Gate valves are inherently suited for full open service. Flow moves in a straight line and practically without resistance when the wedge is fully raised.

There are two basic designs of gate valves, inside screw stem and outside screw stem.

Seating is perpendicular or at right angles to the line of flow - meets it head on. That is one reason why gate valves are impractical for throttling service. When throttling is necessary, globe valves should be used. Repeated movement of the wedge near the point of closure, under high velocity flow, may create a drag on the seating surfaces and cause galling or scoring on the downstream side. A slightly opened wedge may also cause turbulent flow with vibration and chattering of the wedge.

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

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

Typical gate valves in the John Valves range are our figure numbers 59M, 60M, 600 and 601, and more details may be found in our Online Valve Catalogue.

Conclusion: Gate valves, while not designed for throttling are generally ideal for services requiring full or no flow.