WO1999051880A2

WO1999051880A2 - Multi-cylinder piston pump

Info

Publication number: WO1999051880A2
Application number: PCT/IB1999/000550
Authority: WO
Inventors: Allen Norman Geldenhuys; Leon Basil Geldenhuys; Daniel Lucas Geldenhuys
Original assignee: Allen Norman Geldenhuys; Leon Basil Geldenhuys; Daniel Lucas Geldenhuys
Priority date: 1998-04-03
Filing date: 1999-03-31
Publication date: 1999-10-14
Also published as: AU2848999A; WO1999051880A3

Abstract

The invention concerns a multi-cylinder piston pump (10) which includes a cam (18) rotatable about an axis and a series of pumping pistons (30) which reciprocate in cylinders (28) which are spaced apart about the cam axis. The cam (18) includes a peripheral, waviform formation (24) which engages the pistons (30) to cause them to reciprocate in their cylinders (28) when the cam (18) rotates. The pump contains one outlet for each cylinder. Pistons and check valves, valve closures are made of plastic materials for improved corrosion resistance.

Description

MULTI-CYLINDER PISTON PUMP

BACKGROUND TO THE INVENTION

THIS invention relates to a multi-cylinder piston pump.

In one application a pump according to the invention can be used to pump liquid fertiliser. In such application, the pump would be mounted on an agricultural planter so as to pump accurate volumes of liquid fertiliser at required locations, for example where seeds are planted by the planter.

Pumps of generally peristaltic type have conventionally been used to pump liquid fertiliser in agricultural applications. The pump is supplied from a header tank which is mounted on the planter and initially filled with the fertiliser in question. However the output of the known pump is dependent to some degree on the static head of fertiliser in the tank as determined by the level thereof, and this varies as the fertiliser is used up. As a consequence pumps of the known type are inconsistent and inaccurate in operation. This in turn may result in incorrect fertiliser coverage which is obviously undesirable. SUMMARY OF THE INVENTION

According to one aspect of this invention there is provided a multi-cylinder piston pump comprising a cam rotatable about an axis and a plurality of pumping pistons which are reciprocable in cylinders spaced angularly apart from one another about the cam axis, the cam including a peripheral, waviform formation which engages the pistons to cause the pistons to reciprocate in their cylinders when the cam rotates.

In the preferred embodiment, the cam has an outwardly directed, waviform projection engaging in recesses in the pistons.

Typically the pump comprises a pump casing in which the cylinders are located, the pump casing including an inlet for introducing liquid which is to be pumped into the cylinders and at least one outlet through which liquid is pumped from the cylinders by the pistons when the pistons reciprocate. The pistons may be double-acting and there is preferably an outlet for each cylinder. The pump may also include means for closing off at least some of the outlets to prevent liquid being pumped therethrough and for recirculating such liquid to the cylinders.

There may be, at each end of each cylinder, a first check valve controlling entry of liquid into the cylinder and a second check valve controlling flow of pumped liquid to the associated outlet, the first check valve being open when the second check valve is closed and vice versa. The check valves can include valve closures loaded by springs made of plastics material, and the pistons themselves may be made of plastics material. In a preferred embodiment suitable for use in pumping highly corrosive liquids such as liquid fertilisers, seals are provided to seal a central region of each piston from working ends thereof which contact the liquid in use, seals being provided in the cylinders to seal the central region of each piston from its working ends.

As a further measure to reduce corrosion there may be, for each cylinder, a vent passage for venting, to the outside of the pump casing, liquid which penetrates the seals.

The invention extends to the use of a multi-cylinder piston pump as summarised above when used to distribute liquid fertiliser and, in particular, when mounted on an agricultural vehicle and used to distribute liquid fertiliser, at least some outlets of the pump in such application being connected to spaced apart, independent fertiliser distribution nozzles of the vehicle.

