Gate valves get their name because of a flat or tapered disc that can slide vertically in and out of the path of the flow, at right angles to the direction of flow, thus blocking the flow. The vertical disc which is normally referred to as the 'gate' slides along a track which is also referred to as seat of the gate. Large force or torque is required to operate the handwheel lifting the gate, for large sized valves. Hence such valves tend to be operated with automatic actuators.
Due to the structure, these valves are seldom effective for throttling applications. Hence they are mostly used as on-off valves for non-throttling applications. When the gate is fully lifted, the valve offers little or no resistance to the fluid flow causing a very small pressure drop.
Design of the gate valves can vary depending on the design of the gate and the seat.
| Wedge Gate Valves | The gate is wedge shaped and seals on corresponding faces in the valve body. | |
| Double Disc Gate Valves | The gate is formed by two discs which are forced apart by springs. Theses discs provide tight sealing against parallel seats. | |
| Bellows Seal Gate Valves | Designed to minimize leakage of hazardous fluids to the environment through the valve stem. Uses metallic bellows between valve stem and bonnet for sealing. |
Advantages
When the valve is fully open, the pressure drop across a gate valve is very low. These valves can be used for bidirectional action. They are very handy as on-off valves.
Disadvantages
Gate valves need a large force to for operation and large sized valves require automatic actuators. Gate valves are not very quick to open or close compared to some other valves. They take up more space compared to other valves. For some valves facing high temperature fluctuations, thermal expansion and shrinking can lead to unwanted leakage.
Applications of gate valves
- Applications as shut-off valves
- Socket or butt-welding end valves for several services
- Threaded end valve for gaseous or liquid systems
- Water distribution, fire water systems operating at low pressures
