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Valve Terminology



Acme Threads : A common thread pattern used to thread plug stems to actuator stems.

Actuation System : A separate actuator assembly that can be installed on a manual valve and used for either on-off or throttling applications.

Actuator : A power-driven device that provides the force to open, close or throttle a valve.

Actuator Barrier : A dynamic actuator part that separates the actuator chamber from the atmosphere or another actuator chamber. When the actuator barrier is acted upon by the medium in the chamber (s), the actuator moves.

Actuator Stem : A rod used in linear valves to connect the actuator with the stem of the valve.

Air Set : Advice used to limit the air supply to an actuator also known as a pressure regulator.

Air Spring : A fail-safe system for actuators that employs a locked up volume of air to drive the actuator to the failure position.

Angle Valve : A valve-body style where the first port is perpendicular to the second port.

Attenuation : The capability of lowering the sound pressure level radiating from a valve.

Attenuation Plate : An anti-noise device installed downstream from a valve that uses a tortuous path, multiple holes, expanding flow area or sudden expansions and contractions to lower the sound pressure level generated by a valve. A trim installed inside a valve that uses a tortuous path, multiple holes, expanding flow area, or sudden expansions and contractions to lower
the sound pressure level generated by a valve.

Automatic Control Valve : A final control element that receives a signal from a process controller to regulate the pressure, flow or temperature of a liquid or gas process. Also known as a control valve.



Belleville disk spring: A cone shaped metal washer used to produce a constant load to the packing box without retightening.

Block Valves: Simple manual valves that are used to start or stop the process flow. Common block valve include gate, quarter-turn plug, ball, pressure-relief, and tank- bottom valves. Also referred to as on-off valves.

Brinell hardness Number: A number between 111 and 745 that indicates the relative hardness of a material.
As the number increases, the material is designated as harder.

Bubble-tight: A condition where no measurable seat leakage occurs though the closure element of a valve during a certain amount of time. The typical bubble-tight test involves air under-water testing.

Butterfly valve: A quarter-turn rotary valve design that has a narrow body face and a circular disk closure element.

Butt weld end connection: A special end connection used to prepare a valve for welding into the line. A butt weld connection has a series of angles that match up with the similar angles on the pipe and match up with the similar angles on the pipe and connection.
When matched up, the ends present a V shaped gap that is filled with a weld.

Bypass valve: A manual valve used in a bypass line that circumvents a larger valve (usually a control valve). A bypass line usually involves using one or more manual valves, which valve and detour the flow on the downstream side.



Carbon steel: Iron-based metal that contain 0.1 to 0.3 per cent carbon. Carbon steel is a base steel from which alloys are created by mixing other metals with it.

Cavitations: A situation in liquid services when the pressure at the vena contract falls below the vapor pressure, followed by a pressure recovery above the vapor pressure.
The pressure reduction below the vapor bubbles to form, which then collapse as the pressure recovers. This implosion of the vapor bubbles can erode metal surface in both the valve body and downstream piping, as well as cause noise.

Charpoy impact test: A quality test that measures a material’s ability to resist fracture on a V-shaped notch cut into the material when an impact load is applied to the side opposite the notch. Charpoy tests are normally conducted on materials that are subject to extremely cold temperature.

Check valve: A valve that prevents the process flow reversing the closure element of a check valve normally uses gravity fluid, and/or spring force to close the valve and does not require any type of manual operation or actuation.

Charvron packing: A packing style characterized by V-shaped (in cross-section) seamless ring. When axial force is applied to the ring the radial forces cause the thin edges of the ring to press tightly against the wall of the packing box as well as the strong seal with minimal friction in moderate temperatures also referred to as V-ring packing.

Class: A term used in conjunction with a pressure class ie. ANSI Class 2500.

Cold flow: The ability of a soft material to under go plastic deformation under sustained pressure regardless of the temperature.

Concentric butterfly valve: A butterfly valve design with the disk installed in the center of the body.

Control valve: A throttling valve equipped with an actuator or actuation system to respond to an input signal from a controller. Control valves are used to regulate the flow.
temperature. or pressure of a pressure system also known as an automatic control valve.

Cracking pressure: In check valves the positive line pressure that allows the closure element to being opening and allow flow through the valve.

Critical temperature: The
temperature at which a metal’s crystal structure becomes austenite.

Cryogenic valve: A special valve used in services with temperature below 50F (-45C).A cryogenic valve has protective cold box as part of the body to allow a vapor barrier to form between the liquefied gas and the packing box.

C: The term used to measure flow through a valve. The C of valve is used to calculate the ideal valve size to pass the required flow rate while providing overall stability to the process. C is defined as 1 US gallon (3.8 liters) of 60F (16C) water during 1 min with a 1 psi (6.9 k. Pa) pressure drop. Also referred to as valve coefficient or flow coefficient.



