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Automated Valve Glossary

Automated Valve Terminology GlossaryDownload your free copy of the Automated Valve Glossary today!

This handy printable reference offers a comprehensive glossary of widely used valve and valve automation terms.

You will also receive a listing of basic specifications used in the design and manufacturing of valves and fittings.

Keep a copy of this useful guide on your desk as a handy reference.

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Absolute Pressure – The pressure expressed in bar, Pascal or PSI, as measured above a perfect vacuum.

Absolute Temperature – Temperature measured from absolute zero, a point of temperature, theoretically equal to minus 273.18° C or minus 459.72° F; the hypothetical point at which a substance would have no molecular motion and no heat.

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

Air, Compressed – Air at any pressure greater than atmospheric pressure.

Air, Free – Air which is not contained and which is subject only to atmospheric conditions.

Air-to-Close Action – See NORMALLY OPEN.

Air-to-Open Action – See NORMALLY CLOSED.

Air Valve – Valve that is used to control air flow. Flow is generally small.

Alloy Steel – A steel consisting primarily of iron with some percentage of one or more other elements such as chromium, nickel, manganese, or vanadium deliberately added to enhance its properties.

Ambient Temperature – The prevailing temperature of the environment immediately surrounding an object – generally considered to be -20° F to +100° F.

Angle Valve –  A pneumatically actuated valve with a Y body design. The linear pneumatic actuator lifts a piston off the Y body seat to control flow.

ANSI Class – A strength designation for valves which show the maximum pressures at various temperatures at which a valve can be expected to work safely.

ASTM – American Society for Testing and Materials

Austenitic Stainless Steel – The common stainless steel, where the primary microstructure is austenite and the composition primarily iron but also includes both chromium and nickel. The steels are designated as 300 series such as 304, 316, CF8M, etc.

Back Pressure – The pressure exerted on the downstream side of a valve.

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.

Back Seat – A shoulder on the stem of a gate or globe valve which seals against a mating surface inside the bonnet to prevent leakage of media through the bonnet stuffing box when the valve is fully opened.

Baffle Plate – A tray or partition placed in process equipment to direct or change the direction of flow.

Ball – The closure element of a ball valve.

Ball Valve – A valve design using a spherical closure element which is rotated through 90° to open and close the valve.

Batch Process – A process in which the flow of both the control agent and the controlled medium is intermittent or gradually changes over a wide range. A process of relatively small magnitude or time expanse as compared to a continuous process.

Blow-Off System – A piping system used for blowing scale, sediment, etc, from boilers, tanks or receivers. Also  called “blow-down.”

Blow-Off Valve – A valve designed specifically for blow-off service and used in blow-off lines. Also called “blowdown valve”.

Body – The principle 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 (such as body and closures of a trunnion ball valve) are bolted together and 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.

Breakaway Torque – A value depicting the turning force required to initiate rotation of the closure element of a rotary valve.

Bubble Tight – A commonly used term to describe the ability of a control valve or regulator to shut off completely against any pressure on any fluid.

Bushing – A fitting used to reduce the size of an opening.

Butt-Weld End – Lips are formed on the ends of the valve to exactly butt against connecting pipe in the system. These lip ends of both pipe and valve are machined, forming an inside groove to accommodate a backup ring for welding.

Butterfly Valve – A quarter-turn valve design deriving its name from the wing like action of the disc which operates at right angles to the flow. The primary advantage is a seating surface which is not critical. The disc impinges against the resilient liner with low operating torque.

Bypass – An auxiliary loop in a pipeline, usually for diverting flow around a valve, or other piece of equipment.

Bypass Valve – A valve used to divert the flow around or past the part of the system through which it normally passes.

Capacity – The mass flow rate through a valve under specified conditions.

Carbon Steel – Iron containing carbon in the form of carbides, about 0.1 to 0.3 percent carbon with no other alloying elements other than the sulfur, phosphorus, and other elements present in almost all steels.

Cast Iron – The common term for cast gray iron or iron containing flake carbon in the range of 2% to 4.3%. Cast iron is brittle, exhibiting very little ductility before fracturing.

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.

Cavitation – Cavitation is a concern for liquid services where cavities or bubbles form and then collapse. It is the two-stage process of vaporization and condensation of a liquid.

