Pfeiffer Vacuum A Passion for Perfection

2.2.1 Design / Operating principle

(Figure 2.2)
Figure 2.2: Operating principle of a rotary vane pump

A rotary vane vacuum pump is an oil-sealed rotary displacement pump. The pumping system consists of a housing (1), an eccentrically installed rotor (2), vanes that move radially under spring force (3) and the inlet and outlet (4). The outlet valve is oil-sealed. The inlet valve is designed as a vacuum safety valve that is always open during operation. The working chamber (5) is located inside the housing. Rotor and vanes divide the working chamber into two separate spaces having variable volumes. As the rotor turns, gas flows into the enlarging suction chamber until it is sealed off by the second vane. The enclosed gas is compressed until the outlet valve opens against atmospheric pressure. In the case of gas ballast operation, a hole to the outside is opened, which empties into the sealed suction chamber on the front side.

Operating fluid, oil

Pump oil, which is also called as operating fluid, has multiple tasks to perform in a rotary vane pump. It lubricates all moving parts, fills both the harmful space under the outlet valve as well as the narrow gap between inlet and outlet. It compresses the gap between the vanes and the working chamber and additionally ensures an optimal temperature balance through heat transfer.

Multi-stage pumps

Rotary vane vacuum pumps are built in single- and two-stage versions. Two-stage pumps achieve lower ultimate pressures than single-stage pumps. Moreover, the effects of the gas ballast on the ultimate pressure are lower, as the ballast gas is only admitted in the second stage.

Vacuum safety valve

Depending upon the type of pump in question, rotary vane vacuum pumps can be equipped with a vacuum safety valve. The vacuum safety valve disconnects the pump from the vacuum recipient in the event of intentional or unintentional standstill, and uses the displaced gas to vent the pumping system in order to prevent oil from rising into the recipient. After switching on the pump, it opens after a delay once the pressure in the pump has reached the approximate pressure in the recipient.

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