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Valve Glossary

Valve Glossary

1 Piece Ball Valve - Inexpensive and having few potential leak paths (end connections and stem), they are a light-weight and difficult to repair.  Often a reduced port design, typical of OEM and commercial-duty ball valves. 

2 Piece Ball Valve - Industrial standard for flanged ball valves, having only one body joint (potential leak path), they are easier to repair but are more expensive than 1 piece designs due to the increased complexity of the design.

3 Piece Ball Valve - Industrial standard for threaded and welded connections, the central body can be removed without removing the end connections from the pipeline, thus repair is easier.  They can also be supplied with different end configurations.  Having two body joints (potential leak paths), some designs utilize through bolts and others studs with nuts.


Adjustable Stem Packing - A stem seal is used to seal between the shaft of the handle stem and the valve body. This seal is then compressed around the stem by means of a packing gland, which forms a watertight seal around the handle stem assembly.  Over time, due to various environmental conditions, the seal material may expand or contract; thereby affecting the quality of this seal. To combat this (if a leak should occur) you can adjust the packing gland by tightening it slightly.

Anti-static device (ball valve feature) - Ensures an electrical continuity between valve ball, stem, and body thereby reducing static electricity which may exist in the ball or stem of the valve.

Ball Valve - A ¼ turn valve using a hollow sphere used to close, open or control fluid flow.

Blow Out Proof Stem - Ensures the top packing rings can be replaced while the valve is under pressure, without the stem being pushed out.

Bubble Tight Design - A phrase describing the sealing ability of a valve. During air pressure testing of a new valve in the closed position, leakage past the seats is collected and bubbled through water. To qualify as bubble-tight, no bubbles should be observed in a prescribed time span.

Butterfly Valve - Enables quick shut-off of pipeline flow similar to a ball valve, except they typically cost less and more compact than comparable ball valves.

Chain Wheel - Type of manual actuator for difficult to reach (typically high) valves.  The chain wheels can be supplied in a variety of materials.

Control Valve - A valve used to control fluid flow by varying the size of the flow passage, which is accomplished via manual or automated actuation, thus enables the direct control of flow rate and the consequential control of process quantities such as pressure, temperature, and liquid level. 

Cv (Flow Coefficient) - Refers to a scientific standard for volume of water at 60ºF which can pass through a pipe, valve or other pipeline fitting and have a loss or differential pressure drop of 1 PSI.  Therefore the higher the Cv value for a given flow rate, the lower the pressure drop will be across the valve/fitting.

Double Acting Pneumatic Valve Actuator - This type of valve actuator has two compressed air ports; when air is applied to one port and vented by the other, it causes the internal pinion assembly to rotate clockwise.  Just the opposite occurs when air is applied to the other port with the rotation being counter-clockwise.

Double Offset Butterfly Valve - Refers to the position of the valve stem in relation to the centreline of the disc and bore, they are used for higher pressures and fluids with particulate, reduces contact between the valve disc and seat, prolonging the seat life.

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.

Floating (ball valve (ball moves to seat) - Its diverting ball is not anchored to the valve body; rather it floats against the seat to form a seal.  Compared to a Trunnion Valve the sealing is improved and its design is more compact, however they generally have higher torque requirements and thus used for lower pressure applications.

Lug (Butterfly) Valve - Has threaded flange holes to enable removing piping from one side of the valve without affecting its sealing.

Metal Seat - The valve ball or disc interfaces directly against a metal seat.  This style of valve requires periodic operation and maintenance to ensure a leak-free seal.  These types of valves are better for high pressures, extreme temperatures, sanitary/pure fluids and applications with a high percentage of particulates in the fluid.  Metal seats are commonly used for control valves due to higher fluid velocities and related erosion.  Special alloys can be used for enhanced fluid compatibility. 

MSS - Manufacturers Standardization Society of the Valve and Fittings Industry

  • SP-6:Standard Finishes for Contact Faces of Pipe Flanges and Connecting-End Flanges of Valves and Fittings
  • SP-25: Standard marking system for valves, fittings, flanges and unions
  • SP-44:covers pressure-temperature ratings, materials, dimensions, tolerances, marking, and testing for steel pipeline flanges
  • SP-55:Quality Standard for Steel Castings for Valves, Flanges, Fittings, and Other Piping Components – Visual Method for Evaluation of Surface Irregularities
  • SP-67: Butterfly valves
  • SP-72:General purpose ball valves

Multi-Port (Ball Valve design) Valves - which have more than one inlet or outlet, used for diverting flow. 

Pigging - Devices sent through pipelines for cleaning and inspection purposes.  Cleaning could be maintenance or process (cross contamination) related.  Pigging devices are often used during production and only full port ball valves are compatible with pigging processes. 

PTFE - Made from Virgin Teflon, this is the most common sealing material; its chemical compatibility is excellent for almost all media. Temperature -50°F to 400°F.

PTFE Cavity filled Seats Available on request (CF), suitable for filling the void between the body and ball eliminating product build up. Cavity filled seats are standard on our sanitary line of ball valves in both two and three way.

Seal Weld - Eliminates potential leakage at body joints to ensure pressure containment.  Accomplished using automatic welding equipment to create uniform weld penetrations; during the welding procedure a continuous water flow passes through the valve to protect the valve seats and seals from damage.

Spring Return Pneumatic Valve Actuators - Designed to ensure the actuator "fails safe", compressed air is used to compress springs and a counter-clockwise rotation.  Upon venting or loss of pressure, the spring forces clockwise rotation of the valve positioner.

Full Port (Bore) - The bore or ID of the valve matches the ID of the pipe it is connected to, minimizing differential pressure drop.

