Gate valve structure:
A gate valve is a valve with a gate as an opening and closing part. The gate moves up and down along the vertical direction of the center line of the valve body channel, and the direction of movement and the direction of medium flow are also perpendicular to each other. The gate valve is composed of a valve body, a valve seat, a valve stem, a gate plate, a valve cover, and a sealing ring. The common gate valve is driven by a hand wheel. In addition, electric or pneumatic actuators can be installed to realize the automatic operation of the gate valve. The gate valve is installed on the pipeline and can only be fully opened and fully closed. It is used to cut off the flow of the medium and cannot be used as a condition and control flow.
Because of the particularity of the gate valve structure, the gate valve has a large stroke and a long opening and closing time when it is fully opened and fully closed, especially when it is manually operated, which is time-consuming, so the gate valve is usually installed on a pipeline that does not often open and close. . In addition, the internal valve body passage of the gate valve is straight, and the medium can circulate in both directions, and when the gate of the gate valve is fully opened, the flow resistance in the valve body passage tends to zero, and the flow resistance is very small.
Gate valves can be divided into bright stem gate valves and dark stem gate valves according to their different structures.
Rising stem gate valve means that the stem of the gate valve is exposed, and the threads on the stem are also exposed. When the handwheel is turned, the gate will move linearly with the stem. It is also called a lifting stem gate valve. There are trapezoidal threads on the lifting rod of the open-stem gate valve, and the rotation motion can be changed into linear motion through the nut on the top of the valve and the guide groove on the valve body, that is, the operating torque can be turned into operating thrust. The exposed stem gate valve can be used as a very obvious switch sign because the stem is exposed, that is to say, the opening and closing state of the valve can be observed directly through the lifting of the stem.
The dark stem gate valve is different from the rising stem gate valve. Its stem is inside the valve, and the thread on the stem is also located inside the valve body. The operation of the concealed stem gate valve is to manually rotate the valve stem to select in place, and the gate plate is moved up and down through the thread on the valve stem. Therefore, the dark stem gate valve is also called the rotating stem gate valve. Because the valve stem is built-in, the opening and closing state of the dark-stem gate valve cannot be directly observed. Generally, it is switched until it can't be turned.
In the actual use process, in order to take into account the temperature change, the lock-up phenomenon occurs. Whether it is an open-stem gate valve or a concealed-stem gate valve, it is usually opened to the apex position, and then reversed 1/2-1 circle, as the position of the fully open valve.
