a water column or drum for checking water level.

    Gauge Glass Definition: - the transparent part of a water gauge assembly connected directly or through a water column to the boiler, below and above the water line, to indicate the water level in a boiler.

    Gauge Pressure Definition: - pressure measured with atmospheric pressure as a base.

    Globe Valve Definition: - the globe valve effects closure by a plug with a flat or convex bottom lowered onto a matching horizontal seat located in the center of the valve. Raising the plug opens the valve to let flow through. The globe valve is used for on-off service and handles clean service throttling applications.

    Grade Definition: - oil classification according to quality, generally based on astm specifications.

    Grains Per Cu-Ft Definition: - the term for expressing dust loading in weight per unit of gas volume (7000 grains equals one pound).

    Grains (water) Definition: - a unit of measure commonly used in water analysis for the measurement of impurities in water (17.1 grains = 1 part per million - ppm).

    Gravity Definition: - weight index of fuels: liquid, petroleum products expressed either as specific, Baume or API (American Petroleum Institute) gravity; weight index of gaseous fuels as specific gravity related to air under specified conditions; or weight index of solid fuels as specific gravity related to water under specified conditions.

    Green Liquor Definition: - An alkaline liquid, greenish in color containing a significant amount of solids, particularly lime or calcium carbonate and is generally hot.

    Grounding Definition: - grounding implies a requirement for electrical continuity between the various components of a valve. JS Supply offers two types of grounding; option codes -02 and -60.


    Handhole Definition: - an access opening in a pressure part usually not exceeding 6inches in its longest dimension.

    Handhole Cover Definition: - a handhole closure.

    Hardness Definition: - a measure of the amount of calcium and magnesium salts in water. Usually expressed as grains per gallon or ppm as caco3.

    Hard Seat Definition: - applicable to more than just ball valve seats, this general term is used to describe devices with rigid sealing elements, such as "metal to metal", peek, carbon graphite or ceramic.

    Hard Water Definition: - water, which contains calcium or magnesium in an amount, which require an excessive amount of soap to form a lather.

    Heat Definition: - a form of energy causing the agitation of molecules within a substance.

    Heat Available Definition: - the thermal energy above a fixed datum that is capable of being absorbed for useful work.

    Heat Balance Definition: - an accounting of the distribution of the heat input, output and losses.

    Heat Exchanger Definition: - a device for the transfer of heat energy from the source to the conveying medium.

    Heat Flow Definition: - heat flows from a warmer to a cooler substance. The rate depends upon the temperature difference, the area exposed and the type of material.

    Heat Pump Definition: - an air conditioner that contains a valve that allows it to alternate between heating and cooling.

    Heat Transfer Definition: - the three methods of heat transfer are conduction, convection and radiation.

    Heat of Compression Definition: - the heat added to a vapor by the work done on it during compression.

    Heat Of The Liquid Definition: - the increase in total heat (enthalpy) per pound of a saturated liquid as its temperature is increased above a chosen base temperature. (Usually - 400°F for refrigerants). It is expressed in btu’s.

    Heat Release Rate Definition: - rate that describes the heat available per square foot of heat-absorbing surface in the furnace or per cubic foot of volume.

    Heating Efficiency Definition: - is expressed as a Coefficient of Performance (COP). The higher the COP, the more efficient the system. For example, a residential-sized geothermal system might have a COP of 3.4 or higher, meaning for every one unit of energy used to power the system, more than three units are put back into the home as heat. This compares to efficiencies of 0.92 for a high-efficiency natural gas furnace. COP is dependent on many factors, and that high-efficiency equipment comes with a higher price tag - but the energy savings can pay back in the difference in just a few years.

    Heating Surface Definition: - those surfaces, which are exposed to products of combustion on one side and water on the other. This surface is measured on the side receiving the heat.

    Heating Value Definition: - the quantity of heat released by a fuel through complete combustion. It is commonly expressed in btu per lb, per gallon, or cu-ft.

    High Gas Pressure Control Definition: - a control to stop the burner if the gas pressure is too high.

    High Oil Temperature Control Definition: - a control to stop the burner if the oil temperature is too high.

    HSPF Definition: - the Heating Seasonal Performance Factor is a measure of the heating efficiency of a heat pump. The higher the HSPF number, the more efficiently the heat pump heats your home.

    Hydrocarbon Definition: - a chemical compound of hydrogen and carbon.

    Hydrostatic Test Definition: - a strength and tightness test of a closed pressure vessel by water pressure.

    Hydronics Definition: - the name for the use of water as the heat-transfer medium in heating and cooling systems.

    Hypo Definition: - slang term for sodium hypochlorite.


    Ignition Definition: - the initiation of combustion.

    Ignition Temperature Definition: - lowest temperature of a fuel at which combustion becomes self-sustaining.

    Illuminants Definition: - light oil or coal compounds that readily burn with a luminous flame, such as ethylene, propylene and benzene.

    Inches Of Mercury Definition: - atmospheric pressure are equal to 29.92 inches of mercury.

    Incomplete Combustion Definition: - the partial oxidation of the combustible constituents of a fuel.

    Induced Draft Fan Definition: - IDF ia a fan exhausting hot gases from the heat absorbing equipment.

    Inert Gaseous Constituents Definition: - incombustible gases such as nitrogen which may be present in a fuel.

    Inhibitor Definition: - a substance, which selectively retards a chemical action. An example in boiler work is the use of an inhibitor, when using acid to remove scale, to prevent the acid from attacking the boiler metal.

    Injector Definition: - a device utilizing a steam jet to entrain and deliver feed water into a boiler.

    Insulation Definition: - a material of low thermal conductivity used to reduce heat losses.

    Integral Blower Definition: - a blower built as an integral part of a device to supply air thereto.

    Integral-Blower Burner Definition: - a burner of which the blower is an integral part.

    Interlock Definition: - a device to prove the physical state of a required condition, and to furnish that proof to the primary safety control circuit.

    Intermittent Blowdown Definition: - the blowing down of boiler water at intervals.

    Internal Treatment Definition: - the treatment of boiler water by introducing chemicals directly into the boiler.

    Ion Definition: - a charged atom or radical, which may be positive or negative.


