US Patent 7637284 Sanitary diaphragm valve

A sanitary diaphragm valve has a valve body formed of an upper plate and a lower plate, with a flexible resilient diaphragm and a spacer between them. The margin of the diaphragm rests on a peripheral step formed in the lower plate to create a positive space between the lower plate and the edges of the diaphragm. A piston within a cylinder in the upper plate can descend to compress the diaphragm against a valve port to close the valve. The pressure of the liquid product can raise the diaphragm and the piston when control pressure is relieved from the piston.