Gate Valve: Types & Applications
A gate valve controls flow by raising or lowering a flat or wedge-shaped gate perpendicular to the fluid path. It is designed strictly for on/off service and should never be used for throttling. Gate valves are the most common isolation valve in oil and gas piping systems.
| Feature | Details |
|---|---|
| Function | On/off isolation (fully open or fully closed) |
| Flow direction | Bi-directional |
| Pressure drop | Minimal when fully open (full bore) |
| Actuation | Handwheel, gear, electric, pneumatic, hydraulic |
| Cast body standard | API 600 (2” and above) |
| Forged body standard | API 602 / BS 5352 (below 2”) |
| Pipeline standard | API 6D |
| Pressure classes | 150, 300, 600, 900, 1500, 2500 per ASME B16.34 |
| Body materials | ASTM A216 WCB (cast CS), A105 (forged CS), A351 CF8M (cast SS) |
How a Gate Valve Works
The handwheel or actuator rotates the stem, which moves the gate vertically between the seats. In the open position, the gate retracts fully into the bonnet, leaving an unobstructed bore. In the closed position, the gate wedges against the seat faces to create a tight seal.
Gate valves produce very low pressure drop because the flow path is straight and unobstructed. This makes them ideal for mainline isolation in pipelines and process piping. However, partially opening a gate valve causes turbulence, vibration, and rapid erosion of the gate and seats, which is why throttling service requires a globe valve instead.
Gate Valve Types
Three main gate designs exist:
- Solid wedge: single-piece tapered gate. Simple, reliable, and suitable for most services. Risk of thermal binding in high-temperature steam lines.
- Flexible/split wedge: gate with a cut or flex point that accommodates thermal expansion and pipeline stress. Preferred for steam and high-temperature applications.
- Parallel slide: two flat discs held apart by a spring. Eliminates wedging action, avoids thermal binding, and is standard for high-temperature steam per BS 1414.
Knife gate valves use a thin, sharp-edged blade for slurry, pulp, and wastewater service. They are not covered by API 600 but by MSS SP-81.
Stem Types
Gate valves use either a rising stem (OS&Y) or non-rising stem (NRS). Rising-stem designs provide a visual indication of valve position and are required by most project specifications. Non-rising stems save vertical space and are common in underground or confined installations.
Common Applications
Gate valves serve as mainline isolation in refineries, petrochemical plants, power stations, and water distribution. Sizes range from 1/2” to 60”+. For large-diameter pipeline applications, API 6D gate valves with gear operators or actuators are standard.
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