Different types of valves are used in piping. In this article, I have covered classifications of valves and functions of valves. Let’s start with Valve definition.
What is Valve?
Chances are there that you already know this. But there is no harm to refresh the memory.
Valve is a device that regulates, controls or directs the flow of a fluid by opening, closing, or partially obstructing fluid flow. Sound bit complicated? Ok, let me further simplified this. A valve is a mechanical device that controls the flow and pressure of fluid within a system or Process. So basically, it controls flow & pressure.
Types of Valves
In piping following types of valves are used depending on the requirements. The cost of Valve in the piping system is up to 20 to 30% of the overall piping cost. And the cost of a given type and size of the valve can vary 100%. It means that if you choose ball valve over butterfly valve for the same function. It can cost you more. So, the selection of valves is essential to the economics, as well as operation, of the process plants.
- Gate Valve
- Globe Valve
- Check Valve
- Plug valve
- Ball Valve
- Butterfly Valve
- Needle Valve
- Pinch Valve
- Pressure Relief Valve
Let learn about each of them.
Click on the link to Learn about each of valve in more detail.
Gate valve is the most common type of valve in any process plant. It is a linear motion valve used to start or stop fluid flow. In service, these valves are either in fully open or fully closed position. Gate valves are used in almost all fluid services such as air, fuel gas, feedwater, steam, lube oil, hydrocarbon, and all most any services. Gate valve provides good shutoff.
Globe valve is used to stop, start, and regulate the fluid flow. Globe Valves are used in the systems where flow control is required and leak tightness is also necessary. Globe valve provides better shut off as compared to gate valve and it is costlier than gate valve.
The check valve prevents backflow in the piping system. The pressure of the fluid passing through a pipeline opens the valve, while any reversal of flow will close the valve.
Plug valve is Quarter-turn rotary motion Valve that uses a tapered or cylindrical plug to stop or start the flow. The disk is in plug shape, which has a passage to pass the flow. Plug valve used as on-off stop valves and capable of providing bubble tight shutoff. Plug valve can be used in vacuum to high-pressure & temperature applications
A Ball valve is a quarter-turn rotary motion 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 of same size and rating.
A Butterfly valve is a quarter-turn rotary motion valve, that is used to stop, regulate, and start the flow. Butterfly valve has a short circular body. Butterfly Valve is suitable for large valve applications due to Compact, lightweight design that requires considerably less space, as compared to other valves.
Needle valves are similar to a globe valve in design with the biggest difference is the sharp needle like a disk. Needle valves 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.
The pinch valve is also known as clamp valve. It is a linear motion valve. Used to start, regulate, and stop fluid flow. It uses a rubber tube, also known as a pinch tube and a pinch mechanism to control the fluid. Pinch Valve is ideally suited for the handling of slurries, liquids with large amounts of suspended solids, and systems that convey solid material pneumatically.
A pressure Relief valve or pressure safety valve are used to protect equipment or piping system during an overpressure event or in the event of vacuum. This valve releases the pressure or vacuum at pre-defined set pressure.
Valve serve a various function within the piping system. Such as
- Stopping and starting a fluid flow. Depending on whether a valve is open or closed, it let pass the process fluid or halt the fluid.
- Throttling the fluid flow. Some of the valves let you throttle the fluid depending open % of total opening. Lesser the opening higher the throttling and otherwise.
- Controlling the direction of a fluid flow. Multiport valve lets you decide the way fluid will go.
- Regulating a flow or pressure within the piping system. Some of the automatic control valves maintain the flow and pressure within the system by adjusting opening and closing.
- Relieve pressure or vacuum from the piping system and equipment. Pressure and vacuum relief valve safeguard the process system from overpressure and during vacuum condition.
Different types of valves serve these functions. These valves can be classified or categorized based on;
- End connection
- How it operates
- Types of Actuator it used.
Classification of Valves Based on Function
In the above chart, you can see the types of valves and their function.
Isolation valve isolates or cuts the supply of fluid when needed. Gate, ball, plug, piston, diaphragm, butterfly and pinch valve falls under this category.
A control valve that regulates the flow of fluid falls in the regulation category. Globe, needle, butterfly, diaphragm, ball, plug, and pinch valve are used as a control valve. You can see that; some valves serve dual purposes such as globe and ball valve can be used as an isolation as well as a control valve.
Pressure and vacuum relief valve used to prevent overpressure and vacuum with the system that can damage the piping and equipment. Non-return valve such as swing and lift check valve prevents backflow within the system. Whereas, some valves are designed to serve a special purpose. Such as multiport, knife, and line blind valve.
Classification of Valves Based on End Connections
Based on the end connection, valve ends can be
- Screwed or threaded that connect with matching thread on the pipe. Small-bore valve used in instrument connection or as a sample point has a threaded end
- Majority valve used in piping has a Flanged type ends.
- Butt welded valves are used in very high pressure and temperature services.
- Socket Welded valves are used in low-pressure
- Check valve and butterfly valves are available in wafer and lug end construction. These types of ends are used when space is constrained.
You can see the images of all these types of valve end above.
Classification of Valves Based on The Way it Open and Closed
|Valve type||Linear motion||Rotary motion||Quarter turn|
|Swing check valve||X|
|Lift check valve||X|
|Tilting-disc check valve||X|
|Folding-disc check valve||X|
|In-line check valve||X|
|Stop check valve||X||X|
Another way to classify the valve is the way it open and close. Each valve opens and closed by either Liner or rotary motion or by quarter turn which is nothing but a rotary motion.
In the image below, you can see the difference between opening methods of the valve.
Linear motion valves use a closure member that moves in a straight line and cut the flow to start, stop, or throttle the flow. The closure device could be a disc, or flexible material, such as a diaphragm. Linear motion valves are slower in operation, but they provide a higher level of accuracy and stability in the position of the closure member.
Rotary motion valves rotate a disc or swing it from the hinge pin that holds the disk.
A 90° turn of the stem in Quarter turn valves fully open or fully closed the valve. Because of this quick turn, the operation of Quarter turn valve is much faster than linear motion valves. Some rotary motion valves are also known as Quarter turn valve.
In the table, you can see that ball valve, butterfly valve, and plug valve are both rotary and quarter turn valve. Whereas swing check, tilting disk, and other rotary motion valve are not a quarter turn valve.
Classification of Valves Based on Types of Actuator it Used
The last way to classify the valve is, types of the actuator is used to transfer the motion to operate the valve. The valve can be operated manually with the help of handwheel, lever, chain or by a gear wheel. An external power source such as an electric motor, air, hydraulic fluid or solenoid is used to operate valve from the control room. Check valve works automatically when subjected to the backflow.