Positive displacement pump

Rotary positive displacement pump comprising at least one drive section and one product section, wherein the drive section comprises a one-piece drive housing realizing a lubrication chamber, said drive housing being provided with an opening intended to enable access to the lubrication chamber and intended to butt up against a closing cover, the drive housing further comprising bearing seats, arranged in opposite pairs on the same axis, each of said bearing seats engaging at least one bearing, wherein a primary drive shaft and a secondary drive shaft are each rotationally engaged to the bearings with which the opposite bearing seats, of their own axis are provided, each drive shaft being provided with at least one gear which is interposed between the opposite bearing seats to realize a synchronized drive intended for the counter-rotation of the two drive shafts with respect to each other and wherein, within the product section that comprises a treatment chamber, each drive shaft engages a positive displacement screw rotor, placed within a stator body said positive displacement screw rotors being intended to enable the generation of a product flow between a product inlet duct and a product outlet duct with which the product section is provided, characterised in that the gears, are monolithic and at least one of the gears, is axially provided with at least one tubular overhanging collar, wherein the gear provided with an overhanging collar is keyed to the drive shaft by means of a keying device engaged to the overhanging collar.