Diaphragm check valves consist of a rubber diaphragm that flexes open when the inlet pressure increases. Figure shows a normally open diaphragm check valve with ‘minimal’ inlet pressure, which allows media to flow through. As the inlet pressure increases, the diaphragm will flex open, allowing more flow, as seen in Figure. If backpressure occurs (or it is a normally closed diaphragm check valve), the diaphragm will be forced against the opening and will seal it to prevent any backflow, as seen in Figure. Diaphragm check valves are ideal for low-pressure or vacuum applications.