TFM (valve seat material) - Considered to be an upgrade from PTFE material, having an improved thermo-mechanical properties resulting in lower torque and less permeability, cold flow deformation.  In addition deformation recovery is enhanced

Triple Offset Butterfly Valve ( high pressure, dirty fluids, bubble tight performance) - Designed like a Double Offset butterfly valve with the addition of having a tapered shaped seat which matches the sealing disc, eliminating rubbing altogether and enables tight sealing with a metal-to-metal interface.  Due to their compact size, triple offset valves are sometimes a better choice than gate valves due to reduced weight, cost and ease of operation (ergonomics).

Trunnion (ball valve (seat moves to ball) - Has a diverting ball which is physically connected to both the upper and lower parts of the valve body, utilizing line pressure to move the seat against the ball for sealing.  This is typical for larger valves and higher pressure valves.

Two-way/Bi-Directional (ball valve ) - Whichever side has the higher pressure, the seat or ball moves accordingly for sealing.

Wafer (butterfly) valve Has smooth bore flange holes such that the valve is sandwiched between opposing pipe flanges and thus removing one side of the piping and leaving the valve in-place is not possible.

ACCUMULATOR - A vessel in which a gas is trapped and compressed by the liquid in a hydraulic system, thus storing energy to supply liquid under pressure to the system when needed.

ACTUATOR - Device used to operate a valve using electric, pneumatic or hydraulic means. Often used for remote control or sequencing of valve operations.

ADAPTER SPOOL - An extension which is added to a short face-to-face valve, to conform to standard API 6D face-to-face dimensions.

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.

ANCHOR PIN - A pin welded onto the body of ball valves. This pin aligns the adapter plate and restrains the plate and gear operator from moving while the valve is being operated.

ANGLE VALVE - A variation of the globe valve, in which the end connections are at right angles to each other, rather than being inline.

ATMOSPHERIC PRESSURE - The external pressure exerted on a body by the atmosphere: 14.7 psi (absolute) at sea level.

BACK PRESSURE REGULATOR - Regulator designed to control upstream pressure. See "REGULATOR."

BACKSEAT - A Shoulder on the stem of a valve which seals against a mating surface inside the bonnet to permit replacement, under pressure, of stem seals or packing.

BALL CHECK - A fitting with a small ball that seals against a seat preventing flow in one direction and allowing flow in the other direction.

BAR - A metric unit of pressure. One bar equals 14.5 psi.

BDV - BLOW DOWN VALVE A small ball valve that is installed on the above ground end of an extended drain line. This valve also serves to vent body cavity pressure in the "block and bleed" mode. See "Block and Bleed;" "Extended BDV."

BELLEVILLE SPRING - A spring resembling a dished washer, used in some ball valves to push the seats against the ball.

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. The reduction ratio of this gear set determines the multiplication of torque achieved.

BODY - The principal pressure containing part of a valve, in which the closure element and seats are located.

BOLTED BONNET - A bonnet which is connected to a valve body with bolts or studs and nuts.

BOLTED CONSTRUCTION - Describes a valve construction in which the pressure shell elements are bolted together, and thus can be taken apart and repaired in the field.

BOLTING SETS - Bolts, or studs, and nuts sometimes supplied with flanged valves to install the valve between line flanges.

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.

BORE (OR PORT) - The inside diameter of the smallest opening through a valve, e. g., inside diameter of a seat ring, diameter of hole through ball in a ball valve.

BURST PRESSURE - That pressure (PSI) at which rupture of a stressed element or pressure-containing vessel takes place. See "Ultimate Strength."

BUTT WELD END (BWE) - The end connection of a valve suitably prepared for butt welding to a connecting pipe.

BYPASS - A system of pipes and valves permitting the diversion of flow or pressure around a line valve.

CARBON STEEL (CS) - Iron containing carbon in the form of carbides, about 0.1 to 0.3 percent carbon with no other alloying elements other than the sulphur, phosphorus, and other elements present in almost all steels.

CAST IRON - The common term for cast grey iron or iron containing flake carbon. Cast iron is brittle, exhibiting very little ductility before fracturing.

CAST - The form of a particular part of a valve, where the basic shape is formed by moulding rather than fabricating.

CAVITATION - The rapid formation and collapse of vapor pockets in a flowing liquid in localized regions of very low pressure; often a cause of erosive damage to pumps, throttling type valves, and to the piping itself. Can be the cause of excessive noise.

CHAIN WHEEL OPERATED VALVE - An overhead valve operated by a chain drive wheel instead of a handwheel.

CHECK VALVE - A one-directional valve which is opened by the fluid flow in one direction and closed automatically when the flow stops or is reversed.

CLAPPER - The hinged closure element of a swing check valve.

CLEVIS - A "U" shaped connecting yoke at the end of a stem or rod, between the ends of which a gate or other part may be pinned or bolted.

CLOSURE ELEMENT - The moving part of a valve, positioned in the flow stream which controls flow thru the valve. Ball. Gate, Plug, Clapper, Disc, etc., are specific names for closure elements.

CLOSURE - The ends of a ball valve, bolted to the body, which often contain the seat rings. Often referred to as part of the body.

COMPRESSOR - A device which converts mechanical energy into gas pressure.

CONCENTRIC - Having the same centers.

CONTAMINANT - A particle or material which is foreign to the fluid media.

CONTROL VALVE - A valve that controls a process variable, such as pressure, flow or temperature by modulating its opening in response to a signal from a controller. See "Controller"

CONTROLLER - A device that measures a controlled variable, compares it with a predetermined setting and signals the actuator to read just the opening of the valve in order to re-establish the original control setting.

