Types of Valves:
A valve is a device used either to control the flow rate or to stop the flow of a fluid through pipelines and to and from process equipments. Various types of valves are used in the chemical process industry and are constructed out of a variety of materials based upon the service requirements. Various types of valves in use are :
1. Gate Valve
2. Globe Valve
3. Ball Valve
4. Plug Valve
5. Diaphragm Valve
6. Needle Valve
7. Butterfly Valve
8. Check/Non Return Valve
9. Control Valve, etc.
Gate valves are commonly used to minimize the pressure drop in the open position and to stop the flow rather than controlling it. Globe valves are used to control the flow of fluid but pressure drop through this valve is much greater than that through gate valves (due to the change in the direction of flow in the valve body). A needle valve is a modification of the globe valve and generally used for an accurate control of the flow. Plug valves and ball valves are used for on-off service and they operate through 90o. Non-return valve is used when unidirectional flow is desired.
Diaphragm valves are used for fluids such as viscous liquids, slurries or corrosive liquids. They make use of a flexible diaphragm usually of rubber. A butterfly valve is used in a large size pipeline and operate on the same principle as a damper in a stove pipe. Control valves are used in modern chemical processes for controlling the flow automatically. These valves are operated either electrically or pneumatically. Fig. shows various types of valves.
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