valve banner 3Valve, abbreviated as V, is a mechanism used to stop or open and regulate flow.  The type of valve used depends on the application.  In general, there are valves used for on-off (open-closed) applications, and throttling valves which can adjust flow.  All valves fall into two basic types: stop valves and check valves.

  • Stop Valves  -  Stop valves are used to shut off or partially shut off the flow of liquids.  Stop valves are divided into four basic types of valves: gate, globe, ball and butterfly.
  • Check Valves  -  Check valves are used to allow the flow of fluids in only one direction.  There are four basic types: diaphragm check, lift check, swing check, and tilting-disk check.
  • Valve Turns
    • Multi-turn Valves or Linear Motion Valves: Gate Valve, Globe Valve, Pinch Valve, Diaphragm Valve, Needle Valve
    • Quarter Turn Valve or Rotary Valve: Plug Valve, Ball Valve, Butterfly Valve
    • Self-activated Valves: Check Valve, Pressure Relief Valve

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Nomenclature & Symbols


  • \( ACTR \)  -  actuator
  • \( p_a \)  -  atmospheric pressure
  • \( BV \)  -  ball Valve
  • \( BCD \)  -  bolt circle diameter
  • \( BB \)  -  bolted bonnet
  • \( BC \)  -  bolted cap
  • \( BTFLV \)  -  butterfly valve
  • \( CI \)  -  cast iron
  • \( K \)  -  cavitation
  • \( CV \)  -  check valve
  • \( CWP \)  -  cold working pressure
  • \( CRSN \)  -  corrosion
  • \( DMV \)  -  distribution main valve
  • \( DD \)  -  double disk
  • \( DG \)  -  double disk gate
  • \( DI \) = ductile iron
  • \( ECV \)  -  emergency control valve
  • \( F-F \)  -  face to face
  • \( FLG \)  -  flange
  • \( FF \)  -  flat face
  • \( C_v \)  -  flow coefficient
  • \( Q \)  -  flow rate
  • \( F \)  -  force
  • \( f \)  -  friction
  • \( G \)  -  gas
  • \( GSKT \)  -  gasket
  • \( GV \)  -  gate valve
  • \( GLV \)  -  globe valve
  • \( HW \)  -  handwheel
  • \( ID \)  -  inside diameter
  • \( ISNRS \)  -  inside screw non-rising stem
  • \( ISRS \)  -  inside screw rising stem
  • \( IBBM \)  -  iron body bronze mounted
  • \( LIQ \)  -  liquid
  • \( MIV \)  -  main inlet valve
  • \( ND \)  -  nominal diameter
  • \( PV \)  -  plug valve
  • \( p \)  -  pressure
  • \( P-T \)  -  pressure - temperature
  • \( \Delta p \)  -  pressure differential
  • \( \Delta P \)  -  pressure loss
  • \( PRV \)  -  pressure reducing valve
  • \( PRV \)  -  pressure relief valve
  • \( NRS \)  -  non-rising stem
  • \( NC \)  -  normally closed
  • \( NO \)  -  normally open
  • \( OS \)&\( Y \)  -  outside screw and yoke
  • \( RF \)  -  raised face
  • \( RWD \)  -  resilient wedge disk
  • \( RTJ \)  -  ring type joint
  • \( RTJF \)  -  ring type joint flange
  • \( RS \)  -  rising stem
  • \( SCR'D \)  -  screwed
  • \( SIV \)  -  service isolation valve
  • \( SOV \)  -  shut off valve
  • \( SW \)  -  socket weld
  • \( SPW \)  -  spiral wound gasket
  • \( SS \)  -  stainless steel
  • \( WSP \)  -  steam working pressure
  • \(\large{ \sigma }\)  (Greek symbol sigma)  -  stress
  • \( T \)  -  temperature
  • \( TB \)  -  threaded bonnet
  • \( TC \)  -  threaded cap
  • \( TE \)  -  threaded end
  • \(\large{ \tau }\)  (Greek symbol tau)  -  torque
  • \( UB \)  -  union bonnet
  • \( UC \)  -  union cap
  • \( VAC \)  -  vacuum
  • \( V \)  -  valve
  • \( v \)  -  velocity
  • \( n \)  -  viscosity
  • \( Q \)  -  volumetric flow rate
  • \( QO \)  -  quick opening
  • \( WH \)  -  water hammer
  • \( WV \)  -  water valve
  • \( WP \)  -  working pressure
  • \( WOG \)  -  water pressure
  • \( WWP \)  -  water working pressure
  • \( WOG \)  -  working pressure, water, oil, gas
  • \( \sigma \)  (Greek symbol sigma)  -  yield strength