According to another aspect of the invention there is provided a method of distributing liquid fertiliser on an agricultural land, the method comprising the steps of moving a vehicle having a ground-engaging wheel over the land so that the ground-engaging wheel rotates, the vehicle having mounted thereon a multi-cylinder piston pump according to claim 5, driving the cam of the pump in rotation off the land-engaging wheel and directing liquid pumped by the pump from the outlets of the pump to independent, spaced apart distribution nozzles which direct the liquid onto the land. BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which:

Figure 1 shows a perspective view of a cam used in a multi- cylinder piston pump according to this invention;

Figure 2 shows a cross-sectional view through a multi-cylinder piston pump according to the invention, the cross- section being at a position indicated by the line 2-2 in Figure 1;

Figure 3 shows a cross-section at the line 3-3 in Figure 2;

Figure 4 shows a cross-section at the line 4-4 in Figure 2; and

Figure 5 shows a view, corresponding to that of Figure 2, of another embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Figure 2 illustrates a multi-cylinder piston pump 10 which is suitable for accurately pumping liquid agricultural fertiliser. It will however be understood that the pump 10 could be used in many other applications other than pumping of agricultural fertiliser. The pump 10 has a casing 12 including an inlet 14 leading to an internal pump cavity 15. In the specific application of pumping agricultural fertiliser, the inlet 14 will be fed through a suitable conduit from a header tank charged with the liquid fertiliser in question.

Extending centrally through the cavity 15 is a shaft 16 carrying a cam 18 shown in enlarged perspective view in Figure 1. The cam has a circular disc 19 formed with a holed boss 20 through which the shaft passes and which is fastened to the shaft by a screw 22. The outer surface of the disc 18 carries an outwardly directed projection 24 which has a smooth waviform profile as illustrated. In the illustrated case, the projection varies in a generally sinusoidal manner about a central plane of the disc. The disc, boss and projection are integrally machined or cast.

Twelve pairs of cylinders 28 are located equiangularly about the shaft 16, the cylinders in each pair being aligned with one another. Each aligned pair of cylinders accommodates a double-acting piston 30. Each piston 30 has bore 32 extending into it from either end and is sealed with respect to the cylinder by O-rings 34. At their inner ends, the bores 32 intersect cross-bores 36 extending diametrically through the piston. At a position centrally along its length, each piston is formed with a tapered annular recess 38 which has a shape complemental to that of the projection 24 of the cam 18. Each bore 32 has a stepped cross-section and includes an internal shoulder acting as a valve seat. Valve closures 40 are biased inwardly against the valve seats by compression springs, as illustrated, and act as one-way check valves.

The outer end of each cylinder 28 accommodates a plug 46 formed with a bore 48. Each bore 48 has a stepped cross-section and presents an internal shoulder acting as a valve seat against which a valve closure 50 acting as a one-way check valve is biased by a compression spring as shown. The bores 48 in the plugs 46 on the left hand side of Figure 2 open into transverse passages 52 (see also Figure 3) which communicate with return bores 54 leading to transverse passages 56 at the right hand side. The bores 48 in the plugs 46 on the right hand side of Figure 2 open into the transverse passages 56.

Referring also to Figure 4, it will accordingly be seen that the transverse passages 56 communicate with the bores 48 in both the left and right hand plugs 46. The passages 56 also communicate with outlets 58 in the right hand end wall of the pump casing which are aligned with the bores 48, and there is one such outlet 58 for each pair of cylinders 28. In addition, the passages 56 communicate with return bores 60 leading to return inlets 62 in the casing structure which communicate with the interior of the pump cavity 15. As shown in Figure 2 the communication between a transverse passage 56 and the associated return bore 60 is normally blocked by an elongate plug 64 screwed into the right hand end wall of the pump casing from the exterior.

The operation of the illustrated pump is as follows, assuming that the inlet 14 is connected to a source of liquid such as liquid fertiliser and the pump cavity 15 is full of such liquid. An external rotary drive (not shown) is applied to the shaft 16 to rotate the cam 18. Where the pump is used to dispense liquid fertiliser during agricultural planting operations, the shaft drive will typically be a mechanical drive operating off a land wheel of the planter which rolls over the ground. Thus in this case the rotary speed of the cam 18 is determined by the rotary speed of the land wheel.

