Gate valve

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22mm Gate Valve on domestic hot water pipe.

A Gate Valve, or Sluice Valve, as it is sometimes known, is a valve that opens by lifting a round or rectangular gate/wedge out of the path of the fluid. The distinct feature of a gate valve is the sealing surfaces between the gate and seats are planar. The gate faces can form a wedge shape or they can be parallel. 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.

Gate Valves are prone to corrosion. Here the shaft has broken.

Gate valves are characterised as having either a rising or a nonrising stem. Rising stems provide a visual indication of valve position. Nonrising stems are used where vertical space is limited or underground.

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.

Another type of bonnet construction in a gate valve is pressure seal bonnet. This construction is adopted for valves for high pressure service, typically in excess of 15 MPa (2250 psi). The unique feature about the pressure seal bonnet is that the body - bonnet joints seals improves as the internal pressure in the valve increases, compared to other constructions where the increase in internal pressure tends to create leaks in the body-bonnet joint.

Gate valves normally have flanged ends which are drilled according to pipeline compatible flange dimensional standards. Cast Iron, Cast Carbon Steel, Gun Metal, Stainless Steel, Alloy Steels & Forged Steels are different materials in which Gate Valves are made available.

[edit] Maintenance

If a gate valve fails, it is normally best to replace it, provided you can get one of the matching size.

To avoid failure, it is a very good practice to use the valve three or four times a year. From its normal position of nearly full-open: wind it fully closed, then fully open, then half a turn closed. Make sure the system that the pipes are connected to doesn't require water flow whilst you do this.