    J - No terms


    K - No terms


    Lagging Definition: - a light gauge steel covering used over a boiler, usually combined with insulation, to provide a low temperature outer surface.

    Latent Heat Definition: - heat that produces a change of state without a change in temperature; i.e., ice to water at 32°F or water to steam at 212°F.

    Latent Heat Of Condensation Definition: - the amount of heat energy in btu’s that must be removed to change the state of one pound of a vapor to one pound of liquid at the same temperature.

    Latent Heat Of Fusion Definition: - the amount of heat energy, in btu’s required to change the state of one pound of a liquid to one pound of solid at the same temperature.

    Latent Heat Of Melting Definition: - the amount of heat energy, in btu’s, that must be removed to change the state of one pound of solid to one pound of vapor at the same temperature.

    Latent Heat Of Vaporization Definition: - the amount of heat energy in btu’s required to change the state of one pound of a liquid to one pound of vapor at the same temperature.

    Leakage Classification Definition: - There are 6 leakage classes defined in ANSI/FCI 70-2, "control valve seat leakage". Although this standard was written for control valves, it is commonly mis-applied to ball valves. Control valves, as defined by this standard, have actuators that can adjust the loads on the valve seats to effect shut-off. Ball valves are on-off devices not intended for control or throttling applications and seat tightness cannot be effected by the actuation device. Because each classification is based on a different test method direct comparison is difficult, but suffice it to say the Class VI is the most stringent of the requirements. See each rating, Class IV, Class V or Class VI for more details.

    Lift Definition: - to elevate a fluid from one level to a higher level.

    Lime Definition: - Also known as calcium carbonate. A white powder which may be in lump form. Commonly used in the processing of pulp in the paper making process.

    Limit control Definition: - a switching device that completes or breaks an electrical circuit at predetermined pressures or temperatures. Also known as an interlock. See interlock.

    Lining Definition: - the material used on the furnace side of a furnace wall. It is usually of high-grade refractory tile or brick or plastic refractory material.

    Liquid line Definition: - a tube used to convey the liquid refrigerant from the condenser outlet to the refrigerant control device of the evaporator.

    Liquor Definition: - A family of terms commonly used in the pulp and paper industry. Includes black liquor, green liquor and white liquor. See each term individually for further explanation.

    Load Definition: - the rate of output required; also the weight carried.

    Load Factor Definition: - the ratio of the average load in a given period to the maximum load carried during that period.

    Low Gas Pressure Control Definition: - a control to stop the burner if gas pressure is too low.

    Low Oil Temperature Control Definition: - (cold oil switch) a control to prevent burner operation if the temperature of the oil is too low.

    Low Water Cutoff Definition: - safety device that shuts off the boiler/burner in the event of low water, preventing pressure vessel failure.

    LP Gas Definition: - LP gas is a fuel gas formed by the mixture of liquefied petroleum gases, commonly propane and butane. LP gas is produced and frequently stored at reduced temperatures. Depending where a valve is installed in an lp gas system option -14 "vented ball" may be required. This is particularly important on valves which can undergo significant temperature changes. Some LP gas applications will require UL or CSA listed valves of which JD Supply offers several.

    Lug Definition: - any projection, like an ear, used for supporting or grasping.


    Make-up Definition: - the water added to boiler feed to compensate for that lost through exhaust, blowdown, leakage, etc.

    Manhole Definition: - the opening in a pressure vessel of sufficient size to permit a man to enter.

    Manifold Definition: - a pipe or header for collection of a fluid from, or the distribution of a fluid to a number of pipes or tubes.

    Manometer Definition: - a tube filled with a liquid used to measure pressures.

    Manual Gas Shutoff Valve Definition: - a manually operated valve in a gas line for the purpose of completely turning on or shutting off the gas supply.

    Manufactured Gas Definition: - fuel gas manufactured from coal, oil, etc., as differentiated from natural gas.

    Maximum Allowable Working Pressure Definition: - the maximum gauge pressure permissible in a completed boiler. The mawp of the completed boiler shall be less than or equal to the lowest design pressure determined for any of its parts. This pressure is based upon either proof tests or calculations for every pressure part of the boiler using nominal thickness exclusive of allowances for corrosion and thickness required for loadings other than pressure. It is the basis for the pressure setting of the pressure relieving devices protecting the boiler.

    Maximum Continuous Load Definition: - the maximum load which can be maintained for a specified period.

    Maximum Instantaneous Demand Definition: - the sudden load demand on a boiler beyond which an unbalanced condition may be established in the boilers internal flow pattern and/or surface release conditions

    Maximum Working Pressure Definition: - The highest pressure that can be produced in the patient circuit when the ventilator is functioning properly

    MBH Definition: - one MBH is equivalent to 1,000 btu’s per hour.

    Mean Temperature Differences Definition: - the mean of difference between the temperature of a fluid receiving and a fluid yielding heat.

    Mechanical Atomizing Oil Burner Definition: - a burner, which uses the pressure of the oil for atomization.

    Mechanical Draft Definition: - the negative pressure created by mechanical means.

    Melting Point Definition: - the temperature at which the addition of any heat will begin a change of state from a solid to a liquid.

    Mercury Manometer Definition: - used to measure vacuum in inches of mercury.

    MHKZ Definition: - The basic standard used to investigate products in this category is UL842, "valves for flammable fluids". Manually operated valves are intended specifically for use with gas- or oil burning equipment. Metering valves are primarily for use in the burner fuel supply line to manually regulate the flow of fuel to the burner. Shut-off valves are for use in the burner supply line to manually shut off the flow of fuel to the burner.

    Micron Definition: - a unit used to measure high vacuums. One micron equals 1/25,400 of one-inch mercury.

    Miniature Boiler Definition: - fire pressure vessels which do not exceed the following limits: 16 in. Inside diameter of shell; 42 in., overall length to outside of heads at center; 20 sq ft water heating surface; or 100-psi maximum allowable working pressure.

    Moisture Definition: - water in the liquid or vapor phase.

    Moisture In Steam Definition: - particles of water carried in steam, expressed as the percentage by weight.

    Moisture Loss Definition: - the boiler flue gas loss representing the difference in the heat content of the moisture in the exit gases and that at the temperature of the ambient air.

