Valves Types and Operation <br /> <br />Valves are quite diverse and may be classified into a number types. <br /> <br />1. Ball valve, for on/off control without pressure drop, and ideal for quick shut-off, since a 90° turn offers complete shut-off angle, compared to multiple turns required on most manual valves. <br />2. Butterfly valve, for flow regulation in large pipe diameters. <br />3. Ceramic Disc valve, used mainly in high duty cycle applications or on abrasive fluids. Ceramic disc can also provide Class IV seat leakage <br />4. Clapper valve, Used in appliances like the Siamese fire appliance to allow only 1 hose to connected instead of two (the clapper valve blocks the other side from leaking out. <br />5. Check valve or non-return valve, allows the fluid to pass in one direction only. <br />6. Choke valve, a valve that raises or lowers a solid cylinder which is placed around or inside another cylinder which has holes or slots. Used for high pressure drops found in oil and gas wellheads. <br />7. Diaphragm valve, which controls flow by a movement of a diaphragm. Upstream pressure, downstream pressure, or an external source (e.g., pneumatic, hydraulic, etc.) can be used to change the position of the diaphragm. <br />8. Gate valve, mainly for on/off control, with low pressure drop. <br />9. Globe valve, good for regulating flow. <br />10. Knife valve, similar to a gate valve, but usually more compact. Often used for slurries or powders on/off control. <br />11. Needle valve for accurate flow control. <br />12. Pinch valve, for slurry flow regulation and control. <br />13. Piston valve, for regulating fluids that carry solids in suspension. <br />14. Plug valve, slim valve for on/off control but with some pressure drop. <br />15. Poppet valve, commonly used in piston engines to regulate the fuel mixture intake and exhaust <br />16. Spool valve, for hydraulic control <br />17. Thermal expansion valve, used in refrigeration and air conditioning systems. <br />18. Pressure Reducing Valve <br />19. Sampling valves <br />20. Safety valve
