There are very few industries around today that don’t make use of some kind of diaphragm valve. The use of a resilient diaphragm as one of the seating faces enable it to have an excellent isolation feature although it is restricted to pressures and temperatures for which the diaphragm material is suitable. The standard pressure rating is PN16/Class 150 but there are some manufacturers who can offer Class 300 rated valves.
The two basic design types are the “Weir Type” and the “Straight through Type”.
The Weir type has a weir formed in the body above which is mounted an elastomeric diaphragm. When the handwheel is screwed down to close the valve, the diaphragm is pressed against the weir stopping the flow of media. The weir and diaphragm form a vena contracta which creates a pressure drop and allows the valve to be used for regulating service and not just isolation.
The Straight through Type has a circular bore and the flow passage transforms to an ellipse of equal area directly under the coned shaped diaphragm closure device. It has very minimal resistance to flow in the open position and for that reason is often used in slurries. This valve is limited to only act as an isolating valve.