The present invention relates to vehicle-mounted dehumidifying apparatus, a method of dehumidifying a vehicle, a method of making a vehicle-mounted dehumidifying apparatus, and to a vehicle comprising dehumidifying apparatus.

Background to the invention

It is known to transport various cargos by road in enclosed containers or tankers. Such products can include foodstuffs and feedstuffs in the form of powders, such as flour, whey or milk powder, or other finely-divided form (e.g. sugar). Often the product is still warm (freshly-manufactured) when loaded into the container or tanker, and this tends to lead to the development of condensation inside the tanker. This causes several problems. Firstly, moisture can cause powdered products to clag together, making the product difficult to unload. Secondly, moisture encourages the growth of contaminating micro-organisms, especially yeasts and fungi.

Conventionally, the operators of such vehicles thoroughly clean the inside of the tanker or container, typically one day every two weeks or so, in order to remove residual product. However, this is uneconomic, as the vehicle has to be driven to a cleaning station, and is not usable whilst being cleaned. Further, costly energy- consuming processes are required to completely dry the interior of the tanker before it can be re-used. Accordingly, there is considerable demand for an improved solution to the problems caused by condensation inside such tankers.

Moisture can also cause problems in connection with the transport of non- foodstuff or feedstuff cargos. Examples include: wood chips for use as fuel - excessive moisture can permit or exacerbate the growth of mould in the container and/or on the product, in addition very damp chips tend to break up and are difficult to unload; cement powder - again excess moisture can cause clagging, making unloading problematic, and also has a detrimental effect on product quality; glass panels - condensation formed in transit can cause staining or streaking on panels which is unsightly and hard to remove; and steel rolls - moisture can cause tarnishing or rust, the automotive industry in particular will reject steel rolls if they have excessive tarnishing.

The present applicant initially conducted some trials with vehicle-mounted dehumidifying apparatus, which was powered by an integral generator, running from a diesel fuel supply taken from the vehicle. However such equipment was cumbersome and not satisfactory. The applicant therefore set out to devise improved equipment.

Summary of the Invention

In a first aspect the invention provides a dehumidifying apparatus, especially a desiccant-based dehumidifying apparatus, and even more especially a solid desiccant- based apparatus, adapted and configured to be mounted on a road-going vehicle having at least one battery and a cargo storage compartment, the dehumidifying apparatus, in use, supplying a flow of dehumidified air to the interior of the cargo storage compartment, wherein the dehumidifying apparatus is capable of running using, as a sole power source, an electrical power supply taken from the battery of the road-going vehicle.

In a second aspect, the invention provides a road-going vehicle in combination with the dehumidifying apparatus of the first aspect.

The dehumidifying apparatus conveniently comprises an energy-efficient dehumidifying unit, so as to be capable of running using the vehicle's batteries as a sole power source. Suitable dehumidifying units are commercially available components. For example, the applicant supplies the "M190Y Corn-Dry" and the Ml 20 dehumidifying units, but suitable units are available from other sources. These are solid desiccant-type dehumidifiers, with an integral fan and air filter.

Typically, the dehumidifying unit has an electrical power consumption of about 40-45 amps. This would rapidly drain the vehicle's batteries. Accordingly, the unit should normally only be operated in this way when the vehicle's engine is running to recharge the batteries. The apparatus preferably therefore has an automatic cut-out to switch off the dehumidifier unit before the batteries are drained below a predetermined threshold. It will be apparent from the foregoing that the dehumidifying apparatus being capable of running the vehicle's battery as a sole power source is intended to refer to the battery that is used to run the ignition system of the vehicle's engine, rather than some auxiliary battery that might conceivably be present to power some other systems in the vehicle.

Conveniently the cut-out is provided by an integral inverter present in the apparatus, which detects when the vehicle's battery capacity drops to an amount e.g. in the range of 17-25% capacity remaining, at which point it will shut-down the apparatus to prevent further drain on the vehicle's batteries.

A further preferred feature of the apparatus of the invention is a battery disconnect relay, which protects the apparatus if the vehicle engine is rapidly switched on and off.

Conventionally, solid desiccant-based dehumidifier units in the UK are adapted to run using a 50Hz 230 (± 10%>) volt ac supply, whilst the vehicle batteries give a 24 volt dc supply. Accordingly, the apparatus will preferably include an inverter/step-up transformer to convert the battery supply to a 230 volt ac supply suitable for the dehumidifier unit. In other countries, dehumidifier units may be adapted to run at other voltages (and/or frequencies), so equipment intended for supply outside the UK may be modified accordingly.

