The working principle of lubricated pumps is not very different from that of dry pumps, with the addition of oil lubrication that allows to reduce the friction between the moving parts and to reach better absolute pressures.

The presence of the lubricant makes it necessary to filter the air at the outlet in order to recover the oil and to purify the exiting air. When the lubricant is not recovered, the pump is defined as “non returnable oil”. The sizing of the exhaust filters determines the pressure range in which these pumps can be used continuously.

The presence of lubrication causes small amounts of water vapor to be drawn in. To prevent this water vapor from condensing inside the pump, there is a device called gas ballast, which introduces a small amount of air during the compression to modify the vapor saturation pressure and prevent condensation.

The use of non-return valves on the suction side avoids oil backflow in case the pump is stopped with the system under vacuum. Lubricated vacuum pumps are used when the suctioned flow may contain moisture or when better final pressure is required. These pumps may operate continuously within certain pressure ranges or connected to vessels to be evacuated, whose volume is proportionate to the pump’s capacity.

All the pumps of this series are equipped with an oil recovery system after the purifying filter, in order to allow a wider variety of uses. When the quantity of steam sucked in is considerable, it is advisable to use the WR versions, where the effectiveness of the ballast device is considerably increased.