A gate valve is the most common valve for water supply systems. It is generally used to completely shut off fluid flow or, in the fully open position, provide full flow in a pipeline.
Gate valves are are widely used to isolate specific areas of the water supply network during maintenance, repair works, new installations, as well as to reroute water flow throughout the pipeline. They are installed in pipelines as isolating valves and should not be used as control or regulating valves. Gate valves are often used when minimum pressure loss and a free bore is needed.
A gate valve controls the flow by lifting the gate (open) and lowering the gate (closed). Thus it is used either in the fully closed or fully open positions. When fully open, a typical gate valve has no obstruction in the flow path resulting in a very low pressure loss. As the valve has to turn multiple times to go from open to closed position, the slow operation also prevents water hammer effects.
They are suitable for most fluids including steam, water, oil, air, and gas. If the fluid is very viscous a special type of gate valve known as a knife gate valve can be used. Gate valves used in the mainlines carrying oil or gas must be of full bore or through conduit design to enable smooth passage of scrapers or pigs used for cleaning or monitoring pipelines. Such gate valves are referred to as full bore or through conduit gate valves.
Gate valves have more height than ball valves due to their high body and upward stem and gate movement for rising stem design. Gate valves use a sliding plate within the valve body to stop, limit, or permit full flow of fluids. The gate is usually wedge-shaped. When the valve is wide open, the gate is fully drawn into the valve bonnet. This leaves the flow passage through the valve fully open with no flow restrictions.