Non rising stem gate valves are very popular on the ship, in the underground application, or in the vertical space is limited, because they do not take up additional space. Gate valve can be used in high temperature and high pressure environment, such as high requirements of the environment. They are often seen in power plants, water treatment, mining and offshore applications.
Gate valves are characterised as having either a rising or a nonrising stem. Rising stems provide a visual indication of valve position because the stem is attached to the gate such that the gate and stem rise and lower together as the valve is operated. Nonrising stem valves may have a pointer threaded onto the upper end of the stem to indicate valve position, since the gate travels up or down the stem on the threads without raising or lowering the stem. Nonrising stems are used underground or where vertical space is limited.
Bonnets provide leakproof closure for the valve body. Gate valves may have a screw-in, union, or bolted bonnet. Screw-in bonnet is the simplest, offering a durable, pressure-tight seal. Union bonnet is suitable for applications requiring frequent inspection and cleaning. It also gives the body added strength. Bolted bonnet is used for larger valves and higher pressure applications.