Gate valves can be divided into:
1. Open stem gate valve: The stem nut is on the bonnet or bracket. When the gate is opened and closed, the stem is rotated to achieve the lifting of the 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 rod gate valve: The stem nut is in the valve body and directly contacts the medium. When opening and closing the shutter, it is realized by rotating the stem. The advantage of this structure is: the height of the gate valve always remains the same, so the installation space is small, 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 stem thread is not only unable to lubricate, but also directly accepts the medium erosion and is easily damaged.
The main difference between open rod gate valve and hidden rod gate valve:
1. The lifting screw of the hidden rod flange gate valve only rotates without moving up and down, the exposed one is just a rod, the nut is fixed on the gate, and the gate is lifted by the rotation of the screw, there is no visible door frame ; The lifting screw of the exposed rod flange gate valve is exposed, the nut is close to the hand wheel and is fixed (no rotation or axial movement), the gate is lifted by rotating the screw, and the screw and the gate only have relative rotational movement. There is no relative axial displacement, and the appearance is a door-shaped bracket.
2. The dark rod valve can't see the screw, while the bright rod can see the screw.
3. When the dark rod valve is opened and closed, the steering wheel and the valve rod are relatively immovable. It is driven by the valve rod rotating at a fixed point to drive the valve flap up and down to complete the opening and closing. The open stem valve uses the threaded transmission between the stem and steering wheel to raise or lower the flap. To put it simply, the open stem valve is a valve flap that moves up and down with the stem, and the steering wheel is always at a fixed point.