FIELD OF THE INVENTION This invention relates to a vane pump and, more particularly, but not exclusively, to a vane pump that is particularly, but not exclusively, adapted to pump semi-solid and highly viscous materials such as sewage sludge and other barely flowable materials such as the residue from fruit juice extraction plants, in particular, but not exclusively, the residue from grape pressing operations for example in the production of grape juice and wine and also in the pumping of fish as a materials handling operation.

There are numerous other applications in which a vane pump of the type to which this invention relates can be put and the aforegoing are simply examples that are not to be interpreted as being limiting in any way on the scope of this invention.

BACKGROUND TO THE INVENTION Vane pumps used for purposes such as those indicated above typically have a housing within which a rotor is driven by any suitable motor and in which, for example, a pair of vanes extend at right angles to each other diametrically through the rotor. The vanes, in use, move so as to become extended from the rotor during a positive displacement pumping"stroke"which takes place over part of a full rotation and to substantially withdraw into the rotor during the return"stroke"which takes place over another part of a full rotation.

Typically, the pumping"stroke"endures for about one-quarter of a revolution of the rotor as does the return"stroke".

The movement of the vanes into and out of the rotor as the latter rotates is usually effected by one or more cam surfaces cooperating with cam followers carried by the vanes. The cam surfaces are typically defined by the inner periphery of generally annular cam plates each of which has an inner periphery serving as the cam surface and shaped to provide the required movement of the vanes by cooperation with the cam followers on the vanes.

Existing pumps of this nature exhibit what applicant considers to be serious disadvantages. In the first place, these pumps are often difficult to clean.

Accordingly, in food related applications, such pumps, which are generally used somewhat intermittently, need to be cleaned properly. In order to achieve this it is quite common for the pump to be dismantled so that the components can be properly cleaned. Another contributory factor to the difficulty of cleaning such pumps is the fact that many of them have open spaces inside that tend to become filled with compacted material from that being pumped. In addition, there is generally considerable wear and tear on the rotor and vanes where they slide in an out of the rotor and there is also considerable wear on the cams and cam followers which control the movement of the vanes in an out of the rotor. Bearing failure is also a common problem and bearings are usually rather costly.

OBJECT OF THE INVENTION It is an object of this invention to provide a vane pump of the general type outlined but which enables one or more of the disadvantages outlined above to be obviated at least to some extent.

SUMMARY OF THE INVENTION In accordance with one aspect of this invention there is provided a vane pump comprising a housing having an inlet and an outlet with a rotor and

vane mechanism therebetween and wherein the vanes are confined to movement radially in an out of the rotor according to a cam and cam follower assembly associated with the housing and vanes, the pump being characterized in that the interior of the rotor is hollow and a fluid inlet is provided for operatively connecting a supply of fluid under pressure to the interior of the rotor.

In accordance with a second aspect of the invention the cam and cam follower assembly comprise a cam plate on each side of the housing and wherein each cam plate-has an inner periphery defining an endless cam surface with which cam followers carried by the vanes cooperate to control the movement of the vanes into and out of the rotor, the vane pump being characterized in that the cam surface is shaped such that a vane remains at a substantially fixed degree of extension from the rotor during substantially the entire pumping"stroke"during which it is under load.

In accordance with a third aspect of the invention the path between the inlet and outlet from the housing has a substantially continuous surface of which a part cooperates with the outer edge of a vane during a pumping"stroke"and wherein at least a part of the surface cooperating with the outer edge of a vane during a pumping stroke is defined by the surface of a wear resistant insert fitted into an accommodating recess in the housing. The insert is preferably configured so that substantially no void spaces exist in the interior to thereby avoid the accumulation of compacted residues of material being pumped.

In accordance with a fourth aspect of the invention the rotor has each of its two ends confined to rotational movement by means of wear resistant bushes cooperating with its outer periphery at each of its said two ends. The bushes are conveniently cup shaped to receive an end of the rotor and the cup shape may be created either by a single machined bush of a one-piece

construction or it may be created by an annular disc and a ring juxtaposed relative thereto.

In order that the various features of the invention may be more fully understood one embodiment thereof will now be described with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:- Figure 1 is a perspective view of a complete pump assembly according to the invention; Figure 2 is a schematic sectional side elevation of the pump alone illustrating its operative components and, in particular, the vanes in one angular orientation relative to the housing and showing a corresponding degree of extension thereof from the rotor; Figure 3 is an elevation similar to Figure 2 but illustrating the rotor and vanes rotated through a further 45 degrees with the degree of extension of the one vane being correspondingly varied according to the cam profile ; Figure 4 is a cross-section taken along line III-III in Figure 3 and thus through the axis of the rotor with the vanes in the position illustrated in Figure 3; Figure 5 is an end view of a pump according to the invention fitted with an alternative drive arrangement; and,

Figures 6 to 9 are each a side view of the arrangement illustrated in Figure 5 and showing the drive motor with its axis in each of four possible in angular orientations relative to the pump.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS As illustrated particularly in Figure 1, a pump assembly of the general nature provided by this invention comprises a pump, generally indicated by numeral (1), mounted on a mounting frame (2) and coupled to a reduction gearbox (3) by way of a chain drive (4). The reduction gearbox has connected to it, an electric motor (5) as a prime mover and as a source of rotary movement.

The pump has a housing (6) providing an inlet (7) and an outlet (8) the axis of which extends at about 135 degrees to the axis of the inlet for reasons that will become more apparent from the following.

Referring now more particularly to Figures 2 to 4, a rotor and vane assembly, generally indicated by numeral (9), is positioned between the inlet and outlet.

This assembly comprises a rotor (10) having a bore (11) therethrough and two diametrically extending the vanes (12) orientated at right angles to each other. The vanes cross at the centre of the rotor and in order to enable this to take place each vane has a cutaway section (13) (see Figure 4) where they cross.