Another preferred feature is that the apparatus has an alternative mains feed inlet. Thus, for example, if the vehicle is parked, a mains electrical supply may be connected to the apparatus, so that the dehumidifier may be operated without leaving the vehicle's engine running. In addition, the alternative mains feed allows for the possibility of the apparatus, in some embodiments, being dismounted from the vehicle and used in a free standing mode, running off a mains electrical supply, to supply a flow of dehumidified air to objects or spaces other than the interior of the cargo storage compartment of the road vehicle. Conveniently the apparatus will be arranged such that, if a mains electrical supply is connected, the apparatus will automatically run using that as a power source in preference to the vehicle batteries.

As the apparatus of the invention will be primarily used on a road-going vehicle, it will be subjected to a considerable amount of vibration, at a range of frequencies and magnitude. It is necessary therefore that the apparatus is sufficiently robust not to be adversely affected to any significant extent by such vibration. In a preferred embodiment, the apparatus includes housing having a plurality of thicknesses or skins, which houses the dehumidifier unit. Advantageously the housing is double-skinned. Desirably the housing is formed from a synthetic plastics material, typically a mouldable material. Such materials are less dense than metal (and therefore do not significantly increase the fuel consumption of the vehicle), and the use of at least two layers confers sufficient strength and vibration-resistance. The housing may be formed by any convenient process (e.g. injection moulding, vacuum moulding) but the applicant has found that rotational moulding is especially desirable. This allows the housing to be formed with two or more layers or skins, whilst reducing to a minimum the surface area of contact between the two layers or skins, thereby conferring good isolation against vibration to the components inside the housing. Preferably a gap, (e.g. an air- filled gap, or optionally an insulation- filled gap) is provided between the two skins of the housing.

A particularly suitable material for the housing is polyethylene (PE), especially medium density polyethylene ("MDPE", which has a density in the range 0.926-0.940 gm/cm ³ ) and high density polyethylene ("HDPE", which has a density in the range 0.940 to 0.960 gm/cm ³ ). Particularly suitable materials are sold under the registered trade mark "REVOLVE" and are available from Matrix Polymers, Northampton, NN3 6AX, United Kingdom. The applicant has found that a gap of about 20-40mm, preferably about 30mm, between the inner and outer layers of the housing is suitable.

Advantageously the housing comprises at least two sub-units, which are readily separable and connectable. For example, the housing may comprise a base sub-unit and a lid sub-unit. Conveniently the two sub-units fit together with a snap-fit or push- fit connection. Alternatively or additionally over-centre latches or the like may be provided, although other securing or fastening means are of course possible. In one embodiment, the housing comprises a lid sub-unit which is releasably connected to a base sub-unit by pushing the lid in a downwards direction relative to the base sub-unit and may be secured by a plurality of nuts and bolts. A "lift-off lid of this or a similar type allows the lid to be removed from the apparatus whilst the base sub-unit is mounted on the vehicle. Having readily separable and connectable sub-units allows easy access to the interior of the housing to, for example, replace filters, repair electrical components, or service and maintain the dehumidifier unit.

In addition, or alternatively, a hinged hatch or other small closable opening in the housing may be provided to permit inspection of one or more components housed within the housing, (e.g. of a keypad on the dehumidifier unit).

The dehumidifying unit requires a source of air, and an air inlet is conveniently defined by the housing. On a road vehicle, the air entering the air inlet can be expected to contain both particulates and moisture (e.g. from fog, mist, precipitation and/or surface spray). Accordingly, it is desirable to provide the air inlet channel with at least one filter to remove coarse debris and particulates. The filter is advantageously located and retained in the housing by retaining portions created (e.g. projecting flanges which overlap with the edges of the filter) when the two sub-units of the housing are connected together, i.e. the two sub-units preferably co-operate to retain the filter in the desired position.

Preferably the air inlet channel formed in the housing follows a serpentine or sinuous path, to inhibit the ingress of particulates and droplets of moisture. Preferably a first part of the air inlet channel is generally upwards, so as to require droplets of moisture and particulates to move against gravitational attraction if they are to ingress further into the apparatus. Accordingly, the entrance to the air inlet channel is desirably on a lower portion of the apparatus, and the air inlet channel is inclined upwards (typically at an angle to the vertical), partially defined by one or more baffles formed on the inside of the housing.

