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Gate Valves
Please refer to the figure shown here. This graphic illustrates a gate valve; this type of valve is most common in industrial valves.
The gate valves are used for allowing or blocking fluid flow through a pipe. Usually such valves are kept in either full open or full closed position. They are not designed for midway operation to control the flow or pressure of the fluid flowing through them. They are also not designed for frequent operation; therefore, this type of design should not be used in locations where it must be opened and closed frequently.
Each time you use a gate valve, while the fluid is flowing through it, the valve disc is subjected to pressure. Frequent exposure to such pressure is likely to damage (distort) the disc. It may also reduce its ability to move freely, or it may loose its ability to provide a good shutoff.
This figure shows a cutaway view of a large gate valve. Notice the valve disc in the lower part of the valve. The figure is showing the disc in “full closed” position. When the disc is in this position, the valve is said to be “closed” since no fluid can pass through it.
Gate valves are also referred to as “block valves” or “shut-off valves”.