How to Select the Pneumatic Sanitary Diaphragm Valve?
Sanitary diaphragm valve is operated by remote control or manual operation through the handle of the driving device, and there are there standards of the driving device: normally closed type, normally open type and pneumatic type.
Sanitary diaphragm valve has the advantages of simple structure, beautiful shape, quick disassembly and assembly, flexible operation, small fluid resistance, safe and reliable use, so it is suitable for chemical, petroleum, metallurgy, water heating, food, medicine and other industries of water, gas, oil and corrosive medium control.
The pneumatic sanitary diaphragm valve is a special form of cut-off valve, appeared in the 1920s. Its opening and closing parts are made of a piece of the soft material diaphragm, the valve body cavity, and cover cavity and drive parts separated, so it is called pneumatic health diaphragm valve. The most prominent feature of the pneumatic health diaphragm valve is the diaphragm to the lower body cavity and the upper cover cavity separated, so that the valve stem, disc and other parts located above the diaphragm are not subject to medium corrosion, eliminating the packing seal structure, and will not produce medium leakage.
Selection principles of the pneumatic sanitary diaphragm valve
The pneumatic sanitary diaphragm valve is a clamping class valve and is mainly used for opening and closing in the pipeline. It has two main advantages: one is that the valve does not require a separate stem packing seal structure, while the diaphragm plays a role of stem sealing while cutting off the medium; the second is the flexibility of the diaphragm has a reliable closing performance, and it can even do a good cut off sewage. Therefore, the operating mechanism and the media channel completely separated, so that the pneumatic diaphragm valve can not only apply to the food industry and medical and health industry, but also applicable to some difficult to transport medium and the greater risk of the medium.
Usually, the selection of diaphragm valve will be recommended in the requirements of strict sealing performance, mud medium, wear, light structure, low-pressure cut-off (pressure difference is small) to the atmosphere a small amount of leakage, abrasion of the medium.
Pneumatic sanitary diaphragm valves are characterized by a thin, hemispherical metal film clamped to the body as a barrier between stem and fluid, and the valve closure is achieved by pressing the disc against the seat through the stem head and metal film. The valve is opened by an internal spring that lifts the disc when the stem rises and disengages from contact with the film.
As the valve travel is equal to the film travel, so the valve features a much smaller lift than the general valve. To overcome resistance losses due to low lift, the seats and flow area are larger than normal valves to achieve greater flow. Since the valve seat is large, the force is much greater than the normal valve to obtain sufficient sealing force on the disc because there is no direct contact between the stem and the disc. The disc does not move the stem away from the seat, so the valve is suitable for differential pressure unidirectional flow, and the medium is usually "under the seat".However, large amounts of backflow should be avoided in service to avoid affecting valve closure. Generally speaking, the choice of the metal diaphragm valve is economical and effective in the high temperature and high-pressure environment.