Cavity Filler – Teflon seat that fills the area around the ball of a valve eliminating cavities where product can potentially accumulate.

Check Valve – A single-directional valve which automatically prevents back flow when the fluid in the line reverses.

Class – A rating using in valve piping systems. (i.e Class 150# or 300#) Note: The pressure class rating charts do not directly relate to the actual working pressure of the valve itself.

Continuous Process – A process in which the flow of the controlled media is continuous and fluctuates over a narrow range. The opposite of “batch process.”

Continuous Process Control – That process in which materials flow more or less continuously through a plant while being treated.

Control Loop – A control made up of a number of devices acting as individual transfer systems which are joined to form a network.

Control, Mechanical – A control actuated by linkages, gears, cams or other mechanical elements.

Control, Pneumatic – A control actuated by air or other gas pressure.

Control Valve – A valve which regulates the flow or pressure of a medium which affects a controlled process. Control valves are operated by remote signals from independent devices using any of a number of control mechanism such as pneumatic, electric, electro-hydraulic

Cryogenic Valve – A term used to describe valves designed to operate below –40°C.

Cv – Flow coefficient expressed as the number of gallons of 60° water that would flow through an opening, such as a valve port, in 1 minute under a differential pressure of 1 psi pressure drop under stated conditions.

Dead Zone – A range of measured values or variable in which an instrument cannot detect or initiate corrections.

Deviation – The difference at any given time between the control point and the set point.

Dew Point – The central temperature of a gas or liquid at which condensation or evaporation occurs.

Diaphragm Valve – A bi-directional valve, operated by applying force to a diaphragm. They are often used in slurries as well as hygienic applications as they are less susceptible to clog.

Differential Pressure – The maximum difference in pressure measured between the valve inlet and outlet, against which the valve is required to operate.

Direct Acting (Solenoid Valve)– A direct-acting actuator(coil) is one in which the actuator stem extends to push-down-to-close plug and seat orientation.

Direct Acting –(Positioner)-A direct-acting positioner or a direct-acting controller outputs an increase in signal in response to an increase in set point.

Direct Mount Valves – Valves that offer ISO 5211 mounting pads and recessed packing nuts. Can accommodate actuators without mounting brackets making them direct mount.

Double Block and Bleed – The capability of a valve under pressure to obtain a seal across both the upstream and downstream seat rings and to have its body cavity bled down/vented to atmospheric pressure.

Drain Plug – A fitting at the bottom of a valve, the removal of which permits draining and flushing the body cavity.

Duty Cycle – The percentage of time a device is allowed to operate over a given period of time. Expressed in percent it equals “time on” divided by “time off”.

Eccentric Ball Valve – Similar to a ball valve in construction except that it usually contains a segmented ball or half ball. Used typically in Waste Water applications.

Elastomer – A natural or synthetic elastic material, often used for o-ring seals. Typical materials are Viton®, buna-n, EPDM.

Electric Actuator – Electric valve actuators which when mounted on valves in response to a signal, automatically move to a desired position using an outside power source.

Emergency Shut Down Valve (ESD) – A valve that uses energy which is stored in the actuator to close rapidly in an emergency.

End Connection – The type of connection supplied on the ends of a valve which allows it to be connected to various piping -(i.e- butt weld end, flanged end, threaded or socket weld)

Face to Face Dimensions – Is the distance or space between the end to end or flanges of a valve or fitting. These dimensions are governed by ANSI/ISA specifications.

Facing – The finish of the gasket contact surface of a flange.

Feedback – Part of a closed loop system which brings back information about the condition under control for comparison to the target value.

Feedback Controller – A mechanism which measures the value of the controlled variable, accepts the value of command and as the result of comparison, manipulates a controlled system in order to maintain an established relationship between the controlled variable and the command.

Feedback Control System – A control system which maintains a prescribed relationship of one system variable to another by comparing functions of these variables and using the difference as a means of control.

Feedback Signal – The signal responsible to the value of the control variable. This signal is returned to the input of the system and compared with the reference signal to obtain an actuated signal which returns the controlled variable to the desired value.

Fire-Safe – A valve design that is capable of passing a fire test with specified limits on leakage to the atmosphere after being closed or opened subsequent to fire exposure.