Valve Glossary


valve types

Ball Valve  -  A ball valve, abbreviated as BV, is a quarter turn valve used for changing the direction of a process stream (divert or shut off).  Ball valves can be automated to automatically shutdown or open depending on the orientation of the actuator.

  • Full Port Ball Valve, Reduced Port Ball Valve, Standard Port Ball Valve, Three-way Port Ball Valve, Trunnion Ball Valve

Butterfly Valve  -  A butterfly valve, abbreviated as BTFLV, is a quarter turn valve (90° or less) with a circular disk as its closing element.  The standard design has the valve stem running through the disk, giving a symmetrical appearance.

  • Flange Style Butterfly Valve, Lug Style Butterfly Valve, Wafer Style Butterfly Valve

Check Valve  -  Check valves, abbreviated as CV, are valves that are designed to allow the process fluid to flow in only one direction to prevent backflow. Check valves are also known as non-return valves, clack valves or one-way valves.

Control Valve  -

  • Back Pressure Valve, Choke Valve, Flow Control Valve, Level Control Valve, Pressure Control Valve, Temperature Control Valve

Diaphragm Valve  -

Gate Valve  -  The gate valve, abbreviated as GV, is one of the most frequently used valve in piping systems and is classified as either "rising-stem" or "nonrising-stem" valves.  The rising-stem gate valve has the stem attached to the gate, both gate and stem rise and lower together as the valve handwheel or actuator turns the stem.  In the nonrising-stem gate valves the stem is threaded into the wedge, rising and lowering the wedge.

  • Flap Gate Valve, Knife Gate Valve, Slide Gate Valve, Wedge Gate Valve

Globe Valve  -  A globe valve, abbreviated as GLV, is a type of valve used for regulating fluid flow, both on/off and throttling, it is a control valve.  The name globe valve comes from the globular shape of the valve body. 

  • Angle Globe Valve, Cross Globe Valve, Straight Globe Valve

Needle Valve  -

Pig Valve  -  A pigging valve is an alternative to conventional pig launchers.  They are capable of launching and receiving foam, steel, and solid cast pigs in both cylindrical and spherical shapes.  Original designs would only allow spherical shapes but machining innovations and technology have allowed for other shapes of pigs such as cups, disc, brushes and also foam pigs can be used.

Pinch Valve  -

Plug Valve - A plug valve is a quarter turn valve that has a conical or cylindrical plug that is rotated within the valve body to stop flow when needed.  Plug valves function similar to a ball valve where the plug has an opening in the plug that allows fluid to flow through the valve when it is open. 

  • Conical Plug Valve, Cylindrical Plug Valve, Lift Plug Valve, Multi Port Plug Valve

Pressure Relief Valve  -  A pressure safety valve is also known as a pressure relief valve and is used to protect vessels and tanks from overpressure.  It is designed to protect critical system components such as pressure vessels, tanks and flange ratings.

Specialty Valve  -


Valve Datasheets

Valve TypeDatasheets
Valves All Valves, ANSI (in)
Ball Ball Valve, ANSI (in)
Butterfly Butterfly Valve, ANSI (in)
Check Check Valve, ANSI (in)
Gate Gate Valve, ANSI (in)
Globe Globe Valve, ANSI (in)
Plug Plug Valve, ANSI (in)


