Pump for pumping liquid as well as an impeller assembly

1. A pump for pumping liquid, comprising a pump chamber and an impeller arranged to rotate in said pump chamber, said impeller suspended at a lower end of an axially extending drive shaft unit, with said lower end of the drive shaft unit received in a cylinder-shaped recess of the impeller, the impeller comprising an axially extending hole that connects the cylinder-shaped recess and the pump chamber,

wherein the impeller, during operation of the pump, is displaceable back and forth in an axial direction in relation to the drive shaft unit and the drive shaft unit comprises an axially extending pin that projects from said lower end of the drive shaft unit, said pin arranged in said hole to prevent the pumped liquid from entering the cylinder-shaped recess of the impeller;

wherein the drive shaft unit comprises a drive shaft and a sleeve, wherein the sleeve surrounds and is releasably connected to the drive shaft and comprises part of the lower end of the drive shaft unit.

2. A pump according to claim 1 , wherein a liquid seal is arranged at an interface of said hole and said pin.

3. A pump according to claim 2 , wherein the liquid seal comprises an O-ring.

4. A pump according to claim 2 , wherein the liquid seal is arranged in a groove of an inner surface of the hole.

5. A pump according to claim 1 , wherein a lateral surface of the pin abuts an inner surface of the hole.

6. A pump according to claim 1 , wherein an axial section of a lateral surface belonging to the lower end of the drive shaft unit abuts an inner surface of the cylinder-shaped recess.

7. A pump according to claim 1 , wherein the pin is tube-shaped.

8. A pump according to claim 1 , wherein said pin is fixedly connected to said sleeve.

9. A pump according to claim 1 , wherein the impeller is an open impeller comprising a hub, an upper cover plate and at least one blade connected at least to said upper cover plate.

10. A pump according to claim 9 , wherein said cylinder-shaped recess and said hole are arranged in the hub of the impeller.

11. An impeller assembly for placement in a pump chamber of a pump, comprising an impeller having a cylinder-shaped recess and a sleeve, said sleeve received in said cylinder-shaped recess and configured to be connected to an axially extending drive shaft, wherein the impeller, during operation of the pump, is displaceable back and forth in an axial direction in relation to the sleeve and the impeller comprises an axially extending hole that connects the cylinder-shaped recess and the pump chamber, the sleeve comprising an axially extending pin that projects from the sleeve, said pin arranged in said hole to prevent the pumped liquid from entering the cylinder-shaped recess of the impeller.

12. A pump for pumping liquid, comprising a pump chamber and an impeller arranged to rotate in said pump chamber, said impeller suspended at a lower end of an axially extending drive shaft unit, wherein the drive shaft unit comprises a drive shaft and a sleeve that surrounds and is connected to the drive shaft, wherein the sleeve comprises part of the lower end of the drive shaft unit, with said sleeve received in a cylinder-shaped recess of the impeller, the impeller comprising an axially extending hole that connects the cylinder-shaped recess and the pump chamber, wherein the impeller is automatically displaceable back and forth in an axial direction with respect to the drive shaft and the sleeve, and the drive shaft unit further comprises an axially extending pin that projects from said lower end of the drive shaft unit, said pin arranged in said hole to prevent the pumped liquid from entering the cylinder-shaped recess of the impeller.