CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a U.S. National Phase Patent Application of PCT Application No.: PCT/EP2017/061137, filed May 10, 2017, which claims priority to European Patent Application No. 16169846.9, filed May 17, 2016, each of which is incorporated by reference herein in its entirety.

TECHNICAL FIELD OF THE INVENTION

The present invention relates, in general, to the technical field of pumps for pumping liquid, and in particular to the technical field of pumps for pumping liquid comprising solid matter, such as sewage/wastewater which may comprise polymers, hygiene articles, fabrics, rags, etc.

In accordance with a first aspect, the present invention relates to a pump for pumping liquid, comprising an impeller and an axially extending drive shaft assembly, wherein a distal end of the drive shaft assembly is received in a central recess of the impeller, the drive shaft assembly comprising a drive shaft and a connector, wherein the connector comprises a sleeve that is in telescopic engagement with the drive shaft, the impeller during operation of the pump being displaceable in the axial direction in relation to said sleeve between a distal rest position and a proximal position. It shall be pointed out that the terms distal and proximal shall be considered in relation to the center of the drive shaft seen in the axial direction of the drive shaft.

In accordance with a second aspect, the present invention relates to an impeller assembly configured to be installed in a pump chamber of a pump suitable for pumping liquid comprising solid matter.

BACKGROUND OF THE INVENTION

In plants such as sewage treatment plants, septic tanks, wells, pump stations, etc., it occurs that solid matter/contaminations such as socks, sanitary towels, papers, etc. obstruct the pump, for example a submersible pump that is submerged in the basin/receptacle of the plant/station.

When the impeller and the impeller seat are positioned at a fixed distance from each other, the pollutants are sometimes too large to pass through the pump. Large pieces of solid matter may in worst case cause the impeller to wedge, thus seriously damaging the pump. Such an unintentional shutdown is costly since it entails expensive, tedious and unplanned maintenance work.

European patent EP 1899609 discloses a pump that comprises an impeller that is arranged to rotate in a pump housing, said impeller being suspended by a drive shaft, and an impeller seat. The impeller is movable in the axial direction in relation to the impeller seat during operation of the pump in order to allow larger pieces of solid matter to pass through, pieces that otherwise would block the pump or wedge the impeller.

International patent application WO 2015/022601 discloses a similar pump and thereto comprises a connector arranged between the drive shaft and the impeller, wherein the connector is received in a central recess of the impeller and comprises a sleeve that, is in telescopic engagement with the drive shaft. In WO 2015/022601 the impeller has a defined distal/lower rest position in relation to the connector that entails that adjustment of an axial gap between the impeller and the suction cover of the pump may be performed. When the impeller is in the distal rest position, an annular spring member that is arranged in an annular recess of the impeller snaps into an annular groove of the sleeve, in order to secure the impeller in said distal rest position. During mounting and during adjustment/trimming of the axial gap between the impeller and the suction cover the annular spring may snap out of the annular groove in the sleeve. If this happens during adjustment of the axial gap, the entire mounting of the impeller has to be restarted in order to secure that the impeller is located in the distal rest position in relation to the connector. Thereto the mounting and adjustment/trimming of the impeller has to be performed from underneath the pump, i.e. having the pump upright with the drive shaft vertically oriented, the pump inlet facing downwards and the impeller suspended by the lower end of the drive shaft.

It should also be mentioned that submersible pumps of the above kind are used to pump liquid from basins that are difficult to reach for maintenance and that the pumps often operate for 12 or more hours daily. It is therefore utterly desirable to provide a pump with long working life.

OBJECT OF THE INVENTION

The present invention aims at obviating the above-mentioned disadvantages and failings of the previously known pumps and to provide an improved pump. A primary object of the invention is to provide an improved pump and impeller assembly of the type defined in the introduction, wherein the impeller has a well-defined distal rest position that allows adjustment of the axial gap between the impeller and the suction cover of the pump to be performed with great precision.

A further object of the present invention is to provide a pump and an impeller assembly, wherein the mounting and adjustment/trimming of the impeller can be performed having the pump upside-down, i.e. having the pump with the drive shaft vertically oriented and the impeller facing upwards, without the risk that the impeller leaves the distal rest position.

A further object of the present invention is to provide a pump and an impeller assembly, wherein the impeller doesn't run the risk of becoming tilted as a consequence of asymmetrically applied force acting in the axial direction against the impeller.

It is also an object of the present invention to provide an improved pump of the type defined in the introduction, wherein said pump in a reliable manner allows large pieces of solid matter to pass through the pump.

SUMMARY OF THE INVENTION

According to the invention at least the primary object is attained by means of the initially defined pump and impeller assembly having the features defined in the independent claims. Preferred embodiments of the present invention are further defined in the dependent claims.

According to a first aspect of the present invention, there is provided a pump of the initially defined type, which is characterized in that the impeller is biased towards the distal rest position by means of a spring member arranged between the sleeve and the impeller, the connector comprising a hollow adjustment screw that is in threaded engagement with an interior side of the sleeve and configured to limit the maximum degree of telescopic overlap between the sleeve and the drive shaft, wherein an impeller screw extends through the adjustment screw and is in threaded engagement with the drive shaft in order to press the adjustment screw towards the drive shaft.

Thus, the present invention is based on the understanding that a combination of an adjustment screw defining the degree of telescopic engagement with the drive shaft and a spring member biasing the impeller towards the distal rest position, the mounting and adjustment/trimming of an axially displaceable impeller can be performed with great precision.

According to a preferred embodiment of the present invention, the distal/free end of the drive shaft has the shape of a truncated cone and the pump comprises a socket, the socket being wedged between the interior side of the sleeve of the connector and the distal end of the drive shaft.

According to a preferred embodiment, the hub of the impeller comprises a through hole extending in the axial direction, and wherein the sleeve is arranged in said through hole of the impeller, and wherein a gap is arranged between a distal end of the sleeve and the hub of the impeller, said gap being adjacent a cavity that houses said spring member.

According to a second aspect of the present invention, there is provided an impeller assembly configured for a pump suitable for pumping liquid comprising solid matter. The impeller assembly entails that the connector may be pre-mounted into the central recess of the impeller before mounting of the impeller assembly into the pump, whereby the impeller assembly may also be sold as an up-grading kit for existing pumps having axially displaceable impeller.

Further advantages with and features of the invention will be apparent from the other dependent claims as well as from the following detailed description of preferred embodiments.

