Positive displacement pump with bearings, a keying device, and gears

1. A rotary positive displacement pump comprising:

at least one drive section having a one-piece drive housing defining a lubrication chamber, the one-piece drive housing having an opening to the lubrication chamber, the opening abutting a closing cover, the one-piece drive housing having a plurality of bearing units wherein each one of the plurality of bearing units includes a plurality of bearing seats arranged in opposing pairs on a common axis and engaging at least one bearing, wherein a primary drive shaft and a secondary drive shaft are each rotationally engaged to a respective one of the at least one bearing, the primary drive shaft having at least one primary gear, the secondary drive shaft having at least one secondary gear, the at least one primary gear and the at least one secondary gear being interposed between the opposing pairs of the plurality of bearing seats such that the primary drive shaft and the secondary drive shaft counter-rotate with respect to each other; and

a product section having a treatment chamber, wherein each of the primary drive shaft and the secondary drive shaft engage a respective positive displacement screw rotor positioned within a one-piece stator body, forming a pair of positive displacement screw rotors adapted to generate a product flow between at least one product inlet duct and a product outlet duct of said product section, wherein the at least one primary gear and the at least one secondary gear are monolithic, the at least one primary gear having at least one overhanging collar keyed to the primary drive shaft by a keying device, the keying device being engaged with the at least one overhanging collar, wherein the primary drive shaft has a first engagement portion and a second engagement portion, the first engagement portion having a diameter different than a diameter of the second engagement portion, the at least one primary gear having a first keying seat and a second keying seat, the first keying seat having a diameter different than a diameter of the second keying seat, the primary drive shaft has a vertical abutment wall, the vertical abutment wall having a height equal to a difference between the diameter of the second engagement portion and the diameter of the first engagement portion, wherein the first keying seat extends axially over a portion of the at least one primary gear, the second keying seat extending axially over an entire length of the at least one overhanging collar and over a portion of the at least one primary gear not within an area of the first keying seat, the second keying seat having an abutment wall adapted to bear against the vertical abutment wall of the primary drive shaft, wherein the at least one primary gear is centered with respect to an axis of said primary drive shaft when the at least one primary gear is engaged to the primary drive shaft with the first keying seat and the second keying seat on the first engagement portion and on the second engagement portion of the primary drive shaft respectively and with the abutment wall of the second keying seat resting on the vertical abutment wall of the primary drive shaft, the at least one primary gear resting on an internal ring of a corresponding one of said at least one bearing of a first bearing unit of the plurality of bearing units.

2. The rotary positive displacement pump of claim 1 , wherein the secondary drive shaft has at least one vertical wall, the at least one secondary gear resting upon the at least one vertical wall of the secondary drive shaft.

3. The rotary positive displacement pump of claim 2 , wherein the secondary drive shaft has at least one restraint seat having at least one key engageable by a connection seat, the at least one secondary gear having the connection seat thereon, wherein the secondary drive shaft has a vertical wall positioned so as to correspond to an end part of a keying portion occupied by the restraint seat, the at least one secondary gear resting on the vertical wall of the secondary drive shaft.

4. The rotary positive displacement pump of claim 1 , wherein the one-piece drive housing has a back wall with an overhanging portion upon which a separating plate rests, the separating plate having through openings, the through openings allowing a portion of the primary drive shaft and the secondary drive shaft to pass therethrough, the separating plate supporting a mechanical sealing device, the separating plate being engaged with a one-piece stator body, the one-piece stator body having the at least one product inlet duct and includes at least a portion of the treatment chamber, the at least one portion of the treatment chamber having the pair of positive displacement screw rotors therein, the pair of positive displacement screw rotors being engaged with a portion of the primary drive shaft and the secondary drive shaft, wherein the one-piece stator body is engaged with a head body, the head body having the at least one product outlet duct.

5. The rotary positive displacement pump of claim 1 , wherein the primary drive shaft and the secondary drive shaft extend in a direction of the first bearing unit.

6. The rotary positive displacement pump of claim 5 , wherein the first bearing unit is assembled on a first bearing seat of the plurality of bearing seats, a third bearing unit being assembled onto a third bearing seat of the plurality of bearing seats, a second bearing unit having external rings of the plurality of bearing seats and needle crowns as the at least one bearing, a fourth bearing unit having external rings of the plurality of bearing seats and needle crowns of the at least one bearing, the first bearing unit and the third bearing unit being assembled with a bearing locking plate engaged with a head wall of the one-piece drive housing, wherein the primary drive shaft and the secondary drive shaft are assembled to the internal rings of the first bearing unit and the third bearing unit respectively.