Gate Valve

Overview

A gate valve isolates flow by sliding a flat wedge straight across the pipe bore. Fully open, the wedge lifts entirely clear of the flow path, leaving an unobstructed full-bore opening with very little pressure drop; fully closed, the wedge wedges between two seats for a tight shutoff. It is built for the two end states, open or shut, and not for throttling, because a partly open gate suffers seat erosion and vibration from the high-velocity jet around its edge.

The Valve Body forms the flow passage and holds the Gate & Seats; the Bonnet bolts on top and guides the stem out of the pressure boundary. Turning the Actuator drives the Stem Assembly, which raises or lowers the wedge. The Packing & Gland seals the stem where it leaves the bonnet, the Flange Set bolts the valve into the line, and the Position Indicator shows the gate position.

How it works

The valve converts rotary handwheel motion into linear gate travel through an Acme-threaded Valve Stem running in a bronze Stem Nut held in the Yoke. In a rising-stem (OS&Y) design the stem screws up through the nut so the protruding length itself indicates how far the valve is open. As the stem lowers, its tip pulls the Gate Wedge down between the two Seat Ring seats; the final turns drive the tapered wedge into a metal-to-metal seal.

Closing torque sets the seating force, and a powered Actuator uses a Torque Switch to cut the motor at the right torque so the wedge seals without being jammed so hard it cannot be reopened. A flexible wedge is slit so it can flex and seat squarely even when thermal growth distorts the seats, which is why it is common on steam and hot lines.

Sealing the stem matters as much as sealing the bore. The Stem Packing rings are squeezed around the stem by the Gland Follower, and a Backseat Bushing lets the fully open stem seal against the bonnet so the packing can be renewed while the line stays pressurized. The high-Cv, full-bore passage and dead-tight shutoff are what make gate valves the default isolation valve in pipelines, water mains, and process plants.