WO1996008317A1

WO1996008317A1 - Wheeled spraying unit with variable rates of pressurisation

Info

Publication number: WO1996008317A1
Application number: PCT/AU1995/000614
Authority: WO
Inventors: Victor Vivian Miers
Original assignee: Victor Vivian Miers
Priority date: 1994-09-16
Filing date: 1995-09-18
Publication date: 1996-03-21
Also published as: CA2199611A1; AUPM816694A0

Abstract

A hand propelled spraying unit (10), the unit includes a vessel (12) adapted to hold liquid to be sprayed, the vessel (12) having a spraying outlet (14) in fluid communication with the interior of the vessel. The vessel (12) is pressurised in response to rotation of wheels (18) of the unit in any direction over a ground surface, the rate of pressurisation of the vessel by the pressurisation means (pump (20) connecting to pressure accumulator (56) in the vessel) is adjustable with respect to any given rate of travel of the ground engaging wheels (15) over a ground surface. Cogs (30, 32, 34) of different sizes allow adjustment of the rate of pressurisation by pump (20) and hence the rate of pressurisation of the vessel (12) allowing different spraying rates.

Description

WHEELED SPRAYING UNIT WITH VARIABLE RATES OF PRESSURISATION.

TECHNICAL FIELD

The present invention relates to a spraying unit. In particular, the present invention relates to a hand propelled liquid spraying device.

BACKGROUND OF THE INVENTION

Spraying units are used for the distribution of a range of agricultural and horticultural chemicals over areas of ground to be treated. The type of equipment used depends on the area to be treated and on the accessibility of the area. Larger areas of cleared land can be treated with equipment where the pumps are driven by an external energy source such as a petrol or electric motor or the power take off shaft of a tractor.

Such implements are expensive and impractical for smaller areas of land which would typically be treated with a manually carried and operated spraying unit, which for convenience might be carried in a back pack. The liquid to be sprayed is pressurised in the container by use of a hand operated pump which pressurises the air space above the liquid. As the liquid is released the pressure in the air space above the liquid decreases, eventually requiring re-pressurisation before spraying can be continued.

There are obvious disadvantages with a back carried unit in that only a limited amount of liquid can be carried at a time, thus for lager areas a container may need to be re-filled several times to complete the task. Moreover, these units are manually operated and require frequent manual re-pressurisation to ensure adequate spraying, thus interrupting the spraying process. Thus the overall level of manual effort involved is considerable.

These problems have been addressed by the development of spraying units based on hand propelled wheeled vehicles which carry the liquid to be sprayed and derive pressurisation from movement of the ground engaging wheels.

GB862020 describes one such apparatus with a pair of plunger type pumps driven by a crank which is rotated by a sprocket and chain arrangement connected to the single ground wheel in a wheel barrow type frame.

A disadvantage of this method of utilising motion of ground wheels to drive pumps is the supporting framework is necessarily cumbersome and diminishes manoeuvrability of the device.

For some applications, such as applying liquid fertiliser or treating heavy infestations of broad leaf weeds, it is useful for a device to have a high rate of pressurisation to enable continuous spraying at low pressure. Obversely, for treating weeds or trees of moderate height, it is advantageous for a spraying device to apply chemicals at a relatively higher pressure but intermittently, and therefore, a lower rate of pressurisation is acceptable.

A further disadvantage of this type of construction is that it cannot readily be adjusted to switch from high rate of pressurisation but low pressure applications to low rate of pressurisation but high pressure applications. Unless a complex and expensive bicycle type gearing system is employed it can only be achieved with the inconvenience of replacing a sprocket with one of different diameter.

GB 1489747 also utilises a chain and sprocket system and consequently suffers the same disadvantage as the aforementioned.

FR 2668400 describes a device whereby a pump is activated when a connecting lever arm is oscillated on contact with a spur cam fixed to a ground engaging wheel. Whilst attainable pressure can be varied by varying the distance of the spur cam from the hub of the wheel, rate of pressurisation must remain low as it is not continuous and only eventuates on contact of the spur with the lever arm.

GB 951800, US 2069702 and GB 2102662 describe devices where the pump drive shaft and wheel axle are common, thus inhibiting gearing and precluding a feature previously described as desirable.

All of the above devices are constructed to operate by pushing to gain forward motion and with dispersion of chemicals restricted to the direction of movement of the apparatus. This is not always appropriate as less effort is required to pull a wheeled vehicle up an incline. Moreover, some of the above must be in motion to enable spraying, others at rest, and in all cases it is necessary for the operator to traverse the ground to achieve pressurisation. This is inconvenient when, for example, treating a concentrated infestation of weeds where the operator would wish to remain in a confined area for some time.

