Valve Industry Knowledge Base

Valve Glossary

Here is a list of terms the will clarify the valve industry vocabulary. If you have any questions regarding terminology not listed here, please contact us and we will answer you directly.



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Alloy Steel:Steel that consists primarily of iron with a percentage of one or more other elements such as chromium, nickel, manganese, or vanadium added to enhance its properties.
Aluminum:A silvery-white, ductile metallic element, the most abundant in the earth's crust but found only in combination, chiefly in bauxite. Having good conductive and thermal properties, it is used to form many hard, light, corrosion-resistant alloys.
Aluminum Alloys:Mixtures of aluminum with other metals (called an alloy); often with copper, zinc, manganese, silicon, or magnesium. They are much lighter and more corrosion resistant than plain carbon steel and are non-ferrous.
Ambient Temperature:The temperature of the immediate environment surrounding an object.
ASME:The American Society of Mechanical Engineers. The professional body who enables collaboration, knowledge sharing and skill development across all engineering disciplines.
ASQ:The American Society for Quality.
ASTM:American Society for Testing and Materials.
Austenitic Stainless Steel:A common stainless steel, where the primary micro structure is austenite and the composition is primarily iron, but also includes both chromium and nickel. Examples include: The 300 series such as 304, 316 and CF8M, (see "Stainless Steel").
Back Pressure: Pressure caused by a force that is operating in a direction that is opposite of the flow direction.
Body:The principle pressure containing part of a valve in which the closure element and seats are located.
Bore: Inside diameter of the smallest opening through a valve. (See "Port".)
BSP: British Standard Piping.
Bubble Tight:The ability of the valve to seal against gas pressure and not exhibit a detectable bubble of gas leakage in a one minute period during a bubble test.
BUNA / BUNA-N:A synthetic rubber Nitrile (AKA Buna or Buna-N) used for general gasket applications where animal, organic or industrial oils are present.  Nitrile has very good resistance to all synthetic and natural grease products and it is recommended for use in areas where petroleum products are present.
Butt Weld End (BWE): The end connection of a valve suitably prepared for butt welding to a connecting pipe.
Carbon Steel (CS):An iron containing carbon in the form of carbides, about 0.1 to 0.3 percent carbon with no other alloying elements other than the elements present in most all steels.
Cast Iron: The common term for a brittle cast gray iron or iron containing flake carbon in the range of 0-2%.
Casting:A product or the process of making a product by pouring molten metal into a mold and allowing it to solidify into the shape of the mold. 
Check Valve:A unidirectional valve that is opened by the flow of pressure in one direction and closed automatically when the flow stops or is reversed.
Clapper:The hinged closure element of a swing check valve.
CNC: Computer Numerical Control refers to the automation of machine tools that are operated by abstractly programmed commands encoded on a storage medium, as opposed to manually controlled via handwheels or levers, or mechanically automated via cams alone.
CSA: The Canadian Standards Association.
Cv:By definition Cv is the calculation of a valve’s flow potential with 1 PSI of pressure loss.  1 PSI of pressure loss is a constant that can be used to compare the flow potential of different valve styles.  The higher the Cv number the more efficient the valve is, thus providing the lowest pressure loss.
Dezincification:A pitting corrosion that effects zinc bearing copper-based alloys when in contact with sea water or fresh water that is high in O2 & C02.
Differential Pressure:The difference between two levels of pressure.
Disc wafer:A compact wafer-style design that utilizes a round, unobstructed port.
Double Disc or Double Door Valve:A type of valve internal that utilizes a dual clapper closure method instead of a single disc or other configuration.
DownstreamIn a direction away from the source of power in a piping system.
Elastomer Hinge:A check valve style that utilizes an elastomeric material as a hinging element in the valve's internals design.
Elastomer: A natural or synthetic elastic material used for o-ring seals. Typical materials are Viton, Buna-M, EPDM (ethylene propylene diene monomer), etc.
End Connection:A type of connection supplied on the ends of a valve that allows it to be connected to piping, (e.g. flange end, threaded or socket weld.)
