Refrigerated Van Trailers Act as Mobile Storage Units
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SINCE an article was published in the January 13, 1956, issue of The Comtnercial Motor on the transport operations of Britain's largest butter blender and distributor, Adams Butter, Ltd:, Leek, Staffs, the company have developed a simple diesel-driven refrigerating system with automatic control and applied it to 40 insulated vans mounted on maximum-load, single-axle or four-in-line articulated trailers with a payload capacity of 124, tons. After a bulk consignment of butter has been loaded at one of the ports during the summer months, the refrigerating system may operate for several days with the trailer standing in the depot or at the 'Leek factory.
On a typical delivery to a wholesaler's warehouse it is continually in use for the entire run, and sometimes throughout the 24 hours.
Additional refrigeration of the load is often a prerequisite of the blending process, and, if immediate unloading of the bulk butter is not possible, the vehicle may be left on a parking site with the plant running for a relatively long period, to save the expense of transferring the load to a cold store. In both cases the trailer acts as a mobile storage unit.
. The first Adams-designed refrigerating plant to be installed in a trailer as standard equipment has given reliable service for over three years, and the highly favourable record of the system substantiates the claim that it affords increased efficiency at a reduced cost. In contrast to the carriage of, say, frozen foods, refrigeration can be applied to bulk consignments of butter without limit in the time available.
It is considered virtually impossible to reduce • the temperature of the load to such an extent that its condition is adversely affected, and in practice the lowest obtainable temperature is advantageous. Eliminating automatic control reduces the cost of the equipment and of maintenance, and provides a far more suitable and reliable system, without sacrificing efficiency.
Maximum summer temperature of the butter when loaded at a port is normally about 60 degrees F., and before unloading at the processing plant the temperature.is reduced to 40 to 45 degrees F., the normal minimum being 42 degrees F. Although the optimum temperature is 40 degrees F. the butter is acceptable at temperatures down to 33 degrees F. Continued refrigeration after delivery to the plant obviates the necessity to transfer to the cold room before the butter is processed, and greatly reduces handling costs as well as the static storage space required.
50 per cent. Saving on Cost
Fitted in a separate compartment at the front ot the trailer, the Adams refrigerating plant is of the evaporatorplate type, and its application has afforded a saving of more than 50 per cent. on first cost. Moreover, employing a diesel engine as the motive unit has reduced running costs by over two-thirds. The Halls compressor of the refrigerating plant is driven by a Lister single-cylinder air-cooled diesel developing 31 b.h.p., which runs on tax-free gas oil and consumes about half as much fuel as a comparable petrol engine. Power is transmitted through a three-way gearbox from which the condenser and air-circulition fans are also driven. The motive unit is equipped with an electric starter and . a flexible lead, which is plugged into a battery connection on the tractor or can be connected to a servicing trolley if the trailer is standing in the Leek depot.
After extensive experimental work with various forms of air circulation. and tests of evaporator plates in a number of positions, a system was produced which gives virtually uniform refrigeration of the entire load. Air is directed to ducting in the roof with four distribution outlets and is drawn back into the system from an inlet at the base of the front bulkhead. The evaporator plates are fitted to the sides
of the van close to the roof, and the distribution of cool air by the fan is thereby aided by natural convection.
A particular problem originally associated with the use of a diesel engine was to reduce noise to an acceptable level, operation of the plant throughout the night in vehicle parks near residential areas being sometimes necessary. An up-to-date type of intake silencer is fitted to the diesel engine and air is drawn from beneath the vehicle, which is facilitated by the absence of flooring. The refrigerating compartment is lined with acoustic material, and these measures have offset the noise disadvantage of the diesel_ Under construction for experimental application, a blower-coil type of refrigeration equipment should offer space and weight advantages compared with the plant in use. The equipment will be fitted with an automatic defrosting unit, which will employ exhaust gas, as the heating medium. This will also be driven by a Lister diesel engine.
The van bodies are insulated with Onazote, the thickness of the material in the floor and roof being 3 in., whilst a 2-in, layer is applied to the sides and rear door. BonaHack aluminium bodies are employed, timber linings and inserts being fitted at strategic points to reduce heat transfer to a minimum. The four-in-line trailers are of B.T.C. manufacture, whilst the single-axle trailers are Scammell vehicles, both types being equipped with fifth-wheel couplings.