Valve Standards

API Standards

  • API 6D - Specification for Pipeline Valves
  • API 6FA - Fire Test for Valves
  • API 594 - Wafer and Wafer-Lug Check Valve
  • API 598 - Valve Inspection and Testing
  • API 599 - Metal Plug Valve - Flanged and Butt-Welding Ends
  • API 600 - Steel Gate Valves, Flanged and Buttwelding Ends, Bolted and Pressure Seal Bonnets
  • API 602 - Compact Steel Gate Valves - Flanged, Threaded, Welded, and Extended Body Ends
  • API 603 - Class 150, Cast, Corrosion-Resistant, Flanged-End Gate Valve
  • API 607 - Fire Test for Soft Sealed Quarter Turn Valves
  • API 608 - Metal Ball Valves - Flanged and Butt Welding Ends
  • API 609 - Lug and Wafer Type Butterfly Valves

ASME Standards

  • ASME B16.5 - Pipe Flanges and Flanged Fittings
  • ASME B16.10 - Face to Face and End to End Dimensions of Valves
  • ASME B16.11 - Forged Fittings, Socket-Welding and Threaded
  • ASME B16.25 - Butt Welding Ends
  • ASME B16.33 - Manually Operated Metallic Gas Valves for Use in Gas Piping Systems Up to 125 psig (sizes 1/2 through 2)
  • ASME B16.34 - Valves Flanged, Threaded and Welding End
  • ASTM B16.37 - Hydroststic Testing of Control Valves
  • ASTM B16.38 - Large Metallic Valves for Gas Distribution (Manually Operated, NPS 2 1/2 to 12, 125 psig maximum)
  • ASTM B16.40 - Manually Operated Thermoplastic Gs Shutoffs and Valves in Gas Distribution Systems
  • ASME B16.47 - Large Diameter Steel Flanges
  • ASME B31.3 - Chemical Plant and Petroleum Refinery Piping
  • ASME B31.4 - Liquid Petroleum Transportation Piping System
  • ASME B31.8 - Gas Transportation and Distribution Piping System

ASTM Standards

  • ASTM A182 - Specification for Forged or Rolled Alloy Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High Temperature Service
  • ASTM A193 - Specification for Alloy Steel and Stainless Steel Bolting Materials for High Temperature Service
  • ASTM A194 - Specification for Carbon and Alloy Steel Nuts for Bolts for High Pressure and High Temperature Service
  • ASTM A694 - Specification for Carbon and Alloy Steel Forgings for Pipe Flanges, Fittings, Valves, and Parts for High-Pressure Transmission Service

BSI Standards

  • BSI 1414 - Steel Wedge Gate Valve (Flanged and Butt Welding Ends) for the Petroleum, Petrochemical, and Industries
  • BSI 1868 - Steel Check Valve (Flanged and Butt Welding Ends) for the Petroleum, Petrochemical, and Industries
  • BSI 1873 - Steel Globe and Globe Stop and Check Gate Valve (Flanged and Butt Welding Ends) for the Petroleum, Petrochemical, and Industries
  • BSI 5352 - Steel Wedge Gate, Globe and Check Valves 50 mm and smaller for the Petroleum, Petrochemical, and Industries

ISO Standards

  • ISO 15848-1 - Industrial valves -- Measurement, test and qualification procedures for fugitive emissions -- Part 1: Classification system and qualification procedures for type testing of valves
  • ISO 15848-2 - Industrial valves -- Measurement, test and qualification procedures for fugitive emissions -- Part 2: Production acceptance test of valves

MSS Standards

  • MSS SP-6 - Standard Finishes for Contact Faces of Pipe Flanges and Connecting-End Flanges of Valves and Fittings
  • MSS SP-25 - Standard Marking Systems for Valves, Fittings, Flanges and Unions
  • MSS SP-44 -Steel Pipeline Flanges
  • MSS SP-53 - Quality Standards for Steel Castings and Forgings for Valves, Flanges and Fittings and Other Piping Components - Magnetic Particle
  • MSS SP-54 - Quality Standards for Steel Castings and for Valves, Flanges and Fittings and Other Piping Components - Radiographic
  • MSS SP-55 - Quality Standards for Steel Castings and for Valves, Flanges and Fittings and Other Piping Components - Visual
  • MSS SP-61 - Pressure Testing for Steel Valves
  • MSS SP-82 - Valve Pressure Testing Method
  • MSS SP-70 - Cast Iron Gate Valves, Flanged and Threaded Ends
  • MSS SP-71 - Cast Iron Swing Check Valves, Flanged and Threaded Ends
  • MSS SP-79 - Socket-Welding Reducer Inserts
  • MSS SP-80 - Bronz Gate, Globe, Angle and Check Valve
  • MSS SP-82 - Valve Pressure Testing Methods
  • MSS SP-83 - Class 300 Steel Pipe Unions, Socket-Welding and Threaded
  • MSS SP-85 - Cast Iron Globe and Angle Valves, Flanged and Threaded Ends
  • MSS SP-88 - Diaphragm Type Valves

