Gate valves are used when a straight-line flow of fluid and minimum restric¬tion is desired. Gate valves are so named because the part that either stops or allows flow through the valve acts somewhat like the opening or closing of a gate and is called, appropriately, the gate. The gate is usually wedge shaped. When the valve is wide open, the gate is fully drawn up into the valve, leaving an opening for flow through the valve the same size as the pipe in which the valve is installed. Therefore, there is little pressure drop or flow restriction through the valve. Gate valves are not suitable for throttling purposes since the control of flow would be difficult due to valve design and since the flow of fluid slapping against a partially open gate can cause extensive damage to the valve. Except as specifically authorized, gate valves should not be used for throttling.
Gate valves are classified as either RISING STEM or NONRISING STEM valves. On the nonrising-stem gate valve, the stem is threaded on the lower end into the gate. As the handwheel on the stem is rotated, the gate travels up or down the stem on the threads, while the stem remains vertically stationary. This type of valve almost always has a pointer-type indicator threaded onto the upper end of the stem to indicate valve position.
The rising-stem gate valve has the stem attached to the gate; the gate and stem rise and lower together as the valve is operated.
Gate valves used in steam systems have flexible gates. The reason for using a flexible gate is to prevent binding of the gate within the valve when the valve is in the closed position. When steam lines are heated, they will expand, causing some distortion of valve bodies. If a solid gate fits snugly between the seat of a valve in a cold steam system, when the system is heated and pipes elongate, the seats will compress against the gate, wedging the gate between them and clamping the valve shut. This problem is overcome by use of a flexible gate (two circular plates attached to each other with a flexible hub in the middle). This design allows the gate to flex as the valve seat compresses it, thereby preventing clamping.
We can Supply a wide range of Gate Valves covering
Universal Gate Valves of Cast Iron Gate Valve, Ductile Iron Gate Valve, Cast Steel Gate Valve and Forged Steel Gate Valve, Cryogenic Gate Valves, Bellow Sealed Gate Valves and Sliding Gate Valves etc.
All of the Gate Valves are designed, manufactured and tested to API, ASTM, ANSI, JIS, DIN and BS Standards.