GB1595901A - Peristaltic pump and agricultural/horticultural machine - Google Patents

Description

(54) PERISTALTIC PUMP AND AGRICULTURAL/HORTICULTURAL MACHINE (71) We, IMPERIAL CHEMICAL INDUS TRIES LTD, Imperial Chemical House, Millbank, London SW1P 3JF, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a peristaltic pump and to an agricultural/horticultural machine, of which it may be a part.

Pumps of the peristaltic type, in which a fluid is propelled in an elastic tube by constricting the tube and causing the constricted area to move in the desired direction of a flow of fluid, have come into use for a variety of purposes over the last decade or so, especially in situations in which fairly accurately metered flow is required. Usually they comprise a track supporting the tube and moving roller means effective to flatten the tube onto the track. In a convenient form of the pump the track is the inner surface of an arc of a cylinder and is flattened by rollers each at the end of a spoke of a revolving wheel whose centre shaft is at the axis of the cylinder.

We have observed that peristaltic pumps have the defect that the pressure of the delivered fluid is not constant but fluctuates according to the position of the rollers in the pump. This is significant in an agricultural machine in which a liquid is to be delivered to the soil simultaneously with some other operation, for example potato planting, because it causes excessive or deficient local concentrations of the liquid.

We have now devised an improved pump by which this defect can be substantially decreased.

According to the invention a peristaltic pump comprises at least two pumping tubes, as defined hereinafter, disposed equidistantly from a rotor having three equidistant radial spokes each carrying at its extremity a roller effective to constrict the tubes at different points in their pumping cycles as the rotor rotates, and a manifold to which the outlets of both or all the tubes are connected.

In the simplest form of pump according to the invention two tubes of equal capacity are used and the constriction is applied by the rollers to the midpoint of the one tube at the same time as to the end and to the beginning of the other tube. Such a pump provides smooth enough delivery for many purposes, especially if delivery is by way of pipes having some elasticity or if an airreservoir is used. If greater smoothness is required, three tubes can be used, such that constriction at the end and/or beginning of one coincides with constriction at onethird and two-thirds of the length, respectively, of the other two. Still greater numbers of tubes can be used if desired.

A preferred form of the pump comprises two tracks each constituted by an arc of a cylinder and disposed diametrically in opposition about the axis of the cylinder, a peristaltic tube supported by each track, a rotor having three equidistant radial spokes each carrying at its extremity a roller effective to flatten the tube on to the track, and a manifold to which the outlets of both tubes are connected. Each track must, of course, subtend at least one-third of a revolution, so as to ensure that part of each tube is always flattened.

Instead of a single rotor, a plurality of rotors could be used, one for each tube, with suitable drive means. Thus an alternative form of the pump comprises two tracks each constituted by an arc of a cylinder and disposed in different planes perpendicular to the axis of the cylinder, a peristaltic tube supported by each track, two rotors each positioned to co-operate with one of the tubes and having three equidistant radial spokes each carrying at its extremity a roller effective to flatten the tube on to the track, and a manifold to which the outlets of both tubes are connected.

Each tube may lie with most or all of its length in contact with its track. Indeed the term "pumping tubes" is intended to include not only integrally-formed tubes of flexible and resilient material, but also tubes one wall of each of which is inflexible, for example a tube formed by sealing a rubber channel member on to a rigid track therefor. The tubes can be of any suitable cross-sectional shape such as circular, oval or D-shaped.

For better smoothing of flow each tube may be anchored at both ends and be of a length sufficient to afford contact with the track only at the area or areas of constriction. Each tube may be in a state of light stretching at the time of constriction.

The invention provides also a machine for applying a fluid to land or to plants, comprising at least one pump according to the invention. Among the machines provided are sprayers of liquid fertilisers, insecticides, fungicides, weedicides and other crop protection materials and also marker fluids such as foam or foam ingredients in peat-digging.

As a result of the smoothness of fluid delivery, the machine is very suitably one that applies at least one material additional to the fluid delivered by the pump. Thus, for example a combine drill applying both seed and liquid fertiliser, or a potato planter having means for applying both potatoes and liquid fertiliser, may advantageously include a pump according to the invention.

The machine is very suitably one in which the pump and any other applying means are driven by a land wheel, since then the rate of feed fluid is proportional to speed and thus the rate of application per unit area is substantially constant. An example of such a machine is described in our UK specification 1364733.

In the accompanying drawings Figure 1 shows in vertical section one preferred pump according to the invention; Figure 2 shows in vertical section an alternative form of the pump shown in figure 1; and Figure 3 shows in graphs A and B the fluctuations in the delivery pressure of pumps respectively without and with manifolded delivery. These graphs represent measurements made on a combine drill.

In figure 1 the pump body includes two track sections 10 in the shape of arcs of cylinder connected by box shaped tube-end supporting frames 12. Frames 12 each include two apertures 14 each of which includes a tube fixture supporting the tube 16 or 18 against lateral and longitudinal movement.

Tubes 16 and 18 lie respectively in the upper and lower cylindrical sections 10. Tube 16 is connected at its inlet to feed pipe 20 and thence to Y-piece 22. Tube 18 is connected at its inlet to feed pipe 24 and thence to Ypiece 22. (It is not essential to manifold the feeds to tubes 16 and 18 in order to obtain a smoothed delivery, but it will generally be convenient to have a single source of fluid).

At its outlet tube 16 is connected via pipe 26 and tube 18 via pipe 30 to Y-piece 28 constituting the delivery manifold. Y-piece 28 is connected, in a typical machine, to a use that applies a moderate back-pressure, such as a tank or one or more spray-nozzles.

The moving constriction means is provided by rollers 32A-C, each at the end of a radius arm extending from boss 34.

