Types of Rising Stem (multi-turn) Valves

Gate Valves

A gate valve functions by moving a wedge shaped disc obstructer up and down to open and close the flow path through the valve. This linear motion is provided by a threaded rising stem. Turning this threaded stem requires multiple revolutions (multi-turn) to travel from open to closed. The number of revolutions required is usually the valve size in inches x 3 + 2. So a 6 inch valve will require 20 turns of the stem [(6 x 3) + 2 = 20]. They should only be used for on/off applications as throttling for an extended period of time will damage both the obstructer and seals. Use of a gate valve for throttling is also not very effective since most of the reduction of flow will increase in the last 10% of closure.

Globe Valves

Globe valves operate by having a convex disc shaped plug raise and lower via a rising stem into a circular seat around the inside of the globe shaped body at the “equator”. The flow enters the “lower hemisphere” from one side, then travels up through the seat and exits through the outlet on the opposite side of the “northern hemisphere”. Globe valves are suitable for both on/off and throttling applications. There are 2-way globe valves that are a preferred choice for precise flow control and 3-way globe valves that are commonly used for mixing media from two inlet ports and directing that mixture through an outlet port.

Needle Valves

These are very similar to a globe valves with 2 main differences. One, they are smaller and for finer control of flow on smaller lines. Two, instead of a disc shaped plug, they use a “needle” which has a conical shape, and moves in and out of an orifice. While effective as an on/off valve, these would not be the best choice. Needle valves are meant for fine throttling flow control.