The engagement between the cam projection 24 and the pistons 30 and the waviform shape of the projection ensures that as the cam rotates the pistons are caused to reciprocate back and forth in the associated pairs of cylinders 28. The projection 24 has four crests at 90E to one another with four valleys between them. Thus every four pistons which are spaced apart by 9θEfrom one another will be in phase with one another.

The upper piston in Figure 2 is shown at the right hand end of its travel in the associated cylinders 28 and the lower piston at the left hand end of its travel. The next movement of the upper piston will be to the left. During this movement, the pressure of liquid in the space 64 at the left hand end of the piston 30 increases to a level which opens the valve closure 50. The associated valve closure 40 remains closed and liquid is expelled from the space 64 through the associated passage 52, return bore 54 and passage 56 to the outlet 58. At the same time, the corresponding space at the other end of the piston expands and the reduced pressure therein opens the associated valve closure 40 against its spring bias so that liquid is drawn into that space from the cavity 15 through the bores 36 and 32. When the piston then moves to the right again as the cam rotates further, the increased pressure in the latter space opens the valve closure 50 so that liquid is expelled through the passage 56 to the outlet 58. At the same time, the space 64 is once again charged with liquid and the process repeats itself.

It will accordingly be seen that the pistons are double acting so as to pump liquid both on both forward and rearward strokes, and that on each full cycle by each piston similar volumes of liquid are pumped from the ends of the piston to the associated outlet 58. In a full rotation of the cam, the twelve pistons pump twenty-four volumes of liquid to the twelve outlets 58.

In practice, in the application of pumping liquid fertiliser, each of the twelve outlets 58 can be connected to a separate one of twelve distribution nozzles on the planter, so that each nozzle is supplied accurately with the same liquid volume. Because the pump acts with positive displacement of liquid, the volume of liquid delivered to the distribution nozzles remains constant, irrespective of the static head in the header tank.

Also, because the rotary speed of the cam, which determines the flow rate through each outlet, is itself determined by the speed of the land wheel of the planter, the delivery of fertiliser by the pump is automatically determined by the velocity of the planter. A higher planter velocity results in a higher cam speed and accordingly a higher delivery flow rate, and vice versa. In the result, it can be expected that there will be constant and accurate delivery of fertiliser to each delivery site connected to an outlet 58.

Some planters may have less than twelve distribution nozzles. In this case, it is a simple matter to eliminate the required number of outlets 58. This is achieved by screwing stop plugs (not shown) into those outlets from which liquid delivery is not required, and removing the associated plugs 64. This prevents liquid pumped by the relevant pistons from passing through the associated outlet. Instead, the pumped liquid will be returned to the cavity 15 via the relevant passages 56, return bores 60 and inlets 62. Pumped liquid is delivered only through those outlets 58 which are open.

Many variations are possible. For instance, the pistons 30 do not have to be double-acting. Single-acting pistons could equally well be driven by a cam of the type described above. In this case, there would be a single cylinder for each piston.

Also, it is not necessary in all cases that there be a separate outlet for each piston, although this is convenient for supplying multiple nozzles. The deliveries from the pistons could be combined, in a manifold or the like, so as to leave the pump through a single outlet. There could of course be more or less than twelve pistons and cylinders or cylinder pairs.

Figure 5 illustrates another, currently preferred embodiment which operates in similar manner to the first embodiment described above. Components in Figure 5 corresponding to components of the first embodiment are designated with the same reference numerals.

In this case there are two inlets 14 situated at either end of the casing 12. There are again twelve pairs of double-acting pistons 30 arranged equiangularly about the shaft 16 supporting the cam 18. The cam 18 in this embodiment has only two high points or crests spaced 180E apart from one another with valleys between them. Thus pistons spaced apart from one another by 180E will be in phase with one another as the cam rotates.

Whereas the check valves provided by the spring-loaded valve closures 40, 50 are aligned with one another in Figure 2 it will be seen that the corresponding check valves in Figure 5 are radially off-set from one another. The bold lines 70 indicate the route along which the liquid to be pumped enters the cylinders at the left and right hand ends respectively while the bold lines 72 indicate the route followed by the liquid driven from the pump. For clarity of illustration, the paths 70 and 72 are only indicated in relation to the pistons 30 in the upper part of Figure 5, but it will be understood that corresponding paths exist in relation to the other pistons as well.