NACE Standards

  • NACE MR0175 - Standard Material Requirements for Sulfide Stress Cracking Resistant Metallic Materials for Oilfield Equipment


Valve Glossary


  • Actuator  -  An actuator is a device used to open, close, or control valves.  The most commonly used types are electrical, hydraulic, and pneumatic.
  • Actuator stem  -  A part used to connect the valve plug with the piston actuator.
  • Adjusting screw  -  A part used to compress the actuator spring.
  • Angle valve  -  A body configuration with one port perpendicular to the other port.
  • Atmospheric pressure  -  The pressure exerted upon the earth's surface by the air because of the gravitational attraction of the earth.
  • Automatic control valve  -  Final control element used in process systems to regulate flow.


  • Back pressure valve  -  A control valve that is designed to hold back pressure on a process.  This would be desirable to hold a certain level in a vessel or hold a gas pad above a tank.
  • Ball  -  The closing element of a ball valve.
  • Ball check valve  -   A check valve that is much like a swing check valve but instead of having a gate or guided disk, uses a ball to control flow.
  • Ball valve  -  A quarter turn valve used for changing the direction of a process stream (divert or shut off).
  • Barstock valve  -  Barstock valve has a body machined from a solid metal.
  • Bellows sealed valve  -  A bellows is a sealing device which prevents line leaking between the stem and the body of a valve. It is a flexible metal, usually made of stainless steel used to seal the stem through the shafts.
  • Bibb  -  A small valve with the outlet turned down.
  • Blowdown  -  A blow down is the emptying or depressuring of a pipeline or vessel. This is the difference between set pressure and re-seating pressure in a valve.
  • Body  -  The main casing container used for the flow of fluids and to hold the moving parts and seals of the valve.
  • Body rating (actual)  -  The interaction between being safe, acceptable flowing fluid pressure and temperature and the body, excluding all internals.
  • Body rating (normal)  -  The theoretical pressure rating of the body excluding all internals.
  • Bolted bonnet  -  A bonnet that is connected to the body with bolts.
  • Bonnet  -  The top part of a valve that is attached to the body that contains guids, packing, and stem.
  • Bonnet bolts  -  Bolts that hold the bonnet to the body.
  • Bottom flange  -  A flange at the bottom of a valve or opposite the bonnet.
  • Butterfly valve  -  A quarter turn valve (90° or less) with a circular disk as its closing element. 


  • Cavitation  -  The creation and collapse of bubbles in a liquid.
  • Check valve  -  These valves are designed to allow the process fluid to flow in only one direction to prevent backflow.
  • Choke Valve  -  Valves used in severe service valves designed for oil and gas applications.  They are used for controlling the flow rates or pressure on production, steam or water injection.
  • Cold box bonnet  -  A hollow extended bonnet which allows stagnated, moderate temperature gas to form, protecting the packing from cryogenic temperatures.
  • Clapper  -  The hinged closure of a check valve.
  • Close-off rating  -  The maximum pressure drop at which a valve can take without leaking when completely closed.
  • Closing pressure  -  The pressure at which a valve closes or reseats.
  • Control valve  -  This valve controls the flow capability by changing the flow passage size as directed by a signal from a controler.
  • Corrosion  -  The thinning of a pipe wall that is typically caused by a chemical reaction from a corroding fluid or agent and is limited almost exclusively to metal products.
  • Crack a Valve  -  To barely open a valve so that it leaks just a little.