EPDM:Ethylene Propylene Diene Monomer. A popular rubber seal material, compatible with a wide range of chemicals.
Expansion Check Valve:A check valve assembly that expands the bore (port) between the two pipe connections.
Fitting: Any pipe part used to join together two sections of pipe, such as elbows, couplings, bushings, bends, wyes, etc. 
FlangeAny of the various pipe fittings that connect using nuts, bolts and other types of separate hardware.
Flat Face (FF): A flange surface where a gasket sealing area is the entire surface from the ID to the outside edge. Often found in class 125 cast iron valves.
Flexi-Hinge®Check valves manufactured since 1999 by Flexi-Hinge® Valve Company located at 1806 Asbury Road, Erie, PA 16505.
Flow Calculator:An algorithm that calculates the passage of flow over a set time interval, (e.g. GPM or GPH.) See: Flexi-Hinge Flow Calculators.
Flow:A measure of the liquid volume capacity of a pump. Given in gallons per hour (GPH), gallons per minute (GPM), liters per minute (L/min), or milliliters per minute (mL/min.)
Foot Check Valve:A type of check valve with a built-in strainer used at the point of liquid intake to retain liquid in system, preventing loss of prime when liquid source is lower than pump. 
Full Bore:Denotes a valve that has a bore (port) ID size that is equal to the ID size of the attached pipe, (see "Full Port").
Full Penetration Weld: A type of weld that permeates the complete thickness of the parts being mated.
Full Port:Denotes a valve that has a bore (port) ID size that is equal to the ID size of the attached pipe, (see "Full Bore").
Gasket: A gasket is a mechanical seal that fills the space between two objects, generally to prevent leakage between the two objects while under compression.
GPM: Expression of flow in Gallons Per Minute.
Heat Treatment:A controlled process for hardening metal by alternately heating and cooling it.
Huey Test:Corrosion testing in a boiling solution of nitric acid. This test is mainly used to detect the susceptibility of stainless steel to intergranular corrosion.
Hydrostatic Test:Test using non-compressible liquid under pressure at a level equal to or greater than the maximum pressure that will be utilized when in use.
ID: The measurement of the inside diameter of a circular part.
ISA:The Instrumentation Systems and Automation Society.
Liquid Penetrant Inspection:A nondestructive method for revealing discontinuities that are open to the surfaces of solid and essentially nonporous materials. Liquid penetrants seep into various types of minute surface openings by capillary action.
Magnetic Particle Inspection:A method of detecting cracks or defects by establishing a magnetic field in the object and using iron filings to see if the field lines are constant.
Material Test Reports:A document on which the material manufacturer records the results of test examinations or treatments required by the material specification.
Mold:A container into which liquid is poured to create a given shape when it hardens.
MTE:A thread on the outside of a pipe or external threads, sometimes also referred to as NPT.
NEMA:National Electrical Manufacturers Association. 
Next Generation Design:The term used by Flexi-Hinge® to describe valve internals that incorporate a fully supported valve plate configuration. This design eliminates adverse loading of the hinge/seal primary component and offers a naturally closed configuration without the  need of a spring. The 'Next Generation Design' check valves are a departure from manufacturers that still employ inferior springs activated valve internals and wedge plate door design. Such weaknesses hasten failure, resulting in costly down time and valve refitting.
NPS:Nominal Pipe Size. An indication of an average pipe size. 
NPT:National Pipe Thread. The taper on NPT threads allows them to form a seal when torqued as the flanks of the threads compress against each other, as opposed to parallel/straight thread fittings.
OD:The measurement of the outside diameter of a circular part.
O-ring:An elastomeric or synthetic seal ring.
Pinhole:A tiny hole in the surface of, or through, any material; usually occurring as the result of trapped gases in cast parts exposed during machining operations.
Pneumatic Test:A test for leaks in a pipe system where all openings are sealed and compressed air is introduced into the system.
Port:An opening in a valve through which fluid can flow.
Pressure Class:The class rating charts give actual pounds per square inch maximum allowable pressure at a given temperature.
