Primary vacuum pump of dry type and method for controlling the injection of a purge gas

A primary vacuum pump of a dry type, comprising:

• a suction and a discharge;
• pumping stages mounted in series between the suction and the discharge of the vacuum pump;
• two rotors extending in each of the pumping stages, the two rotors being configured to rotate synchronously in a reverse direction to drive a gas to be pumped between the suction and the discharge;
• an injection device configured to distribute a purge gas in each of the pumping stages, the injection device comprising:
• at least one injection member in each of the pumping stages, and
• at least one injection valve with an on or an off control configured to be interposed between a purge gas supply source and the at least one injection member in each of the pumping stages;
• a control device configured to control opening and closing of the at least one injection valve in each of the pumping stages to inject a purge gas by successive pulses,
• wherein the control device is configured to control of the opening and closing of the at least one injection valve in all of the pumping stages such that the purge gas is introduced into each of the pumping stages sequentially in a direction of a flow of the gas from the discharge to the suction and then the purge gas is introduced into each of the pumping stages sequentially in a direction of the flow of the gas from the suction to the discharge.