    MSDS Sheet Definition: - Material Safety Data Sheet is a document used to communicate hazards associated with a substance. JS Supply’s products meet the requirements under the definition of an "article" and are considered exempt from the hazard communication standard 29 cfr 1910.1200. Osha defines an "article" as a manufactured item: (1) which is formed to a specific shape or design during manufacture (2) which has end use function(s) dependent in whole or in part upon its shape or design during end use; and (3) which does not release, or otherwise result in exposure to, a hazardous chemical under normal conditions of use.

    MTR Definition: - Material Test Report documents the compliance of a material to specific published standards. All mtr’s issued by JS Supply for our castings are in fact cmtr’s. Mtr’s issued for bar stock or forged material on the original manufacturer’s letterhead are cmtr’s. Should those results be reproduced and distributed on JS Supply letterhead they would be referred to as mtr’s.

    Muffler Definition: - device installed in hot gas line to silence discharge surges.

    Multifuel Burner Definition: - a burner by means of which more than one fuel can be burned.

    Multiport Burner Definition: - a burner having a number of nozzles from which fuel and air are discharged.


    NACE Definition: - "National Association of Corrosion Engineers" writes standards and recommended practices in regard to the use of materials and the condition of those materials for oil field and other applications.

    Natural Circulation Definition: - the circulation of water in a boiler caused by differences in density.

    Natural Gas Definition: - Natural gas is a fuel gas formed from refined naturally occurring hydrocarbon gases, primarily methane. Depending where a valve is installed in a gas system option -14 "vented ball" may be required. This is particularly important on valves which can undergo significant temperature changes. Some natural gas applications will require ul or csa listed valves of which conbraco offers several.

    Needle Valve Definition: - The needle valve is a volume control valve that restricts flow in small lines. The fluid going through the valve turns 90 degrees and passes through an orifice that is the seat for a rod with a cone-shaped tip. The size of the orifice is changed by positioning the cone in relation to the seat.

    Net Positive Suction Heat (NPSH) Definition: - the liquid pressure that exists at the suction end of a pump. If the npsh is insufficient, the pump can cavitate.

    Nozzle Definition: - a short flanged or welded neck connection on a drum or shell for the outlet or inlet of fluids; also a projecting spout through which a fluid flows.

    NXT Definition: - This is Dupontís trade name for their "super-ptfe". JD Supply offers a similar material.


    Oil Burner Definition: - a burner for firing oil.

    Oil Heating And Pumping Set Definition: - a group of apparatus consisting of a heater for raising the temperature of the oil to produce the desired viscosity, and a pump for delivering the oil at the desired pressure.

    Oil Separator Definition: - a device for separating out oil entrained in the discharge gas from the compressor and returning it to the crankcase.

    Operating Control Definition: - a control to start and stop the burner - must be in addition to the high limit control.

    Operating Pressure Definition: - the pressure at which a boiler is operated.

    Organic Matter Definition: - compounds containing carbon often derived from living organisms.

    Orifice Definition: - (1) the opening from the whirling chamber of a mechanical atomizer or the mixing chamber of a steam atomizer through which the liquid fuel is discharged. (2) A calibrated opening in a plate, inserted in a gas stream for measure velocity of flow.

    Original Equipment Manufacturer (OEM) Definition: - a term that refers to a situation in which one company purchases a manufactured product from another company and resells the product as its own, usually as a part of a larger product it sells. Oem is the company that originally manufactured the product. The term oem was coined in the 1950s by ibm. It designated a customer that purchased ibm computers and resold them as part of a larger product. The first oems sold oil refineries.

    Orsat Definition: - a gas-analysis apparatus in which certain gaseous constituents are measured by absorption in separate chemical solution.

    Overpressure Definition: - minimum-operating pressure of a hot water boiler sufficient to prevent the water from steaming.

    Oxidation Definition: - chemical combination with oxygen.

    Oxidizing Atmosphere Definition: - an atmosphere which tends to promote the oxidation of immersed materials.

    Oxygen Attack Definition: - corrosion or pitting in a boiler caused by oxygen.


    Packaged Boiler Definition: - a boiler supplied with all of its components - burner, controls and auxiliary equipment, designed as a single engineered package, and ready for on-site installation.

    Packaged Steam Generator Definition: - see packaged boiler.

    Partial Pressure Definition: - the pressure exerted by any individual gas in a mixture.

    Particle Size Definition: - a measure of dust size, expressed in microns or percent passing through a standard mesh screen. Pass - a confined passageway, containing heating surface, through which a fluid flows in essentially one direction.

    Perfect Combustion Definition: - the complete oxidation of all the combustible constituents of a fuel, utilizing all the oxygen supplied.

    Peroxide (Valves) Definition: - Peroxide is a strongly oxidizing liquid (examples: Hydrogen Peroxide H2O2, Sodium Peroxide Na2O2). Valves intended for peroxide service must be properly cleaned and vented (option code -57 is appropriate for most Apollo ball valves, but for the top entry ball valve this is option -hh). Carbon steel valves are not generally acceptable in this application. Avoid multi-fill seats and seals, including packing (specify option -35 trim if at all possible).

    Petroleum Definition: - naturally occurring mineral oil consisting predominately of hydrocarbons

    PFA Definition: - PerFluoroAlkoxy. This seat and seal material offers many of the same properties as PTFE, but has the added advantage of being resistant to a phenomena known as "popcorning". PFA is suggested for services containing styrene, butadiene and latex, which all have inflict popcorning on ordinary PTFE based materials.

    PH Definition: - the hydrogen ion concentration of a liquid to denote acidity or alkalinity. A PH of 7 is neutral. A PH above 7 denotes alkalinity while one below 7 denotes acidity. This PH number is the negative exponent of 10 representing Hydrogen ion concentration in grams per liter. For instance a PH of 7 represents 10-7 grams per liter.

    Pilot Definition: - A flame, which is utilized to ignite the fuel at the main burner or burners.

    Pinch Valve Definition: - The pinch valve finds wide application on slurries or liquids with large amounts of suspended solids. It seals by means of one or more flexible elements, such as a rubber tube, that can be pinched to shut off flow.

    Pitch Definition: - the slope of a pipeline for the purpose of improving drainage.