Design pressure: The pressure used to determine overall design criteria for a valve including flange rating. bolting torques and thread wall thickness packing box configurations, bellow seal design etc. The design pressure includes certain allowances and safety factors to compensate for pressure surges water hammer effects or other unexpected phenomena to the process line. For this reason ,the design pressure is always a greater value than the actual operating pressure.

Design temperature: The temperature used to determine overall design criteria for a valve including flange rating bolting wall thickness. Packing-box configurations bellows seals design, etc. The design temperature included certain allowances and safety factors to compensate for unexpected temperature at or beyond the operating temperature .For this reason the design temperature is always a greater value than the actual operating pressure.

Diaphragm valve: A manual valve related to pinch valve that compresses an electrometric diaphragm against the bottom of a metal body to shut off the flow.

Digital positional: A positional that uses a microprocessor to position an actuator and to monitor and record data.

Direct-acting pressure relief valve: A pressure relief valve that allows line pressure elements, while a predetermined spring applies a mechanical load to the other side. When the line pressure reaches its maximum limit, the line pressure overcomes the spring load and the valve opens until the line pressure falls below the present level.

DN: The ISO standard abbreviation for the nominal diameter of a size ie. DN 100.

Double acting actuator: An actuator that can supply and exhaust air to both sides of position or diaphragm at the same time. Double acting designs require at use of a positioned.

Downstream: The process portion of a system following a valve.

Ductile iron: A special cast iron with 18 percent ductility.

Dye penetrate: A quality test that uses bright red or fluorescent dye to detect surface cracks pits or porosity on a nonporous surface. A dye penetrate test involves spraying the special dye on the part. When the excess dye on the surface is wiped away surface flaws are detected when natural of fluorescent light highlights the remaining dye in the crack or pit.

Dynamic seal: A seal that involves two or more elements that physically moves as they act upon each Usually such seals include those associated with the closure element (such as between a plug and a seal, butterfly disk and a seal, ball and a seal etc.). packing box (where a stem or a shaft move against the packing), or the actuator (where a piston may move between two pressure chambers.).



Eccentric butterfly valve: A butterfly valve design in which the valve shaft is slight offset from the center of the disk, allowing the disk to move in an elliptical motion as it leaves the sealing surface. This unique motion permits minimal friction and wear to the closure element.

End-to-end: The dimension from one end connection to the opposite end connection on a valve. End to end is similar to face-to-face, except that it is used with valves that do not have flat-faced surfaces on the end connection, such as butt weld ends.

Equal-percentage characteristic: A flow characteristic characteristic: A flow charters tic that permits a change in flow per unit of valve stroke, which is directly proportional to the flow occurring just before the change is made.

Erosion: Material wear  inside a valve or pipeline caused by the flowing action of the process fluid. Erosion deterioration is often hastened when entrained solids are present in the flow.

Extension bonnet: A bonnet that is longer than normal that is used to protect the packing box and actuator from the effects of severe temperatures. Also referred to as extended bonnet.



Fail-safe: An actuator system that allows a valve to move to a certain position (open or shut) or to retain the current position, should the actuator power supply fail.

FEP: Abbreviation for fluorinated ethylene propylene copolymer.

Fire-safe: The ability of a valve to maintain certain standards after being subjected to a fire test. A fire-safe valve is expected to minimize the amount of process fluid lost down stream or to the atmosphere during a fire lost down stream or to the atmosphere during a fire. Also referred to as fire-tested.

Flangeless body: A body of a rotary valve with a short face-to-face that can be sandwiched between two flanged piping end connections, using long studs and nuts. Also referred to as a wafer-style body.

Flashing: A common valve problem in which the pressure at the vena contract falls below the vapor pressure, followed by a pressure recovery that remains below the vapor pressure. This pressure reduction below the vapor pressure at the vena contract causes
vapor bubbles to form and to continue downstream causes the over all velocity to
accelerate, which can lead to excessive noise and eventual erosion.

Floating ball: A ball or check valve design that features a ball that is not fixed to the valve body.

Floating seat: A seat ring that is not fixed to the valve body. Floating seat can shift position to conform better to the shape of the closure element, providing better shutoff.

Float capacity: The amount of flow that can pass through a valve under certain flow conditions, without the valve choking. Also refer to as capacity or valve capacity.

Flow characteristic: A valve’s relationship between the flow coefficient (C) and the valve stroke ,from 0 to 100 percent. A flow characteristic is usually differentiated as either an inherent flow characteristic or an installed flow characteristic The three most common types of flow characteristic are equal percentage, linear and quick open.

Fluoroplastic: A polymer with a molecular structure similar to hydrocarbons. expect that fluorine atoms take the place of carbon atoms. Also referred to as fluroplastic, politer fluoroethylene of PTFE.

