Pfeiffer Vacuum

2.3.1 Design / Operating principle

Diaphragm vacuum pumps are dry positive-displacement pumps. Their operating principle is explained in Figure 2.5. A crankshaft-driven connecting rod (4) moves the diaphragm (1) that is tensioned between head cover (2) and 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 aligned gas displacement. Pressure-controlled shutter valves made of elastomer materials are used as valves. Because 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 harmful space between the outlet valve and the suction chamber results in only a limited compression ratio. This means that an ultimate pressure of only approximately 70 mbar can be attained with a single pump stage. Connecting multiple pumping stages in series can reduce ultimate pressure to 0.5 mbar. 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.

Figure 2.5
Figure 2.5: Operating principle of a diaphragm pump

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