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Valve Terminology and Glossary

Below are some of the most popular valve-realted pieces of terminology in our glossary. Use the linked text at the bottom of this page to download and view our complete glossary that contains hundreds of terms!
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Butterfly Valve

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

Charpy Test

A mechanical test conducted on a precisely machined coupon of the steel to be tested. The coupon is clamped in a special machine and subjected to a lateral hammer blow. This test provides a relative measure of the toughness of the steel or its resistance to shock or impact loads. Often required for low temperature applications where testing is done at the expected minimum service temperature. (Refer to requirements of API 6D and ISO 14313.)

Check Valve

A one-directional valve that is opened by the fluid flow in one direction and which closes automatically when the flow stops or reverses direction. See “Clapper”.

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. See “Controller”.

Differential Pressure

The difference in pressure across a valve in a pressurized line. The difference in pressure between any two points in a pressurized system under flowing conditions.


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


An elastomeric or synthetic seal ring of circular cross section.


An abbreviation for “pounds per square inch”. The force per unit area exerted against a resisting body.

Rockwell Hardness Number

A numerical expression of the hardness of a metal as determined with a Rockwell Hardness Tester. There are several hardness scales. The most commonly used are the Rockwell B scale for soft metals and the Rockwell C scale for hard materials.

Tensile Strength

The highest tensile stress that a material can withstand before failure or rupture occurs with force being applied in a direction tending to elongate the material.

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