The inventor of the present invention has identified a need for a compact, self- pressurising mechanical device of reasonable carrying capacity which is suited to different types of terrain including uneven and undulating ground and which can be operated by pulling or pushing to suit ease of motion and to enable pressurisation by a rocking motion whilst the operator remains stationary and which can readily be adjusted to accomplish continuous, high volume low pressure spraying or intermittent, low volume high pressure spraying.

It is therefore an object of the present invention to provide a hand propelled spraying unit directed towards the above identified needs.

DISCLOSURE OF THE INVENTION

Therefore, according to a first aspect of the present invention there is provided a spraying unit, the unit being characterised by:

- a vessel adapted to hold liquid to be sprayed, the vessel having a spraying outlet in fluid communication with the interior of the vessel; transport means adapted to support the vessel being supported on a frame having one or more ground engaging wheels attached thereto; pressurisation means adapted to pressurise the vessel, the pressurisation means being operable in response to rotation of the ground engaging wheels in any direction over a ground surface to thereby pressurise the interior of the vessel; and wherein the rate of pressurisation of the vessel by the pressurisation means is adjustable with respect to any given rate of travel of the ground engaging wheels over a ground surface.

Thus, the spraying unit of the present invention is adapted to be rapidly adjustable between a number of spraying modes. For example, the unit may be adjustable between first and second modes which have high and low pressurisation rates respectively. In the first mode, the pressurisation means is adjusted with respect to any given speed of travel of the unit to allow for a high rate of pressurisation. A high rate of pressurisation permits extended spraying period. Therefore, in the first mode it is possible for an operator to continuously spray an area, albeit with a low pressure spray, whilst pressurising the unit by walking slowly or through a backwards/forwards rocking motion of the unit. Thus, in this mode the unit is adapted for the continuous spraying at low pressure of areas of ground heavily infested with low growing weeds.

In a second mode, the unit is adapted for intermittent spraying at high pressure. Thus, whilst the rate of pressurisation may be lower than in the first mode, the pressure developed within the vessel is higher because of the greater leverage obtained from the ground wheels. In such situations the spraying pressure required may typically be higher to allow a spray to reach high growing plants or trees.

The pressurisation means of the unit of the present invention may take a number of alternative forms.

In a preferred embodiment, the pressurisation means is connected to the transport means via a cog system in which a plurality of differently sized drive cogs are arranged co-axially with the ground engaging wheels . One or more reciprocating pumps are driven from the drive cogs through a crank arm arrangement. The pump or pumps can be either a single double-acting pump, or alternatively, a pair of single acting displacement pumps arranged on a double cam with lever arms offset at 180° to each other. By arranging or connection to appropriately sized gears the rate of pressurisation with respect to any given speed of travel of the unit may be varied.

Preferably, the connection between the pump or pumps and the drive cogs takes the form of a respective driven cog to be associated with a respective drive cog, the driven cogs being attached to a drive shaft arranged parallel to the wheel axle. Rotation of the ground engaging wheels and the associated co-axial drive cogs thereby results in a corresponding rotation of the driven cogs and the drive shaft. Rotation of the drive shaft, in turn, leading to reciprocation of the pump or pump shafts and a resulting pressurisation of the vessel.

The rate of pressurisation of the vessel with respect to any given rate of travel of the ground engaging wheels over a ground surface may be adjusted by selecting drive cogs of appropriate sizes.

In a further embodiment, the pressurisation means includes a pump or pumps driven by a crank formed in the wheel axle, the crank being of adjustable length. The pump or pumps can be either a single or a double acting displacement pump. In the case of a pair of single acting displacement pumps, the pumps are arranged on a double cam with lever arms offset at 180° to each other By adjustment of the length of the crank, the rate of pressurisation with respect to any given rate of travel of the wheels over the ground may be varied.

In a further embodiment still, by connecting a pump to a cam arm directly to a wheel of the unit, the pressurisation can be effected. By varying the point of connection of the cam arm between the centre and the circumference of the wheel the length of stroke, and therefore the rate of pressurisation can be varied.

Pressurisation of the vessel may be effected by either direct pressurisation of the air space above the liquid in the entire vessel, through the pumping of air into the vessel, or alternatively, by pumping liquid from a filler tank to an accumulator, thereby using the liquid in the accumulator to pressurise the air space above the liquid in the accumulator.