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.

Fitting, Compression – A fitting which seals and grips by manual adjustable deformation.

Flange – A rim on the end of a pipe, valve or fitting for bolting to another pipe element.

Flange Ends – Refers to a valve or fitting having flanges for joining to other piping elements. Flanged ends can be plain faced, raised face, large male and female, small male and female, large tongue and groove, small tongue and groove and ring joint.

Flow Coefficient (CV) – expressed as the number of gallons of 60° water that would flow through a valve port, in 1 minute under a differential pressure drop of 1 under stated conditions.

Flow Meter – A device which indicates either flow rate, total flow or a combination of both for a given liquid.

Flow Rate – The volume, mass, or weight of a fluid passing through any conductor per unit of time.

Floating Ball – A ball valve design in which the ball is not rigidly held on its rotational axis and so is free to float between the seat rings.

Flow Characteristic – The relationship between valve capacity and valve travel. It is usually expressed graphically in the form of a curve. Control valves have two types of characteristics: inherent and installed.

Full Bore (full opening) – Describes a valve in which the bore (port) is nominally equal to the bore of the connecting pipe.

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

Gate Valve – A straight through pattern valve in which closure element is a wedge 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. Used as a block valve, or on-off valve.

Gland – or gland bushing. The part of the valve which retains or compresses the stem packing in a stuffing box.

Gland Packing – A soft conformable material fitted to a valve stuffing box to create a seal between the process fluid and the atmosphere.

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.

Grease Fitting – A device which permits injection of grease into a bearing surface.

Handwheel – A manual override device used to stroke a valve or limit its travel. The handwheel is sometimes referred to as a hand jack. It may be top-mounted, side-mounted, in-yoke mounted or shaft-mounted and declutchable.

IBBM – Iron body, bronze mounted – common term for valves with cast iron body and bonnet and bronze trim (seating surfaces, stem, bushings).

ID – The measurement of the inside diameter of a pipe.

Integral Flange – A valve body whose flange connection is an integral or cast part of the body.

Integral Seat – The flow control orifice and seat that is an integral part of the valve body or cage. The seat is machined directly out of the valve body and is normally not replaceable without replacing the body itself.

ISO-  International Organization for Standardization (ISO) is an international standard setting body composed of representatives from various national standards organizations.

ISO 5211- The standard that specifies the requirements for the attachment of part-turn actuators, with or without gearboxes, to industrial valves.

Lever – A hand operating device for quarter-turn valves.

Laminar Flow– The flow of a fluid where each particle of the fluid follows a smooth path with all particles moving in straight lines parallel to the pipe walls.

Limit SwitchSet of electrical contacts that are activated mechanically at a preselected position.

Linear Flow Characteristic – A characteristic where flow capacity or (Cv) increases linearly with valve travel. Flow is directly proportional to valve travel. This is the preferred valve characteristic for a control valve that is being used with a distributive control system (DCS) or programmable logic controller (PLC).

Linear Valve – Another name for a globe valve. It refers to the linear or straight-line movement of the plug and stem.

Locking Device – Any valve attachment whose purpose is to prevent the operation of the valve by unauthorized persons.

Manifold – A conductor that provides for multiple connection ports.

Modulating Control Valve – A valve which can be positioned anywhere between fully open and fully closed to proportion the rate of flow in response to a modulating controller.

Mold – A hollow cavity, frequently in packed sand, for giving a desired shape to a material in a molten or plastic shape.

NAMUR – Standardization of drilling patterns on pneumatic actuators allowing interface with solenoid valves.

Needle Valve – A multi-turn device with a needle-shaped closing element. Similar in design to globe valves, but often much smaller. Good in applications with low flow rates.

Normally Closed – Applying to a normally closed control valve assembly: One which closes when the actuator supply air pressure is reduced to atmosphere. In multi-port valves the normal position must be specified.

Normally Open – Applying to a normally open control valve assembly: One which opens when the actuator supply air pressure is reduced to atmosphere. In multi-port valves the normal position must be specified.

Normally Closed Solenoid Valve – A valve in which the inlet orifice is closed when the solenoid coil is de-energized and opened only when the solenoid coil is energized.