It is recognised that pumps according to the invention may have to handle fertiliser and other liquids of a highly corrosive nature. For this reason components of the pump which are in contact with the liquid are preferably made of corrosion resistant material. For less corrosive liquids stainless steel or other suitable materials may be used. In Figure 5 the pistons are made of a suitable plastics material and slide in cast iron sleeves 74 which are isolated from the liquid by seals 76. The valve closures 40 and 50 as well as the springs which bias them are also made of suitable corrosion resistant plastics material. As a further anti-corrosion measure the pump includes a narrow passage 80 which serves to vent liquid to the exterior of the pump rather than permitting leakage thereof past the seals 76 into contact with the sleeves 74.

It will also be noted that whereas in Figure 2 the liquid is introduced to the central pump cavity by the single inlet 14 and hence is able to contact the cam and inner regions of the pistons, the liquid is introduced to the outer ends of the pistons in Figure 5, thereby isolating the cam 18 and inner piston regions from the liquid.

Claims

1. A multi-cylinder piston pump comprising a cam rotatable about an axis and a plurality of pumping pistons which are reciprocable in cylinders spaced angularly apart from one another about the cam axis, the cam including a peripheral, waviform formation which engages the pistons to cause the pistons to reciprocate in their cylinders when the cam rotates.

2. A multi-cylinder piston pump according to claim 1 wherein the cam has an outwardly directed, waviform projection engaging in recesses in the pistons.

3. A multi-cylinder piston pump according to claim 1 or claim 2 wherein the pump comprises a pump casing in which the cylinders are located, the pump casing including an inlet for introducing liquid which is to be pumped into the cylinders and at least one outlet through which liquid is pumped from the cylinders by the pistons when the pistons reciprocate.

4. A multi-cylinder piston pump according to claim 3 wherein the pistons are double-acting.

5. A multi-cylinder piston pump according to claim 3 or claim 4 comprising an outlet for each cylinder.

6. A multi-cylinder piston pump according to claim 5 comprising means for closing off at least some of the outlets to prevent liquid being pumped therethrough and for recirculating such liquid to the cylinders.

7. A multi-cylinder piston pump according to any one of claims 4 to 6 comprising, for each end of each cylinder, a first check valve controlling entry of liquid into the cylinder and a second check valve controlling flow of pumped liquid to the associated outlet, the first check valve being open when the second check valve is closed and vice versa.

8. A multi-cylinder piston pump according to claim 7 wherein the check valves include valve closures loaded by springs made of plastics material.

9. A multi-cylinder piston pump according to any one of claims 3 to 8 wherein the pistons are made of plastics material.

10. A multi-cylinder piston pump according to claim 9 comprising seals for sealing a central region of each piston from working ends thereof which contact the liquid in use, seals being provided in the cylinders to seal the central region of each piston from its working ends.

11. A multi-cylinder piston pump according to claim 10 comprising, for each cylinder, a vent passage for venting, to the outside of the pump casing, liquid which penetrates the seals.

12. A multi-cylinder piston pump according to any one of the preceding claims when used to distribute liquid fertiliser.

13. A multi-cylinder piston pump according to claim 5 when mounted on an agricultural vehicle and used to distribute liquid fertiliser, at least some outlets of the pump being connected to spaced apart, independent fertiliser distribution nozzles of the vehicle.

14. A method of distributing liquid fertiliser on an agricultural land, the method comprising the steps of moving a vehicle having a ground- engaging wheel over the land so that the ground-engaging wheel rotates, the vehicle having mounted thereon a multi-cylinder piston pump according to claim 5, driving the cam of the pump in rotation off the land-engaging wheel and directing liquid pumped by the pump from the outlets of the pump to independent, spaced apart distribution nozzles which direct the liquid onto the land.

15. A multi-cylinder piston pump substantially as herein described with reference to Figures 1 to 4 or Figure 5 of the accompanying drawings.