In either case, the vessel conveniently includes a mechanism which governs the development of any over pressure in the vessel, thus preventing locking of the wheels of the unit.

BRIEF DESCRIPTION OF THE DRAWINGS

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

FIG 1 illustrates in perspective view a schematic spraying unit in accordance with a first aspect of the present invention; FIG 2 illustrates the spraying unit of FIG 1 in cross-sectional side view;

FIGS 3a and 3b show a detail of the wheel and cog of the spraying unit of FIG 1 in two positions;

FIG 4 illustrates a spraying unit in accordance with a second embodiment of the present invention; and

FIG 5 illustrates a spraying unit in accordance with a third embodiment of the present invention;

DETAILED DESCRIPTION OF DRAWINGS

Referring to Figures 1 and 2 there is shown a hand held spraying unit 10. The spraying unit 10 comprises a vessel 12 adapted to hold a liquid to be sprayed and a spraying outlet 14 in fluid communication with the interior of the vessel 12. The vessel 12 is supported on a transport means taking the form of a frame 16, the frame 16 having a pair of ground engaging wheels 18 attached thereto.

The spraying unit 10 further includes a pump 20 serving as a pressurisation means. The pump 20 is arranged so as to be able to pressurise the vessel 12, the rate of pressurisation of the vessel 12 being adjustable with respect to any given rate of travel of the ground engaging wheels 18 over a ground surface.

The frame 16 includes a platform 22 on which the vessel 12 is supported and a handle 24 extending upwardly from the platform 22. A pair of front stands 26 depend from the platform 22, and together with the wheels 18 support the unit 10 when in an upright stationary position.

The wheels 18 are mounted on a wheel axle 28, the wheel axle 28 being supported between two lowermost extensions from the platform 22. The wheels 18 are fixed in position on the wheel axle 28, thus rotation of the wheels 18 results in a corresponding rotation of the wheel axle 28.

Fixed on the innermost side of each wheel 18 are a pair of drive cogs 30 and 32. Each of the cogs 30 and 32 has an apertured surface capable of being engaged by a driven cog 34. The cog 30 is of larger diameter than the cog 32, being approximately twice the diameter of the cog 32, and the cog 32 extends axially inwardly of the cog 30. Thus, each driven cog 34 is able to contact either of a respective drive cog 30 or 32. The driven cog 34 has a number of circumferential projections which engage apertures in the drive cogs 30 and 32.

The driven cogs 34 are mounted on a drive shaft 36, and each cog 34 is secured in position by a respective socket screw. The drive shaft 36 is held by attachment members 38 and is freely moveable therein. The attachment members 38 are connected to a cylindrical support 39 which extends along a rear edge of the frame 16 at approximately the level of the platform 22. The drive shaft 36 is also secured in position by a second pair of attachment members 35 which extend upwardly from a cylindrical support 37 which embraces the wheel axle 28. The attachment members 35 are received in a sleeve 33 which, in turn, rotatably mounted on the drive shaft 36. A socket screw secures each attachment member 35 within its respective sleeve 33 and permits adjustment of the length of the attachment members 35.

In FIG 1 the driven cog 34 is engaged with the larger drive cog 30. To adjust the position of the driven cog 34, the socket screws retaining the cogs 34 on the drive shaft 36 and the screws holding the attachment members 35 in the sleeve 33 are loosened allowing the cogs 34 to be moved inwardly along the drive shaft 36 and to engage the smaller cog 32. The screws are re-tightened and the unit 10 is ready for use. Thus, adjustment of the unit 10 between the two operating positions is achieved easily and quickly.

The drive shaft 36 has a crank 40 therein, a piston rod 42 of the pump 20 being attached to the underside of the crank 40. The pump 20 is therefore mounted generally transversely of the axle 28 and drive shaft 36. Moreover, the pump 20 is mounted so as to be positioned beneath the platform 22 and to be generally inclined such that when the spraying unit 10 is being transported, the pump 20 will rest approximately horizontally. Advantageously, the positioning of the pump 20 allows a high ground clearance to be maintained at all times, thereby easing the movement of the unit 10 over difficult or undulating ground.

Turning to Figure 2, as is shown the pump 20 is a double acting pump and has an inlet 44 located at the front of the spraying unit 10, the inlet end 44 being attached by a flexible tubing 46 to the vessel 12. Similarly, an outlet 48 of the pump 20 located at the rearmost end of the pump has a flexible tubing 50 attached thereto, the tubing 50 also being in fluid communication with the vessel 12.