Four way solenoid: A solenoid used to operate on off actuator, providing two way direction.

Full port valve: Any valve where the opening of closure element (such as a seat or a full ball) has the same area as the inside diameter of the inlet and outlet ports. Also referred to as a full bore valve.



Galling: Damage to two mating parts when microscopic interact and bond together, which when each part moves against the other, results in tearing of the surfaces, Galling typically happens when two parts of the same materials are used together without lubrications. In the case of threaded nuts, bolts or studs, galling can destroy both male and female threads. Galling is also common between guides and stems or shafts, which not only damages smooth surfaces, but can also destroy packing or other soft parts.

Gland bushing: A part found at the top of a packing box protects the packing box from atmospheric elements and transfers force from the gland flange bolting to the packing.



Hardened trim: Valve trim that is overlaid with a special material designed to
withstands the effects of Cavitation, corrosion, or erosion.

High recovery: The inherent ability of a particular valve design to pass flow without taking a large pressure drop, allowing the downstream pressure to recover close to the upstream pressure.

Hydrostatic test: A valve test using water pressure to detect the presence of leaks through sealed joints, vessel walls, or the closure element. As a safety
measure, a hypo test typically generates 1.5 times the pressure called for by the design.



Impact test: A test to determine the toughness of a material by measuring the required to fracture a test specimen.



Lift check valve: A check valve that uses a free-floating closure element, consisting of a piston or puppet and a seat ring.

Linear flow characteristic: The inherent flow characteristic that produces equal changes in flow per unit of valve stroke at a constant pressure drop.

Linear motion valve: A valve with a sliding stem design that pushes the
closure or regulating elements into an open, closed or throttling position. Also
known as a linear valve.

Low recovery: The inherent ability of a particular valve design to take a large pressure drop, resulting in the downstream pressure only slightly recovering in relationship to the upstream pressure. Valves with low recovery factors have similar design characteristic, such as highly contoured internal passageways and closure elements that remain in the flow stream when open ,globe and butterfly valves are good examples of valves with low recovery factors.

Lug body: In butterfly valves a body with an integral flange that has a threaded hole pattern of the piping flanges.



Magnetic particle examination: A method used to discover small cracks or porosity in the surface of a material that cannot be detected by visual examination. Magnetic particle examination involves spreading iron filing over a metal surface and passing an electric current through the metal. Flaws are then revealed as the iron filing cluster around imperfections in the metal.

Maximum allowable operating pressure: The maximum vessel. such as a valve, can safely hold on a continuous basis. The maximum allowable operating pressure is expressed is expressed in psi or bar (or kilopascal) and is determined by the vessel’s material maximum temperature, and given pressure class. Also  referred to as maximum allowable working pressure.



Nonreturn valves: Valves that allows the flow of the process fluid in only one
direction. Nonreturn valves are designed so that any flow or pressure in the opposite direction is mechanically restricted. All check valves are non return valves are design so that any flow or pressure in the opposite direction is mechanically restricted. All check valves are non return valves.



Operating pressure: The pressure that a valve normally operates under during everyday service. The operating pressure should not be confused with the design pressure pressure, which is defined as the operating pressure plus outside factors.

Operating temperature: the temperature that a valve normally operates under during everyday services. The operating temperature should not be confused with the design temperature, which is defined as the operating temperature plus outside factors.

O ring: An elastomer ring that is used to provide force, leverage, mechanical action or torque to open, close or regulate the closure element.



Packing box: The configuration of packing spacer (s), lantern ring, packing spring extrusion, wiper rings, guides, gland flange, live-loading, gland-flange followers etc grouped together in a bonnet. The packing box is designed to prevent process fluid from escaping through the packing box and is used to apply axial force to the packing.

PEEK: Common abbreviation for polyetheretheketone.

Perfluoroalkoxy: A fluoropolymer similar to polytetrafluoroethylene (PTFE), with some different properties that makes it ideal for valve lining, seal or soft
seats. Also abbreviated as PFA.

PFA: Common abbreviation for Perfluoroalkoxy.

Pig: A device the same shape as the inside diameter of a pipe, which is pushed down the pipe line by fluid pressure. A pig has two purposes: First, to act as a barrier between an earlier process fluid and a new fluid, and second to clean the inside walla of the pipe.

Pinch valve: A flexible valve with an elastomeric body that can be closed by using a mechanism of fluid pressure to push the walls of the body together.

Piping schedule: In pressure pipe, a number that describes the thickness of
the pipe wall, such as schedule 40 pipe. The larger the number, the larger the pipe wall and the more pressure the pipe can handle.

Pneumatic actuator: An actuation system that is powered by air pressure.

Poisson effect: The assistance of process pressure to cause deformations of a soft material against a seating surface for shutoff of a closure element.

