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TANKERS for LIQUID LOADS
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of Many Kinds
A Survey of an Interesting Topic With Special Reference to Types of Tank and Methods of Insulation
Which are EmPloyed
UNTIL the advent of the motor tank wagon the conveyance of many classes of liquid was an irksome and sometimes difficult task, involving the use of numerous forms of container, such as carboys, vats, churns, casks, etc., which, by reason of their weight, reduced the volume of liquid it was possible to transport in a single load. Originally introduced for dealing, in the main, with motor spirit and oils,
such machines have advanced in favour to such an extent that they are now used for dealing in bulk with a wide range of other commodities including milk, beer, acids, syrups, rubber latex, bitumen, etc.
The nature of the load and its weight have a bearing on the class of tank chosen, and both steel and aluminium patterns are widely used, whilst for certain liquids tanks of malleable nickel are employed. For milk transport tanks
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of aluminium sometimes have an outer casing of steel. Their capacities range from a few hundred gallons to 3,500 gallons, the largest units often . being divided into a series of compartments or having internal baffles to overcome the effects of surging of the liquid during transit.
In many cases the tanks are glasslined, but, although this is a generally understood trade term, it is not a strictly accurate description. It is true that the interior surface presents a hard and glossy appearance, but this is brought about by applying coats of vitreous enamel and then fusing in high
temperature furnaces. Steel tanks of this kind, which are made by the Glass Lined Steel Tank Co., 19,. Southampton Buildings, London, W.0.2, are easily kept clean and are durable, non-porous and non-flaking.
Special linings have to be used when corrosive liquids are being dealt with. For instance, when carrying diluted sulphuric acid a lead lining is used, whilst ebonite is necessary for hydrochloric acid. Successful results have attended the employment of a soft rubber lining for tanks built for conveying tannic acid. Tanks for such special loads have been built by that old-established concern, Thompson Bros. (13ilston), Ltd., which has also constructed such vessels of stainless steel for the conveyance of milk and beer. Although a tank of this material is rather expensive it has a weight factor which contrasts rather strikingly with the average heavy glasslined vessel.
An . outstanding feature of the aluminium tank is its lightness and its weight is often less than half that of asteel tank of corresponding capacity. In this connection figures prepared by the Aluminium .Plant and Vessel Co., Ltd., Point Pleasant, Wandsworth, London, S.W.18, are deserving of mention. This cornpankgives us the, weight of a faur-corapartment steel tank of 1,500 gallons capacity as 1A. ton, whilst, the weigtt of a similar size tank' in alu
minium is 14 cwt. Incidentally this concern has devised a flexible form of mounting whin 'avoids the need for the use of heavy iron bearers and cradles.
Some tanks are supplied perfectly plain, but for the conveyance of certaiy liquids insulated vessels are used, f,n-anulated cork, slab cork, slag wool and asbestos being some of the materials upon which reliance is placed.
A new and patented form of insulating medium for road tankers, which is now attracting much attention, is Alfol, marketed by Alfol Insulation, Ltd., 216-218, Windsor House, Victoria Street, London, S.W.1. Itis claimed to be suitable for refrigeration purposes or for temperatures up.to 1,000 degrees Pahr., and consists of sheets of highly polished pure aluminium foil,,having-a thickness of only .007 mm. When being applied these sheets are lightly crumpled, an average of three layers to the inch being employed,, and only the ridges make contact at irregular intervals.
The weight per cubic foot of Alfol insulation is 3 oz., as against figures (approximate), _quoted by the company, of l lb. for granulated cork, 11 lb. for slab cork and 18 lb. for slag wool, so that Alfol has distinct claims to recognition on the score of weight saving. The maker claims that the heat-reflecting power of the bright metal surfaces, combined with the low conducltiviV of the separated air spaces between the layers of foil, prevent besot heat by radiation and convection. Moreover, the thinness of the insulation and the fact that the layers touch each other only at intervals renders practically negligible any loss of heat by conduction.
Heating or cooling coils are sometimes incorporated in the interior design of the tank when it is desired to maintain a steady temperature. In cases where heat is required the exhanst gases arc sometimes taken through the tank, and in the case of atonal wagons the boirer is used to provide the necessary steam. Brine is amot the cooling agents often employed.
When bundling in bulk containers liquids such as milk and beer it is desirable to avoid internal fittings which might accumulate a residue or conteminate the liquid being conveyed, but when handling, commodities such as motor spifthit, acid's, ink. etc, such considerations are not of great moment. How ever, it is •esSential not to introduce obstacles likely to impede the flow of the liquid when it is being discharged, especially if it be of a viscous character. Many such liquids involve the v se of special pumps and pipe lines.
Some tank wagons are filled by gravity and the contents discharged in a similar manner, whilst others incorporate an air compressor driven by the motive unit, either petrol or steam engine, for filling the tank and quickly discharging the load.
The arrangements made in this connection by Seammell Lorries, Ltd., 52-54, High Holborn, London, W.C.I, are worthy of special note, in view of the company's unique experience in tankwagon construction. This important concern has supplied six and eightwheeled tankers of the frameless variety for conveying all classes of liquid, and for easy handling of the load the Seammoll patent air compressor is employed. This is of the three-cylinder radial type and is bolted to the front cross-member of the tractor portion of the articulated vehicle, being driven direct by a clutch claw from the crankshaft.
The compressor is designed to work up to a pressure of 4.5 lb. per sq. in., and it can be employed Els a vacuum pump for filling the tank by suction. With hose of 3-in. section, a 3,000-gallon tank can. be emptied in 15 thinutes, whilst a direct lift up to 60 ft. can be dealt with.
A feature . of the compressed air method' is that the hose is completely cleared of the liquid, whilst the flow is steady and silent, the pulsation often set up by piston and rititary pump being absent.
Types of tank in general use vary in shape and size, some being .circular, others elliptical. some 1)-shaped, whilst a tapering form is favoured for others. Registered designs of tank are produced by W. P. Butterfield, Ltd., Shipley, the Steel Barrel Co., Ltd., of Uxbridge, and Thompson Bros. (Bilston), Ltd., of Bilston, amongst others. All types and makes of chassis are used as the bases of tank wagons and iow-loading models find particular favour because they enable the centre of gravity to be reduced, thus contributing to a well-balanced and symmetrical appearance.