A rotary positive displacement pump comprises a housing rotationally supporting first and second parallel and axially extending drive shafts having constantly meshing gears such that the drive shafts rotate in opposite directions. A rotor casing is connected to a front side of the housing and has axial rear and front walls and a circumferential side wall jointly defining a pumping cavity. The casing houses first and second rotors drivingly connected to the first and second drive shafts respectively. The rotors rotate in opposite directions and mutually interact to provide a positive pumping effect on fluid product entering the cavity. First and second sealing arrangements prevent leakage of fluid product from the cavity towards the rear side of the casing along the first/second drive shafts. A heating device is detachably fastened to the rear casing wall to heat the casing, the first/second sealing arrangements and/or any fluid product within the casing.

In at least one aspect, this disclosure relates to a wellsite pump for a well site having a wellbore penetrating a subterranean formation. The well site has a conduit to pass a wellsite fluid about the wellsite. The wellsite pump includes a housing having an intake and an outtake, at least one hydraulic motor to pump the wellsite fluid from the intake and through the outtake, at least one driver coupled to the hydraulic motor and movable therewith, and a power source. The intake is in fluid communication with the conduit, and the outtake is positioned a distance upstream of the intake. The hydraulic motor includes a rotor and a stator. The power source drives the driver and the hydraulic motor coupled thereto whereby the wellsite fluid is advance from the conduit to a location upstream therefrom.

A rotary positive displacement pump comprises a transmission housing having front and rear walls and rotationally supporting first and second drive shafts having constantly meshing gears such that the drive shafts rotate in opposite directions. A rotor casing connected to a front side of the housing has rear and front walls and a circumferential side wall defining an interior pumping cavity. The casing houses first and second rotors drivingly connected to the first and second drive shafts to provide a positive pumping effect on fluid product entering the cavity. The front and rear walls of the housing define an intermediate space through which the drive shafts extend. A first guard is located in the intermediate space and surrounds the drive shafts, or first and second guards are located in the intermediate space and surround the first and second drive shafts respectively, for protecting a person from contacting the drive shafts.

A screw pump comprising a housing defining a chamber and two screw rotors. Wherein each screw rotor comprises a rotor shaft and at least two displacement elements connected with the rotor shaft. Each displacement element having at least one helical protrusion. One of the displacement elements is a suction-side displacement element arranged in a suction-side section of the chamber. Another one of the displacement elements is a pressure-side displacement element arranged in a pressure-side section of the chamber. The suction-side displacement element is designed tapering in the conveying direction. The clearance between the pressure-side displacement element and the pressure-side section of the chamber at least partly decreases in the conveying direction. Furthermore, a screw rotor, a method of manufacturing a screw rotor and a use of a screw pump or a screw rotor.