    Pitot Tube Definition: - an instrument which will register total pressure and static pressure in a gas stream, used to determine its velocity.

    Pitting Definition: - a concentrated attack by oxygen or other corrosive chemicals in a boiler, producing a localized depression in the metal surface.

    Plug Valve Definition: - The plug valve is used primarily for on-off service and some throttling services. It controls flow by means of a cylindrical or tapered plug with a hole in the center that lines up with the flow path of the valve to permit flow. A quarter turn in either direction blocks the flow path. Used on wine casks.

    Poppet Valve Definition: - A valve consisting of a hole, usually round or oval, and a tapered plug, usually a disk shape on the end of a shaft also called a valve stem. The shaft guides the plug portion by sliding through a valve guide. In most applications a pressure differential helps to seal the valve and in some applications also open it.

    Port Definition: - an opening through which fluid passes.

    Post Purge Definition: - a method of scavenging the furnace and boiler passes to remove all combustible gases after flame failure controls have sensed pilot and main burner shutdown and safety shut-off valves are closed.

    PPM Definition: - abbreviation for Parts Per Million. Used in chemical determinations as one part per million parts by weight.

    Precharged Lines Definition: - refrigerant line’s which are filled with refrigerant and are sealed at both ends. The seals are broken when the lines are installed and the line charge becomes part of the total system charge.

    Precipitate Definition: - to separate materials from a solution by the formation of insoluble matter by chemical reaction. The material which is removed.

    Precipitation Definition: - the removal of solid or liquid particles from a fluid.

    Preheated Air Definition: - air at a temperature exceeding that of the ambient air.

    Pressure Definition: - force per unit of area.

    Pressure Drop Definition: - the decrease in pressure due to friction of a fluid or vapor as it passes through a tube or duct or/and lift.

    Pressure Equipment Directive Definition: - a legal document defining common requirements for valves and other devices intended for use within member states of the european union.

    Pressure Temperature Relationship Definition: - the change effected in temperature when pressure is changed or vice versa. Only used at saturated conditions. An increase in pressure results in a temperature increase. A decrease in temperature results in a pressure decrease.

    Pressure Vessel Definition: - a closed vessel or container designed to confine a fluid at a pressure above atmospheric.

    Primary Air Definition: - air introduced with the fuel at the burner.

    Primary Loop Definition: - A loop in a Hydronic Heating System that is connected to a boiler or other heat source and is isolated from the secondary loop, which feeds the radiant panels or other heat output locations. The idea of using a primary loop is to be able to control the flow and temperature of this loop and offer protection to a boiler.

    Priming Definition: - the discharge of steam containing excessive quantities of water in suspension from a boiler, due to violent ebullition.

    Process Steam Definition: - steam used for industrial purposes other than for producing power.

    Products Of Combustion Definition: - the gases, vapors, and solids resulting form the combustion of fuel.

    PTA Definition: - Purified Terrathalic Acid. Generally found in a powdered form. Used as a filler and reinforcing material in plastics and other materials.

    PTFE Definition: - Polytetrafluorethylene. Also know as Teflon® a registered trademark of dupont. The is the polymer used to produce option -35 seats and seals. It is the base polymer for the other reinforced grades offered by conbraco as options -01(glass reinforced ptfe) and -56/64/65 (multi-fill ptfe).

    Psychrometer Definition: - a devices having both a dry and wet bulb thermometer. It is used to determine the relative humidity in a conditioned space. Most have an indexed scale to allow direct conversion from the temperature readings to the percentage of relative humidity.

    Psychrometric Chart Definition: - a chart on which can be found the properties of air under varying conditions of temperature, water vapor content, volume, etc.

    Pulsation Definition: - rapid fluctuations in pressure.

    Pumpdown Definition: - process of pumping refrigerant out of the evaporator and suction line at the end of the on- cycle by closing a solenoid valve in the liquid line and letting the compressor shut-off by the low pressure control.

    Purge Definition: - to introduce air into the furnace and the boiler flue passages in such volume and manner as to completely replace the air or gas-air mixture contained therein.


    Quick Connect Definition: - name given to the end connections on precharged lines which screw on to mated fittings of the outdoor and indoor sections. Tightening the quick connections ruptures the seals on the fittings and the line charge becomes part of the total system charge.


    Radiation Definition: - the transfer of heat without an intervening medium. It is absorbed on contact with a solid surface.

    Rated Capacity Definition: - the manufacturers stated capacity rating for mechanical equipment; for instance, the maximum continuous capacity in pounds of steam per hour for which a boiler is designed.

    Rate Of Blowdown Definition: - a rate normally expressed as a percentage of the water fed.

    Raw Water Definition: - water supplied to the plant before any treatment.

    Reaction Definition: - a chemical transformation or change brought about by the interaction of two substances.

    Reassociation Definition: - the recombination of the products of dissociation.

    Receiver Definition: - a vessel for holding refrigerant liquefied by the condenser.

    Recirculation Definition: - the reintroduction of part of the flowing fluid to repeat the cycle of circulation.

    Recovery Capacity Definition: - the amount of water in gallons per hour raised 100 degrees F at a given thermal efficiency and BTU per hour input.

    Reduced Pressure (RP) Backflow Prevention Device Definition: - A device used to protect the potable water supply from contaminated water. An rp valve consists of an automatic pressure relief valve in between two check valves. The pressure relief valve opens to the atmosphere in the event of a reduction in the pressure between the two check valves. The assembly is considered to provide redundant means of protection, through the use of the check valves, which keep water flowing only in one direction, and the relief valve in the event that one or both check valves fail. Reduced pressure backflow preventers can be abbreviated rp rpp and rpz. Rp assemblies protect against back-siphonage and backpressure, and may be used where a potential hazard exists. Rp valves can be found in commercial buildings, hospitals, and industrial applications.

    Reducing Atmosphere Definition: - an atmosphere which tends to: 1) promote the removal of oxygen from a chemical compound; 2) promote the reduction of immersed materials.

    Reduction Definition: - removal of oxygen from a chemical compound.

    Refractory Definition: - brickwork or castable used in boilers to protect metal surfaces and for boiler baffles.