In a preferred embodiment, there is an air intake filter located at or near the bottom of the air inlet channel. In this way, liquid (e.g. coalesced droplets of surface spray from the road) running back down the inclined surfaces of the air inlet channel will backwash the filter and tend to remove larger particulates (e.g. leaves, insects) which would otherwise tend to block the filter. The air intake filter is typically a grade G2 filter (according to European Standard EN 779:2002).

Conveniently at least one further filter is provided in the housing, through which the air must pass before entering the dehumidifying unit. The further filter(s) will preferably be finer than the air intake filter, to remove smaller particles. The further filter may typically comprise a G4 filter (according to EN 779:2002). A suitable filter is the "Intrepid V line" filter available from, for example, JASUN Envirocare PLC.

In preferred embodiments a further air filter may be provided as an integral component of the dehumidifying unit, such that there may be at least three air filters within the apparatus. The integral dehumidifying unit filter may typically comprise a G3 filter (according to EN 779:2002).

Another preferred feature of the housing is that the bottom surface thereof is not planar. Preferably the bottom surface is formed with one or more, (preferably a plurality) of downward projections such as legs, runners or ribs. Conveniently a moist air outlet from the dehumidifier unit passes through the bottom surface of the housing. In the preferred embodiment, if the apparatus is detached from a vehicle and used in free-standing mode, the downward projections or ribs on the bottom surface of the housing slightly raise the apparatus (e.g. by l-5cm) above the floor or other flat surface on which the projections are standing, such that the moist air outlet is not blocked by the flat surface and the unit will continue to operate effectively. The dehumidified air exiting the dehumidifier unit preferably exits the housing via a replaceable spigot. Desirably the spigot is located and retained in the housing by retaining portions, which preferably are formed by co-operation between two sub- units of the housing, in a similar manner to the retention of the air intake filter as described previously. Accordingly, opening the housing, e.g. by separating the two sub-units thereof, facilitates the insertion of a spigot with the desired dimensions, so that a variety of differently- sized spigots may be used with the apparatus, to fit any particular hose, pipe or the like which may be standard in the particular country, industry or the like. The spigot may conveniently be formed of steel or other metal where the apparatus is intended for use in heavy industrial settings. In other applications the spigot (and/or associated hose or tubing) may be formed from a synthetic plastics material.

The outlet end of the spigot is typically connected to a hose, pipe or other delivery tube, to deliver the dehumidified air to the interior of the cargo storage compartment. Advantageously the hose or pipe will comprise at least a portion which is flexible, to allow for movement of the housing relative to the cargo storage compartment (e.g. as when a 'tipper' vehicle discharges its load). In some embodiments the hose or piping may be formed of metal and welded or coupled in some other way to a metal spigot as aforesaid.

Preferably the apparatus will comprise a valve e.g. solenoid valve or the like, to regulate the flow of dehumidified air from the apparatus into the storage compartment of the vehicle. Desirably the valve will be closed when the apparatus is not actively supplying dehumidified air to the storage compartment, so as to reduce the risk of powder or other product carried in the storage compartment from backing up into the apparatus, which could damage the apparatus or at least inhibit the air flow from the apparatus.

Conveniently the storage compartment of the vehicle may also be modified to include an air outlet, and an associated outlet valve, to permit air to be purged from the storage compartment. It is conventional for such an outlet/valve to be present on many commercial cargo-carrying road vehicles, but the inventor has found that this may require upgrading to permit a higher rate of flow.

Some embodiments of the invention may additionally comprise a small pneumatic air bleed to the inlet and outlet valves. A short air burst before the inlet valves opens and after the outlet valve opens would blow the internal tanker pipe openings free of any powder contamination from the loading or unloading operation, which would keep the pipe free of product and enable optimal air flow rates to be maintained, and possibly reduce maintenance.

The applicant has appreciated that the apparatus of the invention can provide satisfactory results even if not run continuously. Thus, for example, once the storage compartment of the vehicle has been loaded with its normal volume of cargo there is a relatively small head-space (the "ullage") above the cargo within the storage compartment. Discontinuous running of the apparatus to purge the ullage space with dehumidified air is sufficient to keep the cargo dry and prevent clogging. As a result, it is possible to run the apparatus from the vehicle's batteries.

