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Pneumatic diaphragm valves are a special form of cut valves that appeared in the 1920s. Its opening and closing parts is a piece of diaphragm made of soft material, the control valve body chamber and the valve cover chamber and drive parts separated, so it is called the pneumatic diaphragm valve. The most prominent feature of the pneumatic diaphragm valve is that the diaphragm separates the lower part of the valve body from the upper valve cap inner cavity, so that the valve stem and valve flap located above the diaphragm are free from medium corrosion, eliminating the packing sealing structure, and will not produce medium leakage.
Pneumatic diaphragm valve is usually divided into: normally closed pneumatic diaphragm valve, normally open pneumatic diaphragm valve and reciprocating pneumatic valve.
Features: The diaphragm separates the lower valve body chamber from the upper valve cover chamber, so that the valve stem and valve flap located above the diaphragm are free from medium corrosion, eliminating the packing sealing structure, and will not produce medium leakage.
1. The Plastic Diaphragm Valve made of soft seal such as rubber or plastic has good sealing performance. As the diaphragm is vulnerable parts, Diaphragm Valve Penumatic should be replaced periodically depending on the medium characteristics.
2. Due to the limitation of the diaphragm material, the diaphragm valve is suitable for low pressure and relatively low temperature.
3. The PVC diaphragm valve can be divided into house, DC, namely: stop, through, gate and rectangular; usually flange connected; manual, electric and pneumatic, divided into normally open, normally closed and reciprocating.
4. Generally, UPVC Diaphragm Valve is not suitable to be used in pipelines with temperature above 60 degrees and transporting organic solvents and strong oxidation media, nor in using pneumatic diaphragm valves in pipelines with high pressure.
Selection principle: the pneumatic diaphragm valve belongs to the clamping valve, which is mainly used for opening and closing on the pipe.
Pneumatic diaphragm valve has two main advantages: one is that the valve does not need a separate valve stem packing sealing structure, the diaphragm in cutting off the medium at the same time of the valve stem sealing role, the other is a strong flexibility of the diaphragm closing reliable, even the sewage can do good cut off. Therefore, the control mechanism and the medium channel are completely separated, so that the pneumatic diaphragm valve can be not only applicable to the food industry and the medical and health industry, but also applicable to some difficult delivery medium and more dangerous medium.
Usually, the use of conditions or in the requirements of strict sealing performance, mud medium, wear, light structure, low pressure cut-off (small pressure difference) to a small atmospheric leakage, abrasion of the medium recommended to choose diaphragm valve. The diaphragm valve can be used in dual adjustment, throttling, channel shrinkage, low noise, cavitation and vaporization phenomenon, and small control torque. Under the conditions of high temperature medium, high pressure medium, high pressure cut-off (large pressure difference), fast opening and closing action, and short structure length, the diaphragm valve is not selected during the day, except for the metal diaphragm valve.
The structure of the pneumatic diaphragm valve features a set of thin hemispherical metal films clamped into the valve body, acting as a barrier between the valve stem and the fluid. Valve closure is achieved by pressing the disc over the seat through the stem head and metal film. The valve opens through an internal spring, raising the disc as the stem rises and breaks into contact with the film. Because the stroke of the valve is equal to that of the film, the characteristic rise of this valve is much smaller than the general valve. In order to overcome the resistance loss caused by the low lift, the valve seat and the circulation area is larger than the general valve, in order to get a greater flow rate. Since this valve seat is larger, the force is much greater than the usual valve to get enough sealing force on the disc, because there is no direct contact between the stem and the disc. The disc does not leave the seat through the stem, so the valve is suitable for one-way flow with differential pressure, and usually the medium is from under the seat. However, a large amount of backflow should be avoided in use, so as not to affect the closure of the valve. Generally speaking, in the high temperature, high pressure to choose metal diaphragm valve is economic, effective the valve can also be selected in the low temperature, synthetic rubber diaphragm valve does not want to use low temperature occasions.
July 03, 2023
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