Basic Gate Valve Design

Gate valves are by far the most widely used in industrial piping. That's because most valves are needed as stop valves - to fully shut off or fully turn on flow - the only job for which gate valves are recommended.

Gate valves are inherently suited for wide-open service. Flow moves in a straight line, and practically without resistance when disc is fully raised.

Seating is perpendicular or at right angle to the line of flow - meets it head on. That's one reason why gate valves are impractical for throttling service and for too frequent operation.

For instance, a 6-inch gate valve holding fluid at 300 psi, puts a load of over 4 tons on one side of the disc, if there is only atmospheric pressure on the other. While seated tight, there's no wear or undue strain on disc or seats. But each time the valve is "cracked open," there's a threat of wire drawing and erosion of seating surfaces by the high-velocity flow.

Repeated movement of disc near point of closure under high-velocity flow, may create a drag on seating surfaces and cause galling or scoring on downstream side. A slightly opened disc may cause turbulent flow with vibration and chattering of disc.

A gate valve usually requires more turns - more work - to open it fully. Also, unlike many globe valves, the volume of flow through the valve is not in direct relation to number of turns of handwheel.

Since most gate valves used have wedge disc with matching tapered seats, refacing or repairing of the seating surfaces is not a simple operation.

CONCLUSION: Gate valves, while not designed for throttling or too frequent operation are generally ideal for services requiring full flow or no flow.

Gate valves are not designed for throttling

In a slightly opened position high-velocity flow will cause wire drawing and erosion of seating surfaces in gate valves.

Repeated movement of disc near point of closure under high-pressure flow may gall or score seating surfaces on downstream side.

Slightly opened disc in turbulent flow may cause troublesome vibration and chattering.