Normally Open Solenoid Valve – A valve in which the inlet orifice is open when the solenoid coil is de-energized and closed only when the solenoid coil is energized.

NPS Nominal Pipe Size – dimensionless number used to indicate sizes of pressure pipe and valves – used interchangeably with valve size in inches.

NPT National Pipe Thread – standard tapered thread for pressure pipe and components. Requirements defined in ASME B1.20.1.

OD – The measurement of the outside diameter of a pipe.

On-Off Control – A control system in which the final control element has only two positions from which to select. Also known as two-position control.

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

OS&Y – Outside Screw & Yoke – A valve design in which the stem threads are above the packing gland or outside the valve body and there is a yoke to support the top or outer end of the stem.

Packing – A sealing system that normally consists of a deformable material such as PTFE, graphite, etc. It is usually in the form of solid or split rings contained in a packing box that are compressed so as to provide an effective pressure seal.

Packing Box – The chamber located in the bonnet that surrounds the stem and contains the packing and other stem-sealing components.

Pilot-Operated – A device in which energy transmitted through the primary element is either supplemented or amplified by energy from another source.

Pilot Valve – Device for controlling the flow of an auxiliary fluid used to amplify the power of a controller measuring system in effecting control, i.e. a small valve used to operate a large valve.

Pinch Valve – A flexible hose, pinched between two or more moving elements to stop flow. It is commonly used in slurry applications since it does not easily clog.

Pinion Shaft – The external input shaft of certain gear operators which drive the internal reduction gearing.

Plug Valve – A quarter turn valve which uses a rotating plug as the closing element. When the valve is open, the media flows through a hole in the plug, which can be cylindrical or truncated.

Position Switch – A switch that is normally fitted on the actuator to detect extremes of valve travel. The switch is normally electric.

Position Transmitter – A device that is mechanically connected to the valve stem and will generate and transmit either a pneumatic or electric signal that represents the valve stem position.

Positioner – A device used to position a valve with regard to a signal. The positioner compares the input signal with a mechanical feedback link from the actuator. It then produces the force necessary to move the actuator output until the mechanical output position feedback corresponds with the pneumatic signal value.

Pneumatic Actuator – A device which converts pneumatic energy into mechanical motion.

Pneumatic Test – A test in which a valve is tested with air – usually a seat closure test.

Poppet Valve – A mushroom or tulip shaped valve made of head resisting steel, commonly used for inlet and exhaust valves.

Port – An internal-external terminus of a passage in a component. The inlet or outlet of a valve. Sometimes used to refer to the valve seat opening.

Position Indicator – Any external device which visually indicates the open and closed position of valve.

Pressure Differential – The difference in pressure between any two points of a system or a component. Also known as pressure drop or ΔP.

Pressure-Temperature Ratings – The maximum allowable working pressures at specified temperatures. For steel valves, the ratings are defined by “classes” and found in ASME B16.34. For iron and bronze valves, the ratings are defined in the applicable MSS specifications.

PSI – (Pounds per square inch) The force per unit area exerted against a resisting body.

Pump – Any of various machines which force a gas or liquid into, or draw it out of something, as by suction or pressure.

Ra (surface finish) Ra is calculated as the roughness average of a surfaces measured microscopic peaks and valleys.

Rack and Pinion – A type of actuator that comprises a pair of gears which convert rotational motion into linear motion.

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 Class 600 and up have a 0.25” RF.

Rate of Flow – An expression of measurement of the medium flowing through a given space in a given time; expressed as GPM (Gallons per Minute), CFH (Cubic Feet per Hour), LBH (Pounds per Hour), etc.

Reduced Port – A valve port opening that is smaller than the line size or the valve end connection size.

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.

Resilient Seat – A valve seat containing a soft seal such as an o-ring or plastic to assure tight shut-off.

Restrictor – A device for producing a deliberate pressure drop or resistance in a line by reducing the cross-sectional flow area.

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

Rotary Valve – A valve style in which the flow closure member is rotated in the flow stream to modify the amount of fluid passing through the valve.

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.

Running Torque – The determination of how much turning force is required to keep the closure element of a rotary valve rotating at a constant angular velocity once it starts rotating.