CORROSION - The deterioration of a material due to chemical action.

CRYOGENIC TEMPERATURE - Any temperature below about -240°F.

CRYOGENIC VALVE - A valve capable of functioning at cryogenic temperatures.

CYCLE - A single complete operation or process returning to the starting point. A valve, stroked from full open to full close and back to full open, has undergone one cycle.

CYLINDER OPERATOR - A power-piston valve operator using either hydraulic or pneumatic pressure. A sealed piston converts applied pressure into a linear piston rod (stem) motion. See "Power Operators."

DEZINCIFICATION - A form of pitting corrosion which attacks certain zinc.

DIAPHRAGM - A round, thin flexible sealing device secured and sealed around its outer edge - and sometimes around a central hole in the diaphragm - with its unsupported area free to move by flexing.

DIFFERENTIAL PRESSURE - The difference in pressure across a valve in a pressurized line. The difference in pressure between any two points in a pressurized system under flowing conditions.

DISC - The closure element of a globe angle or small regulator valve. The disc (sometimes referred to as "valve," "poppet" or "plug") moves to and from the seat in a direction perpendicular to the seat face. Depends on stem force for tight shutoff.

DISTRIBUTION LINE - A pipeline which distributes gas to the service lines of individual consumers. Most generally it is small in diameter (6 inch and under) and low pressure (under 150 psi).

DRAIN PLUG - A fitting at the bottom of a valve, the removal of which permits draining and flushing the body cavity.

DRIVE PINS - The two pins which fit into the bottom of a ball valve stem and engage corresponding holes in the ball. As the operator turns the stem, the drive pins turn the ball.

ECCENTRIC - Not having the same centre.

ELASTOMER - A natural or synthetic elastic material often used for o-ring seals. Typical materials are viton, buna-n, EPDM (ethylene propylene dimonomer), etc.

ELBOW - A female threaded, or socket fitting used for changing direction in a run of pipe or tubing. See "Ell," "Street Ell."

ELECTROLESS NICKEL PLATING - A plating process which requires no external electrical power and is the result of a chemical reaction between the part and the plating solution. A uniform consistent deposit and plating rate can be produced by controlling and adjusting the chemistry of the plating bath.

ELL - A pipe or tubing fitting that has the shape of an "L." See "Elbow."

EMERGENCY SEAT SEAL - To obtain tight shut off in an emergency situation, a sealant can be injected into a specially designed groove in the seat rings. Available for most ball valves and gate valves.

EMO - ELECTRIC MOTOR OPERATED - The actuation of a valve by electric motor. See "Power Operator."

END BEVEL Weld end preparations for butt welding. Governed by ASME B16.25.

END CONNECTION - The type of connection supplied on the ends of a valve which allows it to be installed in a pipeline. Weld end (WE), raised face flange (RF), ring type joint (RTJ), screwed end (SC).

EROSION - The mechanical wearing away of a metal surface or part due to fluid impingement. The presence of entrained solid particles accelerates this process.

ESDV - EMERGENCY SHUT DOWN VALVES - A valve or a system of valves which, when activated, initiate a shut-down of the plant, process, or platform they are tied to.

EXPANDING GATE VALVE - A gate valve that is comprised of a separate gate and segment that as the valve operates the gate and segment move without touching the seats, permitting the valve to be opened and closed without wear. In the closed position the gate and segment are forced against the seat. Continued downward movement of the gate causes the gate and segment to expand against the seats. When the valve reaches its fully open position, the gate and segment seal off against the seats while the flow is isolated from the valve body.

EXPLOSION PROOF - The prevention of explosion, triggered by electrical components, through containment in special housings. A requirement for electrical devices, such as solenoids and switches, when exposed to a potentially explosive environment.

EXTENSIONS - The equipment applied to buried valves to provide above ground accessibility to operating gear, blowdown and seat lubrication systems.

EXTERNAL COATING - Coating applied to protect valves against various environments - sea air, salt water, earth buried, normal air exposure.

FABRICATED VALVE - One in which the body and hub parts are not cast - but rather are formed from plate or pipe and the welded or bolted together.

FACE-TO-FACE - The overall dimension from the inlet face of a valve to the outlet face of the valve (one end to the other). This dimension is governed by ASME B16.10 and API-6D to ensure that such valves are mutually inter changeable, regardless of the manufacturer.

FACING - The finish of the contact surface of flanged fittings.

FAIL SAFE VALVE - A valve designed to fail in a preferred position (open or closed) in order to avoid an undesirable consequence in a piping system.

FEMALE THREAD - An internal screw thread designed to mate with a component having male (external) threads of the same size and type.

FIRE GATE A gate or ball valve which is positioned in a pipeline at the entrance to a compressor station. This valve is closed in case of fire in the compressor station. Closing the valve prevents the gas in the pipeline from feeding the fire.

FIRE SAFE - A statement associated with a valve design which is capable of passing certain specified leakage and operational tests after exposure to fire. Must be referenced to a particular specification. See API Spec. 6FA and BS Spec 6755.

FITTING - Any component, other than valves, used with pipe as part of the pressure system and normally referring to items covered by a national standard.

FLANGE - A cast or formed pipe fitting consisting of a projecting radial collar with bolt holes to provide means of attachment to piping components having a similar fitting. The end piece of flanged-end valves.

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.

FLEXIBLE TUBE VALVE - A special valve using a flexible sleeve or tube which acts as the closure element. Pressure applied to the jacket space surrounding the outside of the tube, controls the opening and closing of the valve.

FLOAT VALVE - A valve which automatically opens or closes as the level of a liquid changes. The valve is operated mechanically by a float which rests on the top of the liquid.