  • Design pressure  -  The maximum pressure at which a valve can operate.
  • Direct pressure  -  Pressure applied by the flow against the back of the closure and/or opposite the seat end of the valve.
  • Disk  -  A valve assembly part that comes in contact with the seat to close off the flow.
  • Disk stroke  -  When the valve stem moves from a closed to open position.
  • Double-acting  -  Term used to describe supplying and exhausting air to both sides of the pistonsimultaneously.
  • Double block and bleed  -  When under pressure the valve has the capability to maintain a seal across both the upstream and downstream seat rings and have the body cavity bleed down to atmospheric pressure.
  • Double top-guided  -  A packing box configuration which uses two widely spaced guides, one at each end of the packing box, to guide the plug.
  • Drain plug  -  A plug at the bottom of a valve, when removed it drains and flushes the body cavity.


  • Electric actuator  -  It is mounted on a valve and receive a signal that moves the closing element to the desired position.
  • Eccentric ball  -  Similar to a ball valve except it usually contains a segmented ball or half ball.
  • Eccentric plug  -  Has an vertical rectangular opening in the body of a plug valve where the closure is rotated and seated against.
  • Expanded outlet  -  A body configuration with standard trim gallery and oversized ports.
  • Extended bonnet  -  A longer than normal bonnet which protects the packing and actuator from extreme heat or cold.
  • Extension  -  Equipment used to provide operating gear accessibility to a below grade valve.


  • Face-to-face  -  The distance from end to end of the valve.  These dimensions are goverened by ANSI specifications.
  • Facing  -  The contact surface finish of a flange.
  • Fail-safe  -  A system designed to open, close, or hold in last position should the air supply fail.
  • Flange  -  A bolted connection where two pieces of pipe, equipment, fittings or valves are connected together to form a piping system.
  • Flange safety spray shield  -  Spray shields also known as flange guard, are used on equipment (flanges in this case) where fluids are under pressure and need to be prevented from leaking or spraying on other equipment or people.
  • Floating ball  -  A closing element of a ball valve designed not to be held rigidly on a rotational axis but floats free between the seat rings.  When under fluid pressure the ball will be pushed against the downstream seat.
  • Floating ball valve  -  Used in low pressure or small bore processes.
  • Flow coefficient  -  Can be described as the volume (in US gallons) of water at 60°F that will flow per minute through a valve with a pressure drop of 1 psi across the valve. 
  • Force  -  The push or pull of an object resulting in a change from rest or motion.
  • Four-way (four-port)  -  These closure elements come with two seperate passageways in L shapes.  Each passageway connects to two different lines.
  • Friction  -  The mechanical resistance to the relative movement of two surfaces.
  • Full port (full bore)  -  A valve port opening that is equal to the pipe size or valve opening.
  • Flow rate  -  The amount of fluid that flows in a given time past a specific point.


  • Gas  -  The able to be compressed to fit a confined space and expanded when released.
  • Gasket  -  A seal between two components, usually bolted.
  • Gate valve  -  One of the most frequently used valve in piping systems and is classified as either "rising-stem" or "nonrising-stem" valves.
  • Gland flange  -  A part used to retain and control the compression force on the packing on the bonnet.
  • Globe valve  -  A type of valve used for regulating fluid flow, both on/off and throttling, it is a control valve.


  • Handlever  -  A device attached to rotary-motion valve with preset positions to manually position, open or closed, the valve.
  • Handwheel  -  A wheel operator used to turn the stem and open or close the closure elements.  Handwheels can be found on ball, gate, and globe valves.
  • High performance butterfly valve  -  HPBV is not a butterfly valve but its function and dimensions are equivalent.
  • Holiday  -  A discontinuity in painted or coated surfaces.


  • Inhibitor  -  Can reduce the corrosion rate by presenting a protective film.
  • Instrumentation  -  The ability to control a process by measuring the value or the parameters set for the process.




  • Leakage  -  The amount of fluid that will pass through a control valve when it is fully closed at a given pressure and temperature.
  • Lever  -  A device used for quarter-turn valves.
  • Lift check valve  -  A check valve that is very much like a piston check valve where the flow lifts a disk when the valve is open.
  • Limit stop  -  A device attached to the actuator used to limit or restrict the motion of the actuator.
  • Limit switch  -  A switch used to indicate a valve's open, closed, or intermediate position.
  • Lockout/tagout  -  Lockout/tagout procedures can vary significantly from project to project.  For this reason everyone working on a project should know the policies for equipment lockout/tagout to create a safe work place.
  • Lock closed  -  Used on valves that must be closed during normal operating conditions.
  • Lock open  -  Used on valves that must be open during normal operating conditions.
  • Lock-up system  -  A system used to hold the actuator in last operating position upon air failure.
  • Liquid  -  A specific volume and can hold any shape it is contained within.
  • Lubricator  -  A device that supplies lubricant to the packing box.
  • Lug butterfly valve  -  Connects directly to the flanges by means of a lug or machine bolt.


