Glossary of Valve Terms

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Glossary of Valve Terms - All

The full Glossary of valve terms is available to download here: Glossary of Valve Terms

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Glossary of Valve Terms - A

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

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Glossary of Valve Terms - B

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

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Glossary of Valve Terms - C

Cap Screw: A fastener generally having a head with hexagonal drive and whose shank is normally threaded for its full length. 

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Glossary of Valve Terms - D

Dampener: (Slam Retarder). A device designed to prevent the disc / 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.

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Glossary of Valve Terms - E

Elastomer: A natural or synthetic elastic material, often used for O-ring seals. Typical materials include Nitrile, Viton, Buna-n, etc. 

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Glossary of Valve Terms - F

Face-To-Face: The overall dimension from the inlet face of a valve to the outlet face of the valve. This dimension is governed by various standards, including ANSI B16.10 and API-6D to ensure that such valves are mutually interchangeable, regardless of the manufacturer.

Facing: The finish of the contact surface of flanged fittings, often expressed as a roughness value.

Fail Safe Valve: A valve designed to fail in a preferred position (open, closed or in-place) in order to avoid an undesirable consequence in a piping system.

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Glossary of Valve Terms - G

Galling: The tearing of metal surfaces when two elements rub against each other.  Usually caused by lack of lubrication or extreme contact pressure of materials of a similar hardness value.

Gas: A compressible fluid – such as air, hydrogen, nitrogen, etc.

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 effect the seal. 

Gate Valve: A straight-thru pattern valve whose 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.

Gate: The closure member of a gate valve (sometimes called wedge). 

Gland: That part of a valve which retains or compresses the stem packing. Sometimes manually adjustable.

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Glossary of Valve Terms - H

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 galling, abrasion and or corrosion. 

Heat Treatment: Describes any process or procedure by which the internal structure of a material is altered by heating to produce desired physical characteristics.  This is usually accomplished by furnace heating followed by controlled cooling.

Holiday: An imperfection or “bare spot” in a coating, paint or plating.

Hot tears: A defect occurring in castings caused where partially solidified or weak, newly solidified sections are subjected to a pull resulting from the contraction of thinner parts that have solidified earlier. A hot tear is an inter-granular failure. 

Hydraulic Motor Actuator (Operator): A device by which rotation of a hydraulically powered motor is converted into mechanical motion.

Hydrostatic Test (Shell Test): A test in which a valve is completely filled with water and pressure tested.  Used to test the integrity of the pressure-containing parts.

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Glossary of Valve Terms - I

Incompressible Flow: A fluid such as water, which has no significant change in volume and density as the pressure increases.

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Glossary of Valve Terms - L

Lever: A handle type operating device for quarter-turn valves. 

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Glossary of Valve Terms - M

Magnetic Particle Inspection: An inspection procedure for detecting surface cracks in welded areas thru the use of fine iron particles in an electrical field. Cannot be used on non-magnetic non-ferrous materials.

Male Thread: The external thread on pipe, fittings or valves used in making a connection with mating female (internal) threaded parts.

Material Test Reports: Certificates provided by the material manufacturer indicating the chemical analysis and mechanical properties of a specific batch of material traced by heat numbers. 

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Glossary of Valve Terms - N

NiAlBr: Nickel Aluminium / Aluminum Bronze alloy.  Renowned has having high strength and ductility which is retained at low temperatures, good shock & wear resistance, good casting qualities as well as being easy to machine. Additionally it is easy to weld and has good thermal and electrical conductivity properties. It has exceptional corrosion resistance due to a tough oxide layer. Heat treatment further increases its seawater corrosion properties, making it an ideal choice in marine environments with the material being used for seawater valves and ships components.

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Glossary of Valve Terms - O

Operator: A device which converts manual, hydraulic, pneumatic or electrical energy into mechanical motion to open and close a valve

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Glossary of Valve Terms - P

Packing Gland: That part of a valve which retains or compresses the stem packing. Sometimes manually adjustable.

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.

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Glossary of Valve Terms - Q

Quality Assurance: Planned regular and/or preventive actions which are used to ensure that materials, products, or services will meet specified requirements.

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Glossary of Valve Terms - R

Radiographic inspection: A non-destructive inspection method using x-rays to locate internal flaws in castings, fabricated parts and welds. Abbreviated as RT. 

Raised Face (RF): The raised area of a flange face which is the gasket sealing surface between mating flanges. RF flanges should not be used on brittle or soft ductile materials to avoid cracking or bending of the flange.

Reduced Port (RP): A valve port opening that is smaller than the line size or the valve end connection size. A reduced port is used for several reasons including, adjusting a large valve to handle smaller flow requirements, reduced inlet and outlet fluid velocities, and correct errors in over sizing.

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. 

Relief Valve: A spring loaded valve that opens (relieves) when the pressure exceeds the spring setting.  Occasionally fitted to the body cavity of ball and gate valves to relieve thermal overpressure in liquid services.

Resilient Seat: A valve seat containing a soft seal, such as an O-ring, to assure tight shut-off.

Rim Pull Force: The force required at the edge of the hand wheel to generate the required on the stem. 

Ring Type Joint (RTJ): A flange connection using a specially shaped soft metal ring as a gasket. Generally used on high pressure valves.

Rising Stem: A valve stem which rises as it is turned and the valve is opened.

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Glossary of Valve Terms - S

Sampling Valve: A valve that can be used to take samples from a vessel or piping system.

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Glossary of Valve Terms - T

Tensile test: A destructive test performed on a specially machined specimen taken from material in its delivered condition to determine mechanical properties, such as tensile strength, yield strength, and percent elongation. 

Test Certificates: Documents provided by a manufacturer certifying that required tests were performed and the results of those tests.

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Glossary of Valve Terms - U

Ultrasonic Inspection: An inspection procedure using high frequency sound waves to detect voids and imperfections throughout the thickness of metal parts.

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Glossary of Valve Terms - V

Glossary of Valve Terms - W

Wafer Style Valve: A valve that does not have integral line flanges, sometimes referred to as a flangeless valve. The valve is installed by bolting it between the companion flanges with a set of bolts or studs, called line bolting.

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. Can be caused by a valve closing too quickly.

Weld End: The end connection of a valve which is to be installed by welding into the line.

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Glossary of Valve Terms - X

X-RAY Inspection: (Radiographic Inspection). A non-destructive inspection method using x-rays to locate internal flaws in castings, fabricated parts and welds. 

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Glossary of Valve Terms - Y

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

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