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Absolute Pressure: The pressure expressed in bar, Pascal or PSI, as measured above a perfect vacuum.
Actuator: A device connected to the valve that allows remote movement of the valve. It can be an air, fluid or electrically powered device.
Aerodynamic Noise: Noise produced by a gas accelerating to supersonic velocity at critical or higher pressure drops through the valve trim.
Air Valve: Solenoid Valve.Valve that is used to control air flow to actuator or line.
Alloy steel: A steel consisting primarily of iron with some percentage of one or more other elements such as chromium, nickel, manganese, or vanadium deliberately added to enhance its properties.
Ambient temperature: The prevailing temperature of the environment immediately surrounding an object – generally considered to be 20°C
ANSI Class: A strength designation for valves which show the max pressures at various temperatures at which a valve can work safely.
ASTM: American Society for Testing and Materials
Austenitic stainless steel: The common stainless steel, where the primary microstructure is austenite and the composition primarily iron but also includes both chromium and nickel. The steels are designated as 300 series such as 304, 316, CF8M, etc.
Atmospheric Pressure: The pressure exerted by the atmosphere.
Back Pressure: The pressure exerted on the downstream side of a valve.
Back seat: A shoulder on the stem of a gate or globe valve which seals against a mating surface inside the bonnet to prevent leakage of media through the bonnet stuffing box when the valve is fully opened.
Bellows Seal Bonnet: A bonnet which uses a bellows for sealing against leakage around the valve plug stem.
Bevel gear operator: Device facilitating operation of a gate or globe valve by means of a set of bevel gears having the axis of the pinion gear at right angles to that of the larger ring gear
Body: The body of the valve is the main pressure boundary. It provides the pipe connecting ends and the fluid flow passageway.
Bonnet: The top part of a valve, attached to the body, which contains the packing gland, guides the stem, and adapts to extensions or operators
Bolted bonnet: A bonnet which is connected to a valve body with bolts or studs and nuts.
Bore: or Port : The inside diameter of the smallest opening through a valve
Bubble Tight: A commonly used term to describe the ability of a control valve or regulator to shut off completely against any pressure on any fluid. Control valves are tested to ANSI B16.104 and FCI 70: 2: 1976 which is the American National Standard for Control Valve Seat Leakage. (allows a number of bubbles per minute leakage, depending on the port size of the valve)
Butt weld end: The end connection of a valve suitably prepared for butt welding to a connecting pipe.
Cage: A hollow cylindrical trim element that is sometimes used as a guide to align the movement of a valve plug with a seat ring. It can be modified for some types of valve, to characterize the flow through the valve. The cage may also act as a noise attenuation or anti-cavitation device.
Carbon Steel: Iron containing carbon in the form of carbides, about 0.1 to 0.3 percent carbon with no other alloying elements other than the sulfur, phosphorus, and other elements present in almost all steels
Casting: A product or the act of producing a product made by pouring molten metal into a mold and allowing it to solidify
Cast Iron: The common term for cast gray iron or iron containing flake carbon in the range of _% to 2 _%.
Cavitation: Cavitation is a concern for liquid services where cavities or bubbles form and then collapse.
Class: A pressure rating expressed as a dimensionless number. The class rating charts give actual pounds per square inch maximum allowable pressure at a given temperature.
Closure Member: The movable part of the valve which is positioned in the flow path to modify the rate of flow through the valve. Some of the different types of closure members are the Ball, Disk, Gate, and Plug.
Cold Rating: The maximum pressure that a valve or fitting is designed to withstand at room temperature.
Control Valve: A power-operated device used to modify the fluid flow rate in a process control system. It usually consists of a body or valve and an actuator, which responds to a signal from the controlling system and changes the position of a flow controlling element in the valve.
Cryogenic Valve: A term used to describe valves designed to operate below –40°C.
CV: Valve Flow Coefficient: Flow coefficient expressed as the number of gallons of water that would flow through an opening, such as a valve port, in 1 minute under a differential pressure of 1 psi.
