Gate Valve Working Principle

The gate valve, as shown in figure, is a valve that opens by lifting a round or rectangular gate/wedge out of the path of the fluid. The distinct feature of a gate valve is that 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.

Gate valves are primarily used to permit or prevent the flow of liquids, but typical gate valves shouldn’t be used for regulating flow, unless they are specifically designed for that purpose. Due to their ability to cut through liquids, gate valves are often used in the petroleum industry. For extremely thick fluids, a specialty valve often known as a knife valve is used to cut through the liquid. When open, the gate valve’s flow path is enlarged in a highly nonlinear manner with respect to percent of opening. This means that 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 characterized as having either a rising or a non-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 raise and lower together as the valve is operated. 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 provide leak proof closure for the valve body. Gate valves may have a screw-in, union, or bolted bonnet. Screw-in bonnets are the simplest, offering a durable, pressure-tight seal. Union bonnets are suitable for applications requiring frequent inspection and cleaning. They also give the body added strength. Bolted bonnets are used for larger valves and higher pressure applications.

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Gate valve is basically used in fluid pipelines for controlling the flow of fluid . There will be one gate or wedge in gate valve and it will control the fluid flow. Shape of gate or wedge of gate valve will be a type of flat circular plate or rectangular plate. Sometimes, gate or wedge is also termed as disc of gate valve.

valve which is used to open and close the gate valve. When handle wheel will be rotated, it will move the gate or wedge in upward or downward direction across the line of fluid flow.

Working mechanism of a gate valve

When handle wheel will be rotated in clockwise direction, steam and gate will move in downward direction across the fluid flow line and gate will be tightly located between the two seats. Hence there will not be any leakage of fluid through the valve once valve is closed completely.

When handle wheel will be rotated in anti-clockwise direction, steam and gate will move in upward direction across the fluid flow line and valve will be opened from closed position and will permit the flow of fluid through the gate valve. Once gate valve is completely opened, it will permit no resistance or very little resistance to the flow of fluid.

We can use gate valve in semi-open condition also but there will be one issue of erosion of gate as fluid will strike the gate if valve is partially open. Therefore gate valve should be used in completely closed or completely open condition.