Glossary of Valve Terms

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.

ALL WELDED CONSTRUCTION
Pertains to a valve construction in which the body is completely welded and cannot be disassembled and repaired in the field.

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.

API - Spec 6D
An API specification dealing with pipeline valves. Most pipeline valves are manufactured to this specification, and, if so, can be identified with the API 6D monogram.

API - SPEC 6FA
The API specification dealing with the fire testing of pipeline valves. Once a particular size and pressure class valve is tested and passes the API-firetest, like valves can be identified with the above monogram. API-6FA supersedes API-RP-6F.

B.R.V. - Body Relief Valve
A relief valve (optional) installed on ball valves used in liquid service to provide for the relief of excess body pressure caused by thermal expansion.

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.

BALL VALVE
A valve using a spherical closure element (ball) which is rotated thru 90° to open and close the valve.

BALL
The spherical closure element of a ball valve.

BDV - Blow Down Valve
A small ball valve that is installed on the aboveground end of an extended drain line. This valve also serves to vent body cavity pressure in the "block and bleed" mode.

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 gearsetdetermines the multiplication of torque achieved.

BLOCK AND BLEED
The capability of obtaining a seal across the upstream and downstream seat rings of a valve when the body pressure is bled off to atmosphere thru blow down valves or vent plugs. Useful in testingfor integrityof seat seals and in accomplishing minor repairs under pressure.

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.

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.

BS 6755
The British Standard specification dealing with the fire testing of pipeline valves. Once a particular size and pressure class valve is tested and passes the BS 6755 fire test, like valves can bealso identified with the BS 6755 standard.

BUBBLE-TIGHT SHUT-OFF
A phrase used in 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 thru water. To qualify as "bubble tight," no bubbles should be observed in a prescribed time span.

BURIED SERVICE
An application in which valves are installed in lines which are buried below ground level.

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

BUTTERFLY VALVE
A short face-to-face valve which has a movable vane, in the center of the flow stream, which rotates 90 degrees as the butterfly valve opens and closes.

BVR - BALL VALVE REGULATOR
An automatic throttling valve controlling flow or pressure in a pipeline; comprising a package involving al ball valve actuator, positioner, and controlling instrument.

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

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

CASTING
A product or the act of producing a product made by pouring molten metal into a mold and allowing it to solidify, thus taking the shape of the mold.

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

CHARACTERIZED GATE OR BALL
A ball or gate, the shape of whose port has been specially altered to provide a specific throttling capability.

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.

CITY GATE - CITY GATE STATION
The metering and pressure reducing station where gas is transferred from a high pressure cross-country transmission line to a low pressure distribution piping system within a city.

CLAPPER
The hinged closure element of a swing check valve.

CLOSURE ELEMENT
The moving part of a valve, positioned in the flowstream 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.

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.

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.

COULISSE
Of or using runners or slides as a guiding mechanism; as in a "Coulisse" style gate valve.

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.

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.

DIP TUBE
Extending the blow down valve on large gate valves requires a tube which is located inside of the valve. The tube is called the "dip tube" and extends through the bonnet to the bottom of the body cavity.

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.

"DOUBLE" PISTON EFFECT PRINCIPAL (DPE)
The sealing principal of a ball valve whereby line pressure is used on both the upstream and downstream floating seats to effect a dead-tight seal simultaneously on both sides of the ball. With the DPE seat configuration when the upstream seat leaks, the pressure entering into the body cavity acts on the down stream seat, which being of the PPE design, is then pushed against the ball and the valve seals in both directions.

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.

DROOP
A drop in set (outlet) pressure of a regulator or control valve due to the travel of its valve or poppet, as the required flow increases from low to maximum. A slight change in the control spring length due to the valve travel, will result in spring force variations, translating into a change of set (outlet) pressure.

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

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.

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 full open position, the gate and segment seal off against the seats while the flow is isolated from the valve body.