A typical embodiment of the invention produces dehumidified air at a rate of between about 130 and 200 m ³ /hr. The higher figure represents operation under optimal conditions: dust and the like can slightly restrict the outlet pipe and, over time, the filters can become blocked. A typical road tanker silo has a volume of 58 m ³ , so an empty storage compartment can be purged with dehumidified air (one full air change) in about 20 to 25 minutes. In a loaded tanker, the volume of air remaining (in the ullage space) is of course much less, and the ullage space can be purged within about 3-5 minutes.

A major risk area for growth of mould is around the lids of the filling points (usually in the roof or upper part of the storage compartment), since these parts do not present a smooth surface (so powder product can easily lodge in discontinuities and accumulate) and are exposed to air and prone to condensation. The high purge rate for a loaded vehicle is able to provide a lot of protection (in terms of moisture- prevention) to the lids of the filling points. Desirably, purging the ullage space can be commenced substantially immediately after loading, and can be accomplished, for a typical loaded lorry, within about 3-5 minutes.

In preferred embodiments the housing is sufficiently compact and lightweight that the apparatus can readily be retro-fitted to existing vehicles without requiring any significant modifications to the vehicle. The housing may conveniently be formed with a plurality of anchorage points and/or apertures at different locations, to facilitate attachment to different vehicles.

In a third aspect, the invention provides a method of making the apparatus of the first aspect, the method comprising the steps of assembling a dehumidifier unit in operable relationship with one or more additional components, the dehumidifier unit being housed within a housing.

In a fourth aspect, the invention provides a method of making a vehicle/dehumidifying apparatus combination in accordance with the second aspect of the invention, the method comprising the step of mounting a dehumidifying apparatus, in accordance with the first aspect of the invention, on a road-going vehicle having at least one battery and a cargo storage compartment. The method will typically further comprise the steps of making an electrical power supply connection, to supply electrical power from the vehicle's battery (or batteries) to the dehumidifying apparatus, and/or providing a fluidic connection (such as a hose, pipe, tube or the like) between a dehumidified air outlet from the dehumidifying apparatus and an air inlet to supply dehumidified air to the interior of the vehicle's cargo storage compartment.

In a fifth aspect, the invention provides a method of dehumidifying the cargo storage compartment of a cargo -transporting road vehicle, such as a bulk silo tanker, the method comprising the steps of operating a vehicle on the road with at least one battery and a cargo storage compartment, and causing (preferably intermittently) flow of dehumidified air into the cargo storage compartment using dehumidifying apparatus in accordance with the first aspect of the invention. Typically the supply of dehumidified air to the ullage space above a cargo in the cargo storage compartment, is commenced conveniently within 20 minutes, preferably within 10 minutes, most preferably within 5 minutes or substantially immediately after completing loading of the storage compartment with the cargo. Desirably the flow of dehumidified air is provided only when the vehicle's engine is running, so as not to drain the vehicle's battery or batteries, which battery or batteries, in normal operation, are the sole source of power to the dehumidifying apparatus.

In some embodiments of the various aspects of the invention, it may be desirable to provide for re-circulation of some or all of the dehumidified air from the vehicle cargo storage compartment back to the dehumidifying apparatus. This would increase efficiency substantially, by allowing much drier air to be circulated. It may also reduce power consumption. Such re-circulation of dehumidified air is not appropriate if the cargo carried by the vehicle is in powder or other finely-divided form, as the cargo would enter the apparatus and cause it to become blocked, clog filters etc. However, such embodiments are feasible, and may be especially desirable, where the cargo comprises relatively large solid articles such as sheets of glass or rolls of steel or the like. All that would be required is a fluid connection from the air outlet of the cargo storage compartment to the air path or air intake feeding into the dehumidifier unit.

However, in a preferred embodiment, the apparatus runs using substantially 100% fresh air supply i.e. substantially without recirculation of dehumidified air. As explained above, this embodiment is especially suitable for use with vehicles carrying cargo in powder or other finely-divided form. A typical example of such cargo might be flour. Another instance in which the apparatus of the invention running substantially without recirculation of dehumidified air would be advantageous is in the transport of bread especially sliced bread: supplying dehumidified fresh air to the cargo storage compartment, rather than recirculating dehumidified air, prevents the risk of over-drying the bread whilst still preventing the risk of condensation formation. For the avoidance of doubt it is hereby expressly stated that features described herein as "preferred", "advantageous", "desirable", "convenient" or the like may be present in the invention in isolation, or may be present in combination with any one or more other features so described, unless the context dictates otherwise. Furthermore, features described as "preferred", "advantageous", "desirable", "convenient" or the like in relation to one aspect of the invention will be understood to apply to the other aspects of the invention, mutatis mutandis, unless the context dictates otherwise.

