What divide the working chamber into two spaces are the rotor and the vanes of the pump. Once the rotor rotates, the enlarging chamber draws in the gas which is then sealed off by the second vane. The gas is then compressed until the atmospheric pressure opens the outlet valve. The pressure required to open the valve is achieved at a lower compression in the case of gas ballast operation since there’s a hole to the outside that’s opened to empty the sealed suction chamber. This results in a gas being displaced before it begins to condense. As such, the final pressure during the pumping operation with a gas ballast is much higher than the one without it.
The operating fluid or pump oil plays a crucial role in the operation of a rotary vane vacuum pump. It has multiple functions that enable a successful pumping operation. For one, it helps to compress the gas in the chamber while ensuring that optimal temperature balance is achieved through heat transfer. Moreover, the oil lubricates all the moving components of the pump, making sure that every part works properly for optimum performance of the pump.
When it comes to design, a rotary vane vacuum pump comes either as a single-stage and two-stage versions. Between them, the two-stage version achieves lower ultimate pressures, most especially in the case of gas ballast operation. Finally, the pump may also come with a vacuum safety valve which isolates the pump from its vacuum chamber in case standstill occurs, whether intentional or not. This prevents the oil from reaching into the vacuum chamber and when the pump is turned on, the chamber only opens up once the pressure is sufficient enough for the pump to safely operate again.