Gate valves block flow using a sliding wedge. They are designed to be fully open or closed and are not used for flow control. They have two connectors and a hood with a handle for raising and lowering the cap. The method of connecting the cover impacts use. A properly designed valve should have no impact on overall pressure.
A gate valve is a type of plug that is placed on a piping system to block flow. These valves simply prevent the passage of liquid by using a wedge that slides in and out of the pipe. In most cases, the gate valve is designed to be fully open or fully closed. Consequently, these valves are rarely used as a means of flow control; they generally shut off the flow completely or are not used. Partially closed gate valves can increase pressure in a system in unpredictable ways or cause vibrations in the liquid.
The construction of a gate valve is quite simple. They generally have two threaded connectors that snap into the pipe system. It is possible for a gate connector to have more than two connections, but this is very rare. A post, called a hood, stands above the connectors; this area contains the wheel chock and the mechanism for raising and lowering it. Finally, on the upper part of the bonnet, there is a handle which controls the raising and lowering of the cap.
When the handle is turned, it moves the cork inside the valve. The stopper slides into the tube and prevents the passage of the liquid. The valve will typically indicate the position of the cap on the outside of the valve, or the handle will twist and unscrew to show the relative height of the cap. The valve body is slightly wider than the connected pipes, allowing the cap to fully cover the opening and make it completely liquid-tight.
The method used to connect the cover to the valve has an impact on the use of the gate valve. If the lid is simply screwed on, the valve will work fine for light duty applications. Bolt-on hoods work well for heavy-duty work, but cannot be taken apart for repair or cleaning. Union-bond hoods can be disassembled easily, but also have the highest leak rate. The last style is a pressure-sealed hood – it works well in many different environments, but it’s also the most expensive style.
Since a gate valve should be fully open or fully closed, it should have no impact on the overall pressure. A properly designed valve will have the same dimensions inside the pipe, as any narrowing or widening of the opening will change the flow rate. When the gate is closed, the pressure should be constant in the system, as there is no movement.
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