Valves, types and its classification

What is Valve?

Valve is a mechanical device that controls the flow and pressure within a system or process and also directs the flow of a fluid by opening, closing, or partially obstructing fluid flow. The cost of Valve in the piping system is up to 20 to 30% of the overall piping cost. Thus selection of valve is very important in piping system.

Functions of a valve

•          Stopping and starting flow
•          Reduce or increase a flow
•          Controlling the direction of flow
•          Regulating a flow or process pressure
•          Relieve a pipe system of a certain pressure

Types of valve

There are several types of valves present in a piping system. Here we discuss about the valves which are most commonly used in piping system. They are                                                                                                                   

•          Gate valve
•          Globe valve
•          Check Valve
•         Plug valve
•          Ball Valve
•          Butterfly Valve
•          Needle Valve
•          Pressure Relief Valve

Gate valve

     Gate valve is a linear motion valve used to start or stop fluid flow. These valves are used in almost all fluid services such as air, fuel gas, hydrocarbon, and all most any services. It is the most common type of valve in any process plant. These valves are either in fully open or fully closed position. Gate valve provides good shutoff.

Globe valve

       Globe valve is similar to the gate valve, and also regulates the fluid flow. These valves are used in the systems where flow control is required and leak tightness is necessary. Globe valve provides better shut off as compared to gate valve and it is costlier than gate valve.

Check valve

         Check valve is also known as Non Return Valve (NRV). These valves are used to prevent the back flow of the fluid. The pressure of the fluid passing through a pipeline opens the valve, while any reversal of flow will close the valve.

Plug valve

       Plug valve is a quarter-turn rotary motion valve that uses a cylindrical plug to stop or continue the flow. The disk is in the form of a plug which has a passage for moving the liquid. Plug valve used as on - off stop valves and able to ensure a fast shutdown.

Ball valve

                A Ball valve is similar to the Plug valve that uses a ball-shaped disk to stop or start the flow. Most ball valves are of the quick-acting type, which requires a 90° turn of the valve handle to operate the valve. The ball valve is Smaller and lighter than a gate valve.

Butterfly valve

Butterfly valve is a quarter-turn rotational motion valve, which is used to stop, regulate, and start flow. A butterfly valve has a disc which is mounted on a rotating shaft. When the butterfly valve is fully closed, the disk completely blocks the line. When the butterfly valve is fully opened, the disc is at a right angle to the flow of gas or liquid. Butterfly valves are easy and fast to open. A 90° rotation of the handle provides a complete closure or opening of the valve.

Needle Valve

                Needle valves are similar to a globe valve in design, but the main difference is the sharp needle shaped disc. These are designed to give very accurate control of flow in small diameter piping systems. They get their name from their sharp-pointed conical disc and matching seat.

Pressure Relief valve

 Pressure Relief valve is also known as pressure safety valve which are used to protect equipment or piping system during an over pressure event or in the event of vacuum. This valve releases the pressure or vacuum at pre-defined set pressure.

Classification of Valves

The following are some of the commonly used valve classifications, based on mechanical motion:

•          Linear Motion Valves. The valves in which the closure member, as in gate, globe, diaphragm, pinch, and lift Check Valves, moves in a straight line to allow, stop, or throttle the flow.
•          Rotary Motion Valves. When the valve-closure member travels along an angular or circular path, as in butterfly, ball, plug, eccentric- and Swing Check Valves, the valves are called rotary motion valves.
•          Quarter Turn Valves. Some rotary motion valves require approximately a quarter turn, 0 through 90°, motion of the stem to go to fully open from a fully closed position or vice versa.

Reference

·        http://www.wermac.org/valves/

·        https://assuredautomation.com/actuated-valve-training/types-of-valves.php

·        https://hardhatengineer.com/

By: Mohammed Zubair Ahmed M

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