Bushing assembly and positive displacement rotary pump comprising said bushing assembly

1. A bushing assembly for a positive displacement rotary pump, arranged to be inserted into an internal cavity of a positive displacement rotary pump, axially floating therewithin, and to support the ends of a pair of shafts bearing the rotors of said positive displacement rotary pump;

said bushing assembly comprising an inner face, facing, while in use, the rotors;

an opposed outer face;

wherein, while in use, the bushing assembly is free to axially slide within the internal cavity due to fluid pressures acting on the inner and external faces;

the bushing assembly further comprising: a lateral surface which connects the two inner and outer faces, said lateral surface being arranged to be coupled within the internal cavity with a first portion facing a suction side and a second portion facing a discharge side;

at least one compensation tank on the first portion of said lateral surface, in a position closer to the inner face than to the outer face;

and at least one bleed channel which connects said at least one compensation tank to the second portion of the lateral surface;

wherein the at least one compensation tank is laterally closed on both sides of the inner face and the outer face of the bushing assembly, wherein the at least one compensation tank does not open on the inner face nor on the external face of the bushing assembly.

2. The bushing assembly according to claim 1 , shaped as two sleeve-shaped semigroups coupled to each other, said semigroups being made in one piece or separated from each other.

3. The bushing assembly according to claim 2 , wherein said lateral surfaces comprise two cylindrical portions connected or juxtaposed in two coupling areas of the semigroups, on the discharge side and on the suction side respectively.

4. The bushing assembly according to claim 3 , wherein said bleed channel connects, while in use, the coupling area on the discharge side with the at least one compensation tank; and

wherein said bleed channel does not reach the coupling area on the suction side.

5. The bushing assembly according to claim 3 , wherein said bleed channel takes the form of an external circumferential groove formed on at least one of the cylindrical portions of the lateral surface.

6. The bushing assembly according to claim 5 , wherein said at least one compensation tank takes the form of a widening in the axial direction of the circumferential groove which defines the bleed channel.

7. The bushing assembly according to claim 6 , wherein said at least one compensation tank extends axially towards the inner face with respect to the bleed channel.

8. The bushing assembly according to claim 6 , wherein said at least one compensation tank has a substantially parallelepiped conformation.

9. The bushing assembly according to claim 6 , wherein said at least one compensation tank and said bleed channel have the same depth.

10. The bushing assembly according to claim 6 , wherein said at least one compensation tank comprises at least two compensation tanks for each semigroup.

11. The bushing assembly according to claim 10 , wherein the two compensation tanks of each semigroup are connected by the same bleed channel.

12. The bushing assembly according to claim 11 , wherein the at least one compensation tank is at least one intermediate compensation tank which intercepts the extension of the bleed channel, and at least one terminal compensation tank, whereat the bleed channel ends.

13. The bushing assembly according to claim 1 , comprising a bushing ring, monolithic or in two pieces, which is associated with two inner bushings, the bleed channel and at the least one compensation tank being made on the bushing ring.

14. A positive displacement rotary pump comprising: a casing provided with an internal cavity with a discharge port opening on a discharge side and a suction port opening on an opposite suction side; a pair of shafts which bear, in their intermediate portion, as many intermeshing rotors rotating within the internal cavity for pumping a fluid from the discharge port to the suction port; two bushing assemblies according to claim 1 , said bushing assemblies being arranged at the opposite ends of the rotors for supporting the shafts with the inner face facing the rotors and the lateral side coupled within the internal cavity; said compensation tank facing the suction side of the internal cavity; and said at least one bleed channel connecting said compensation tank to a portion of the lateral surface facing the discharge side, wherein, while in use, said compensation tank is filled with fluid under pressure defining a straightening torque on the respective bushing assembly.