    Refrigerant Definition: - A group of hydrocarbon gases with particularly advantageous thermodynamic properties. Among these are freon (an entire family of materials in itself) and ammonia. In systems where ammonia is the refrigerant, brass or bronze valves should be used with caution. Carbon steel valves are more commonly used in ammonia refrigeration systems.

    Refrigerant Control Definition: - a device used to meter the amount of refrigerant to an evaporator. It also serves as a dividing point between the high and low-pressure sides of the system.

    Refrigerant Distributor Definition: - a device which meters equal quantities of refrigerant to independent circuits in the evaporator coil.

    Refrigerant Migration Definition: - the movement of refrigerant through the system to the compressor crankcase during the off-cycle, caused by its attraction to oil.

    Refrigerant Operating Charge Definition: - the total amount of refrigerant required by a system for correct operation.

    Refrigerant Velocity Definition: - the rate at which refrigerant is moving at a given point in a system, usually given in feet per minute (fpm).

    Refrigeration Definition: - the transfer of heat from a place where it is not wanted to a place where its presence is not desirable.

    Refrigeration Effect Definition: - the amount of heat a given quantity of refrigerant will absorb in changing from a liquid to a vapor at a given evaporating pressure.

    Relative Humidity Definition: - the percentage of water vapor present in a given quantity air compared to the amount it can hold at its temperature.

    Relay Definition: - a device used to open and close an electrical circuit. The relay may be actuated by a bimetal electrically heated strip, a rod wrapped with a fine resistance wire causing expansion when energized, a bellows actuated by expansion of a fluid or gas or an electromagnetic coil.

    Relief Valve (safety relief valve) Definition: - an automatic pressure relieving device actuated by the pressure upstream of the valve and characterized by opening pop action with further increase in lift with an increase in pressure over popping pressure.

    Residual Fuels Definition: - products remaining from crude petroleum by removal of some of the water and an appreciable percentage of the more volatile hydrocarbons.

    Resin Definition: - a bead-like material used in chemical exchange for softeners and dealkalizers.

    Resistance Definition: - impediment to gas flow, such as pressure drop or draft loss through a dust collector. Usually measured in inches water column (iwc).

    Return Flow Oil Burner Definition: - a mechanical atomizing oil burner in which part of the oil supplied to the atomizer is withdrawn and returned to storage or to the oil line supplying the atomizer.

    Reversing Valve Definition: - a device in a heat pump that is electrically controlled to reverse the flow of refrigerant as the system is switched from cooling to heating; also called a four-way valve.

    Ringelmann Chart Definition: - a series of four rectangular grids of black lines of varying widths printed on a white background, and used as a criterion of blackness for determining smoke density in stack gas streams.

    Riser Definition: - a vertical tube or pipe, which carries refrigerant in any form from a lower to a higher level.

    Rotary Oil Burner Definition: - a burner in which atomization is accomplished by feeding oil to the inside of a rapidly rotating cup.


    Saddle Definition: - a casting, fabricated chair, or member used for the purpose of support.

    Safety Relief Valve (SRV) Definition: - a valve mechanism for the automatic release of a gas from a boiler, pressure vessel, or other system when the pressure or temperature exceeds preset limits. They are often called by more specific names such as pressure relief valve, t&p valves, or temperature and pressure relief valves.

    Safety Shut-Off Valve Definition: - a manually opened, electrically latched, electrically operated safety shut-off valve designed to automatically shut off fuel when de-energized.

    Sampling Definition: - the removal of a portion of a material for examination or analysis.

    Saturated Air Definition: - air which contains the maximum amount of water vapor that it can hold at its temperature and pressure.

    Saturated Steam Definition: - steam at the temperature and pressure at which evaporation occurs.

    Saturated Temperature Definition: - the temperature at which evaporation occurs at a particular pressure.

    Saturated Vapor Definition: - vapor in contact with a liquid.

    Saturated Water Definition: - water at its boiling point.

    Saturation Definition: - a condition of stable equilibrium of a vapor and a liquid. Sensible heat that can be measured or felt. Sensible heat always causes a temperature rise.

    Scale Definition: - a hard coating or layer of materials on surfaces of boiler pressure parts.

    Secondary Air Definition: - air for combustion supplied to the furnace to supplement the primary air.

    Secondary Loop Definition: - a loop in a Hydronic Heating System that is seperated from the heat source, so that the system is not a direct heat system. This allows a specific flow rate and temperature to be set for the secondary loop. The secondary loop has the heat output sources, such as Radiant panels, running off of them.

    Secondary Treatment Definition: - treatment of boiler feed water or internal treatment of boiler-water after primary treatment.

    Sediment Definition: - (1) matter in water which can be removed from suspension by gravity or mechanical means. (2) A non-combustible solid matter which settles out at bottom of a liquid; a small percentage is present in residual fuel oils. Segregation - the tendency of refuse of varying compositions to deposit selectively in difference parts of the unit.

    SEER Definition: - Seasonal Energy Efficiency Ratio is most commonly used to measure the efficiency of a central air conditioner. It measures how efficiently a cooling system will operate over an entire season. The higher the SEER, the more efficient the air conditioner. Technically speaking, SEER is the ratio of the cooling output in Btu divided by the power consumption in watts per hour.

    Self-Relieving Seats Definition: - defined by api 6d as seats that automatically reduce the pressure in a closed valve’s body cavity to atmospheric pressures if the trapped pressure exceeds 133% of the valves nominal rating. Trunnion mounted ball valves are capable of relieving trapped body cavity pressure to a safe predetermined level, but not necessarily atmospheric pressure. The concept of self-relieving seats in soft seated floating ball valves is largely a myth and none of the competitive valves tested have come close to meeting api 6d’s definition. Apollo’s ball valve seats are not promoted as "self-relieving".

    Self-Supporting Steel Stack Definition: - a steel stack of sufficient strength to require no lateral support.

    Service Water Definition: - general-purpose water which may or may not have been treated for a special purpose.

    Shell Definition: - the cylindrical portion of a pressure vessel.

    Sight Glass Definition: - a glass installed in the liquid line permitting visual inspection of the liquid refrigerant for the purpose of detecting vapor in the liquid. They also generally have a device included to monitor moisture content of the refrigerant.

