The present invention refers to a centrifugal pump for fluids containing large or long solid objects. Primarily this means wooden chips, textile-and fibre parts, plastic and other solid pieces in the size order of 5-150 mm. Pumps according to the invention are especially intended for pumping of liquid have a large content of solid material which may be up to about 50 %.

Solid objects cause problems by pumping with centrifugal pumps thereby that they both stick on the edges of the shovels of the pump wheel and force their way in between the pump wheel and the housing and get stuck to either one of these where they may cause the pump wheel to slow down or get stuck. The larger objects may also bridge between two shovels. Objects which have stuck and rotate together with the pump wheel easiiy gather more objects and the aggregate often grows rapidly. In all cases the flow through the pump is disturbed and its capacity is reduced. When such problems occur the pump has to be stopped and cleaned which often brings with a stop for the entire process in which the pump is included.

The present invention is for a centrifugal pump by which the above mentioned drawbacks are avoided. The object of the present invention is a pump of the above mentioned kind such that as far as possible it is avoided that solid objects stick to the pump wheel or housing. It is another object of the invention to achieve that objects which have become stuck are released as soon as possible without having to stop the pump or take any other special action. A centrifugal pump according to the invention has the characteristics which are mentioned in claim 1. Embodiments of a pump according to the invention have those characteristics which are apparent from the other claims.

The invention will below be described with reference to the examples of embodiments which are shown in the enclosed figures.

Figure 1 is a cross-section of a pump according to the invention.

Figures 2 and 3 is a cross-section and front view of a pump wheel of a pump according to the invention.

Figure 4 is a cross-section of some parts of a pump of figure 1.

The pump shown in figure 1 has a conventionally designed housing 1 in which there is a pump wheel 2 which is connected to a driving shaft 10. In the embodiments shown in the figures the pump wheel has four shovels 11,12,13 and 14. The housing of the pump has an inner lining or wear disc 1A the inside of which is adapted to the shape of the shovels of the pump wheel. At the back of the pump wheel the housing comprises a pump cover 17. Bearing and sealing of the pump shaft is made in known manner.

At prior art pumps the shovels extend themselves only a short distance upwards from the disc of the pump wheel 2 and the end of the shovels is approximately along the broken line 3 which is marked on the shovels. At centrifugal pumps according to the invention the shovels extends themselves considerably further towards the inflowing fluid so that the edge of the shovel which closest to the outlet follows the inside wear disc 1A continuously extends itself up to an extension of the shaft 10 and in a plane in the direction of the pump shaft is at an acute angle therewith. Long large objects can not stick to the front edges of the shovels but are directed into the pump wheel in a direction which generally coincides with the direction of the flow thus eliminating the risk of bridging between two adjacent shovels. Preferably the shovels also are at an acute angle to the shaft of rotation in a vertical plane at right angle to the plane which is shown in the figure.

In some applications the pump wheel also has intermediate shovel in order to attain the required pressure at pumping. Such an intermediate shovel (18) is shown in figure 2 from which is apparent that it starts some distance outwards on the pump wheel as seen from its hub. The edge of the intermediate shovel slopes from the starting point slightly upwards from the plane of the pump wheel until it has the same height as the other, larger shovels (11,12,13,14). From this point and on to the periphery of the pump wheel the intermediate shovel (18) has mainly the same shape as the other shovels. The number of intermediate shovel is in most cases the same as the number of the other shovels. By this design of the intermediate shovels it is achieved that solid particles do not stick to the intermediate shovels but are thrown at the wear disc in the same way as at the other, larger shovels.

At the inside of the wall of the housing 1-1A there are one or more grooves 4,16. The grooves extend themselves from the outer outlet channel in the housing along the whole of the part of the wall adjacent to the shovels and some distance further. Objects

of a size such that they may get into the slit between shovel and housing are hooked by the grooves and ground to pieces. The slit 5,15 between shovel and housing is so designed that it, at least at an end section thereof, widens in the direction of the flow and towards the periphery of the pump wheel. Due to this design all particles which get in between shovel and housing are ground and conveyed out with the fluid flow.

The pump wheel may also have back side shovels 6,8. In this case also the cover 17, which is facing the back of the pump wheel, has one or more grooves 7,9. This brings with it that solid objects which get in between the pump wheel and the cover are ground when they are hooked by the grooves 7,9 and hit by the back side shovels 6, 8. The slit between the pump wheel and the cover preferably widens continuously outwards from the shaft in order to make it easier for objects which have got into the slit to get out to the outlet channel.

Further embodiments of the centrifugal pump are possible within the frame of the inventive idea. The grooves both in the housing and the cover of the pump may in other embodiments of the invention be replaced by ridges or similar edges at the housing and the cover. The grooves or ridges may then form a straight or bent line along the surface at which they are positioned. The also ought to have a rounded bottom or outside to facilitate the loosening of temporarily stuck objects. The front part of the shovels may together with the corresponding part of the shaft be a separate addition to conventional pump wheels.