The various features of the invention will now be described by way of illustrative embodiment, and with reference to the accompanying drawings, in which:

Figure 1 is a perspective view of the exterior of the housing of one embodiment of apparatus in accordance with the invention;

Figure 2A is a plan view (to a different scale) of the embodiment of Figure 1 with the lid of the housing removed, to show the interior;

Figure 2B is a perspective view of the lid part of the housing of the embodiment shown in the preceding figures;

Figure 3 is a perspective view (to a different scale) from beneath of the embodiment shown in Figures 1 and 2;

Figure 4 is a sectional view (to a different scale) of the housing of the embodiment shown in Figures 1-3;

Figure 5 is a bottom elevation of the housing of the embodiment;

Figure 6 is a detailed sectional view (to a different scale) of part of the housing shown in Figure 4;

Figure 7 is an end elevation of the embodiment shown in the preceding Figures; Figures 8 & 9 are electronics wiring diagrams to show the arrangement of the electrical components used in an embodiment of the invention; and

Figure 10 is a perspective view of a road going vehicle on which is mounted the embodiment of the apparatus shown in the preceding Figures.

Detailed Description of an Embodiment

Referring first to Figures 1 & 2, one embodiment of apparatus in accordance with the invention comprises a desiccant-based M190Y Corn-Dry dehumidifier unit 2, commercially available from the applicant. The dehumidifier unit 2 is contained with a rotationally-moulded MDPE housing 4. The housing comprises a base sub-unit 6 and a lid sub-unit 8. The base and lid sub-units fit together and are held by a plurality of nuts and bolts, and so can be readily separated to permit access to the interior of the housing 4 e.g. to service and maintain the dehumidifier unit 2. The housing has approximate dimensions of about 1075 mm length, by 440 mm depth, by 535 mm height.

Electrical power to the apparatus is supplied from the vehicle's batteries via a standard Anderson plug 54. An alternative mains supply can be provided to the apparatus via mains inlet feed 56.

As best seen in Figure 2 A, the housing 4 is double-skinned, having an outer layer 10 and inner layer 12. The double-skinned nature of the housing helps to isolate the components of the apparatus inside the housing from vibration, especially whilst the vehicle is in transit. An air gap of about 30mm is provided between the outer and inner layers.

The dehumidifier unit 2 is releasably secured to the base sub-unit 6 by means of a conventional luggage strap 14.

The housing additionally comprises a box 16, which contains most of the electrical components. The box 16 provides further protection to the electrical components, shielding them against vibration. In addition, the box 16, and other electrical components within the housing 4 in general, are raised up from the floor of the housing to reduce the likelihood of damage by water entering the housing. The electronics box 16 allows simple "plug and play" installation or removal of the dehumidifier unit 2. There is also an option to fit a pneumatic switch to control remotely external tanker air inlet and outlet valves - to permit this an air line may be fitted which enters and leaves the housing via a gland plate.

External ambient air enters the housing via an air intake, denoted generally in Figure 2A by reference numeral 18. The housing intake acts as a plenum chamber feeding the dehumidifier unit 2. The incoming air flow also provides forced ventilation for the main electronic components, keeping them cool. The forward motion of the vehicle helps force air into the intake, which faces the direction of travel (unless the vehicle is reversing).

It is however perfectly feasible to mount the apparatus in the opposite orientation i.e. with the air intake 18 facing the rear of the vehicle. The internal fan located in the dehumidifier unit is sufficiently powerful to draw in sufficient air, and the intake facing towards the rear has the advantage of providing greater protection against damage from debris or the like.