FLOATING BALL - A ball valve having a non-trunnion mounted ball. The ball is free to float between the seat rings, and thus causes higher torques.

FLOW COEFFICIENT - The number of gallons of water per minute that will flow through a valve with a pressure drop of 1 psi. Also referred to as the Cv of the valve.

FLOW LAMINAR - The flow of a viscous fluid in which the fluid moves in parallel layers with a fixed velocity gradient from the centreline to the containing walls of the conduit. Sometimes referred to as "streamline" flow.

FLOW METER - An instrument used to measure flow rate or total flow or both.

FLOW RATE - The volume or weight of a fluid passing thru a pipeline or conductor per unit of time, i.e., 3000 barrels of oil per day; 4 MMCF of gas per hour.

FLOW, TURBULENT - The random flow of a fluid in which the velocity at a certain point in the fluid varies irregularly.

FLOW - A fluid in motion in a conducting line.

FLUID - Any non-solid substance that can be made to flow. Both liquids and gases are fluids.

FORCE - The intensity of an influence tending to produce motion, distortion or change of shape. The product of unit force (PSI) and the area over which it acts. Usually expressed in pounds.

FORGING - A metalworking process that involves hammering or squeezing, with or without a die, at hot working temperatures to form a specific shape.

FRICTION - The resistance to motion between two contacting surfaces or substances. Friction is also developed between a flowing fluid and the inner wall of the conducting pipe - resulting in a drop in pressure.

FULL BORE (FULL PORT) - Describes a valve in which the bore (port) is nominally equal to the bore of the connecting pipe.

FULL OPENING - Describes a valve whose bore (port) is nominally equal to the bore of the connecting pipe.

GALLING - The tearing of metal when two elements rub against each other. Usually caused by lack of lubrication or extreme contact pressure.

GAS - A compressible fluid - such as air, hydrogen, nitrogen, etc.

GASKET - A component whose purpose is to seal a joint between two larger components, softer than the surfaces of the joint being sealed and usually squeezed by means of bolting to affect the seal.

GATE VALVE - A straight-thru pattern valve whose closure element is a wedge or parallel-sided slab, situated between two fixed seating surfaces, with means to move it in or out of the flow stream in a direction perpendicular to the pipeline axis.

GATE - The closure element of a gate valve (sometimes called wedge or disc).

GAUGE, PRESSURE - An instrument, usually with a threaded connection, for measuring and indicating the pressure in a piping system at the point at which it is connected.

GLAND FOLLOWER OR GLAND FLANGE - The component used to hold down or retain the gland in the stuffing box.

GLAND OR GLAND BUSHING - That part of a valve which retains or compresses the stem packing in a stuffing box (where used) or retains a stem O-ring, lip seal, or stem O-ring bushing. Sometimes manually adjustable. See "Packing," "StuffingBox."

GLAND PLATE - The plate in a valve which retains the gland, gland bushing or stem seals and sometimes guides the stem.

GLOBE VALVE - A valve whose closure element is a flat disc or conical plug sealing on a seat which is usually parallel to the flow axis. Can be used for throttling services.

GO - GEAR OPERATED - The actuation of a valve thru a - ear set which multiplies the torque applied to the valve stem. See "BGO", "MGO."

GRAPHITE - Flexible carbon material used to make gaskets and packing. The gaskets may be flat graphite sheet or have metal inserts for added strength. The packing is a combination of lattice braided rings used as anti-extrusion or wiper rings and die-formed rings which are compressed to affect the seal.

GREASE FITTING - A fitting through which lubricant or sealant is injected.

HAND WHEEL - A wheel-shaped valve operating device intended to be grasped with one or both hands which allows turning the valve stem or operator shaft to which it is attached.

HARD FACING - 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.

HUBS - The end connection tubes on a gate valve.

HUEY TEST - A corrosion resistance test for stainless steels, most useful for predicting resistance to intergranular corrosion.

HWO - HANDWHEEL OPERATED - A valve on which the handwheel drives the stem directly to operate the valve.

HYDRAULIC MOTOR ACTUATOR (OPERATOR) - A device by which rotation of a hydraulically powered motor is converted into mechanical motion.

HYDRAULIC SEATS - The movement of the seats in a valve that are controlled by using water, oil, or other liquids under pressure.

HYDRAULIC - Pertaining to, or using, water, oil, or other liquids.

HYDROSTATIC TEST (SHELL TEST) - A test in which a valve is completely filled with water and pressure tested. Used for conducting proof pressure testing. See "Proof Pressure."

ID - The measurement of the inside diameter of a circular part.

INCREMENTAL SEAT TEST - The leakage testing of valve seats in an assembled valve by increasing the applied pressure in prescribed pressure steps.

INLET PORT - That end of a valve which is connected to the upstream pressure zone of a fluid system.

INNER SEAT RING - The inner part of a two-piece valve seat assembly.

INSIDE-OUT AIR SEAT TEST - A pressure test that can be performed only on independent seating trunnion mounted ball valves. By closing the valve and pressurizing the body cavity, all of the seals in an independent seating ball valve can then be pressure tested.

"INSITU" (MAINTENANCE) - To maintain or repair a product "in its original place," such as a top entry ball valve or regulator.

INTERNAL PRESSURE RELIEF - A self-relieving feature in non-independent seating valves that automatically relieves excessive internal body pressure caused by sudden changes in line pressures. By means of the piston effect principal the excessive body pressure will move the seat away from its seating surface and relieve it to the lower pressure side.

ISO (INTERNATIONAL STANDARDS ORGANIZATION) - An organization which sets minimum international standards for a wide variety of items manufactured and used in pipeline services.

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.

