The gate valve consists of a gate that serves as the opening and closing part. The gate moves perpendicularly to the fluid's direction. It is important to note that the gate valve can only be fully opened or fully closed; it does not offer the option for adjustment or throttling. The gate has two sealing surfaces, typically forming a wedge shape. The wedge angle may vary depending on the valve parameters, usually around 5°, but it can be 2°52' when the medium temperature is not too high.
There are two types of gates used in wedge gate valves. The first one is a rigid gate, which remains unchanged when in use. The second type is an elastic gate, which can undergo some deformation to improve its craftsmanship and compensate for any deviation in the sealing surface angle during the manufacturing process.
When the gate valve is closed, the sealing surface relies on the medium pressure to achieve a tight seal. The pressure of the medium presses the gate's sealing surface against the valve seat on the opposite side, ensuring a secure seal. This self-sealing mechanism is sufficient for most gate valves. However, some gate valves require external force to force the gate against the valve seat when closing, ensuring a tighter seal.
The gate of the gate valve moves in a linear motion along with the valve stem, known as a lift-rod gate valve or a rising-rod gate valve. The valve stem typically has trapezoidal threads, which, when rotated using the nut at the top of the valve and the guide groove on the valve body, convert the rotary motion into linear motion. This transformation allows the operating torque to become an operating thrust.
When the valve is fully open, the lift height of the gate is equal to the valve's diameter, ensuring an unobstructed flow path for the fluid. However, this fully open position is not typically monitored during operation. Instead, the position where the valve stem cannot be turned further is used as an indicator of the fully open position. To account for potential locking due to temperature changes, the valve is usually opened to the top position and then turned back 1/2 to 1 full turn to establish the fully open position. Hence, the stroke of the gate determines the fully open position of the valve.
In some gate valves, the stem nut is located on the gate itself. The rotation of the handwheel drives the valve stem to rotate, causing the gate to lift. This variation of the gate valve is known as a rotating stem gate valve or a dark stem gate valve. The usage of these valves offers a different operational approach compared to the lift-rod gate valves.