The pump shown in figure 2 differs from that of figure 1 only in that the external connection to each tube is through an anglepiece and in that each tube is in contact with the track only at the areas of constriction by the rollers. The angle-piece arrangement shortens the external connections.

In the operation of the pump shown in figure 1, the rotor turns in the direction shown. If we consider tube 16 in isolation, it is apparent that with the rotor in the position shown the fluid is at a pressure that is balanced by the back-pressure downstream of Ypiece 28 and any elasticity afforded by pipe 26 and the small downstream end of tube 16. After the rotor has turned a short distance, roller 32A will have passed point Q and allowed tube 16 to open. The fluid now occupies a greater volume owing to the opening of the tube and is at a pressure that is balanced by the inner part of tube 16 between roller 32B and point Q in addition to the balancing pressures previously mentioned, that is, at a significantly lower pressure.

As roller 32B advances towards point Q, the inner part of tube 16 shortens and the pressure rises once more. This mode of operation of a single-tube pump turning at 63 rpm is shown in graph A of figure 3. It is to be noted that a rise in pressure occurs rapidly after the fall in pressure because the fluid (in the case tested, a liquid fertiliser solution) does not flow rapidly enough at the start of the traverse of roller 32B from point P, but that the rise falters as the elasticity of the external pipes and the rate of delivery downstream of 2 respond to the increased pressure. This response is complete by the time point Q is reached and thus a peak pressure level is attained. The same fluctuation would occur if tube 18 were operated in isolation.

If we now consider both tubes co-operating according to the invention, it is apparent that the fluid is at present at a pressure balanced by any elasticity afforded by pipe 30 and the downstream half of tube 18 as well as by the back pressure downstream of Y-piece 28, elasticity afforded by pipe 26 and of the small downstream end of tube 16. From graph A it is evident that the pressure would be 20 psi just before roller 32A has left point Q and 10 psi just after.

In the two-tube pump the delivery at Ypiece 28 includes also fluid from tube 18 which, since its roller is half-way between points R and S, will be supplying at about 15 psi. As roller 32A leaves point Q, the fall in pressure in tube 16 is compensated for by a small increase in pressure in tube 18, as well as by any relaxation of pipe 30 and the downstream part of tube 18. The net change in pressure is very small, as is evident from graph B of figure 3. (It is to be noted that the rotor turns at 63 rpm in the single-tube pump but only 31-5 rpm in the double-tube pump. The total length of tube traversed in unit time is the same, however).

The operation of the pump shown in figure 2 is similar, except for the minor effect of the smaller tube length inside the pump.

The alternative arrangement in which the tubes inside the pump are parallel instead of diametrically opposed and are each constricted by its own rotor, the arms of one rotor being 60 out of phase with those of the other, can be readily visualised. In this arrangement the manifolding of the inlet and delivery connections is simpler because both inlets are at the same side of the pump casing and so also are both outlets.

In the pumps described, tubes 16 and 18 were 1 inch bore polyurethane rubber hose of 3/32 inch wall thickness and pipes 20, 24, 26 and 30 were 1-25 inch bore nylonreinforced PVC hose supplied under the Registered Trade Mark "FLEXILENT".

Although much less flexible than rubber and of low elasticity, the smoothing of the flow through these pipes was fully acceptable.

For simplicity the additional integers of the agricultural or horticultural machine of which the pump forms part, namely the framework, land wheel drive, liquid storage tank and liquid application means such as a spray boom or drill, have been omitted from the drawings.

Analogous arrangements in which the tubes are angularly displaced from one another and the rotor arms are less out of phase or even symmetrical could be used.

Other numbers of rotor arms can of course, be used.

WHAT WE CLAIM IS: 1. A peristaltic pump comrising at least two pumping tubes, as defined hereinbefore, disposed equidistantly from a rotor having three equidistant radial spokes each carrying at its extremity a roller effective to constrict the tubes at different points in their pumping cycles as the rotor rotates, and a manifold to which the outlets of both or all the tubes are connected.

2. A pump according to claim 1 in which two tubes of equal capacity are used and the constriction is applied by the rollers to the midpoint of the one tube at the same time as to the beginning and to the end of the other tube.

3. A pump according to claim 1 or claim 2 comprising two tracks each constituted by an arc of a cylinder and disposed diametrically in opposition about the axis of a cylinder, a peristaltic tube supported by each track, a rotor having three equidistant radial spokes each carrying at its extremity a roller effective to flatten the tube on to the track, and a manifold to which the outlets of both tubes are connected.

4. A pump according to claim 1 or claim 2 comprising two tracks each constituted by an arc of a cylinder and disposed in different planes perpendicular to the axis of the cylinder, a peristaltic tube supported by each track two rotors each positioned to cooperate with one of the tubes and having three equidistant radial spokes each carrying at its extremity a roller effective to flatten the tube on to the track, and a manifold to which the outlets of both tubes are connected.

5. A pump according to any one of the preceding claims in which each tube is anchored at both ends and its length is sufficient to afford contact with the track only at the area or areas of constriction.

6. A pump substantially as described with respect to figure 1 or figure 2 of the accompanying drawings.

7. A machine for applying a fluid to land or to plants, comprising at least one pump according to any one of the preceding

Claims (1)

1. claims.

   8. A machine according to claim 7 including also means to apply at least one material additional to the fluid delivered by the pump.

   9. A machine according to claim 8 which is a combine-drill having means for applying seed and liquid fertiliser.

   10. A machine according to claim 8 which is a potato-planter having means for applying potatoes and liquid fertiliser.

   11. A machine according to any one of claims 7 to 10 in which the pump and any other applying means are driven by a land wheel.

   12. A machine according to any one of claims 7 to 11 in which the use of the pumped liquid applies a moderate back-pressure and the pipes from the pump to the use are elastic at the pressure involved.