KEY STOP - A method of restricting the travel of a ball valve from fully open to fully closed. The stem key bears against the ends of an arc machined in the adaptor plate.

LEVER - A handle type operating device for quarter-turn valves.

LIFTING LUGS - Lugs provided on large ball, gate, and check valves, for lifting and positioning valves. Also called lifting eyes.

LIMIT SWITCH - An electrical device providing a signal to a remote observation station indicating when the valve is in the fully open or fully closed position. Usually a component of a valve operator.

LINE - A pipe, tube or hose for conducting fluids.

LIP SEAL - A circular seal ring of "U" shaped cross section encompassing an elastomeric O-ring which provides resiliency and ensures a seal at the inner and out lips of the "U."

LNG - LIQUEFIED NATURAL GAS - Natural gas in the liquid state. To remain liquefied, the temperature must be maintained in the cryogenic region. The liquid occupies far less volume than an equivalent volume of gas, and it can be readily transported by ship and stored a shore in insulated tanks to await re-gasification.

LOCK UP PRESSURE - The differential pressure required to produce tight shutoff in a regulator. It is usually a few PSI.

LOCKING DEVICE - A mechanism provided on valve operators to prevent unauthorized operation or tampering.

LPG - LIQUID PETROLEUM GAS - Gases such as butane or propane in the liquid state. LPG, under relatively low pressure, remains a liquid at normal ambient temperature.

MAGNETIC PARTICLE INSPECTION - An inspection procedure for detecting surface cracks in welded areas thru the use of fine iron particles in an electrical field.

MALE THREAD - The external thread on pipe, fittings or valves used in making a connection with mating female (internal) threaded parts.

MANIFOLD (HEADER) - A common pipe or chamber having several lateral outlets.

MAOP - Maximum allowable operating pressure. Determined in accordance with piping codes, DOT regulations, etc.

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.

MDS - MATERIAL DATA SHEET - The material data sheet defines the minimum requirements for the required materials, i.e., chemical requirements, manufacturing, qualification of supplier, mechanical testing and properties, non-destructive examination, repair, marking, and certification.

MECHANICAL SEAL - In a valve, a shut off that is accomplished by a mechanical means rather than with fluid or line pressure. The wedging action of a gate against the seats or the seat springs pushing the seat against the ball or gate are examples of mechanical seals in a valve.

METAL-TO-METAL SEAL - The seal produced by metal-to-metal contact between the sealing face of the seat ring and the closure element, without benefit of a synthetic seal.

METER RUN - A section of pipeline in which a meter is installed to measure the volume of fluid passing thru the line.

MGO - MANUAL GEAR OPERATOR  - A gear operator that is operated manually (with a handwheel).

MONITORING - MONITOR SERVICE - A field procedure whereby two valves - usually regulators - are installed in series and adjusted in such a manner that, should the primary regulator fail, the standby regulator will automatically take over at a slightly higher pressure setting.

MWP - MAXIMUM WORKING PRESSURE OR CWP (COLD WORKING PRESSURE) - The maximum working pressure (pounds per square inch) at which a valve can be operated. The maximum working pressures for various pressure classes. (Table 2.1 of API-6D, within temperature limits of -20°Fand +100°F)

NEEDLE VALVE - A type of small valve, used for flow metering, having a tapered needle-point plug or closure element and a seat having a small orifice.

NIPPLE -  A short length of small size pipe, threaded on both ends. Used on end connections of screwed-end valves and in small size piping systems.

NITROGEN/HELIUM TEST - A pressure test conducted using nitrogen or helium (inert gases) instead of air, water, or other gases to prevent any dangers of fires or explosions. Generally specified by the purchaser when buying a valve or regulator product.

NON-DESTRUCTIVE TESTS - Those inspection tests which are not destructive to the valve structure or function. See "Radiography," "Dye Penetrant," "Magnetic Particle" and "Ultrasonic Testing."

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 line fluids.

NORMALLY CLOSED SOLENOID VALVE - An electrically operated valve whose inlet orifice is closed when the solenoid coil is not energized. Energize to open. See "Solenoid Valve."

NPS: NOMINAL PIPE SIZE - Dimensionless number used to indicate sizes of pressure pipe and valves - used interchangeably with valve size in inches.

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.

O.D. - OUTSIDE DIAMETER - The measurement of the outermost diameter of a circular part.

OD - The measurement of the outside diameter of a circular part.

OPERATING TIME - The time required for a power operator to stroke the valve from the full open to full closed position, or vice-versa.

OPERATOR - A device which converts manual, hydraulic, pneumatic or electrical energy into mechanical motion to open and close a valve. See "Power Operator,"; "EMO"; "GO"; "HWO"; "MGO"; "MO."

O-RING - An elastomeric or synthetic seal ring of circular cross-section.

OS&Y - OUTSIDE SCREW & YOKE - A valve in which the fluid does not come in contact with the stem threads. The stem sealing elements is between the valve body and the stem threads.

OUTER SEAT RING - The outer metal piece of a two-piece seat ring unit. See "Inner Seat Ring."

PIG - A device, closely conforming to the pipe bore, which is forced thru a pipeline to clean the pipe of all foreign material and debris. The valves in a pipeline that will be pigged, must be thru-conduit, full port, otherwise the pig will not pass through them.

PILOT - A spring loaded pressure regulator used to control the pressure and flow of other larger pressure regulators or instruments.

PILOT-OPERATED REGULATOR - A regulator which is controlled by a second small volume high accuracy regulator or pilot. This arrangement has the advantages of improving performance by minimizing the effects of unbalance and droop. The number of possible applications are also increased since a wide range of pilot configurations are feasible.

