Rotary positive displacement pump

Method for assembling a rotary positive displacement pump for pumping a fluid product, the pump having a pump front side and a pump rear side, the method comprising:

• providing a main body giving rotational support to a pair of parallel, axially extending, shafts with gears in constant mesh condition, such that the pair of shafts are arranged to rotate in opposite directions,
• providing a rotor case body having:
• a stationary interior pumping cavity defined by an axial rear wall, a circumferential side wall, and a removable front cover,
• a fluid product inlet opening,
• a fluid product outlet opening, and
• a pair of cylindrical rotor case hubs extending from the rear wall, wherein the rotor case body is located on a front side of the main body, and wherein each cylindrical rotor case hub receives internally one of the pair of shafts,
• providing a pair of rotors, each having at least one rotor wing and a rotor drive element,
• mounting each rotor drive element torque proof on a rotor seat at an end region of one of the pair of shafts, wherein each rotor seat has an axial abutment surface facing in an axial direction towards the pump front side of the pump and a mounting surface facing radially outwards,
• mounting a fastener on an end region of each of the pair of shafts,
• tightening the pair of fasteners for exerting an axial clamping force on each rotor drive element against the axial abutment surface of one of the rotor seats, wherein the axial abutment surface of each rotor seat is located axially outside, towards the pump front side, of the associated hub, and
• mounting the removable front cover on the rotor case body.

Method for providing maintenance to a sealing arrangement of a rotary positive displacement pump having a pump front side and a pump rear side, two parallel axially extending shafts each carrying a rotor having at least one rotor wing and a rotor drive element, and an interior pumping cavity including a pair of cylindrical rotor case hubs each extending towards the pump front side from a rear wall of the interior pumping cavity, wherein each shaft has a rotor seat with an axial abutment surface facing in an axial direction towards the pump front side, the method comprising:

• removing a removable front cover of the pump,
• removing at least one of the pair of rotors from the associated shaft for enabling access to the sealing arrangement configured for preventing leakage along a gap between the associated shaft and the associated cylindrical rotor case hub,
• servicing the sealing arrangement,
• mounting the at least one removed rotor on the associated shaft and abutting the rotor drive element against the axial abutment surface of an associated rotor seat, wherein the axial abutment surface of each rotor seat is located axially outside, towards the pump front side, of the associated hub, and
• mounting the removable front cover on the pump.