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.
- 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
By: Mohammed Zubair Ahmed M
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