The air is dried by the dehumidifier unit 2 and the dehumidified air exits the housing 4 via steel spigot 20. The waste moist air generated by the dehumidifying unit is exhausted through right-angled elbow pipe 22 and exits the housing 4 on the underside, via outlet 24, as best seen in Figures 3 and 5. The underside of the housing is not planar, but is instead formed with four parallel ribs, 26 extending longitudinally along the bottom of the base sub-unit 6. The ribs 26 extend downwards beyond the rest of the bottom surface and serve to raise the outlet 24 above the floor when the apparatus is dismounted from a vehicle and being operated in free-standing mode. Accordingly, in such a mode of operation, the outlet 24 is not occluded, and the dehumidifier unit 2 can function properly.

Referring now to Figure 4, an air intake channel 30 is defined between the base sub- unit 6 and the lid 8. An upward-projecting portion 32 of the base 6 acts as a baffle, forcing the air to take a serpentine or sinuous path into the interior of the housing 4. An inlet air filter 34 is provided in the air intake channel 30, to remove coarse particulates from the air entering the housing. The filter is retained in place by retaining portions formed by co-operation between the base sub-unit 6 and the lid 8. Inlet air filter 34 is of rugged construction, formed of stainless steel mesh and rated G2 (according to European Standard EN 779:2002).

The co-operation between the lid and base sub-units forms a substantially air tight seal and defines the air path into and, at least partly, through the housing. An initial part of the air intake channel 30, in which the first filter is located, follows an upward path. Accordingly water from surface spray, or other origins, entering the housing will tend to run back down the surfaces of the housing defining the air intake channel, under the influence of gravity. In so doing the water will back-wash the first air filter, and so tend to remove debris from the filter (e.g. leaves, dead insects and the like) and so help keep the filter clear.

The air inlet filter 34 can also be seen in Figure 2B. It may be secured by a factional fit between two projecting fingers of the housing formed on the base sub-unit 6, and also by similar projecting fingers formed on the lid sub-unit 8.

A further, internal filter 36 is located downstream of air intake filter 34. The further filter 36 may be retained by factional fit with the sides of a slot formed in downwardly projecting portion 38 of the lid subunit and/or by a factional fit with the sides of a slot formed in the base sub-unit 6. The filter 36 is much finer than the air intake filter 34, and is a G4 rated (EN 779:2002) filter with a cardboard frame and a pleat type V line panel filter element, (available from Jasun Envirocare PLC, Bridgwater TA6 5LB, United Kingdom).

Also clearly seen in Figure 2B is the spigot 20 through which the dehumidified air exits the housing 4. The spigot 20 is formed with an integral flange plate 40, approximately mid way along the length of the spigot, and substantially at right angles to the bore thereof. The integral flange is held, at its upper end, by factional engagement between two downwardly projecting portions on the inside of the lid sub- unit 8. The flange 40 is similarly held, at its lower end, by factional engagement between two upwardly projecting portions on the inside of the base sub-unit 6.

Figure 6 shows a more detailed view of that part of the housing circled with a dotted line, labelled B, in Figure 4. Figure 6 shows the retention of the lower end of the flange 40 of the spigot 20 in the base sub-unit 6 of the housing.

Figure 8 shows a wiring diagram for a simple embodiment of the invention, in which the dehumidifier unit 2 is supplied with electrical power only from the batteries of the vehicle. In Figure 8, 'L', 'N' and Έ' are abbreviations respectively for live, neutral and earth. Some of the components and much of the wiring are shielded by a protective box 16 contained within the housing of the apparatus.

The components include a l,000W-rated 24 volt dc to 230/240 volt ac inverter 50, to convert the 24 volt dc supply from the vehicle's batteries to a 230 or 240 volt ac supply, at either 50 or 60 Hz suitable for the commercial dehumidifier 2. A battery disconnect relay, R2, (51) ensures the apparatus is disconnected from the battery if the power drops below a threshold level, e.g. as when the truck engine is started.

The relay R2 will drop out as soon as it detects any change in the supply voltage. This protects the inverter from tripping out due to low voltage. R2 will re-engage only when the 24v supply is at the correct level.

Another feature of R2 is that it handles the full load on the 24v supply (40-45 amps). It is also interfaced with the on/off switch so the switch can operate at a much lower dc current level, using thinner wiring and components, to reduce cost etc.

The inverter 50 has an integral cut-out which detects when the battery capacity drops (as noted previously) to protect the truck battery from being drained too far.

A standard "Anderson" plug 54 supplies electrical power to the apparatus from the vehicle batteries. The plug 54 is also shown in Figure 1. An option for a remote switch (not shown) is also provided, to allow the apparatus to be switched on or off from an instrument panel, typically located at the rear of the vehicle cargo storage compartment, where remote switches and controls for other items of equipment are conventionally located.

