The closure member slides across the flow at right angles: either a wedge that jams between two inclined seats or a flat parallel slide. Fully open, the bore is almost unobstructed, so pressure drop is tiny and the line can be rodded straight through. It is built for on-off duty: run partly open, the gate vibrates and the high-velocity jet cuts the seats.
Isolation on the cooling water header is a 12 inch gate valve, so bring the big wheel key and plan on about forty turns.
If you see a gate valve cracked a quarter open for months, expect it to pass when someone finally tries to shut it.
Also heard as
- sluice valve
Do not mix it up with
- Globe valve: A globe valve is designed to throttle and has a tortuous flow path; a gate valve is a straight-through isolation valve that should be either full open or shut.
Related terms
Wedge
The tapered closure member of a gate valve that is driven down between two inclined seats to seal.
OS&Y
Outside screw and yoke: a rising-stem valve design with its stem threads above the packing, out of the fluid.
Globe valve
A linear-motion valve that throttles well because its disc moves straight onto a seat across an S-shaped flow path.
Wire drawing
Erosion of thin grooves across a valve seat by a high-velocity jet leaking through a tiny gap.
Knife gate valve
A gate valve with a thin, sharp-edged blade that cuts through slurry, pulp or solids as it closes.