A gate valve is a valve that operates using a round/rectangular gate (wedge) out of the path of the fluid. The distinct feature of a gate valve is the sealing surfaces between the gate and seats are planar, so gate valves are often used when a straight-line flow of fluid and minimum restriction is desired. The gate faces can form a wedge shape or they can be parallel. Typical gate valves should never be used for regulating flow, unless they are specifically designed for that purpose.
On opening the gate valve, the flow path is enlarged in a highly nonlinear manner with respect to percent of opening. This means that the flow rate does not change evenly with stem travel. Also, a partially open gate disk tends to vibrate from the fluid flow. Most of the flow change occurs near shutoff with a relatively high fluid velocity causing disk and seat wear and eventual leakage if used to regulate flow.
Typical gate valves are designed to be fully opened or closed. When fully open, the typical gate valve has no obstruction in the flow path, resulting in very low friction loss.
Gate valves are ideally suited for petroleum applications because they perform well with viscous fluids.
Type of gate valves as follows:
- Parallel Slide GateValve
- Pressure Seal Gate Valve
- Wedge Gate Valve
- Expanding Gate Valve
- Geothermal Gate Valve
- API 6D Pipeline Gate Valve
- API 6A Wellhead Gates Valve
Stem of gate valves can be :
- Rising Stem
- Rising stems provide a visual indication of valve position because the stem is attached to the gate such that the gate and stem rise and lower together as the valve is operated.
- Non-Rising Stem
- Non-rising stem valves may have a pointer threaded onto the upper end of the stem to indicate valve position, since the gate travels up or down the stem on the threads without raising or lowering the stem.
- Non-rising stems are used underground or where vertical space is limited
Bonnets of gate valves can be :
- Bonnets provide leak proof closure for the valve body.
- Simplest, offering a durable, pressure-tight seal
- Suitable for applications requiring frequent inspection and cleaning
- Also gives the body added strength
- Bolted Bonnet
- Used for larger valves and higher pressure applications
- Pressure Seal Bonnet
- This construction is adopted for valves for high pressure service
- A unqiue benefit of a pressure seal bonnet design is that the seal improves as the internal pressure in the valve increases
- Compared to other constructions where the increase in internal pressure tends to create leaks in the body-bonnet joint