Glossary Terms

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ANSI – American National Standards Institute - The principle standards writing organization in the United States, who sets standards for a wide variety of items, including the design, fabrication and testing of pressure piping, systems and components for various pipeline services.

 

API – American Petroleum Institute – The principal United States oil company trade association.  It has some standards and specification writing functions, such as wellhead components and pipeline valves.

 

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.

  

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

 

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

 

BGO- Bevel Gear Operated (Operator) – The actuation of a 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.  Used on gate valves.

 

BACK SEAT – 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 VALVE – A valve using a ball that is rotated through 90 degrees to open and close the valve.

 

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 through blow down valves or vent plugs.  Useful in testing for integrity of seat seals and in accomplishing minor repairs under pressure.

 

BONNET – The top part of a valve, attached to the body, which guides the stem and adapts to extensions or operators.  Provides leak proof closure for the valve body. The threaded section of stem goes through a hole with matching threads in the bonnet. Globe valves may have a screw-in, union, or bolted bonnet. Screw-in bonnet is the simplest bonnet, offering a durable, pressure-tight seal. Union bonnet is suitable for applications requiring frequent inspection or cleaning. It also gives the body added strength. A bonnet attached with bolts is used for larger or higher pressure applications. Bonnets also contain the packing, which is a wearable material that maintains the seal between the bonnet and the stem during valve cycling operations

 

BODY – The main pressure containing structure of the valve and the most easily identified as it forms the mass of the valve. It contains all of the valve's internal parts that will come in contact with the substance being controlled by the valve. The bonnet is connected to the body and provides the containment of the fluid, gas, or slurry that is being controlled.

BORE – The inside diameter of the smallest opening through a valve; i.e. the diameter of the hole in the ball of a ball valve; the diameter of the hole in the gate of a gate valve.

 

BUTT WELD ENDS – The end connection of a valve suitably prepared for butt-welding to connecting piping.

 

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

 

CHECK VALVE – A one-directional hinged closure (clapper) valve which is opened by the fluid flow in one direction and which closes automatically when the flow stops or reverses direction.

 

CLASS - A designation of pressure capability

 

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 readjust the opening of the valve in order to re-establish the original control setting.

 

DTR-DIFFERENTIAL THERMAL RELIEF – A relief valve mounted at a tee on the valve bonnet, pipes excess pressure to the upstream throat of the valve.  This system functions only when the valve is closed. A manual body bleed valve is included. This bleed valve, installed at the tee, is opened after the valve is closed. Seal effectiveness can be immediately evaluated. This bleed valve must be closed before the valve is reopened. An isolation valve installed in the upstream throat tap is also included. It must be left open to permit the relief system to relieve pressure upstream and is closed only for repair.

 

DOUBLE BLOCK & BLEED – The capability of a valve, in a pipeline under pressure, to have its body cavity bled down to atmospheric pressure when the valve is in either the fully closed or fully open position.

 

ELASTOMER – A natural or synthetic elastic material.  Used in synthetic rubber parts such as O-rings.

 

END CONNECTION – The type of connection supplied on the ends of a valve that allows it to be installed in a pipeline.  Weld end, flanged end, screwed end.

 

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-grade accessibility to operating gear, blow-down and seat lubrication systems.

 

F.O.B. – Freight On Board – Transportation charges are absorbed by vendor to the FOB point.  Transportation charges pass to the customer when shipment leaves the FOB point.

 

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 ANSI B16.10 and API 6D to ensure that such valves are mutually interchangeable, regardless of the manufacturer.

 

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

 

FLANGE – A cast or formed pipefitting 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.

 

FLOATING BALL – A ball valve having a non-trunnion mounted ball.  The ball is free to float between the seat rings.

 

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.

 

GASKET – A seal or packing placed between mechanical joints (such as flanges) to prevent the escape of the flowing medium

 

GATE VALVE – A straight through pattern valve whose closure element is a sedge 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.

 

GLOBE VALVE – A valve whose closure element is a flat disc or conical plug sealing on a seat that is usually parallel to the flow axis.  The tortuous flow path produces a relatively high-pressure loss.

A Globe valve is a type of valve used for regulating flow in a pipeline, consisting of a movable disk-type element and a stationary ring seat in a generally spherical body. Globe Valves are named for their spherical body shape with the two halves of the body being separated by an internal baffle. This has an opening that forms a seat onto which a movable plug can be screwed in to close (or shut) the valve. The plug is also called a disc or disk. In globe valves, the plug is connected to a stem which is operated by screw action in manual valves. Typically, automated valves use sliding stems. Automated globe valves have a smooth stem rather than threaded and are opened and closed by an actuator assembly. When a globe valve is manually operated, the stem is turned by a handwheel.

