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Valve Terminology

Commonly Used Terms in the Valve World

ABS: Acrylonitrile Butadien Styrene. A rugged plastic compound typically used for housings, some external parts. A form of ABS is also used for low-pressure air piping systems in harsh environments.

AFLAS: An elastomer used for high temperature/high purity or highly aggressive applications; particularly suited to ozone-treated water. Aflas® is a trademark of 3M

ASQ: American Society for Quality

ASTM: Short for American Society for Testing and Materials. An organization created to establish conformity in American Class Standards.  Click here for more information on "What are the Different ANSI Classes for Valves?"

ANSI: American National Standards Institute 

BCF: Bead and crevice free. Also known as fusion. A means of connecting pipes, valves and fitting via heat fusion, with a perfectly smooth internal joint.

BPVR: Back Pressure Regulating Valve

BREAKING PRESSURE: The minimum pressure required to produce flow through a valve.

BS, BSP: British standard, British Standard Piping. A piping specification

BUNA or BUNA-N: Nitrile rubber, used to make o-rings and other seals used in valves. Buna-N is the least expensive type of seal, and it lacks the chemical compatibility of other more costly elastomers.

CHEMRAZ: A fluorinated elastomer used for high temperature/high purity or highly aggressive applications. Chemraz® is a trademark of Green-Tweed.

CNC: Computer numerically controlled. Popular type of control system for vertical machining centers, lathes, injection molding machines, and other tools used to fabricate a valve.

CORZAN, CPVC: Chlorinated polyvinyl chloride. While not as popular as PVC, it is able to withstand higher temperatures.

CSA: Canadian Standards Association.

DIVERTER: A three-way valve; the flow can be diverted from one outlet to another, or different inlets can be selected and sent to a common outlet.

EPDM: Ethylene propylene diene monomer. A popular rubber seal material, compatible with a wide range of chemicals.

FLANGE: A type of pipe fitting that attaches via nuts and bolts.

FLARE: A type of pipe fitting that uses a socket and a type of union nut to form a connection with minimal crevice, for ultrapure processes. Usually seen on fluoropolymer or natural polypropylene valves.


FLOW PATTERNS: A diagram showing how flow can be directed using a particular valve. (See the “Flow Patterns” box below for further explanation.)

FRP: Fiberglass Reinforced Pipe

GPM: Gallons per minute. Express volume of flow.

GPP: Glass-filled polypropylene. Offers the chemical resistance of polypropylene, with glass fibers added for strength.

HALAR: Ethylene-Chlorotrifluoroethylene. Used for some external components; it is also a valve body material for high temperature/high purity applications.

IAPD: International Association of Plastics Disbributors. Formerly NAPD, National Assoc. etc.

IBBT: Iron Body Bronze Trim

ISA: The Instrumentation Systems and Automation Society. Formerly Instrument Society of America.

JORLON: A patented product made by Jordan Valve, similar to Teflon, used for diaphragms.

KALREZ: A fluorinated elastomer used for high temperature/high purity or highly aggressive applications. Kalrez® is a trademark of DuPont Dow Elastomers.

KYNAR: Brand of Polyvinylidene fluoride. A dense, high purity plastic that is used in critical applications, such as semiconductor manufacturing.

LAMINAR FLOW: Sometimes known as streamline flow, occurs when a fluid flows in parallel layers, with no disruption between the layers. In fluid dynamics, laminar flow is a flow regime characterized by high momentum diffusion, low momentum convection, and velocity independence from time. It is the opposite of turbulent flow. In nonscientific terms laminar flow is “smooth,” while turbulent flow is “rough.”

NATIONAL ELECTRICAL MANUFACTURERS ASSOCIATION: Used in valve terminology to define the level of external resistance an enclosure or solenoid coil is suited. i.e. NEMA 1 is dusttight, NEMA 9 is explosion proof, etc.

NATURAL: Describes resins, frequently PP or PVDF, that have not had colorants, fibers, or other components added prior to processing. Sometimes mistakenly interchanged with “virgin”.

NC: Normally closed, valve stays closed in de-energized state; opens when energized.

NEMA: National Electrical Manufacturers Association defines the level of external resistance. i.e. NEMA 1 – Dust tight, NEMA 9 is explosion proof.

NO: Normally open, valve stays open in de-energized state; closes when energized.

NPT: National Pipe Thread

O-RING: A type of seal. An O-ring is a round elastomeric ring, ideally suited to be a compressed, static seal between non-moving parts. O-rings can be used as a face seal on a valve and used on rotating shafts inside a valve.


  • Open Stem and Yoke (valve)
  • Outside Screw and Yoke (gate valve mechanism)
  • Outside Stem & Yoke (valve)

PECTFE: Ethylene-chlorotrifluoroethylene. This material used in HALAR brand, for some external components; it is also a valve body material for high temperature/high purity applications.

PET or PETRA: Polyethylene terephthalate. (PETRA is a brand) Used on certain housings.

Pneumatic: A pneumatic valve uses pressure or air to open and close the valve.

PP or PPL, POLYPROPYLENE: A lightweight plastic that offers relatively high purity characteristics at a price well below PVDF or PTFE. Impervious to many chemicals.

PRESSURE DIFFERENTIAL or PRESSURE DROP: The difference between the inlet and the outlet pressure through a valve. The outlet pressure is lower than the inlet pressure due to the restriction caused by the valve.

PRV: Pressure Reducing Valve

PSI: Pounds per square inch. Used to indicate the amount of pressure in a given piping system.

PTFE BELLOWS: A sealing mechanism that is made of PTFE, formed in a bellows shape, used on many solenoid valves.

PTFE: Polytetrafluoroethylene, a type of fluorinated thermoplastic with outstanding chemical resistance, low leachability, and excellent lubricity.

