Diaphragm vacuum pumps are dry positive-displacement pumps. A crankshaft-driven connecting rod (4) moves the diaphragm (1) that is tensioned between the head cover (2) and the housing (3). The space between the head cover and the diaphragm forms the suction chamber (5). Diaphragm pumps require inlet valves and outlet valves (6) to achieve targeted gas displacement. Pressure-controlled shutter valves made of elastomer materials are used as valves. Since the suction chamber is hermetically sealed off from the drive by the diaphragm, the pump medium can neither be contaminated by oil nor can aggressive media corrode the mechanics. The dead volume between the outlet valve and the suction chamber results in a restricted compression ratio which means that with just one pumping stage it is only possible to achieve an ultimate pressure of approximately 70 hPa. Connecting multiple pumping stages in series makes it possible to attain an ultimate pressure of 0.5 hPa. Lower pressures cannot be achieved, as in this case there is no longer sufficient force to open the inlet valve. The principle of the diaphragm pump is particularly well suited for low pumping speeds of up to approximately 10 m3· h-1.
