All valves are designed to stop, allow or throttle the flow of a process fluid. Gate valves, one of the original valve designs, are ideally suited for on/off, primarily liquid, service.
A gate valve functions by lifting a rectangular or circular gate out of the path of the fluid. When the valve is fully open, gate valves are full bore, meaning there is nothing to obstruct the flow because the gate and pipeline diameter have the same opening. This bore diameter also determines the valve size. An advantage of this full-bore design is very low friction loss, which saves energy and reduces total cost of ownership.
Gate valves can have either a rising or non-rising stem design. Rising stems are attached directly to the gate and provide a visual indicator of the valve position. Non-rising stems are generally threaded into the upper part of the gate and have a pointer threaded onto the top to indicate position. Non-rising stem designs are ideally suited for applications where vertical space is limited, in well applications and where scraping/pigging is not required.
Gate valves are designed with a sealing unit to provide a tight seal around the stem. Single Loaded Spring (SLS) stem seal design, used exclusively on gate valves, provides superior leak protection and a self-adjusting seal designed to reduce maintenance.
Gate valves generally have one of four types of bonnets, which provide closure from leaks for the body of the valve. Screw-in bonnets are simple, durable sealing units that use pressure to affect a seal. Union bonnets provide easy access to the valve body for applications that may require frequent maintenance or inspection. Bolted bonnets are generally used for larger valves in higher pressure applications. Finally, pressure seal bonnets are designed for services with high pressure in excess of 15MPa (2250 psi).