In addition, the embodiment illustrated in Figure 8 powers a 230v ac solenoid valve 58, which can open and close the air valve between the tanker storage compartment and the air outlet from the apparatus thus controlling the flow of dehumidified air from the apparatus into the storage compartment and, importantly, closing the valve when appropriate to prevent product from the storage compartment backing into the apparatus.

Figure 9 shows a wiring diagram for an alternative embodiment. The alternative embodiment is very similar to that illustrated in Figure 8, but is additionally able to run using an alternative power supply, such as an external electrical mains supply via mains inlet 56.

Coupling a mains supply to mains inlet 56 energises relay Rl (58), which closes the switches from the mains inlet 56 to the dehumidifier unit 2, and opens the switches between the inverter 50 and the dehumidifier unit, thus preventing power being drawn from the vehicle's batteries.

Apparatus fitted with the 240v mains feed option may advantageously be provided with an earthing stud on the facia plate for connection to the tank chassis.

The road vehicle of use in the various aspects of the invention is likely to be one in which the cargo storage compartment is metal-skinned, such as a tanker, especially a silo bulk tanker. Two such types of vehicle are known: tipper and belly-emptying. The tipper type discharges its load by tipping upwards, whilst the belly type discharges under gravity via vents in its belly. Both types may additionally employ compressed air to assist in discharging. The present applicant has found that, in addition to the various advantages of the invention, in overcoming the need for regular washing and drying of vehicles, and inhibiting the growth of spoilage organisms, the invention can significantly reduce the time required to unload cargo from the storage compartment, by reducing clogging and preserving the fluidity of the cargo.

Figure 10 is a perspective view of a vehicle of the type known as a road silo bulk tanker, to which is retro-fitted apparatus in accordance with the invention. The embodiment of the apparatus is the same as that illustrated in the previous figures. The housing is fitted below the silo and secured by nuts and bolts behind the vehicle's existing crash barriers. Dehumidified air is fed, from the steel spigot at the rear of the housing, via a short length of flexible hosing of 100mm diameter section. This hosing in turn is connected to an aluminium air supply pipe, which includes both a length of rigid pipe and a length of flexible pipe. The pipe (not shown) runs to an air inlet on the top of the silo and towards the 'cab' end thereof. A 100mm pneumatic solenoid valve controls the opening and closing of the air inlet into the silo.

This valve is closed when the apparatus is turned off to prevent the risk of product contamination or over-pressure as the tanker is filled, emptied or cleaned. Most tankers have a dump valve system which is used to release tank pressure and is left open in transit for safety reasons. This is typically a 50mm outlet with a small control valve. After tests this was found to be insufficient to allow enough dry air to pass through the ullage space or the empty tanker. Accordingly, a dedicated 100mm pneumatic solenoid outlet valve is used. This is closed when the apparatus is turned off and opened to allow an outlet path for the dry air stream. The outlet point would normally be at the opposite end to the inlet valve and be as near as possible to the top of the road silo tanker. (In this embodiment, the air outlet is at the top towards the rear of the silo).

The location of both valves is relevant to maximise the air flow and minimise the risk of contamination/blockage from transported product. The dry air is supplied at around 140-180m3/hr with an external pressure of 300 pascals. The air pipe size is also important to provide a minimum pressure drop so allowing a good airflow into the road tanker silo, increasing the moisture pick-up as the air passes through and will allow a faster pull down time during the running period. The extra velocity will encourage rapid mixing of the air in the tank with the dry inlet air. This will help to keep the relative humidity as low as possible.

The unrestricted dry airflow achieved in this embodiment means a typical empty silo tanker can be purged in 25 minutes or less and the small ullage space left in a fully loaded tanker will be purged much quicker. This means intermittent running (using vehicle battery power only) of the apparatus during normal delivery runs is sufficient to inhibit mould growth and help prevent product from clogging and sticking to the side of the tanker.

While it is running, the apparatus will replace the air in the tanker to maintain a dewpoint lower than the ambient temperature, thereby reducing the possibility of condensation on the inside of the tanker. When running it can remove between about 0.7 and 0.6 kg/hour of moisture, depending on the relative humidity in the tanker and the ambient relative humidity.