What are the types and structures of diaphragm valves?

The opening and closing part (diaphragm) is driven by the valve stem, moves up and down along the axis of the valve stem, and separates the action mechanism from the medium. It is called a diaphragm valve.

Diaphragm valves are cut-off valves, mainly used for corrosive media and situations where external leakage is not allowed. At present, roof-type diaphragm valves are mostly produced in China. The parameter range is as follows: nominal size DN15～400; nominal pressure ≤PN40; working temperature t≤170℃. Diaphragm valves are different from ordinary valves in that they mainly use a soft rubber diaphragm as a component to control fluid on-off or regulate flow. It has a simple structure, good sealing, smooth flow channel and relatively small flow resistance coefficient. It is widely used in pipelines with viscous media, micro-particle fluids and corrosive media, especially in water treatment devices of thermal power systems. Applications.

Due to the function of the rubber diaphragm valve, no matter the valve is in the open or closed position, the corrosive medium in the flow channel is always isolated from the driving parts of the valve. The valve body is mostly made of carbon steel, ductile iron, aluminum alloy and stainless steel. The inner cavity of the valve can be lined with a variety of rubber, fluoroplastics, enamel, etc., so the diaphragm valve can use ordinary materials instead of precious metals and has corrosion resistance and wear resistance.

At present, the production of diaphragm valves has two major development directions. One is large-scale and high-parameterization, mainly to adapt to various special requirements. For example, the nominal pressure can reach PN16~40, its maximum pressure level can reach 4.5MPa, the working temperature can reach -65~200℃, and the maximum temperature can reach 300℃. In addition to meeting the water treatment systems of 300MW, 600MW and 1000MW large thermal power generating units, diaphragm valves are also used in 900MW nuclear power plants. Second, it can meet the matching needs of general industrial pipelines to adapt to a variety of corrosive media, and is suitable for nearly 400 to 700 types of media. The rubber diaphragm has a service life of more than 100,000 times and a maximum of 270,000 to 500,000 times. Its operation and driving forms include manual, pneumatic, electric, hand-pneumatic, etc.

According to the structural form, diaphragm valves can be divided into the following types: weir type diaphragm valve, globe type diaphragm valve, gate type diaphragm valve.

Due to the use of a diaphragm, the valve cover, valve stem, valve disc and other parts located above the diaphragm are not corroded by the medium and will not cause leakage of the medium; no packing mechanism is needed, the structure is simple and easy to maintain.

Limited by the diaphragm material, its application range is small and is only used in low-pressure and low-temperature situations.

Diaphragm valve is mainly composed of valve body, valve cover, valve stem, diaphragm valve disc, lining layer and transmission device. Figure 1-1 shows a commonly used weir-lined diaphragm valve.

Figure 1-1 G41 type weir lined diaphragm valve

The structure of the valve body is commonly weir type. In addition, there are cut-off type (Figure 1-2) and gate type (Figure 1-3), etc., but they are rarely used. The valve body has an integral casting and forge welding structure, and can also be made of various corrosion-resistant materials or cast iron or cast steel lined with enamel, rubber, plastic, etc.

Figure 1-2 Globe diaphragm valve

Figure 1-3 Gate type diaphragm valve

G41 roof type diaphragm valve, G45 DC type diaphragm valve, G641 pneumatic diaphragm diaphragm valve (normally closed type), G641 pneumatic diaphragm diaphragm valve (normally open type)