PVC: Polyvinyl chloride. This is the most popular material used for plastic piping systems.

PVDF: Polyvinylidene fluoride. A dense, high-purity plastic that is used in critical applications, such as semiconductor manufacturing. Plast-O-Matic is an authorized reseller of Kynar® PVDF. Kynar is a trademark of Elf-Atochem.

PVF: Pipes, valves fittings. Used to describe a segment of the plastics industry or distributors who specialize in these products.

REGRIND: Thermoplastic that has been processed once, then is placed in a grinder to be shredded/pelletized for re-molding. In injection molding, runners etc. are often re-ground. No thermoplastic can be successfully reground and remolded indefinitely; eventually the molecular bond begins to break down and the plastic is no longer usable.

ROLLING DIAPHRAGM: A type of seal, also senses pressure. This is a diaphragm formed in a convoluted shape. It gets its name because as the stem moves, the diaphragm “rolls” at the convolution. It is frequently used in a manner similar to a u-cup, that is, to seal the gap between a linear moving shaft and the valve body.

SOLENOID VALVE: A valve that uses an electromagnetic coil for actuation.

SPIGOT: A type of fitting, essentially a section of pipe fused cleanly into a valve. This protruding pipe is then fused into the piping system. Usually found in high purity systems.

TEFLON: This is the brand name for a number of fluorinated polymers manufactured by E. I. DuPont de Nemours. Many valve manufacturers use this term illegally, when in fact their products are not Teflon® but generic PTFE, PFA etc.

TEMPRITE: This is a formulation of Corzan® CPVC that is used for injection molded valve bodies.

THERMOPLASTIC, THERMOSET: Two basic types of plastic resins. Thermoplastics are resins that can be reground after molding and molded again. Thermosets can be molded once only. They tend to be denser materials for special purposes. PVC is a thermoplastic. A PVC valve could conceivable be reground, then molded into a coffee mug. The resin used on a solenoid coil is a thermoset. A good analogy is paraffin wax vs. paraffin paste; both are petroleum products, but the wax can be melted and reformed while the lubricant cannot. Just as paraffin cannot be melted and reshaped indefinitely, no thermoplastic can be successfully reground and remolded indefinitely. Eventually the molecular bond begins to break down and the plastic is no longer usable. In another popular analogy, thermosets are often compared to an egg; once the egg is hard boiled it can’t be returned to a liquid and recooked as a sunny side up.

3 Way VALVES:  3 Way Valves has three (3) ports. Depending on the particular valve, all three (3) ports may be open, two (2) ports may be open, or all ports may be closed.

2 Way VALVES: A 2 way valve as a single inlet port and a single outlet port.

U-CUP: A type of seal. A u-cup is an o-ring formed into a u-shaped channel. Liquid or air pressure “inflates” the u-cup and affects a seal. The u-cup is used in instances where an o-ring is not desirable.

VIRGIN: Describes thermoplastic resins that have no “regrind” in the processing mix. Sometimes mistakenly interchanged with “natural”.

VISCOSITY: Is a measure of the resistance of a fluid to deform under shear stress. It is commonly perceived as “thickness”, or resistance to flow.

VITON: a fluorinated elastomer used in making o-rings and other seals. Viton® is a trade mark of DuPont Dow Elastomers.

WOG: Water/Oil/Gas, describes a common type of brass valve.

X-VALVE: A term used to describe any type of custom valve. “Q-valve” is used to describe custom ball valves.

What is a Cv?
The Cv, also known as the flow coefficient, is 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.

Pressure Reducing Valve (PRV): The purpose of a pressure-reducing valve is to reduce the pressure from an upstream pressure to a desired downstream pressure. A PRV is normally open; an increase in pressure on the downstream side of the valve causes it to start modulating closed.

Back Pressure Regulating Valve (BPRV): A backpressure regulator’s purpose is to maintain a constant upstream pressure by relieving excel pressure in a process. A BPRV is normally closed; an increase in pressure on the upstream side of the valve causes it to start modulating open.

Temperature Regulator: Temperature regulators maintain a constant temperature in a process by inserting a thermal probe (bulb) in the process where the temperature needs to be maintained. This thermal system consists of a liquid or vapor interface. As the liquid boils, it creates vapor pressure, which will exert pressure to overcome the spring tension on the valve body. This movement allows the valve to move to allow steam or other medium through the valve.

Ball Valve: Ball valves are generally used for on off service and can be turned 90° which turns a ball with a port (hole) through it so the hole is either facing the direction of the process (open) or is perpendicular to it (closed). These valves can be either manual or automated.

Butterfly Valve: Butterfly valves act like a flat disc sitting in a line. When the disc is perpendicular to the line, the valve is closed. When the disc is parallel to the line, the valve is open. These valves are generally used for larger scale pipes, over ball valves, due to the fact that they are considerably less expensive.

Check Valve: Check valves prevent the backflow of a process in a pipe. Wither a spring-loaded disc or a flapper type device located in a pipe accomplishes this.

Safety Relief Valve: Designed to ‘pop’ or relieve at a given set pressure. These valves are used on steam, water, air, and other processes. These valves generally reset or reseat at 20-30% of the set value of to relieve. i.e. – a valve set at 100 psi will not reseat until 70-8- psi.

Gauge: A gauge is a pressure indicator that is inserted into a process to show pressure. A bimetal thermometer is the same thing for temperature.

Heat Exchanger: Heats up or cools down a process typically by inserting steam or a cooling agent into a tube bundle and passing the process over the bundle.

Actuator: An actuator by definition moves something. In our industry, an actuator opens or closes valves or dampers. The most common applications are on ball and butterfly valves.

Filter: A filter is used to remove a specific size particulate from a liquid by means of a screen, either fabric or metal.