The gate valve is an opening and closing gate. The movement direction of the gate is perpendicular to the direction of the fluid. The gate valve can only be fully opened and fully closed, and cannot be adjusted or throttled. The gate valve is sealed by the contact between the valve seat and the gate plate. Usually, the sealing surface will be surfacing with metal materials to increase wear resistance, such as surfacing 1Cr13, STL6, stainless steel, etc.
Gate valves can be divided into:
1. Rising stem gate valve: The stem nut is on the bonnet or bracket. When opening and closing the gate, the stem nut is rotated to realize the lifting and lowering of the valve stem. This structure is beneficial to the lubrication of the valve stem, and the degree of opening and closing is obvious, so it is widely used.
2 Dark stem gate valve: The stem nut is in the valve body and is in direct contact with the medium. When opening and closing the gate, it is realized by rotating the valve stem. The advantage of this structure is that the height of the gate valve remains the same, so the installation space is small, and it is suitable for gate valves with large diameter or limited installation space. This structure should be equipped with an opening and closing indicator to indicate the degree of opening and closing. The disadvantage of this structure is that the valve stem thread is not only unable to lubricate, but also directly corroded by the medium and easily damaged.
The main difference between the rising stem gate valve and the dark stem gate valve:
1. The lifting screw of the dark rod flange gate valve only rotates without moving up and down. Only a rod is exposed, and its nut is fixed on the gate. The gate is lifted by the rotation of the screw, and there is no visible gantry. ; The lifting screw of the rising stem flange gate valve is exposed, and the nut is close to the handwheel and is fixed (not rotating or moving axially). The gate is lifted by rotating the screw. There is no relative axial displacement, and the appearance is a portal bracket.
2. The dark rod valve cannot see the lead screw, and the open rod valve can see the lead screw.
3. When the dark stem valve is switched on and off, the steering wheel and the valve stem are connected together and are relatively stationary. It is opened and closed by the valve stem rotating at a fixed point to drive the valve disc to lift up and lower the gate to complete the opening and closing. The rising stem valve lifts or lowers the valve disc through the threaded transmission of the valve stem and the steering wheel.
To put it simply, the rising stem valve is a valve disc connected to the valve stem to move up and down together, and the steering wheel is always at a fixed point.