A 22 mm gate valve is a type of plumbing valve that controls the flow of water in a piping system by using a gate or wedge-shaped disc to block or allow the flow of water. The 22 mm refers to the size of the valve, which is designed to fit on a 22 mm pipe. When the valve is in the closed position, the gate or wedge-shaped disc is lowered to block the flow of water, and when it is in the open position, the gate is raised to allow the water to flow through. Gate valves are commonly used in applications where a full flow is required, such as in irrigation systems or large water supply systems. They are generally not recommended for use in applications where frequent adjustments to the valve are required, as they can become stiff or difficult to operate over time.