    Sludge Definition: - a soft water-formed sedimentary deposit, which normally can be removed by blowing down.

    Slug Definition: - a large "dose" of chemical treatment applied internally to a steam boiler intermittently. Also used sometimes instead of "priming" to denote a discharge of water out through a boiler steam outlet in relatively large intermittent amounts.

    Slugging Definition: - a condition in which a quantity of liquid enters the compressor causing hammering and possible compressor damage.

    Smoke Definition: - small gas borne particles of carbon or soot, less than 1 micron in size, resulting from incomplete combustion of carbonaceous materials and of sufficient number to be observable.

    Sodium Hypochlorite Definition: - in a dilute form, this is the technical name for household bleach.

    Softening Definition: - the act of reducing scale forming calcium and magnesium impurities from water.

    Soft Seat Definition: - applicable to more than just ball valve seats, this general term is used to describe devices with either elastomeric (rubber) or resilient polymer (flexible plastic) sealing elements. For apollo, soft seats are made from either ptfe, rptfe, tfm, uhmwpe, nylon or acetal (delrin).

    Soft Water Definition: - water which contains little or no calcium or magnesium salts, or water from which scale forming impurities have been removed or reduced.

    Solution Definition: - a liquid, such as boiler water, containing dissolved substances.

    Solvent Definition: - a volatile hydrocarbon. Generally flammable to explosive. Frequently requires consideration of "fire tested" valves. Usually requires vented valves.

    Soot Definition: - unburned particles of carbon derived from hydrocarbons.

    Soot Blower Definition: - a mechanical device for discharging steam or air to clean heat absorbing surfaces.

    Spalling Definition: - the breaking off of the surface of refractory material as a result of internal stresses.

    Specific Heat Definition: - the quantity of heat, expressed in btu, required to raise the temperature of 1 lb of a substance 1°F.

    Specific Humidity Definition: - the weight of water vapor in a gas water-vapor mixture per unit weight of dry gas.

    Specific Heat Definition: - the amount of heat necessary to change the temperature of one pound of a substance 10 f.

    Specific Volume Definition: - the volume of a substance per unit of mass; i.e., standard air 13.33 cubic feet per pound. The reciprocal of density.

    Spray Angle Definition: - the angle included between the sides of the cone formed by liquid fuel discharged from mechanical, rotary atomizers and by some forms of steam or air atomizers.

    Spray Nozzle Definition: - a nozzle from which a liquid fuel is discharged in the form of a spray.

    Stack Definition: - a vertical conduit, which due to the difference in density between internal and external gases creates a draft at its base.

    Stack Draft Definition: - the magnitude of the draft measured at the inlet to the stack.

    Stack Effect Definition: - that portion of a pressure differential resulting from difference in elevation of the points of measurement.

    Stack Effluent Definition: - gas and solid products discharged from stacks.

    Stagnation Definition: - the condition of being free from movement or lacking circulation.

    Standard Air Density Definition: - .075 pounds per cubic foot. Equivalent to dry air at 700 f and at sea level pressure.

    Standard Flue Gas Definition: - gas weighing 0.078 lb per cu ft at sea level (29.92 in. Barometric pressure) and 70°F.

    State Condition Definition: - substances can exist in three states - solid, liquid or vapor.

    Static Pressure Definition: - the normal force per unit area at a small hole in the wall of a duct.

    Static Tap Definition: - a means by which static pressures of a duct system may be read directly, usually consisting of a small diameter hole in the side of the duct connected to a manometer.

    Steam Definition: - the vapor phase of water, unmixed with other gases.

    Steam Atomizing Oil Burner Definition: - a burner for firing oil which is atomized by steam. It may be of the inside or outside mixing type.

    Steam Binding Definition: - a restriction in circulation due to a steam pocket or a rapid steam formation.

    Steam Gauge Definition: - a gauge for indicating the pressure of steam.

    Steam Generating Unit Definition: - a unit to which water, fuel, and air are supplied and in which steam is generated. It consists of a boiler furnace, and fuel burning equipment, and may include as component parts water walls, super heater, reheater, economizer, air heater, or any combination thereof.

    Steam Purity Definition: - the degree of contamination. Contamination is expressed in ppm.

    Steam Quality Definition: - the percent by weight of vapor in a steam and water mixture.

    Steam Separator Definition: - a device for removing the entrained water from steam.

    Strainer Definition: - a device, such as a filter, to retain solid particles allowing a liquid to pass.

    Stratification Definition: - non-homogeneity existing transversely in a gas stream.

    Stud Definition: - a projecting pin serving as a support or means of attachment.

    Sub Cooling Definition: - cooling of a liquid, at a constant pressure, below the point at which it was condensed.

    Sublimation Definition: - a condition where a substance changes from a solid to a gas without becoming a liquid.

    Suction Line Definition: - a tube used to convey the refrigerant vapor from the evaporator outlet to the suction inlet of compressor.

    Suction Line Accumulator Definition: - a device located in the suction line that intercepts quantities of a liquid refrigerant and thereby prevents damage to the compressor.

    Superheat Definition: - heat added to a vapor after all liquid has been vaporized.

    Superheated Steam Definition: - steam with its temperature raised above that of saturation. The temperature in excess of its saturation temperature is referred to as superheat.

    Surface Blowoff Definition: - removal of water, foam, etc. From the surface at the water level in a boiler. The equipment for such removal.

    Surge Definition: - the sudden displacement or movement of water in a closed vessel or drum.

    Suspended Solids Definition: - undissolved solids in boiler water.

    Swinging Load Definition: - a load that changes at relatively short intervals.


    Teflon® Definition: - a registered trademark of PTFE made by Dupont. The word can only be used when specifically licensed to do so by Dupont and only in strict reference to materials produced by Dupont. Not to be used as a generic name for PTFE or materials containing PTFE.

    Temperature Definition: - a measurement of heat intensity.

    Tertiary Air Definition: - air for combustion supplied to the furnace to supplement the primary and secondary air.

    Theoretical Air Definition: - the quantity of air required for perfect combustion.

    Theoretical Draft Definition: - the draft, which would be available at the base of a stack if there were no friction or acceleration losses in the stack.

    Therm Definition: - a unit of heat applied especially to gas. One therm = 100,000 btu.