The vanes can move in reciprocal manner in a diametrical direction and are guided for movement by means of the inner edge of a generally annular cam plate (14) of which there is one at each side of the housing. The inner edge of each cam plate is identical to the other and forms a cam surface indicated by numeral (15). In each case the cam surface (15) cooperates with an end (16) of a cam follower (17) one of which is secured to each side edge of

each vane. Thus, as the rotor rotates about it axis, which is offset towards one side of the axis of the cam plates, the vanes will move to and fro in a diametrical direction relative to the rotor in a manner that will be well understood to one skilled in the art.

The path for material being pumped comprises the inlet (7) followed by a passage (18) formed between the inner surface of the housing on one side and the nearer surface of the rotor on the other side, and in turn followed by the outlet (8). The vanes are arranged to"sweep"material being pumped through the passage (18) in consequence of rotation of the rotor and the vanes in unison therewith.

The cam surface is shaped such that the outer edge of each vane will cooperate with the inner surface (19) of the housing through an arc of about 90 degrees and between the two positions of the vanes shown in Figure 2. In order to achieve this the outlet has its axis at said angle of 135 degrees to the inlet so that the vanes can remain in cooperating relationship with the inner surface (19) for a full 90 degrees of rotation of the rotor. Thus, during the movement of a vane between the two angular positions illustrated in Figure 2, it is under load.

In terms of one aspect of the invention the cam surface is shaped (as is the inner surface of the housing) so that the outer edges of the vanes remain at a fixed distance from the axis of the rotor to prevent any sliding movement of the vane relative to the rotor whilst the vane is under load. This expedient is aimed at diminishing wear and tear by allowing sliding movement of the vane relative to the rotor only when the vane is not under direct load.

Accordingly the portions of the cam surface corresponding to angular movement of the vanes between the two positions illustrated in Figure 2 will be part-circular in shape with the centre of arc coincident with the axis of rotation of the rotor. The portions of the cam surface connecting these two

part-circular portions are shaped to move the vanes in a most expeditious way from the one position corresponding to a pumping position to a position in which the opposite end of the vane assumes the pumping position relative to the rotor. A transitional situation is illustrated in Figure 3 in which the generally horizontally orientated vane has moved halfway from one position to the other.

In terms of another aspect of the invention the inner surface (19) of the housing communicates smoothly with the surface of the inlet as indicated by numeral (20) and also with the surface (21) of the outlet. The inner surface of the housing between the inlet and outlet is formed in a replaceable, wear resistant insert (22) made, for example, of a suitable grade of polyethylene or polyurethane. Also, for the purposes of reducing wear and tear, the inner surface (23) of a replaceable insert (24) made of a similar material is provided on the side of the housing opposite the passage (18). Thus, the entire inner surface of the housing which cooperates with the outer edges of the vanes is made of the wear resistant material of replaceable inserts.

In terms of a still further aspect of the invention each end of the rotor (10) is confined to rotary movement by means of wear resistant bushes (25) of generally cup shape (see Figure 4). These bushes can be made of a suitable friction reducing material and, most particularly, they can be made of an injection moulded material. Most importantly they are also easily replaceable as in the case of the inserts (22) and (24). The cup shape may also be created by using an annular disc and a ring left in combination defiantly cup shape. A material which is considered to be particularly appropriate is one sold under the trade name"VESCONITE". There are thus no conventional bearings which are also a source of failure and maintenance costs in the case of many existing types of pumps.

In terms of the remaining aspect of the invention, there is provided a fluid inlet (26) on the side of the housing opposite the drive shaft (27) utilized to

drive the rotor. The inlet communicates with the bore (11) of the rotor so that air, clean water, or any special cleaning fluid can be introduced by way of the inlet into the bore to flush out the passages and spaces surrounding the vanes.

It will be understood that, in use, the pump as described above will, first of all, be very easily cleaned as and when required simply by flushing it using a suitable flushing fluid such as water optionally having detergent, disinfectant or sterilising agents dissolved therein. The flushing fluid will also flow between the rotor and bushes.

The fluid inlet to the centre of the rotor can also be used to introduce a fluid such as water or air, into the pump during operation thereof for any one of a number of different purposes. Such purpose could be simply to lubricate and flush the pump during use; to add water to a substance which is rather dry in order to render it more fluid ; or to add a gas, in particular air, to the substance being pumped in order to aerate it.

The provision of replaceable inserts defining the portions of the passage which are subject to substantial wear and also to fill up otherwise empty spaces and to form a smooth continuous surface to the passage through the pump gives highly desirable results and greatly facilitates maintenance. The same may be said of the easily replaceable bushes that confine the rotor to its rotational movement.

Clearly the shape of the cam surface described above also contributes significantly to decreasing wear and tear where the vanes slide against the rotor in consequence of movement of the vane relative to the rotor being obviated whilst the vane is under load.

It will be understood that numerous variations may be made to the embodiment of the invention described above without departing from the

scope hereof. In particular, any combination of one to three of the aspects of the invention may be used instead of the combination of all four as in the case of the embodiment of the invention described herein.

Also, as indicated above, the drive arrangement for the pump can be varied widely and a particularly useful variation is illustrated in Figure 5 to 9. In this case the drive motor (28) can be arranged such that its axis extends radially relative to the drive shaft of the pump. The drive motor and associated gearbox (29) are attached to the housing (30) by way of flanged connections (31) and in this case four equally angularly offset bolts (32) are used to connect the two flanges together. This provides an added advantage in that, as illustrated in Figures 6 to 9, the drive motor can be arranged in four different angularly offset positions, one of which can be selected as and when required according to spatial considerations at an installation site.