The gate valve is a gate with opening and closing parts. The movement direction of the gate valve is perpendicular to the fluid direction. The gate valve can only be fully opened and fully closed, not adjusted and throttled. The gate valve is sealed by the contact between the valve seat and the gate. Usually, the sealing surface will be overlaid with metal materials to increase the wear resistance, such as overlaying 1Cr13, stl6, stainless steel, etc.

There are many domestic manufacturers of gate valves, and most of the connection sizes are not unified. It is mainly divided into the following categories:

1. Standard valves of the Ministry of machinery produced according to structural length of gate valves (JB / t2203-1999).

2. National standard valves produced according to GB / t12221-2005 structural length of metal valves.

3. American Standard valves produced according to ASME b16.10-2009 face to face and end-to-end dimensions of valves.

Gate valves can be divided into:

1. Rising stem gate valve: the valve stem nut is on the valve cover or support. When opening and closing the gate, rotate the valve stem nut to realize the lifting of the valve stem. This structure is beneficial to the lubrication of the valve stem and has obvious opening and closing degree, so it is widely used.

2. Non rising stem gate valve: the valve stem nut is in the valve body and in direct contact with the medium. When opening and closing the ram, it is realized by rotating the valve rod.

Advantages of the structure: the height of the gate valve remains unchanged, so the installation space is small. It is suitable for gate valves with large diameter or limited installation space. The structure shall be equipped with an opening and closing indicator to indicate the opening and closing degree.

Disadvantages of the structure: the stem thread is not only unable to be lubricated, but also directly subject to medium erosion and easy to be damaged.

Main differences between rising stem gate valve and Non rising stem gate valve:

1. The lifting screw of Non rising stem flange gate valve only rotates without moving up and down. Only one rod is exposed, and its nut is fixed on the ram. The ram is lifted through 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 hand wheel and fixed (neither rotating nor axially moving). The ram is lifted by rotating the screw. The screw and the ram have only relative rotational movement without relative axial displacement, and the appearance is a gate support.

2. The lead screw cannot be seen in the Non rising stem valve, while the lead screw can be seen in the rising stem valve.

3. When the Non rising stem valve is opened and closed, the steering wheel and the valve stem are connected together and relatively immobile. It drives the valve disc to lift up and close down by rotating the valve stem at the fixed point. The rising stem valve raises or lowers the valve disc through the threaded transmission between the valve stem and the steering wheel.

To put it simply, the rising stem valve is that the valve disc moves up and down with the valve stem, and the steering wheel is always at the fixed point.