Employing couplings of this type was a necessity, because of the location of the refrigerating system at the front of the vehicle, and it is significant that, operationally, the higher loading of the tractor's driving axle has been of great benefit to vehicles negotiating steep giadients in wintry weather. Effective axle loading has been increased from 5 tons to nearly 9 tons.
Multiple Shelf Sections As an aid to refrigerating efficiency, one of the bodies has been experimentally equipped with multiple shelf sections for the carriage Of hied butter, as distinct from the transport of butter in barrels. Made in the workshops, each shelf comprises back-to-back extruded light-alloy panels of top-hat section', and slides in -runners fitted to the sides of the body, the total extra weight of the shelves being less than 5 cwt. The boxes are' stacked three high on the floor of the vehicle and also on the shelves, and this allows air to circulate over the entire surface of the cases, apart from the bottom surfaces of those stacked on the floor. In addition to aiding air circulation, this practice obviates crushing of the lower boxes by a heavy imposed load when packeted butter is being delivered. • Easy removal of the shelves allows the vehicle to be employed for normal work
at short notice. • Technicians of the company are particularly interested in the potential of demountable bodies and have investigated the possible advantages of employing one of the established systems. None of the types available would, however, cater for the company's particular requirements, and a system has been planned with these in mind.
The first outfit to be employed will be based on a Dodge 8-ton rigid chassis, which will be used in conjunction with three bodies. These will be loaded and unloaded by means of a four-post static " expanding-type" installation equipped with hydraulic jacking units. Bodies will be handled in the depot after mounting on a works-modified trailer by a shunting tractor, which will also be used for other work. Because old vehicles will be used, the cost of the shunting tractor and trailers will' be negligible, and the trailer will occupy less space than the rigid lorry.
Looking further into the future, it is envisaged that two demountable 12-ft. bodies will be fitted to a maximum-load eight-wheeler for long-distance trunking runs, and that each body will be transferred to a 5-ton chassis for local delivery in the destination area, Refrigeration equipment of the design evolved for the 12+-ton trailers will be fitted to the bodies.
The 21 tractive units of the Leek fleet include II A.E.C. Mercurys and four A.E.C. Mandators, the remainder• comprising three Leylancis, one Albion and two Bedfords. Additional units are employed at the London and Grimsby docks.
Apart from a recently purchased A.E.C. Mammoth Major-eight-wheeled platform lorry, rigid vehicles comprise Bedford 7-tanners and Bedfords of 3-7-ton capacity, all of which are equipped with insulated light-alloy van bodies. Smaller vehicles include Standard 5-cwt. vans, which are mainly employed for the transport of materials and so on. Of the total of 70 trailers, 20 are of the standard 10-ton type and two are Boden tandem-axle maximum-load• vehicles, the latter being employed for the transport. of frozen butter. These are equipped with Hendrickson bogies with rubber suspension and have given extremely good service, particularly 'with regard to handling and suspension characteristics on the road, and reduced maintenance.
A workshop staff of 13 provide a 24-hr. maintenance service, and on average vehicles are washed down every other day in a special building, equipped with an Essex power-brush washer, which adjoins the refuelling bay.
At least two tractor-trailer outfits travel on M i in both directions every 24 hours on trunking runs to London, and the higher average speeds afforded by the motorway give valuable latitude with regard to the normal running schedule. Although the drivers report that they "often feel lonely" (mainly because most of the trunking vehicles travel at the same speed and there is very little overtaking), the reduction in journey time is welcomed. Motorway running has little effect on fuel consumption or on tyre wear, Michelin 1120 covers being fitted to all trunking vehicles operating on the London route.
A.E.C. Mandators are normally used on this route and are equipped with six-speed gearboxes with overdrive top gear, and it is considered that this transmission reduces fuel consumption and engine wear and tear, as well as improving conditions for the driver, by reducing the average r.p.m. of the power Unit.
Trunking vehicles normally cover 100,000 miles in a period of 13-14 months, and are withdrawn from service after completing around 200,000 miles. They are then completely overhauled in the workshops before being taken back into service to operate on shorter runs. The total mileage of a vehicle before replacement may exceed 500,000.