 

HARD FACING – A surface preparation in which an alloy is deposited on a metal surface, usually by weld overlay, to increase abrasion and/or corrosion resistance.

 

HOT TAPPING – The process by which a pipeline, under pressure, is cut into to provide a side outlet.  A flanged fitting is saddle welded to the pipeline and a full port valve bolted to the flange.  The hot tapping machine, bolted to the outboard valve flange, operates through the open valve.  After cutting out a circular piece from the pipe wall, the tapping machine is removed and the valve closed.

 

HYDROSTATIC TEST – A shell test in which a valve is completely filled with water and pressure tested.  Used for conducting proof pressure testing.

 

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 actuator.

 

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

 

MAXIMUM 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 within temperature limits of –20F degrees and +100F degrees.

 

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.

 

NACE – NATIONAL ASSOCIATION OF CORROSION ENGINEERS – The technical association publishes papers, articles and standards on all aspects of corrosion, and has written the definitive standard for valve materials for sour gas service.

 

NEMA – NATIONAL ELECTRICAL MANUFACTURERS ASSOCIATION – An association which has set up guidelines for the manufacture of electrical equipment.  Generally applicable to specifications for switches, etc., for electric operators.

 

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.

 

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 that converts manual, hydraulic, pneumatic or electrical energy into mechanical motion to open and close a valve.

 

PIG – A device, closely conforming to the pipe bore, which is forced through 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.

 

PLUG - The closure member of the valve. Plugs are connected to the stem which is slid or screwed up or down to throttle the flow. Plugs are typically of the balance or unbalanced type. Unbalanced plugs are solid and are used with smaller valves or with low pressure drops across the valve. The advantages are simpler design, with one possible leak path at the seat and usually lower cost. The disadvantages are the limited size; with a large unbalanced plug the forces needed to seat and hold the flow off become impractical. Balanced plugs have holes through the plug. Advantages include easier shut off as the plug does not have to overcome static forces. However, a second leak path is created between the plug and the cage, cost is generally higher.

 

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.

 

RTJ-RING TYPE JOINT – A flanged connection using a specific shaped soft metal ring as a gasket. Generally used on high pressure valves.

 

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.

 

SAFETY VALVE – A safety valve is a valve mechanism for the automatic release of a gas from a valve when the pressure or temperature exceeds preset limits. It is part of a bigger set named Pressure Safety Valves (PSV), Pressure Relief Valves (PRV) or Differential Thermal Relief (DTR). The other parts of the set are named relief valves, safety relief valves, pilot-operated safety relief valves, low pressure safety valves, vacuum pressure safety valves .

 

SEAT (Seat Ring) – That part of a valve against which the closure element (gate, ball) effects a tight shut-off.

 

STEM – The stem serves as a connector from the actuator to the inside of the valve and transmits this actuation force. Stems are either smooth for actuator controlled valves or threaded for manual valves. The smooth stems are surrounded by packing material to prevent leaking material from the valve. This packing is a wear material and will have to be replaced during maintenance. With a smooth stem the ends are threaded to allow connection to the plug and the actuator. The stem must not only withstand a large amount of compression force during valve closure, but also have high tensile strength during valve opening. In addition, the stem must be very straight, or have low runout, in order to ensure good valve closure. This minimum runout also minimizes wear of the packing contained in the bonnet, which provides the seal against leakage. The stem may be provided with a shroud over the packing nut to prevent foreign bodies entering the packing material, which would accelerate wear.

 

STUFFING BOX – The annular chamber provided around a valve stem in a sealing system into which the 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.

 

THRU-CONDUIT – An expression characterizing valves, when in the open position, wherein the bore presents a smooth uninterrupted interior surface across seat rings and through 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.

 

TRUNNION – That part of a ball valve which holds the ball on a fixed vertical axis and about which the ball turns.

 

VALVE – A valve is a device that regulates the flow of materials (gases, fluidized solids, slurries, or liquids) by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but usually are discussed separately.

 

 

W.O.G. (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.

 

WORM GEARS – Gears used to transmit motion or power between right angle shafts when a high-ratio reduction is necessary. The worm is the small gear which drives the larger ring gear. Worm threads resemble screw threads and are available in various leads and pitches.

 

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