The principle and main classification of plug valve

The plug valve is a rotary valve in the shape of a closing member or a plunger. By rotating 90 degrees, the channel port on the valve plug is the same as or separated from the channel port on the valve body, so as to realize the opening or closing of a valve.

The shape of the plug of the plug valve can be cylindrical or conical. In cylindrical valve plugs, the passages are generally rectangular; in conical valve plugs, the passages are trapezoidal. These shapes make the structure of the plug valve light, but at the same time, it also produces a certain loss. Plug valves are more suitable for shutting off and connecting media and for diversion, but depending on the nature of the application and the erosion resistance of the sealing surface, they can also be used for throttling. Turn the plug clockwise to make the groove parallel to the pipe to open, and turn the plug 90 degrees counterclockwise to make the groove perpendicular to the pipe to close.

The types of plug valves are mainly divided into the following categories:

1. Tightened plug valve

Tight-type plug valves are usually used in low-pressure straight-through pipelines. The sealing performance depends entirely on the fit between the plug and the plug body. The compression of the sealing surface is achieved by tightening the lower nut. Generally used for PN≤0.6Mpa.

2. Packing plug valve

Packed plug valve is to achieve plug and plug body sealing by compressing the packing. Due to the packing, the sealing performance is better. Usually this kind of plug valve has a packing gland, and the plug does not need to protrude from the valve body, thus reducing a leakage path of the working medium. This kind of plug valve is widely used for the pressure of PN≤1Mpa.

3. Self-sealing plug valve

The self-sealing plug valve realizes the compression seal between the plug and the plug body through the pressure of the medium itself. The small end of the plug protrudes upward out of the body, and the medium enters the large end of the plug through the small hole at the inlet, and the plug is pressed upwards. This structure is generally used for air media.

4. Oil-sealed plug valve

In recent years, the application range of plug valves has been continuously expanded, and oil-sealed plug valves with forced lubrication have appeared. Due to the forced lubrication, an oil film is formed between the sealing surface of the plug and the plug body. In this way, the sealing performance is better, the opening and closing is labor-saving, and the sealing surface is prevented from being damaged. In other occasions, due to different materials and changes in cross-section, different expansions will inevitably occur, which will cause certain deformation. It should be noted that when the two gates are free to expand and contract, the spring should also expand and contract with it.

Post time: Jul-25-2022