PINHOLE - Numerous small gas holes at the surface or just below the surface of castings, generally occurring in the thicker parts of the casting as a reduction in the solubility of gases in the metal as the metal cools.

PISTON EFFECT - The sealing principle involved in utilizing line pressure to affect a seal across the floating seats of some valves.

PLASTICS - A broad classification covering a variety of non-metallic, synthetic or organic materials capable of being moulded or formed into desired shapes. Also used as a protective coating for valves.

PLUG VALVE - A quarter turn valve whose closure element is usually a tapered plug having a rectangular port.

PLUG - The rotating closure element of a plug valve. Also a threaded fitting used to close off and seal an opening into a pressure containing chamber, e.g., pipe plug.

PNEUMATIC TEST - A test in which a valve is tested with air - usually a seat closure test.

PNEUMATIC - Pertaining to, or using, air or gas.

POSITION INDICATOR - Any external device which visually indicates the open and closed position of a valve. See "Stem Indicators."

POWER OPERATOR - Powered valve operators are of the following general types: Electric Motor, Pneumatic or Hydraulic Motor, Pneumatic or Hydraulic Cylinder. Operators can either be adapted directly to the valve stem or side mounted on existing gear or scotch-yoke operators.

PRESSURE 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.

PRESSURE DROP - The decrease in pressure along the direction of flow in a piping system, caused by fluid friction, restrictions, and by change-of-direction fittings. Pressure drop is related to velocity, specific gravity, viscosity and to the size and roughness of the pipe interior. See "Differential Pressure."

PRESSURE REDUCING REGULATOR - Regulator designed to control downstream pressure. See "REGULATOR."

PRESSURE SWITCH - A switch (usually electric) activated by a rise or drop in pressure.

PRESSURE TEST - A test using specified pressures of liquid or gases, which can be used to check sealing, integrity, design standards, etc. of a particular product.

PRESSURE-TEMPERATURE RATINGS - The maximum allowable working pressures at specified temperatures. For steel valves, the ratings are defined by "classes".

PROOF PRESSURE - A hydrostatic test pressure, usually 1 ½ times the rated working pressure, applied to an assembled valve to verify the structural integrity of the pressure containing parts. Synonymous with hydrostatic shell test. (Table 5.1, API-6D).

PROTECTIVE SLEEVES - A circular "pipe like" sleeve inserted in place of the ball and seats of a top entry ball valve. This protective sleeve remains in place inside the valve during valve installation and ultimate pigging of a pipeline to clear debris from the line before placing the pipeline into service. Once the pipeline has been purged of all debris, the protective sleeve is removed entirely from the ball valve cavity and operating trim (i.e. ball and seats) is then installed for normal service conditions.

PSI (PSI) - POUNDS PER SQUARE INCH - Force per unit area exerted against a resisting body.

PULSATION - Rhythmical throbbing or vibrating. In pipelines, flow or pressure oscillation which is identically repeated in every fixed time interval. Pulsation is an inherent characteristic of reciprocating gas compressors and reciprocating liquid pumps. Pressure and flow pulsations interact with piping systems to cause vibration, metering errors, and potential equipment damage.

PUMP CONTROL VALVE - A ball valve that is not meant for on-off service, but whose specific function is to control flow and prevent cavitation in pumps on liquid pipelines.

PUMP - A rotary or reciprocating device using mechanical energy to propel liquids thru pipelines or to draw liquids from tanks or sumps by suction.

RACHET DRIVE - A shaft or valve that is operated by means of a ratchet mechanism. The ratchet delivers an intermittent stepped rotation through a gear in one direction only.

RAISED FACED (RF) - The raised area of a flange face which is the gasket sealing surface between mating flanges. Defined in ASME B16.5. Class 150 and 300 valves have 0.06" RF and Classes 600 and up have a 0.25" RF.

REDUCED PORT - A valve port opening that is smaller than the line size or the valve end connection size.

REGULAR PORT VALVE - A term usually applied to plug valves. The "regular" port of such a valve is customarily about 40% of the line pipe area. Hence, it corresponds to a venture or reduced bore valve of like nominal pipe size. Venturi ball valves are often a logical alternative to plug valves with advantages in price, torque, and low maintenance.

REGULATOR - A throttling valve which exercises automatic control over some variable (usually pressure). Not an on-off valve.

RELIEF VALVE - A quick acting, spring loaded valve that opens (relieves) when the pressure exceeds the spring setting. Often installed on the body cavity of ball and gate valves to relieve thermal overpressure in liquid services. See "B.R.V.".

REMOTE CONTROL - The operation of a valve or other flow control device from a point at a distance from the device being controlled. Can be accomplished by electrical, pneumatic or hydraulic means.

RESILIENT SEAT - A valve seat containing a soft seal, such as an o-ring, to assure tight shut-off.

RF (RAISED FACE) - The raised area of a flange face which affords a seal with a mating flange face by means of a flat gasket of the same diameter as the raised face.

RING TYPE JOINT (RTJ) - A flange connection using a specially shaped soft metal ring as a gasket. Generally used on high pressure valves. May be the body and bonnet connection and/or the end flange connection.

RISING STEM - A valve stem which rises as the valve is opened.

RS Rising stem - A valve stem with threads arranged so that as the stem turns, the threads engage a stationary threaded area and lift the stem along with the closure element attached to it.

RTJ Ring Type Joint - A flange connection using a specially shaped soft metal ring as a gasket. Generally used on high pressure valves and not widely used in the pipeline industry.

RUPTURE DISC (BLOW-OUT DISC) - An emergency over-pressure relief device, employing a relatively thin diaphragm, designed to burst at a specified pressure. Cannot be reset - must be replaced after rupture event.