EXTENDED BDV (Blow Down Valve)
Used on buried valves where the drain plug is inaccessible. Instead, a line is piped above grade, terminating in a small valve. Line pressure is used to blowout condensates and other material which settles out in the bottom of the body cavity.

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

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.

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.

FIELD SERVICEABLE
A statement indicating that normal repair of the valve or replacement of operating parts can be accomplished in the field without return to the manufacturer.

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.

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.

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.

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).

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.

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.

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.

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.

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.

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.

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.

MGO - Manual Gear Operator
A gear operator that is operated manually (with a handwheel).

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.

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.

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.

OPERATOR
A device which converts manual, hydraulic, pheumatic or electrical energy into mechanical motion to open and close a valve.

OSandY - Outside Screw and 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.

PACKING
The deformable sealing material inserted into a valve stem stuffing box, which, when compressed by a gland, provides a tight seal about the stem.

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

POLY PAK STEM SEAL
An O-ring energized lip-seal which replaces O-ring stem seals in certain gate valves. Also used for stem seals in some ball valves.

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

PROOF PPRESSURE
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.

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.

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.

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 bor valveof like nominalpipe 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.

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.

Rim pull
The force required at the edge of the handwheel to generate the required torque at the center of the handwheel.

RISING STEM BALL VALVE
A single seated ball valve that is designed to seal by using the valves stem to mechanically wedge the valves ball into a stationary seat effecting a bubble tight seal. The valves stem operates througha guide sleeve assembly that guides the stem through a quarter turn of rotation as the stem is raised or lowered by a handwheel (or actuator). The mechanical action of the stem moves the ball away fromthe seat prior to the 90° rotation of the ball. This design provides lower operating torques and longer seat life while assuring bubble tight shut off.

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.

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 oft he torque output in the center of its stroke.

SEAT
That 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.

SHORT GATE
A gate valve whose seat rings contact the gate only in the closed position. Such valves are not through conduit, as the gate is completely withdrawn from the flow area in the open position.

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."

SLAB GATE
A gate having flat, finely finished, parallel faces - as opposed to a wedge gate. Such a closure element slides across the seats and does not depend on stem force to achieve tight shut off.

SLAM RETARDER
A device designed to prevent the clapper of a check valve from slamming as it closes upon flow reversal. Hydraulic damping cylinders, rotary vanes, and torsional springs are all used for this purpose.

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

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.

Square operating nut
A nut, usually 2" x 2", which is attached to a valve stem or the pinion shaft of a gear operator allowing use of wrenches to quickly operate the valve.

SSIV (SUB SEA ISOLATION VALVE)
A valve used underwater, generally in a manifold that will close and isolate a particular pipeline or process in an emergency.

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.

STOP COLLAR
The collar on a ball valve which restricts the ball to 90° of rotation from the fully open to the fully closed position.

STUFFING BOX
The annular chamber provided around a valve stem in a sealing system into which deformable packing is introduced.

SWING CHECK VALVE
A check valve in which the closure element is a hinged clapper which swings or rotates about a supporting shaft.

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 pressuredrop. 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 tot he clappershaft 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.

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 specifythe 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 centerline of the disc, and its cone axis is offset from the centerline of the disc. This particular designis 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 floatingball 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.

TWO INCH SQUARE OPERATING NUT
A nut attached to the valve stem or to the pinion shaft of a gear operator. Valves so equipped are usually situated below grade in road boxes and are operated by long handled "T" wrenches.

TWO-WAY SPHERE-LOK
A Sphere-Lok with two ports.

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.

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.

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 pressurecan 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.

VENTURI VALVE
A reduced bore valve. A valve having a bore smaller in diameter than the inlet or outlet. For example, an 8"x 6" x 8" ball valve has 8" inlet and outlet connections while the ball and seats are 6". The flow through a venture valve will be reduced because of the smaller port. Venturi valves can often be economically substituted for plug valves.

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 thicknes
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
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.

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.

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