CWP: Cold working pressure – the maximum allowable pressure under nonshock conditions at ambient temperature ( -20° F to +100° F).
Delta-P: Differential Pressure. The inlet pressure (Pl) minus the outlet pressure (P2).
Diaphragm: A flexible pressure-responsive element that transmits force to the diaphragm plate and actuator stem.
Diaphragm Actuator: Is a fluid (usually pneumatic) pressure-operated, spring-opposed diaphragm assembly which positions the valve stem in response to an input signal.
Differential Pressure: The maximum difference in pressure measured between the valve inlet and outlet, against which the valve is required to operate.
Electric Actuator: uses an electrically operated motor-driven gear train or screw to position the actuator/valve stem.
Elastomer: A natural or synthetic elastic material, often used for o-ring seals. Typical materials are viton, buna-n, EPDM (ethylene propylene dimonomer), etc.
ESD: Emergency Shut Down Valve (ESD): A valve that uses energy which is stored in the actuator to close rapidly in an emergency.
End Connection: The type of connection supplied on the ends of a valve – may be weld end, flanged end, threaded or socketweld.
Equal Percentage: A term used to describe a type of valve flow characteristic where, for equal increments of valve plug travel, the change in flow rate with respect to travel may be expressed as a constant percent of the flow rate at the time of the change.
Face–To–Face: The overall dimension from the inlet face of a valve to the outlet face of a valve (one end to another) allowing valves of the same size and pressure class to be mutually interchangeable, regardless of manufacturer.
Fail–Safe: A term used to describe the desired failure position of a control valve. It could be fail-closed, fail-open, or fail-in-place.
Fail–Closed(FC): Or Normally Closed: Another way of describing an Air-To-Open actuator. An increase in air pressure to the actuator is required to cause the valve to open. Approximately 80% of all spring-return diaphragm operators in the field are of this construction.
Fail-Open (FO): Or Normally Open: Another way of describing an air-to-close actuator. An increase in air pressure to the actuator is required to cause the valve to close.
Fail-In-Place: Fail-In-Place or Fail-Stay-Put: A term used to describe the ability of an actuator to stay at the same percent of travel it was in when it lost its air supply. On spring return actuators this is accomplished by means of a lock-up valve.
Feedback Signal: An example would be where a control valve is equipped with a positioner. The return signal is usually a mechanical indication of valve plug stem position which is fed back into the positioner.
Fire Safe: A valve design that is capable of passing a fire test with specified limits on leakage to the atmosphere and downstream after being closed subsequent to fire exposure.
Flangeless: A valve that does not have integral line flanges, sometimes referred to as a Wafer Style valve.
Flange Facing : The finish of the gasket contact surface of a flange.
Flat Face (FF): A flange surface in which the gasket sealing area is the entire surface from the ID to the outside edge. Usually used for class 125 cast iron valves.
Flashing: Is the boiling or vaporizing of a liquid.
Flow Characteristic: The relationship between valve capacity and valve travel.
Forging: A metalworking process that involves hammering or squeezing, with or without a die, at hot working temperatures to form
Full Bore: Describes a valve in which the bore (port) is nominally equal to the bore of the connecting pipe
Gasket: A component softer than the parts to be sealed, which is compressed between two flanges to prevent the system fluid leaking to atmosphere.
Gland: The component that is used to compress the gland packing.
Gland Nut: The gland nuts are used to exert a force on the gland.
Gland Packing: A soft conformable material fitted to a valve stuffing box to create a seal between the process fluid and the atmosphere.
Graphite: Flexible carbon material used to make gaskets and packing. The gaskets may be flat graphite sheet or have metal inserts.
Handwheel: A manual override device used to stroke a valve or limit its travel.
Hardfacing : A surface preparation in which an alloy is deposited on a metal surface usually by weld overlay to increase resistance to abrasion and or corrosion.
Heat treatment: Describes any process or procedure by which the internal structure of steel is altered by heating to produce desired physical and mechanical characteristics.