The vessel 12 is divided into two separate portions. A larger portion includes a filler tank 52 to which the inlet 44 of the pump 20 is attached. The attachment is made through an aperture 54 in the base of the tank 12. A further portion of the tank 12 serves as an accumulator 56, the outlet of the pump 20 being connected to the accumulator 56. The location of the accumulator 56 within in the vessel 12 is depicted in dotted lines in Figure 1.

The effect of the pump 20 is therefore to take liquid stored in the filler tank 52 through the pump and to the accumulator 56, the compressed air space above the liquid in the accumulator 56 serving to pressurise this portion of the vessel 12. The spraying outlet 14 is connected by an aperture 58 to the accumulator 56. The general fluid flow in the spraying unit 10 in use is shown by a series of arrows in Figure 2.

To prevent any build up of overpressure in the accumulator 56 an adjustable pressure release mechanism 60 allows access fluid to be transferred back from the accumulator 56 to the filler tank 52. The vessel 12 is further supplied with uppermost openings 62 and 64 which allow liquid to be added to both the filler tank 52 and the accumulator 56 and for the flushing of the filler tank and the accumulator after use.

The connection of the pump 20 to the cogs 30 or 32 therefore allows the operation of the spraying unit 10 to be adjustable between first and second modes, being modes including a high rate of pressurisation or a low rate of pressurisation of the accumulator 56. The position of the driven cogs 34 and the drive cogs 30, 32 in the respective high rate of pressurisation and low rate of pressurisation modes is shown in Figures 3a and 3b.

In the first mode, the driven cogs 34 are attached to the larger outermost drive cogs 30, such that as the wheels 18 move over a ground surface the rate of the pumping of the pump 20, and therefore the rate of pressurisation of the accumulator 56 is relatively high for any given rate of rotation of the wheels 18. In the second, or low rate of pressurisation mode, the driven cogs 34 are attached to the smaller innermost drive cogs 32, the rate of pressurisation of the accumulator 56 being lower for any given rate of rotation of the wheels 18. Importantly, however, in the second position, shown in FIG 3b, greater leverage is obtained from the wheels and the maximum pressure that can be developed in the accumulator 56 is higher than the pressure available from the position shown in FIG 3a.

Thus, in use, where it is desired to spray a large ground area it is convenient to have the unit adjusted such that a high rate of pressurisation can be achieved. Therefore with only a minimum movement of the unit 10 pressurisation can be maintained to such that continuous spraying is possible. For example if the operator of the unit is in a stationary position the unit can be rocked back and forth to enable the accumulator 56 to be continuously pressurised sufficient to maintain an appropriate spraying pressure. Conversely, where a lower rate of pressurisation is acceptable, although a higher spraying pressure may be required, because of a greater travel of the unit, the driven cogs 34 can be attached to the innermost cogs 32. Thus where an operator desires to spray at a higher pressure but on a more intermittent basis this mode of operation is preferable.

The pressure available from the unit 10 of the present invention is dependent on a number of factors, including the weight of the unit and any liquid contained in the unit, the width and radius of the ground wheels 18, the radius of the respective drive cogs 30,32 and the driven cogs 34, the length of the crank 40.

In one particular example of the present invention the following conditions have been used:

Carrying capacity 40L

Weight of unit (including 4L of liquid) 22 Kg

Ground Wheel -width: 40 mm

-radius 153 mm

Drive Cog Radius 110 mm Driven Cog Radius 55 mm

Length of crank 55 mm

Liquid transferred per revolution of ground wheel 43 ml

Pressure Generated 960 KPa

A second embodiment of the present invention, in the form of a spraying unit 100 is illustrated in Figure 4. The spraying unit 100 includes a vessel 102 the vessel 102 having a spraying outlet 104 extending therefrom. The vessel 102 is mounted on a frame 106 located below which are a pair of ground engaging wheels 108. A pump, 110 of the single action type is attached to a crank 112 found in the axle connecting the wheels 108.

The vessel 102 is an undivided vessel having liquid contained therein and an air space located above the liquid. The pump 110 is a single acting pump and is connected so as to be able to pressurise the air space above the liquid in the vessel 102. A flexible connection 115 connects an outlet end of the pump 110 to the vessel 102.

A piston rod 114 of the pump 110 is mounted so as to be freely moveable over the crank 112, the piston rod 114 having a collar 113 at one end thereof, the crank 112 being inserted through the collar 113

Furthermore, the crank 112 is of adjustable length being moveable between a number of positions by adjusting the crank between apertures 116 in the side members of the crank. Thus, the length of stroke of the piston 114, is adjustable, thereby allowing an adjustment to be made to the rate of pressurisation of the vessel 102.

