Rotary lobe vacuum pumps R-VWP can be used in many applications that need coarse or fine vacuum. Two symmetrically shaped rotors rotate against each other, synchronised by a pair of gear wheels. The pumps are dry running, and consequently the compression chamber is free of grease or oil. Gear box and bearings are oil lubricated. A bypass valve integrated in the housing enables the start of the pump together with the backing pump to avoid an overload of the motor at high differential pressures.