More specifically the invention relates to an apparatus and method for marking lines using a mixed liquid supplied under pressure on roads, sports fields, or the like.

A line-marking machine is a hand driven or motor driven vehicle arranged to dispense a mixture of paint and water via an outlet to the substrate. The paint and water are pre- mixed on site to the intended concentration by the operator. The emulsion formed is then pressurised by passing it through a pump, and then it is sprayed onto the substrate through a spray head. It is necessary to rely on the operator to ensure that the paint is mixed to the correct ratio, as well as to clean the machinery thoroughly after use to prevent residual paint from blocking the pump. This problem is particularly acute because the pump can be blocked if paint is left inside, even over a lunch break, as the mixed suspension or emulsion has a short useful life so the solids tend to fall out of emulsion quickly. These factors impose a high standard of work on the operators who have to put up with repeated cleaning of the machines if the machines are to work reliably.

It is desirable to provide an apparatus and method for mixing two liquids under pressure which reduces or eliminates the risk of contamination of the pump, and which prevents the wastage of unused pre-mixed paints.

FR-A-2424521 discloses an apparatus for mixing first and second liquids, the apparatus comprising a first vessel arranged to contain the first liquid and a second vessel arranged to contain the second liquid, pumping means arranged to pump the first liquid to the first vessel and pressure-transmitting means arranged to transmit pressure from the first to the second liquid, whereby the second liquid is not passed through the pumping means but is impelled with the first liquid to an outlet port of the apparatus.

The apparatus of the present invention is characterised in that the pressure-transmitting means comprises an air pocket which, in use, is maintained within the apparatus.

The term"air pocket"is not restricted to"air"as the gas. Indeed, it may be desirable, in certain circumstances, to employ non-reactive gas, for example, if either the first or second liquids are oxidisable.

This feature enables the second vessel to be easily re-filled with second liquid (e. g. paint).

Preferably the apparatus comprises valve means having a first condition in which the air pocket is compressed by the first liquid being pumped into the first vessel and a second condition in which the air pocket is decompressed by allowing the first liquid to flow out of the first vessel.

This feature further enhances the ease of re-filling, particularly when the second vessel is flexible and liable to be collapsed by surrounding pressure.

Preferably the apparatus is mounted on a hand driven or powered vehicle and arranged to dispense a mixture of water as the first liquid and paint as the second liquid. However, the invention is not limited to this use. For example, such a method and apparatus may be useful for mixing agrochemicals such as insecticides and fertilisers prior to their application to a field, or for mixing a resin and a curing agent prior to application to a surface such as a car panel. The first liquid and/or the second liquid may optionally be a mixture of materials.

Preferably the apparatus is powered by a single source of electrical power mounted on the vehicle. This is usually a battery pack.

Preferably the apparatus also has a pressure release valve for draining the first fluid back into the first vessel to decrease the pressure on the second liquid, when appropriate.

In one embodiment, the apparatus is preferably operated by -activating a single dry battery power supply; -activating a pump to pressurise a first liquid drawn from a first vessel ; -allowing the pump to urge the pressurised first liquid into an air tight pressure transmitting means, thereby compressing the air in the pressure transmitting means, and then transmitting the pressure to the second liquid in the second vessel;

-allowing the pressure in the pressure transmitting means to reach a preset level which is monitored using a pressure gauge installed in the pressure transmitting means; and -switching valves present between each of the two vessels and an outlet means to the open condition, allowing first and second liquids to be mixed and urging the mixture under pressure onto an external substrate.

In order that the invention may be well understood it will now be described by way of example only with reference to the following diagrammatic drawings, in which: Figure 1 is an elevation of a line-marking machine according to the invention; and Figure 2 is a diagram showing the operation of a further line-marking machine according to the invention.

The line-marking machine 1 shown in Figure 1 is a hand pushed machine comprising a basic frame having a platform 2, supported on axles having front and rear wheels 3, and a handle 4. Two separate liquid containing vessels 5,6 are mounted on the platform 2. The first vessel 5 is a relatively large water tank. The second vessel 6 has an internal chamber 7 to securely receive a relatively smaller paint bottle 8. A diaphragm pump 9, a battery pack 10, and a pressure transmitting reservoir vessel 11 are also mounted on the platform 2. A spray head 12 projects from the front of the platform 2, and is connected to the two liquid containing vessels via pipelines 13 and 14.