  • Maximum pressure  -  The maximum pressire limitations of the fluid that a valve can withstand.
  • Maximum temperature  -  The maximum temperature limitations of the fluid that a valve can withstand.
  • Mixing valve  -  Has two inlet ports and one common outlet port.
  • Multiport  -  These valves can either be three-way or four way valves.


  • Normally closed  -  A valve that is designated on the P&IDs as normally closed, is one that is closed during normal operating conditions.
  • Normally closed  -  A valve that is designated on the P&IDs as normally open, is one that is open during normal operating conditions.


  • Offset globe body  -  Body configuration with inlet and outlet ports parallel but offset.  They are not in-line.
  • On-off valve  -  A type of valve that only has two positions, either open or closed and can not be a throttling valve.
  • OS&Y (outside screw and yoke)  -  A valve design in which the stem threads are above the packing gland or outside the valve body and there is a yoke to support the top or outer end of the stem.


  • Packing  -  Material uesd to seal the valve from leaking around the plug stem.
  • Packing box  -  Internal bore of bonnet which contains guiding and packing.
  • Pig valve  -  An alternative to conventional pig launchers with the capable of launching and receiving.
  • Piping and instrumentation diagram  -  In the design process, a piping and instrumentation diagram, abbreviated as P&ID, is created following the Block Flow Diagram and Process Flow Diagram.
  • Piping and instrumentation diagram/how to  -  It is important that the Piping and Instrumentation Diagram contains all the information for the process because this is the basis for the Piping Design and HazOP.
  • Piston  -  Part used to seperate two air chambers of piston actuator.
  • Piston actuator  -  Double-acting actuator design with piston inside actuator.  
  • Plug valve  -  A quarter turn valve that has a conical or cylindrical plug that is rotated within the valve body to stop flow when needed. 
  • Poppet valve (mushroom valve)  -  An oval, round, tapered plug, or disk shaped end with a shaft, used to control the closing and opening for gas and vapor.  
  • Port  -  A passageway that allow fluid to flow through the closure element / valve.
  • Positioner  -  A device that attaches to a valve actuator that receives an electronic or pneumatic signal and moves the valve to a certain position.
  • Position indicator  -  Any external device which helps you get a clear visually view of whether a valve is in the closed and open position.
  • Pressure  -  It is the force exerted perpendicular to the surface of an object and is expressed as force per unit area.
  • Pressure loss  -  The difference in upstream and downstream pressure.


  • Quarter turn  -  A shut-off valve that turns one-quarter on the center vertical axis to close or open the valve.
  • Quick-opening  -  A two-way valve that creates the maximum flow capacity as soon as the stem raises.


  • Reduced port (reduced bore)  -  A valve port opening that is smaller than the pipe size or valve opening.
  • Reduced port ball valve (standard or regular)  -  A reduced bore valve has a smaller bore diameter in the ball than the internal diameter of the pipe.
  • Regulating valve  -  A valve that controls the flow rate or pressure in a process.
  • Reverse flow  -  When the flow moves in the oposite direction of the norman system operation.
  • Reverse pressure  -  The pressure applied against the face of a valve closure.
  • Rising stem  -  A stem that rises as the valve is opened.