    Thermal Efficiency Definition: - the efficiency of a boiler, based on the ratio of heat absorbed to total heat input. This does not include heat loss from the boiler shell.

    Thermal Shock Definition: - a cycle of temperature swings that result in failure of metal due to expansion and contraction.

    Thermistor Definition: - basically a semiconductor, which has electrical resistance, that varies inversely with temperature.

    Thermocouple Definition: - a temperature-measuring instrument.

    Thermostat Definition: - a bimetal actuated switch to close and open a circuit to indicate or terminate operation of a heating or air conditioning system.

    Thermostatic Expansion Valve Definition: - refrigerant control which monitors the flow rate according to the superheat at the evaporator outlet.

    Thermostat Subbase Definition: - when installed with a thermostat it permits selection of function for heating, cooling, automatic changeover and blower cycling or continuous operation.

    Thermostatic Mixing Valve (TMV) Definition: - a valve that blends hot water (stored at temperatures high enough to kill bacteria) with cold water to ensure constant, safe outlet temperatures preventing scalding. The storage of water at high temperature removes one possible breeding ground for legionella; the use of a thermostat rather than a static mixing valve provides increased safety against scalding, and increased user comfort because the hot-water temperature remains constant. Many tmvs use a wax thermostat for regulation. They also shut-off rapidly in the event of a hot or cold supply failure to prevent scalding or thermal shock. It is increasingly common practice around the world to regulate the storage water temperature to above 60c, and to circulate or distribute water at a temperature less than 50c. Water above these temperatures can cause life threatening scald injuries. Many countries, states, or municipalities now require that the temperature of all bath water in new build and extensively refurbished domestic properties be controlled to a maximum of 48c. Installing thermostatic mixing valves (tmvs) can ensure that water is delivered at the required temperature thereby reducing the risk of scalding accidents; it also makes the hot water supply last longer than one that is maintained at a lower temperature.

    Three-Way Valves Definition: - a valve with three ports / openings. 3-way valves are commonly made such that flow coming in at one port can be directed to either the second port in one position or the third port in another position or in an intermediate position so all flow is stopped. Often such 3-way valves are ball or rotor valves. Many faucets are made so that incoming cold and hot water can be regulated in varying degrees to give out coming water at a desired temperature.

    Tickle Definition: - Slang term for titanium tetrachloride, chemical symbol TICl3.

    Tile Definition: - a preformed refractory, usually applied to shapes other than standard brick.

    Ton Of Refrigeration Definition: - the amount of heat necessary to completely melt one ton of 320f ice in 24 hours. 200 btus per minute, 12,000 btus per hour, 288,000 btus in 24 hours. This is based on the latent heat of fusion for ice which is 144 btus per pound.

    Total Air Definition: - the total quantity of air supplied to the fuel and products of combustion. Percent total air is the ratio of total air to theoretical air, expressed as percent.

    Total Heat (enthalpy) Definition: - total heat energy in a substance. The sum of sensible and latent heat.

    Total Pressure Definition: - the sum of all partial pressures in a mixture of gases.

    Total Solids Concentration Definition: - the weight of dissolved and suspended impurities in a unit weight of boiler water, usually expressed in ppm.

    Transformer Definition: - is a device that transfers electrical energy from one circuit to another through inductively coupled electrical conductors. A changing current in the first circuit (the primary) creates a changing magnetic field; in turn, this magnetic field induces a changing voltage in the second circuit (the secondary). By adding a load to the secondary circuit, one can make current flow in the transformer, thus transferring energy from one circuit to the other

    Treated Water Definition: - water which has been chemically treated to make it suitable for boiler feed.

    Trim Definition: - the definition varies by manufacturer. Some manufacturers refer to "trim" as the stem and ball or closure member. Some use the term in reference to soft goods, such as seats, seals and gaskets. Mss defines trim as the "functional parts of a valve that are exposed to the line fluid", which would encompass both of the above interpretations.

    Trunnion Mounted Definition: - as opposed to a "float ball", the ball on a "trunnion" or "trunnion mounted" valve is supported by bearings within the valve body and the valve seats are typically loaded against the ball. Trunnion mounted valves have a few unique capabilities; the valve seals on the upstream seat, the seats tend to be somewhat self-relieving and the valve is generally capable of double block and bleed, two characteristics not normally found in floating ball valves.

    Tube Definition: - a hollow cylinder for conveying fluids.

    Tube Hole Definition: - a hole in a drum, heater, or tube sheet to accommodate a tube.

    Turbulent Burner Definition: - a burner in which fuel and air are mixed and discharged into the furnace in such a manner as to produce turbulent flow from the burner.

    Turndown Ratio Definition: - ratio of maximum to minimum fuel or steam input or boiler output.

    Two-Way valves Definition: - a valve with two ports / openings. Operating positions for such valves can be either shut (closed) so that no flow at all goes through, fully open for maximum flow or sometimes partially open to any degree in between. Many valves are not designed to precisely control intermediate degree of flow; such valves are considered to be either open or shut, with maybe qualitative descriptions in between. Some valves are specially designed to regulate varying amounts of flow. Such valves have been called by various names like regulating, throttling, metering, or needle valves. For example, needle valves have elongated conically-tapered discs and matching seats for fine flow control. For some valves, there may be a mechanism to indicate how much the valve is open, but in many cases other indications of flow rate are used, such as separate flow meters.


    UL Definition: - Underwriters Laboratories

    Unaccounted-For Loss Definition: - that portion of a boiler heat balance, which represents the difference between 100 per cent and the sum of the heat absorbed by the unit and all the classified losses expressed as per cent.

    Unburned Combustible Definition: - the combustible portion of the fuel, which is not completely oxidized.

    Unfired Pressure Vessel Definition: - a vessel designed to withstand internal pressure, neither subjected to heat from products of combustion nor an integral part of a fired pressure vessel system.

    Union, Dielectric Definition: - dielectric unions are required in some application by code. In particular on water heaters, in the transition from black pipe to copper. The basis for their use is to prevent galvanic corrosion of the black iron pipe. Whether or not they are technically necessary depends largely on water chemistry. In applications with dissolved electrolytes their use would be beneficial.