Hydrostatic Test: A pressure test in which a valve is tested with water to detect leaks – may be a shell test or a seat closure test.
Integral Flange: A valve body whose flange connection is an integral or cast part of the body. This kind of valves usually called as “Compact”
Integral Seat: The flow control orifice and seat that is an integral part of the valve body or cage. The seat is machined directly out of the valve body and is not replaceable without replacing the body itself – although some can be repaired by welding and re-machining.
ISRS: Inside screw, rising stem – common term for any valve design in which the stem threads are exposed to the fluid below the packing and the stem rises up through the packing when the valve is opened
ID: The measurement of the inside diameter of a circular part.
Leakage Classification: A term used to describe certain standardized testing procedures for control valves with a flow coefficient greater than 0. 1 (Cv).
Lever: Hand-Lever: Wrench: An operating device for quarter-turn valves
Linear Flow Characteristic: A characteristic where flow capacity or (Cv) increases linearly with valve travel. Flow is directly proportional to valve travel.
Linear Valve: It refers to the linear or straight-line movement of the plug and stem.
Locking device: Any valve attachment whose purpose is to prevent the operation of the valve by unauthorized persons.
MPI: Magnetic particle inspection: A nondestructive method of detecting the presence of surface cracks and imperfections through use of fine iron particles in an electrical field. Abbreviated as MPI or MT.
Material Test Reports: Certificates provided by the steel manufacturer indicating the chemical analysis and mechanical properties of a specific batch of steel traced by sequentially assigned heat numbers or codes.
NACE: National Association of Corrosion Engineers
NDE: Non-Destructive Examination. A collective term used to describe examination techniques such as radiographic and ultrasonic
NPS: Nominal pipe size – dimensionless number used to indicate sizes of pressure pipe and valves used interchangeably with valve size in inches
NPT: National Pipe Thread – standard tapered thread for pressure pipe and components. Requirements defined in ASME B1.20.1
NRS: Non-rising stem – A gate valve having its stem threaded into the gate. As the stem turns the gate moves but the stem does not rise. Stem threads are exposed to the line fluid.
OD: The measurement of the outside diameter of a circular part.
O-ring: An elastomeric or synthetic seal ring of circular cross section
OS&Y: Outside Screw & Yoke – A valve design in which the stem threads are above the packing gland or outside the valve body and there is a yoke to support the top or outer end of the stem.
P1: Used to designate Inlet Pressure.
P2: Used to designate Outlet Pressure.
Packing: A sealing system that normally consists of a deformable material such as PTFE, graphite, etc.
Packing Box: The chamber located in the bonnet that surrounds the stem and contains the packing and other stem-sealing components.
Piston Actuator: A device in which the fluid acts upon a movable cylindrical member, the piston, to provide linear motion to the actuator stem.
PMI: Positive material identification – a method for cross checking the identity of a piece of material, often using a portable spectrometer, usually with x-rays.
Pneumatic test: A test in which a valve is tested with air – usually a seat closure test.
Position Switch: A switch that is normally fitted on the actuator to detect extremes of valve travel. The switch is normally electric.
Position Transmitter: A device that is mechanically connected to the valve stem and will generate and transmit either a pneumatic or electric signal that represents the valve stem position.
Positioner: A device used to position a valve with regard to a signal. The positioner compares the input signal with a mechanical feedback link from the actuator. It then produces the force necessary to move the actuator output until the mechanical output position feedback corresponds with the pneumatic signal value.
Position indicator: Any external device which visually indicates the open and closed position of valve.
Pressure Sealed Bonnet: : A type of bonnet design where the fluid pressure is used to produce the seal between the body and bonnet.
PTFE: (Polytetrafluoroethylene): a soft polymer that is compatible with almost any substance.
Pressure-Temp. Ratings: 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 – the force per unit area exerted against a resisting body
Quarter–turn: A method of valve operation involving a 90 degree turn of the stem to move from fully open to fully closed. This describes valves such as ball, plug, and butterfly.