Pressure:The force exerted on the walls of a tank, pipe, etc., by a liquid. Normally measured in pounds per square inch (PSI).
Pressure Drop:Is also called pressure differential and represents the difference between two pressure levels.
Pressure Loss:The loss of pressure when a liquid or gas flows through a pipe as a result of  the energy required to overcome the viscous or frictional forces exerted by the walls of the pipe. (See: "What causes pressure loss?" in the FAQ.)
Pressure-Temperature Rating:The maximum allowable working pressures at specified temperatures. For steel valves, the ratings are defined by "classes" and found in ASME B16.34. For iron and bronze valves, the ratings are defined in the applicable MSS specifications.
PSI:Pounds Per Square Inch. 
Raised Faced (RF):The raised area of a flange face which is the gasket sealing surface between mating flanges.
Reduced Port: A valve bore (port) opening that is smaller than the line size or the valve end connection size.
Resilient Seat:A valve seat containing a soft seal to assure tight closure.
Schedule:A system for indicating the wall thickness of pipe. The higher the schedule number, the thicker the wall for a certain pipe size.
Seal Weld: A weld used to obtain fluid tightness as opposed to mechanical strength.
Seat:The part of a valve against which the closure element effects shut-off.
Silicone:Any of a large class of siloxanes that are unusually stable over a wide range of temperatures. Gasket temperature resistance from -100 to +500 Degrees Fahrenheit.
Sour Gas:Natural gas containing significant amounts of hydrogen sulfide (H2S). 
Specification:An explicit set of requirements to be satisfied by a material, product or service.
Stainless Steel (SS):A type of steel containing chromium that makes it resistant to corrosion.
Strainer:A device installed in the inlet of a pump or valve to prevent foreign particles from damaging the internal parts.
Stud:Any of several types of strong fastening rods, pins, or screws, usually threaded to receive a nut.
Swing Check Valve: A check valve in which the closure element is hinged, swings or rotates about a supporting shaft.
TEFLON: A non-stick surface engineered to reduce the ability of other materials to stick to it.
Tensile Strength: The strength of material expressed as the greatest longitudinal stress it can bear without tearing apart.
Tensile Test:A destructive test carried out on metal specimens of standard dimensions to investigate the ability of the metal to withstand tensile loading.
Throttling: Modulating control as opposed to ON/OFF control by partially closing or opening a valve.
Torque: The tendency of a force to rotate an object about an axis, fulcrum, or pivot.
Ultrasonic Inspection:A means of locating defects in steel. When acoustic energy in the ultrasonic range is passed through steel, the sound waves tend to travel in straight lines. 
UpstreamIn a direction toward the source of power in a piping system.
Vacuum:A volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure.
Valve Blog:A shared on-line journal where users can post and comment about their personal and professional experiences with valves and the valve industry. (See Flexi-Hinge Valve Blog.)
Valve:A device in a pipe or tubing that regulates the flow of gases, liquids or loose material through the pipe by opening, closing or obstructing ports or passageways.
Viscosity:The "thickness" of a liquid or its ability to flow. Most liquids decrease in viscosity and flow more easily as they get warmer. 
Viton:Viton is a brand of synthetic rubber. A fluoropolymer elastomer commonly used in O-rings and other molded or extruded goods. The name is a registered trademark of DuPont Performance Elastomers L.L.C..
Water Hammer:The result of pressure fluctuations that develop in a pipe when flow is changed quickly.
Wafer Valve:A type of valve that sandwiches between to companion flanges with locating holes on the valve body to ensure correct placement.
Wall Thickness: The thickness of metal, per side, between the shank diameter and the counterbore diameter.
WOG: Water-oil-gas - a rating designation generally used for small valves chiefly in low ratings. Indicates maximum working pressure at ambient + 32° F to +100º F. Also called Nonshock Rating. 
Working Pressure:The normal pressure of a system which does not include the maximum surge the system may be subjected to.
Yield Strength:The stress point at which a steel specimen exhibits permanent deformation.



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