Polytheretheketone: A rigid elstomer that is used in high temperature services. Also abbreviated as PEEK.

Polyterafluoroethylene: A common and inexpensive gasket and packing material. Polytetrafluoroethylene is widely used in general services because it
is highly elastic, generates little friction, and requires minimal compression to
achieve a strong seal . Abbreviated as PTFE.

Positioned: A feedback device that receives a signal (pneumatic or electric) from a controller and compares that signal to the actual position of the valve .If the valve positions and the signal are not the same, the positioned sends or bleeds air pressure to or from the actuator until the correct valve positions is achieved.

Pressure relief valve: A self-actuated valve designed to move to the wide open position when the upstream pressure reaches a preset pressure, relieving pressure from the line. When the pressure is under the preset value, a spring or puppet keeps the closure element to open. Also referred to as a relief valve for liquid applications and a safety valve for gas applications.

Psia: Standard abbreviation of pounds per square inch, gage (gauge). The unit psia is used when pressure is expressed to standard atmospheric pressure (noted as 14.7 psia).



Quak exhaust valve: An actuator accessory that is designed to quacked vent one side of a double acting actuator when a full-open or full-closed position is
required immediately.

Quick-open flow characteristic: An inherent flow characteristic that produces a maximum amount of flow with minimal lift or turn of the closure  element.



Rack-and-pinion actuator: An actuation system used with quarter turn valves. The actuator uses a pneumatic or hydraulic force to move a flat toothed rack, turning a gear to move the closure element.

Raised-face flange: A valve and piping end connection that includes a flange (either integral or separable). The flat portion of the valve hub extends farther than the flange. This flat portion, which is called the raised face, permits a greater load on the gasket between the valve and pipe than comparable flat-faced end connections. Raised faces are usually spiral serrated or concentric grooved for better gasket sealing.

Ram valve: A valve placed at the bottom of a tank that allow for drainage. Usually the actuator or hand lever faces down with the closure element facing up into the tank. Also known as a tank bottom valve.

Relief valve: In liquid services, a self-actuated valve designed to move to the wide open position when the upstream pressure reaches a preset pressure, thus relieving pressure from the line. When the pressure is under the preset
valve, a spring or puppet keeps the closure element closed. However, when the pressure builds, the spring or puppet tension is overcome, allowing the closure element to open.

Resilient seat: A seat in a closure element that is made wholly or partially with a flexible or semi flexible electrometer.



Shut off valve: A valve that is used to block (or shutoff) the flow. Shutoff valves are usually used for emergency shutdown situations.

Sliding valve: A manual valve that uses a flat perpendicular closure element that intersects the flow, such as a gate valve design.

Solenoid: An actuator accessory that acts as a control device to supply air to an actuator in on-off application or to control signal pressure in throttling applications.

Static seal: Any sealing design that occurs between two parts that do not move after being secured into place. Because friction is limited, static seals have a longer life and are generally more reliable than dynamic seals. Common static seals include joints between the body and bonnet, body and the seat ring, yoke and the actuator casing etc.

Swing check valve: A check valve designed with the closure element attached to the top of the cap. The closure element can be pushed aside by the flow, but swings back into the closed position if the flow reverses.



Threaded end connection: A valve’s end connection that is designed with female NTP threads, which mates eight the piping end connection design with male NTP threads.

Three-way solenoid: An actuator accessory used to interrupt a signal to a pneumatic positional or to operate a spring diaphragm valve.

Throttling: Regulating the position of a valve between the full-open and full-closed positions so that pressure or fluid are adjusted to meet the requirements of the process system.

Thrust: The force generated by an actuator, actuation system or a manually operated actuation device.

Trim: A term for wetted parts and related parts of the closure element in a linear globe valve. The trim usually includes the following parts: the cage (or seat retainer or severe service cartridge or stack), plug, and seat ring.

Trunnion-mounted ball: A ball that is supported by both a shaft and a post opposite the shaft.



Vena contract: The narrowest constriction in the fluid stream as process flow
moves through a valve. The vena contract can be caused by a small orifice or a valve seat or seal. At that point, the flow velocity is at its highest rate,  while pressure is at its lowest point. 



Wafer body: In rotary valves, a body that has a short face-to-face that can be sandwiched between two flanged piping end connections, using special length studs and nuts. Also refer to as a flangeless body.

Water-hammer effect: In liquid services, the reaction caused when a valve is suddenly closed )or a pump is turned off), which causes a shock wave to be transmitted by the liquid throughout the piping system. Although water hammer causes noise, the primary disadvantage of allowing it to happen is the damage to piping and equipment installed in the piping system.

Weir: In diaphragm and enclosed body pinch valves, an integral bar cast into the bottom of the metal body that is used to help compress the electrometric
diaphragm or liner.