Quick Closing: Quick closing and quick opening refers to a valve designed to require a smaller turn to be fully closed or opened.
Quick Opening: A flow characteristic that provides maximum change in flow rate at low travels.This normally happens when the valve characteristic is used for on/off control.
Ra: Abbreviation for “arithmetic average roughness height” – the measure of the roughness of a surface expressed in microinches. The higher the number, the rougher the surface. Used to designate the desired surface finish for end flange raised faces.
Raised faced (RF): The raised area of a flange face which is the gasket sealing surface between mating flanges.
Radiographic Inspection: An NDE technique that uses X-rays to detect internal flaws that are not detectable using other externally applied methods
Rangeability: The range over which a control valve can operate. It is the ratio of the maximum to minimum controllable flow coefficients. Rangeability is affected by three factors: the geometry of the valve, the seat leakage and the actuator’s accuracy
Rating: An alpha numeric classification used to define the pressure capability of a pipework system.
Reduced Port: A valve port opening that is smaller than the line size or the valve end connection size
Reverse Flow: Flow of fluid in the opposite direction from that normally considered the standard direction.
Resilient seat: A valve seat containing a soft seal such as an o-ring or plastic to assure tight shut-off.
Ring type joint (RTJ): A flange connection using a specially shaped soft metal ring as a gasket. Generally used on high pressure valves.
RS – Rising stem: valve stem with threads arranged so that as the stem turns, the threads engage a stationary threaded area lift the stem along with the closure element attached to it.
Seat: The part of a valve against which the closure element effects a tight shut-off.
Seat Ring: A part of the flow passageway that is used in conjunction with the closure member to modify the rate of flow through the valve.
Schedule: A system for indicating the wall thickness of pipe. The higher the schedule number, the thicker the wall for a certain pipe size.
Socket Weld: A connection made by entering a pipe into a matching socket in the end of a valve fitting, and welding the two together.
Special Class: A term applied to a Class designated threaded or weld end valve, where the body and cover have been subjected to non-destructive examination (NDE) and any defects removed. This allows the valve to have a higher pressure capacity than a standard class valve.
Split Body: A valve whose body is split. This design allows for easy plug and seat removal.
Stem: or shaft: The valve plug stem is a rod extending through the bonnet assembly to permit positioning of the plug or closure member.
Stem Guide: A guide bushing closely fitted to the valve stem and aligned with the seat.
Stroke or Travel : The distance the plug or stem moves to go from a fully closed to a fully open position.
Supply Pressure: The pressure at the supply port of a device such as a controller, positioner or transducer.
Stainless steel: Any of a number of types of iron alloy with chrome, nickel, or other elements that does not oxidize in free air
Stuffing box: The annular chamber provided around a valve stem in a sealing system into which deformable packing is placed.
Throttling: Modulating control as opposed to on/off control.
Transducer: An element or device that receives information in the form of one quantity and coverts it to information in the form of the same or another quantity.
Trim: Includes all the parts that are in flowing contact with the process fluid except the body, bonnet and body flanges and gaskets.
plug, seats, stem, guides, bushings and cage are some of the parts included in the term trim.
Torque: The rotational force imposed on or through a shaft
Vapor Pressure: A pressure at which, for a given temperature, vapor bubbles form in the liquid.
Wall thickness: The thickness of the wall of the pressure vessel or valve. For steel valves, minimum thickness requirements are defined in ASME B16.34, API 600, and API 602
Water Hammer: Shock waves generated in a pipework system caused by a valve closing too quickly.
Working pressure: The pressure (pounds per square inch) at which a valve is designed to operate.
Worm gears: Gearbox or Gear with Handwheel. A gear set in which the input shaft is offset from and perpendicular to the output shaft, and driving gear is very small and perpendicular to the driven gear
Yoke: The part of gate or globe valve which acts as a bracket to support the top or outer end of the stem and stem bearing
