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A sluice valve, which is also called a gate valve, is a type of valve that opens by raising a barrier (gate) to allow the fluid to pass through. Industrial gate valves take up minimal space along the pipe and do not significantly impede the flow of fluid when fully open. The gate surfaces can be either parallel or wedge-shaped, with the latter design allowing for better sealing by applying pressure.
Gate valves are primarily used to stop the flow of liquids, as opposed to regulating the flow, which is typically done with a globe valve. When fully open, a gate valve allows for unobstructed flow, resulting in minimal resistance. The size of the flow path changes in a non-linear manner as the gate is moved, meaning that the flow rate does not change consistently with the movement of the stem. Depending on the design, a partially open gate may vibrate due to the fluid flow.
Gate valves are commonly used in larger pipe diameters (ranging from 2" to the largest pipelines) because they are simpler to construct compared to other valve types in larger sizes.
At high pressures, friction can pose a challenge. The pressure of the medium pushes the gate against its guiding rail, making it more difficult to operate the valve. In some cases, larger gate valves are equipped with a bypass that is controlled by a smaller valve, allowing for pressure reduction before operating the gate valve itself.
Gate valves that do not have an additional sealing ring on the gate or the seat are used in applications where minor leakage is not a concern, such as heating circuits or sewer pipes.
Gate valves are operated by a stem that is connected to an actuator, such as a handwheel or motor. These valves can have either a rising or nonrising stem, depending on where the threading is located. Rising stems are connected to the gate and move up and down together when the valve is operated, allowing for a visual indication of the valve's position. The actuator is connected to a nut that rotates around the threaded stem to move it. Nonrising stem valves are connected to the actuator and rotate with it, with the threading going into the gate. These valves may have a pointer attached to the stem to show the valve's position, as the gate's movement is hidden inside the valve. Nonrising stems are used in situations where there is limited vertical space.
Gate valves can have flanged ends that are drilled according to the standards of compatible pipeline flanges. They are commonly made from materials such as cast iron, cast carbon steel, ductile iron, gunmetal, stainless steel, alloy steels, and forged steels.
In ultra-high vacuum chambers, all-metal gate valves are used to separate different regions of the chamber.
Bonnet
Valve bodies are effectively sealed by bonnets, ensuring no leaks occur. Screw-in, union, or bolted bonnets can be found on gate valves. The simplest option is the screw-in bonnet, which provides a strong and reliable seal. For applications that require regular inspection and cleaning, a union bonnet is recommended. This type of bonnet also enhances the strength of the valve body. On the other hand, bolted bonnets are utilized for larger valves and situations involving higher pressure.
Pressure seal bonnet
A different kind of bonnet design found in gate valves is called pressure seal bonnet. This design is used for valves that handle high pressure situations, usually over 2250 psi (15 MPa). What sets the pressure seal bonnet apart is that it has a cup-shaped end that fits into the valve body. When the pressure inside the valve rises, the cup expands outward, creating a better seal between the body and the bonnet. Other designs that rely on external clamping pressure often result in leaks at the joint between the body and the bonnet.
Knife gate valve
A specialized valve called a knife gate valve is utilized to halt the movement of plastic solids and thick slurries like paper pulp by slicing through them. Unlike wedge-shaped valves, a knife gate valve features a tapered knife-like edge on its lower surface.