SAFETY VALVE - A quick opening, pop action valve used for fast relief of excessive pressure.

SCOTCH YOKE OPERATOR (USED ON QUARTER TURN VALVES) - A quarter turn operator using a scotch yoke mechanism rather than gears. The "Scotch Yoke" has a torque output at the beginning and ending of its stroke that is generally twice the magnitude of the torque output in the centre of its stroke.

SCREWED ENDS - Internally threaded end connections supplied on some valves. Usually BSP or NPT.

SEAL WELD - A weld that does not contribute anything to the mechanical integrity of an assembly but is made purely to seal or prevent leakage from, for instance, a threaded joint.

SEAL, DYNAMIC - A sealing element used between parts that have relative motion, i.e., stem seals, seat seal O-rings, etc.

SEAL, STATIC - A sealing element used as a gasket between two non-moving parts, i.e. valve bonnet o-ring, ball valve body o-ring, flange gasket.

SEAT - part of a valve against which the closure element (gate, ball) effects a tight shut-off. In many ball valves and gate valves, it is a floating member containing a soft seating element (usually an o-ring).

SELF RELIEVING - The process whereby excessive internal body pressure, in some valves, is automatically relieved either into the upstream or downstream line by forcing the seats away from the closure element.

SEPARATOR - A special tank used to separate gas from oil in some crude oil gathering systems.

SHORT PATTERN VALVE - A valve whose face-to-face dimension is less than the API-6D standard.

SHUT-OFF VALVE - A valve designed only for on/off service. Not a throttling valve. Sometimes referred to as a "block valve."

SLURRY SERVICE - An application involving a flow medium consisting of small solid particles suspended in a liquid. Coal slurry consisting of about equal parts of coal and water, is transported by pipeline from coal mines to power plants where the coal is de-watered and burned.

SNG - SYNTHETIC NATURAL GAS - A substitute natural gas made from the by-products of chemical plants and refineries. Also, see "Coal Gasification."

SOCKET END - An end connection in which a pipe or tube is inserted into a counterbored hole and then brazed, or fillet welded.

SOCKET WELD END (SWE) - The end connection of a valve suitably prepared for socket welding to a connecting pipe.

SOLENOID VALVE - A small electrically operated valve used in the control piping of powered by hydraulic or pneumatic cylinder operators.

SOUR GAS - Natural gas containing significant amounts of hydrogen sulphide (H2S). Requires special material treatments to avoid failures from sulphide corrosion cracking.


SPECIFIC GRAVITY - The ratio of the weight of a given volume of fluid to the weight of an equal volume of water (if the fluid is a liquid) or to the weight of an equal volume of air (if the fluid is a gas).

SPECIFICATION - A document that defines the requirements that a finished product must conform to - may include chemical and mechanical properties, tolerances, marking, shipping, etc.

SPOOL PIECE See "Adapter Spool"

SPST - SINGLE-POLE, SINGLE THROW - Refers to the function of an electrical switch often used in the control system of electric valve operators.

SPUR GEAR - The simplest of gears. In a gear set, the input spur gear and output spur gear are aligned on parallel shafts. An idler gear may be used to the direction of rotation on the two shafts is in the same direction.

STAINLESS STEEL (SS) - Any of a number of types of iron alloy with chrome, nickel, or other elements that does not oxidize in free air.

STEM INDICATOR (VPI - VISIBLE POSITION INDICATOR) - A position indicating rod supplied with gate valves. It extends from the top of the valve stem and serves to indicate the relative position of the gate.

STEM NUT - A one or two-piece nut which engages the stem threads of a valve and transmits torque from an operator to the valve stem.

STEM - A rod or shaft used to transmit motion from an operator to the closure element of a valve.

STREET ELBOW A 90° - pipe fitting with male thread and female threaded or socket weld ends.

STUD - A bolt, threaded on both ends, often used in bolting together two members, one of which has blind tapped bolt holes.

SUBMERSIBLE SERVICE - Underwater or subsea installation. Valves require special treatment to protect against corrosion and external seawater pressure.

SURGE - To rise suddenly to an excessive or abnormal value; a transient sudden rise of pressure in a pipeline. Pipeline surges can be positive or negative and are caused most frequently by the sudden closure of a block valve or emergency shutdown of a pump. Surge pressures in excess of the rated capacity of a pipeline can cause ruptures of the piping system.

SWEET GAS - Natural gas having no significant hydrogen sulphide content.

SWING CHECK VALVE - A check valve in which the closure element is a hinged clapper which swings or rotates about a supporting shaft. See "Clapper"; "Check Valve".

SY - SCOTCH YOKE See "Scotch Yoke Operator"

TEE - A pipe or tubing fitting with a side outlet at right angles. Resembles a "T".

TENSILE TEST - A destructive test performed on a specially machined specimen taken from material in its delivered condition to determine mechanical properties, such as tensile strength, yield strength, and percent elongation.

THROTTLING - The intentional restriction of flow by partially closing or opening a valve. A wide range of throttling is accomplished automatically in regulators and control valves.

THRU-CONDUIT - An expression characterizing valves when in the open position, wherein the bore presents a smooth uninterrupted interior surface across seat rings and thru the valve port, thus affording minimum pressure drop. There are no cavities or large gaps in the bore between seat rings and body closures or between seat rings and ball/gate. Consequently, there are no areas that can accumulate debris to impede pipeline cleaning equipment or restrict the valve's motion.

THRUST - The net force applied to a part in a particular direction - e.g., on the end of a valve stem.

TOP ENTRY - The design of a particular valve or regulator where the unit can be serviced or repaired by leaving its body in the line, and its internals can be accessed by removing a top portion of the unit.

