Gate valve
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A gate valve is a valve that opens by lifting a round or rectangular gate out of the path of the fluid. Gate valves are sometimes used for regulating flow, but many are not suited for that purpose, having been designed to be fully opened or closed. When fully open, the typical gate valve has no obstruction in the flow path, resulting in very low friction loss.
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Gate_valve.gif
Image:Gate_valve.gif
Most gate valves have a rising or a nonrising stem. Rising stems give a visual indication of valve position. Nonrising stems are used where vertical space is limited.
Bonnets provide leakproof closure for the valve body. Gate valves may have a screw-in, union, or bolted bonnet. Screw-in bonnet is the simplest, offering a durable, pressure-tight seal. Union bonnet is suitable for applications requiring frequent inspection and cleaning. It also gives the body added strength. Bolted bonnet is used for larger valves and higher pressure applications.