Rotary displacement pumps

Claim 1

A ROTARY-DISPLACEMENT PUMP COMPRISING A HOUSING CONTAINING A PUMPING CHAMBER HAVING TWO PARALLEL SIDE WALLS SPACED BY A PERIPHERAL WALL, A PAIR OF INTERMESHING LOBED ROTORS, MOUNTED FOR ROTATION IN SAID CHAMBER IN SEALING CONTACT WITH THE WALLS THEREOF, MEANS FOR APPLYING ROTATIONAL TORQUE TO ONE OF THE ROTORS IN A PREDETERMINED DIRECTION TO PRODUCE SEALING CONTACT OF THE LEADING FLANK OF EACH LOBE OF ONE OF THE ROTORS WITH THE TRAILING FLANK OF A LOBE OF THE OTHER ROTOR DURING THE PASSAGE OF SAID FLANKS THROUGH THE ZONE OF INTERMESH, FLUID-ADMISSION MEANS CASING FLUID TO ENTER THE CHAMBER AXIALLY OF THE ROTORS AT ONE SIDE OF THE PLANE CONTAINING THE ROTOR AXES, AND FLUID-OUTLET MEANS COMMUNICATING WITH THE CHAMBER AT THE OTHER SIDE OF SAID PLANE, THE OTHER FLANK OF EACH LOBE OF AT LEAST ONE OF THE TWO ROTORS BEING RELIEVED FOR PART OF ITS AXIAL LENGTH FROM THE SIDE OF THE ROTOR FACING THE FLUID INLET TO CLEAR THE ADJACENT LOBE OF THE OTHER ROTOR, WHILE MAKING CONTACT WITH THE PROFILE OF SAID LOBE ON ANOTHER PART OF ITS AXIAL LENGTH.