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# Classification of Valves used in Piping

Valves are mechanical devices that are used to direct, start , stop, mix, regulate the flow, pressure, level, temperature of process fulids.

## Classification of valves used in piping are c;assified based on:

• Mechanical motion

• Size

• Pressure-temperature rating

• Based on functions

### Classification based on mechanical motion

Valves are open and closed by the mecahanical motion by the closer member.

• Linear

• Rotary.

• Quarter turn

In linear motion valve, the closer member moves in a straight line to allow, stop, throttle the flow as in gate, globe, diaphragm, pinch and lift check valve.

In rotary motion valve, the closer member travel to allow an angle, circular part as in butterfly, ball, plug valve etc.

In quarter turn valve allows either a zero or 90 degrees that mean the motion of the fully open to a fully closed valve.

### Classification based on nominal pipe size

Which is equal to the size of valve connecting to the pipe or the flange size. The valve size is not necessary to the equal diameter of the valve that means 6 inch valve does not require 6 inch opening. So based on pipe size valves are classifies as

• Small size valve

• Large size valve

Small size valves are normally NPS 2 and smaller while large size valves are NPS 2 ½ and larger. Sizing classification can be different for different companies.

### Classification based on pressure- temperature rating

Valves are classified based on :

• Class number similar to flanges(class number 150,300, 900,1500 and 2500)

• Material used for the valve construction

### Classification based on functions

Valves serves various functions within the piping system such as stopping and starting of the fluid flow, throttling of the fluid flow, controlling the direction of the fluid flow, regulating the fluid flow or pressure within the piping system. Different types of valves are used to serve these functions. Valves are classified as follows:

• Isolation

• Regulation

• Relief valve

• Non-return

• Special purpose

The isolation valve cuts or stop the supply of fluid when needed. Valves in the regulation category regulates the flow of fluid. Pressure and vaccum valves are used to prevent the over-pressure in the system that can damage the piping and the equipment. Non-return valves prevents the back flow whereas some valves are designed to serve a special purpose such as multi port, knife, line etc.