  • Seat  -  The inner surface of the valve body which creates a tight shut-off.
  • Seat load  -  The contact force between the seat and the valve disk.
  • Seat retainer  -  Trim component that clamps the seat ring in place.
  • Seat ring  -  Creates a tight shut-off surface inside the body for the disk.
  • Service classification  -  A service classification or service class is a one to three letter designation that shows what service the line is in.
  • Set pressure  -  The set pressure is the point where a pressure relief valve (PRV) is set to start opening.
  • Shaft  -  Component in a rotary valve that connects the closure member to the actuator.
  • Shut-off pressure  -  The differential pressure against the closure when closed.
  • Shut-off valve  -  A block valve that only has two positions, either open or closed and can not be a throttling valve.  Sometimes used for emergeny shutdown of the system.
  • Spring button  -  A part that prevents movement of the actuator spring and permits the adjustment screw to compress the spring.
  • Stem (shaft)  -  A shaft that is connected to the handwheel or gear operator and then to the closing element of the valve.
  • Stem extension  -  An extension of the valve stem used to provide operating gear accessibility to a below grade valve.
  • Stem nut  -  A threaded nut that surrounds the valve stem threads and causes the stem to move when rotated.
  • Stop-check valve  -  Essentially, two valves built into one.  It can act as a globe valve to isolate or control the flow rate.  It also acts as a check valve by preventing reverse flow.
  • Stop Valve  -  Used to shut off or partially shut off the flow of liquids.
  • Stress  -  The force per unit area of cross-section.
  • Stroke  -  The distance the valve piston, plug, or stem, moves from a fully closed to fully open position or vice versa.
  • Stuffing box  -  The chamber surrounding the stem where it emerges from a pressurized space used to contain the packing.
  • Superimposed backpressure  -  The pressure that is on the discharge side of a pressure relief valve (PRV) when the device is required to operate.
  • Swing check valve  -  It is inexpensive and simple to operate and repair.  A check valve that has a disk that pivots about a hinge pin. 


  • Temperature  -  Normally described as the amount of heat or cold, but it is neither heat or cold.
  • Tension strength  -  The capacity of a material to resist a force tending to stretch it.
  • Three-way (three-port)  -  These closure elements come in T or L shaped passageways.  The passageway connects to two or three different lines.
  • Torque  -  The rotational force used to move a shart.
  • Transducer  -  A device used to transfer an electrical signal to a pneumatic signal.
  • Transfer case  -  Component in a ball and butterfly valve that converts linear actuator motion to rotary shaft motion. 
  • Trim  -  Valve trim is the inner components of the valve that are exposed to the process fluid.  Because they are exposed to the process, they are more likely to wear out than other components like the valve body or the bonnett.  Because of this, valve trim is usually designed to be removed and replaced when necessary.
  • Trunnion ball  -  You can tell the difference between the floating and trunnion ball valve by the fixed shaft on the bottom of the body and grease injection fitting.
  • Trunnion ball valve  -  Trunnion design is simply the use of upper and lower supports to retain the ball under pressure.
  • Two-way (two-port)  -  These closure elements come in straight through passageways.  The passageway connects to one line. 



  • Vacuum  -  A contained space having little or no matter or a volume having a pressure lower than the outside atmospheric pressure.
  • Valve installation guide  -  The valve should be inspected to make sure the opening is free from dirt and foreign matter.
  • Vapor  -  The gas state of a liquid or solid.  Both vapor and gas are basically the same thing.
  • V port  -  The ball closure element has a V shape opening turned on its side.  This allows the closure to be opened and closed so to control the flow much better.
  • Velocity  -  The rate of change or displacement with time. 
  • Vena Contracta  -  The point immediately downstream from an orifice or valve seat which is the point of lowest pressure and highest velocity.
  • Viscosity  -  The measure of the internal friction/resistance to the flow of a liquid. 
  • Volume booster  -  A device used to increase the actuator stroking speed.
  • Volume tank  -  Air tank used to supply additional air to stroke the valve upon air failure.


  • Wafer butterfly valve  -  A valve that is sandwiched between two flanges.
  • Water hammer  -  Occurs when a valve is suddenly opened or closed.
  • Wedge  -  The closure element of a gate valve.  A wedge is opened and closed by the stem.
  • Working pressure  -  Working pressure, abbreviated as WPR, is the normal pressure that a system operates at.



  • Yield strength  -  Yield strength, abbreviated as \(\sigma\) (Greek symbol sigma), also called yield stress, is the minimum stress that leads to permanent deformation of the material.
  • Yoke  -  A bracket to support the top or outer end of the stem and stem bearing used in gate and globe valves.




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Back Pressure Valve
Ball Check Valve
Ball Valve

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