TORQUE SWITCH - An electrical device on a motor operator which cuts off power to the operator when allowable torque is exceeded, thus preventing damage to the valve and/or the operator.

TORQUE - The turning effort required to operate a valve. Usually expressed in "pound-feet" and referred to the stem nut, handwheel or operator pinion shaft.

TORSIONAL SPRING - A coiled spring which exerts a force by twisting about its axis rather than by compression or elongation. The spring in a check valve slam retarder which is restrained at one end and fastened to the clapper shaft on the other end. As the clapper opens, the spring resists the motion creating a closing force. During a rapid decrease in flow rate, the clapper is urged toward the closed position and is virtually closed just prior to the instant of actual flow reversal - thus slamming is avoided.

TRANSITION PIECE - A length of pipe that is welded to a valve hub or closure. Generally provided by the customer, it serves as a transition from the customer's piping to the valve to compensate for differences in material or size.

TRIM - Commonly refers to the valve's working parts and to their materials. Usually includes seat ring sealing surfaces, closure element sealing surfaces, stems, and back seats. Trim numbers which specify the materials are defined in API 600 and API 602.

TRIPLE ECCENTRIC (BUTTERFLY VALVES) - A particular design of a butterfly valve where the stem is located behind the disc, below the centreline of the disc, and its cone axis is offset from the centreline of the disc. This particular design is capable of a very tight shutoff at temperatures well above 100°F.

TRUNNION - That part of a ball valve which holds the ball on a fixed vertical axis and about which the ball turns. The torque requirement of a trunnion mounted ball valve is significantly less than that for a floating ball design.

TURNS TO OPERATE - The number of complete revolutions of a handwheel or the pinion shaft of a gear operator required to stroke a valve from fully open to fully closed or vice versa

U-CUP (RING-PACKING) - A "U" cross-section ring located on the tail end of certain ball valve seats to retain the grease in an emergency seat seal system.

UNION BONNET - A type of valve construction in which the bonnet is held on by a union nut with threads on the body.

UNION CONNECTION - A small 3-piece fitting used to join two lengths of pipe. A female piece is installed on each of the two pipe ends and the connection is mechanically sealed by an external nut.

VACUUM - A space from which air or gas has been exhausted until its pressure is less than atmospheric pressure, i.e., any pressure below 14.7 psi absolute.

VALVE - A device used to control the flow of fluid contained in a pipe line.

VARIABLE ORIFICE - A small variable profile valve put in a flow line and used with a pilot to restrict the flow into the pilot and make the pilot more or less sensitive to changing conditions.

VDS - VALVE DATA SHEET - A data sheet defining the minimum level of a valve design, including the materials, testing, inspection, and certification requirements.

VELOCITY - The speed at which a fluid flows thru a line in a specified direction. Usually expressed in "feet per second."

VENT PLUG - (VENT PLUG ASSEMBLY) - (SAFETY VENT PLUG) - A special pipe plug having a small Allen-wrench operated vent valve. These special plugs are located at the bottom of most ball valves. With the line valve closed (and under pressure) the body cavity pressure can be vented thru this small valve to check tightness of seat seals or to make minor repairs. Having vented the body pressure, the vent plug may be removed to blow out debris and foreign material or to flush the body cavity. On some gate valves, the vent plug is installed on the bonnet for the sole purpose of venting the body. Such valves have separate drain valves. See "Block and Bleed"; "Drain Valve."

VISCOSITY - A measure of the internal friction of a fluid or the resistance of a fluid to flow. Two fluids of identical specific gravity may have quite different viscosities.


W.O. - WRENCH OPERATED - The operation of a valve by means of a handle or lever. Used on smaller size and lower pressure class valves.

WALL THICKNESS - The thickness of the wall of the pressure vessel or valve. For steel valves, minimum thickness requirements.

WATER HAMMER - The physical effect, often accompanied by loud banging, produced by pressure waves generated within the piping by rapid change of velocity in a liquid system.

WE OR W.E. - WELD END - The end connection of a valve which is to be installed by welding into the line. To prepare the end bevel, it is necessary to know the wall thickness and specified minimum yield strength of the connecting pipe. See "End Bevel."

WEAR TEST - Verification of a components resistance under specific wear conditions.

WEATHER PROOF - Describes a valve operator or other device that is protected against intrusion of water, sand, dust, or other atmospheric contamination.

WEDGE GATE - A gate whose seating surfaces are inclined to the direction of closing thrust so that mechanical force on the stem produces tight contact with the inclined seat rings.

WELD NECK FLANGE - A flanged piping element with a weld neck used in pipeline construction to provide a companion flange for installation of flanged valves. Also used to convert weld end valves to flanged valves or vice versa.

WELD REDUCERS - A reducing fitting used on weld end piping components to adapt from a large sized pipe to a smaller diameter pipe, or vice versa.

WOG - (WATER - OIL - GAS) - Used in connection with a pressure rating. Thus: 100 WOG indicates the rated pressure is 100 psi in water, oil, or gas service, at normal ambient temperatures.

WORKING PRESSURE - The pressure (pounds per square inch) at which a valve is designed to operate.

WP - WORKING PRESSURE - The pressure (pounds per square inch) at which a valve is designed to operate. Same as "operating pressure rating."

YIELD STRENGTH - The limiting stress (psi) beyond which a material will sustain permanent deformation. Up to the yield strength, the material will spring back to its original dimension when the pressure is removed. Often in valve specs, the yield strength will be designated. This allows proper material selection.

YOKE - That part of a gate valve which serves as a spacer between the bonnet and the operator or actuator.