Therefore, the spraying unit 100, as with the spraying unit 10, allows operation in both forwards and backwards motion, and allows an adjustment between modes in which the unit is operated at high or low rates of pressurisation. As with the unit 10, the maximum pressure obtainable from the unit 100 varies with the selection of high or low pressurisation rate. A pressure relief valve 117 allows adjustment of the maximum pressure preventing an excessively high pressure developing in the vessel 102 and the locking of the wheels. A further example of a spraying unit in accordance with the present invention is disclosed in Figure 5. In this Figure the spraying unit 120 includes a vessel 122 attached to a frame 124 having a pair of ground engaging wheels 126 attached thereto. The pressurisation means in the form of a pair of double acting pumps 128 are attached to the unit 120 by virtue of a connection to each of the ground engaging wheels 126. The pumps 128 are arranged such that the outlets of the pumps are in fluid communication with an accumulator 130 located within the vessel 122, the liquid being drawn from a surrounding filler tank portion 132 . The liquid is drawn from the underside of the vessel 122 and being distributed through flexible connections 134 to the inlet end of the pumps 128. The connection of the pumps 128 to the wheels 126 of the unit 120 is adjustable so as to allow a variation in the rate of pressurisation. This is achieved by having the length of stroke of the pumps connectable to different positions 136 on a radius of the wheel. As with the unit 10 and the unit 100, there is provided an adjustable pressure relief valve 138 in the vessel which allows the maximum permissible pressure in the accumulator to be controlled.

Thus, as with the embodiment shown in Figures 1 and 4, the rate of pressurisation of the vessel with respect to any given rate of travel of the vessel over a ground surface is readily adjustable. Moreover, the unit is capable of pressurisation moving in both forwards and backwards directions.

Modification and variations of the present invention such as would be apparent to a skilled addressee are deemed to be within the scope of the present invention. Thus, for example, the unit of the present invention has been described with reference to various two-wheeled examples of the invention, it is not beyond the scope of the invention for embodiments having four or more wheels to be contemplated. In the case of spraying units having four or more wheels, it is possible for the units to be attached to other devices such as lawn mowing devices. A unit having four or more wheels could also have a greater carrying capacity than a two wheeled version. The examples described are for the purpose of illustration only and are not to be taken as limiting the scope of the invention.

Claims

CLAIMS:

1. A spraying unit, the unit being characterised by:

a vessel adapted to hold liquid to be sprayed, the vessel having a spraying outlet in fluid communication with the interior of the vessel; - transport means adapted to support the vessel, the transport means having one or more ground engaging wheels attached thereto; pressurisation means adapted to pressurise the vessel, the pressurisation means being operable in response to rotation of the ground engaging wheels in any direction over a ground surface to thereby pressurise the interior of the vessel; and wherein the rate of pressurisation of the vessel by the pressurisation means is adjustable with respect to any given rate of travel of the ground engaging wheels over a ground surface.

2. A spraying unit according to claim 1 , characterised in that the unit is adjustable between first and second modes which have high and low pressurisation rates respectively, the maximum pressure obtainable in the vessel being higher at a lower pressurisation rate.

3. A spraying unit according to claim 1 or claim 2, characterised in that the pressurisation means of the unit of the present invention comprises one or more single acting or double acting pumps.

4. A spraying unit according to any one of the preceding claims, characterised in that the pressurisation means is connected to the ground engaging wheels via a cog system in which a plurality of differently sized drive cogs are arranged co-axial ly with the ground engaging wheels, and wherein one or more reciprocating pumps are driven from the drive cogs through a crank arm arrangement.

5. A spraying unit according to claim 4, characterised in that the connection between the pump or pumps and the drive cogs takes the form of a respective driven cog to be associated with a respective drive cog, the driven cogs being attached to a drive shaft arranged parallel to the wheel axle, whereby rotation of the ground engaging wheels and the associated drive cogs on the wheel axle thereby results in a corresponding rotation of the driven cogs and the drive shaft, rotation of the drive shaft, in turn, leading to reciprocation of the pump or pump shafts and a resulting pressurisation of the vessel.

6. A spraying unit according to any one of the claims 1-3, characterised in that the pressurisation means is connected to the transport means via a crank formed in the wheel axle, the crank being of adjustable length, the pressurisation means comprising one or more pumps, whereby by adjustment of the length of the crank, the length of stroke of the pump, and therefore the rate of pressurisation with respect to any given rate of travel of the wheels over the ground may be varied.

