Rising Stem & Non-Rising Stem Gate Valve

Function & Structure: rising stem & non-rising stem

Rising-stem and nonrising-stem are both typically applied in gate valve design.

For rising-stem gate valve, the stem is fixed to the closure member(gate disc) and doesn't turn with the operator but stays stationary with the gate. As the handwheel is turned, the threads of the stem, which are located above the packing box, retract the gate from the flow stream perpendicularly, causing the threaded portion of the stem to rise above the handwheel. The nut assembled between the handwheel and stem turns the handwheel's rotational movement to the stem's perpendicularly linear movement.

For a nonrising-stem gate valve, the stem is threaded to the gate disc by using a nut. The gate moves up or down linearly along the stem while turning the handwheel. The stem has only rotational movement without up-and-down movement.

Differences between rising stem & non-rising stem gate valves

Rising stem are often with outside screw & yoke(OS&Y) structure with the stem threads being isolated from the medium by stem packing whilst the threads of non-rising stem are exposed to the medium. Therefore, the threads of rising stem can be easily lubricated while the threads of non-rising stem are more likely to be subject to corrosion and erosion. Workers at site may easily tell the on/off status of a rising-stem gate valve by observing its stem position. A position indicator is required to show the open or close position of a non-rising stem gate valve. Non-rising stem gate valves are mainly used in services where limited space is inevitable. Besides, a non-rising stem gate valve is much cheaper than a rising-stem gate valve in the same size, pressure rating and material.

See the typical design of rising stem gate valves and non-rising stem gate valves.

Views: Author：hbmetals Date:15/05/15