Safety Valve – A self-operated quick opening valve used for fast relief of excessive pressures.

Sanitary Valve – Valve designed for use in applications requiring clean or sterile processing. Contact surfaces are highly polished, crevice free and easy to clean. Commonly used in dairy, food, pharmaceutical, medical, and chemical applications. Valve types include globe, diaphragm, pinch, knife, needle, butterfly, ball, and plug.

Schedule – A system for indicating the wall thickness of pipe. The higher the schedule number, the thicker the wall for a certain pipe size.

Scotch Yoke – A type of actuator that translates linear motion to rotary motion. The linear motion is defined by a pin or roller element trapped within a channel in the rotary element.

Seat – The part of a valve against which the closure element effects a tight shut-off.

Seat Load – The contact force between the seat and the valve plug. When an actuator is selected for a given control valve, it must be able to generate enough force to overcome static, stem and dynamic unbalance with an allowance made for seat load.

Self-relieving – The process by which excessive internal body cavity pressure is automatically relieved either into the upstream or downstream line – generally found in ball valves.

Signal – Information relayed from one point in the system to another.

Socket Weld End (SW) – A valve or fitting which slips over end of pipe and is made pressure tight by welding.

SPST- A single-pole, single-throw (SPST) switch is as simple as it gets. It’s got one output and one input. The switch will either be closed or completely disconnected. SPSTs are perfect for on-off switching. They’re also a very common form of momentary switches. SPST switches should only require two terminals

SPDT – A single-pole, double-throw (SPDT)have three terminals: one common pin and two pins which vie for connection to the common. SPDTs are great for selecting between two power sources, swapping inputs, or whatever it is you do with two circuits trying to go one place. SPDT switches should usually have three terminals. (Sidenote: in a pinch an SPDT can actually be made into an SPST by just leaving one of the switch throws unconnected).

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

Split Body – A valve whose body is split. This design allows for easy plug and seat removal. Split-bodied valves are made in both the straight-through and angle versions.

Stainless Steel – Any of a number of types of iron alloy with chrome, nickel, or other elements that does not oxidize in free air.

Stem – The valve plug stem is a rod extending through the bonnet assembly to permit positioning of the plug or closure member. The actuator stem is a rod or shaft which connects to the valve stem and transmits motion or force from the actuator to the valve.

Stroke – The distance the plug or stem moves to go from a fully closed to a fully open position. Also referred to as Travel.

Supply Pressure – The pressure at the supply port of a device such as a controller, positioner or transducer. Common values of control valves supply pressure are 20 psig. for a 3-15 psig. output and 35 psig. for a 6-30 psig. output.

Three Way Valve – A multi-orifice flow control valve with supply return and control ports arranged so that valve stem action in one direction opens supply to control port and reversed valve action opens the control port to return.

Throttling – The intentional restriction of flow by partially closing or opening a valve.

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

Torque – The rotational force imposed on or through a shaft, usually expressed in foot-pounds.

Travel – The distance the plug or stem moves to go from a fully closed to a fully open position. Also referred to as Stroke.

Trim – Includes all the parts that are in flowing contact with the process fluid except the body, bonnet and body flanges and gaskets. The plug, seats, stem, guides, bushings and cage are some of the parts included in the term trim.

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

Turbulent flowturbulence– irregular flow that is characterized by tiny whirlpool regions

Valve – A device used to control the flow of fluid contained in a pipe line.

Viscosity– The thickness of a fluid or the friction between the molecules in a fluid

Water Hammer – Shock waves generated in a pipework system caused by a valve closing too quickly.

WOG – Water-oil-gas – a rating designation generally used for small valves chiefly in low ratings. Indicates maximum working pressure at ambient + 32° F to +100° F. Also called Non-shock Rating.

Working Pressure – The pressure (pounds per square inch) at which a valve is designed to operate.

Worm Gear- mechanical arrangement consisting of a toothed wheel worked by a short revolving cylinder (worm) bearing a screw thread.


Below is a listing of the basic specifications used in the design and manufacture of valves and fittings.

American Petroleum Institute

American Society of Mechanical Engineers/American National Standards Institute

Manufacturers Standardization Society of the Valves and Fittings Industry

British Standards Institute

International Organization for Standardization


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