Diaphragm valves offer advantages in certain low-pressure applications not possible with other types of valves. Their fluid passages are smooth and streamlined, minimizing pressure drop. They are suitable for moderate throttling applications, and they exhibit excellent leak tight characteristics, even when conveying liquids containing suspended solids.
The fluid stream is isolated from the working parts of the valve, preventing contamination of the fluid and corrosion of the operating mechanism. Since there is no leak path around the valve stem, the valve is virtually leak-tight. This feature makes the valve indispensable where leakage into or out of the system cannot be tolerated.
Diaphragm valves consist of a rigid body formed with a weir placed in the flow-path, a flexible diaphragm which forms the upper pressure boundary of the valve, a compressor which is used to force the diaphragm against the weir, and the bonnet and hand wheel which secure the diaphragm to the body and actuate the compressor.
The maximum pressure that these valves can be subjected to is a function of the diaphragm material and the service temperature. Also, the rated design life of the valve is influenced by the service conditions. Furthermore, the system hydrostatic test pressure must not exceed the maximum pressure rating of the diaphragm.