    Use Factor Definition: - the ratio of hours in operation to the total hours in that period.


    VA Definition: - Volt-Amperes.

    Vacuum Definition: - any pressure below atmospheric pressure.

    Valve Definition: - a device that regulates the flow of substances (gases, fluidized solids, slurries, or liquids) by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but usually are discussed separately.

    Valve Seat Definition: - a valve seat is the interior surface in the body which contacts or could contact the disc to form a seal which should be leak-tight, particularly when the valve is shut (closed). If the disc moves linearly as the valve is controlled, the disc comes into contact with the seat when the valve is shut. When the valve has a rotor, the seat is always in contact with the rotor, but the surface area of contact on the rotor changes as the rotor is turned. If the disc swings on a hinge, as in a swing check valve, it contacts the seat to shut the valve and stop flow. In all the above cases, the seat remains stationary while the disc or rotor moves. The body and the seat could both come in one piece of solid material, or the seat could be a separate piece attached or fixed to the inside of the valve body, depending on the valve design.

    Valve Stem Definition: - a stem is a rod or similar piece spanning the inside and the outside of the valve, transmitting motion to control the internal disc or rotor from outside the valve. Inside the valve, the rod is joined to or contacts the disc/rotor. Outside the valve the stem is attached to a handle or another controlling device. Between inside and outside, the stem typically goes through a valve bonnet if there is one. In some cases, the stem and the disc can be combined in one piece, or the stem and the handle are combined in one piece.

    Vapor Definition: - the gaseous product of evaporation.

    Vapor Barrier Definition: - the term applied to an impervious layer of material superimposed upon a layer of insulation. Vapor barriers are always applied on the warm side of the insulation layer.

    Vapor Pressure Definition: - the pressure exerted by vapor.

    Vaporization Definition: - the change from liquid or solid phase to the vapor phase.

    Velocity Pressure Definition: - in a moving fluid, the pressure capable of causing an equivalent velocity as applied to move the same fluid through an orifice such that all pressure energy expanded is converted into kinetic energy.

    Vent Definition: - an opening in a vessel or other enclosed space for the removal of gas or vapor.

    Venting Definition: - venting is done to prevent the build-up of pressure in the body cavity of a valve. All carbon steel and stainless steel balls are slot vented as standard. Option -20, "slot vented ball may be ordered on any brass or bronze valves and option -14, "side vented ball", is available on either brass or stainless balls.

    Vertical Firing Definition: - an arrangement of a burner such that air and fuel are discharged into the furnace in practically a vertical direction.

    Viscosity Definition: - measure of the internal friction of a fluid or its resistance to flow.

    Volume Of Air Definition: - the number of cu ft of air per min expressed at fan outlet conditions.


    Waste Heat Definition: - sensible heat in non-combustible gases discharged to the environment.

    Water Definition: - a liquid composed of two parts of hydrogen and sixteen parts oxygen by weight.

    Water Column Definition: - a vertical tubular member connected at its top and bottom to the steam and water space respectively of a boiler, to which the water gauge, water level controls, and fuel cutoff may be connected.

    Water Gauge Definition: - the gauge glass and its fittings for attachment.

    Water Hammer Definition: - a sudden increase in pressure of water due to an instantaneous conversion of momentum to pressure.

    Water Level Definition: - the elevation of the surface of the water in a boiler.

    Water Manometer Definition: - used to measure pressure in inches of water.

    Water Softener Definition: - removes hardness (caco3) from water through an ion exchange of sodium with calcium and magnesium.

    Water Tube Definition: - a tube in a boiler having the water and steam on the inside and heat applied to the outside.

    Water Vapor Definition: - a synonym for steam, usually used to denote steam of low absolute pressure.

    Weep Definition: - a term usually applied to a minute leak in a boiler joint which forms droplets (or tears) of water very slowly.

    Wetback Boiler Definition: - firetube boiler design wherein the back portion of the boiler has a water jacket.

    Wet Bulb Temperature Definition: - temperature read with a thermometer whose bulb is encased in a wetted wick

    Wetted Parts Definition: - any component of a device subject to contact with the fluids it contains. For ball valves, the metallic wetted parts are generally assumed to be the body, retainer or bonnet, ball and stem. Seats and seals are also wetted parts.

    Wetness Definition: - a term used to designate the percentage of water in steam. Also used to describe the presence of a water film on heating surface interiors.

    Wet Steam Definition: - steam containing moisture.

    White Liquor Definition: - a golden or light brown liquid. Highly alkaline. Can contain significant solids particularly lime or calcium carbonate.

    Windbox Definition: - a chamber below the grate or surrounding a burner, through which air under pressure is supplied for combustion of the fuel.

    Windbox Pressure Definition: - the static pressure in the windbox of a burner or stoker.


    X - No terms


    YRBX Definition: - Guide (category code) YRXB. The basic standard used to investigate products in this category is UL842, "valves for flammable fluids". These are ball valves designed for use in pipe lines or equipment assemblies for gasoline, kerosene, fuel oil, petroleum dry cleaning solvent, etc. Valves may be of the manual or self-closing remote control.

    YRPV Definition: - Guide (category code) YRVP. The basic standard used to investigate products in this category is UL842, "valves for flammable fluids". These are manual gas shut-off valves intended for use in lines conveying fuel gases.

    YSDT Definition: - Guide (category code) YSDT. The basic standard used to investigate gas line service valves is UL125, "valves for anhydrous ammonia and lp-gas (other than safety relief)". Lp-gas shut-off valves include department of transportation (dot) shipping container (cylinder) valves, gas line service valves, emergency shut-off valves. These valves are intended to be installed and used in accordance with the standard of the national fire protection association for the storage and handling of liquefied petroleum gases, nfpa 58. They are suitable for use with lp-gas in either the liquid or gaseous phase at working pressures of at least 250 psi. Those suitable for use at pressures in excess of 250 psi are marked with the maximum pressure. These valves are, suitable for installation where a positive shut-off is required.


    Zero Leakage Definition: - this term has no verifiable meaning on its own. Most test standards for soft seated valves allow no leakage for the period of the test, commonly called zero leakage. But, the period of these tests is usually measured in seconds, or even occasionally minutes. Zero leakage on its own would imply that a device would never leak.

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