Referring now to Figure 2, in which the same numerals as in Figure 1 have been used for identical components, there is shown a line-marking machine 1'having a five port 2-way valve 25 which is connected at port a thereof to line 16 from vessel 6 and which is connected by port b thereof to line 20 from vessel 5 and is further connected at port d thereof to an outlet on pump 9. The remaining ports c and e are connected to line 19 which communicates with the air space of vessel 6. The air space provides a pressure transmitting reservoir 11'. As can be seen, the pressure transmitting reservoir 11'is not a distinct component as in the case of the line-marking machine 1, shown in Figure 1. It will be appreciated that, provided the seals between the reservoir 11 and vessel 6 are sound, and that there is no blockage in the conduit therebetween the two configurations, shown in Figures 1 and 2, are functionally equivalent.

During normal operation, the valve 25 is set to a position in which port b is connected to port e and port a is connected to port d as represented by the arrows pointing upwardly and to the right. Pump 9 sucks water from vessel 5 via line 20 and the flow path between ports b and e and pumps water via a flow path connecting d and a to line 16 and hence to vessel 6, thereby pressurising air in air space 11'. This pressure is transmitted to paint bottle 8 which has flexible walls and is located within air space 11'. Hence paint flows out of paint bottle 8 via line 14 and reaches line 18. Besides the flow from port d to port a in this position of valve 25 there is also a flow from port d to line 13 and hence to line 18, resulting in mixing of the paint and water at junction P. The resulting mixture flows through line 18 to spray-head 12 under the control of an electrically operated solenoid valve 17. The mixing ratio of paint and water is adjusted by a flow control valve 26 in line 13.

When the paint in paint bottle 8 is exhausted and it is desired to refill the paint bottle, the valve 25 is set to its other position in which port b is connected to port d and port a is connected to port c, as represented by the arrows pointing upwardly to the right. In this position, pump 9 sucks water from vessel 6 via line 16 and the flow path connected to ports a and c and expels the water via the flow path connected to ports b and d along line 20 to vessel 5.

In the"reverse flow"position of valve 25 (flow paths represented by upward and rightward- pointing arrows) any excess pressure in vessel 6 is transmitted by line 16, ports a and c and line 19 to vessel 5, via a non-return valve 24 in line 19. Vessel 5 has a vent 21 to the atmosphere. The pressure in vessel 6 is monitored by a gauge 15.

Non-return valves 22 and 23 in paint line 14 and water line 13 prevent contamination of the paint by reverse flow of water and water by reverse flow of paint respectively.

The paint mixing point (P) is selected to be the shortest possible distance from the exit point of the spray head 12 to minimise the amount of pipework containing mixed paint.

The machine 1,1'is capable of spraying 100 per cent water or 100 per cent paint, or any desired ratio in between. This system is self-regulating as the pressure of the water is directly proportional to the pressure on the paint. A fluctuation in the voltage at the pump 9 may temporarily raise or lower the pressure of the water, but as water pressure in the vessel 11,11'determines the pressure on the paint, the pressure increase or decrease is adjusted correspondingly.

The apparatus has several advantages. Paint contamination of the tank 5, pump 9, and associated pipework is reduced or eliminated. Washing and cleaning may be done in a matter of seconds, not minutes. The ratio of paint-to-water can be adjusted by the operator whilst marking to prevent the need to over-mark at a later stage if a greater concentration of paint is required at specific points. Several lines may be sprayed at once, without loss of pressure across the several nozzles. Lines may be sprayed in different colours or the same colour to different shades.

The invention is not limited to the embodiment shown. For example the positioning of the components on the platform 2 may differ, and indeed, the machine 1,1'may be constructed from a single compartmentalised tank having recesses for the components. The spray device may be a hand lance. All components may be replaced by equivalents, for example, the diaphragm pump 9 may be replaced by an alternative pump. The vessel 6 may be shaped internally to receive any suitable paint container. An alarm may be fitted to the machine 1,1'to warn the operator if the pressure in the pressure transmitting vessel 11,11' is too high. The machine may be used to dispense any mixture of liquids where mutual ratios are important. The charging of the pressure transmitting vessel 11,11'may be achieved using an external pressure source or a provided pressure source that is independent of the primary pump 9.

Although for convenience the invention has been described in relation to line marking in practice it may be applied to other situations in which two liquids are to be mixed under pressure. For example, the first liquid in vessel 8 may be a pesticide or herbicide or, more generally, could be any liquid which is not suitable for being pumped directly.