7. A spraying unit according to any one of claims 1-3, characterised in that the pressurisation means is connected to the transport means by connecting a pump to a cam arm directly to a wheel of the unit, the pressurisation can be effected, whereby by varying the point of connection of the cam arm between the centre and the circumference of the wheel the length of stroke of the pump, and therefore the rate of pressurisation with respect to any given rate of travel of the wheels over the ground may be varied.

8. A spraying unit according to any one of the preceding claims, characterised in that pressurisation of the vessel may be effected by either direct pressurisation of the air space above the liquid in the vessel, through the pumping of air into the vessel, or alternatively, by pumping liquid from a filler tank to an accumulator, thereby using the liquid in the accumulator to pressurise the air space above the liquid in the accumulator.

9. A spraying unit according to any one of the preceding claims, characterised in that the vessel further comprises a mechanism which governs the development of any over pressure in the vessel. AMENDED CLAIMS

[received by the International Bureau on 22 February 1996 (22.02.96) ; original claims 1-9 replaced by amended claims 1 -10 (2 pages) ]

1. A liquid spraying unit adapted for manual propulsion, the unit being characterised by:

a vessel adapted to hold liquid to be sprayed, the vessel having a spraying outlet in fluid communication with the interior of the vessel; transport means adapted to support the vessel, the transport means having one or more ground engaging wheels attached thereto; pressurisation means adapted to pressurise the vessel, the pressurisation means being operable in response to rotation of the ground engaging wheels in any direction over a ground surface to thereby pressurise the interior of the vessel; and the unit being adapted for spraying whilst moving or stationary.

2. A liquid spraying unit according to claim 1 , characterised in that the rate of pressurisation in the vessel by the pressurisation means is adjustable with respect to any given rate of travel of the ground engaging wheels over a ground surface.

3. A liquid spraying unit according to claim 2, characterised in that the unit is adjustable between first and second modes which have high and low pressurisation rates respectively, the maximum pressure obtainable in the vessel being higher at a lower pressurisation rate.

4. A liquid spraying unit according to claim 1 , characterised in that the pressurisation means of the unit of the present invention comprises one or more single acting or double acting pumps.

5. A liquid spraying unit according to any one of the preceding claims, characterised in that the pressurisation means is connected to the ground engaging wheels via a cog wheel system in which one or more pairs of differently sized drive cog-wheels are arranged co-axially with the ground engaging wheels, and wherein one or more reciprocating pumps are driven from the drive cog-wheels through a crank arm arrangement.

6. A liquid spraying unit according to claim 5, characterised in that the connection between the pump or pumps and the drive cog-wheels takes the form of a respective driven cog-wheel to be associated with a respective drive cog-wheel, the driven cog-wheels being attached to a drive shaft arranged parallel to the wheel axle, whereby rotation of the ground engaging wheels and the associated drive cog-wheels on the wheel axle thereby results in a corresponding rotation of the driven cog-wheels and the drive shaft, rotation of the drive shaft, in turn, leading to reciprocation of the pump or pump shafts and a resulting pressurisation of the vessel.

7. A liquid spraying unit according to any one of the claims 1-4, characterised in that the pressurisation means is connected to the transport means via a crank formed in the wheel axle, the crank being of adjustable length, the pressurisation means comprising one or more pumps, whereby by adjustment of the length of the crank, the length of stroke of the pump, and therefore the rate of pressurisation with respect to any given rate of travel of the wheels over the ground may be varied.

8. A liquid spraying unit according to any one of claims 1-4, characterised in that the pressurisation means is connected to the transport means by connecting a pump to a cam arm directly to a wheel of the unit, the pressurisation can be effected, whereby by varying the point of connection of the cam arm between the centre and the circumference of the wheel the length of stroke of the pump, and therefore the rate of pressurisation with respect to any given rate of travel of the wheels over the ground may be varied.

9. A liquid spraying unit according to any one of the preceding claims, characterised in that pressurisation of the vessel may be effected by either direct pressurisation of the air space above the liquid in the vessel, through the pumping of air into the vessel, or alternatively, by pumping liquid from a filler tank to an accumulator, thereby using the liquid in the accumulator to pressurise the air space above the liquid in the accumulator.

10. A liquid spraying unit according to any one of the preceding claims, characterised in that the vessel further comprises a mechanism which governs the development of any over pressure in the vessel.