Aircraft expertise aids tank manufacturer
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Aluminium has won out in this field. How and why, Bill Brock learned at the Hawker Group's Gloster Saro works
ALUMINIUM, the most popular material employed in the construction of petroleum product tankers, gives a big payload advantage over the alternative of steel, For example with a maximum gvw of 32 tons, its specification can make a difference of between 300 to 400 gallons in payload.
Although it is initially more expensive, running costs soon swing the balance in favour of the lighter material.
As road petrol tankers are restricted in operation to a maximum payload of 30,000 litres (6,600gal), a figure very difficult to attain within existing weight limitations, every pound saved on the vehicle's unladen weight can be reflected in an increase in payload.
Gloster Saro, part of the Hawker Siddeley Group, emerged from the Gloster aircraft company in the early Sixties.
Bill Page is general manager of the road vehicle division, which occupies the factory which produced such aircraft as the Javelin all-weather fighter and the Meteor, and is now one of the principal manufacturers of petroleum road tankers.
Bill, whose background is in the tank building industry, joined GSL some 18 years ago bringing with him an element of road transport expertise with which he tempered the engineering practices of the aircraft industry to make them applicable to a commercial operation.
Today, the company, with two divisions, maintains the same high levels in design and construction. The road vehicle division incorporates the manufacture of tank transporters for petroleum-based products, aircraft refuellers and dispensers, also airfield fire-fighting vehicles ranging from the 28-ton 550bhp Javelin down to a six-wheel rapid intervention vehicle based on the Range Rover chassis.
Other products are heavy fabrications, which include housings for very large portable generators, of 30 megawatt capacity, and the construction and refurbishing of airbridges used to convey passengers from the airport terminal to the aircraft.
The lnsumat division concerns itself mainly with the production of thermal and acoustic insula tion for the aircraft, shipbuildil and other general commerc applications.
Home demands and milite sales account for about 30/501 cent of production; the r mainder goes for export around the world.
Of the 650 employees worki at the plant, 400 are engaged the road vehicle division, wh is able to accommodate build of 50 vehicles at any c time dependent upon their si and has an annual output cal city of between 250 and specialised vehicles.
Capitalising on stress analy techniques inherited from • aircraft industry, Gloster Si claims to provide maxim' strength with minimum wei, penalty. The semi-trailer wei, of five tonnes for a 30,000-1 tanker has recently been p duced and is said to have best payload performance the market.
Specification from custor to customer can vary greatly, all the major oil companies Texaco, Shell, BP and Essc operate Gloster Saro tank constructed to their own sp, fications.
Construction is carried out
Flow-line basis and pre-tooling !Ips to speed up assembly iile ensuring high quality.
The degree of tooling is norally determined by the size of I order. At the outset of each iild, all sheet, angle irons, and bes are cut to size and shape in le area. Sub-assemblies such hose reels, toolboxes and eter frames are also built in a parate assembly area, but the am n tank build begins with the iderframe, which is laid down d bolted to its assembly jig. This prevents distortion, as a thick bottom skin is tack
welded into place. Separate compartments are formed with the introduction of divisions. Baffles are added to restrict surging.
The top skin is fitted next, followed by the side skins and finally the end caps. Still only tack welded, the whole assembly is transferred to a turnover rig where welding is completed in the down-hand position.
Compartment size and position are determined by the customer's delivery pattern and governed by a maximum compartment capacity of 5,000 litres (1,100gal). GSL manufacturing techniques maintain a consistent volume control over indi vidual vessels. The capacity of a 30,000-litre tank will be accurate within 50 litres overall.
An alternative method used to construct smaller tanks, such as the ones just decri bed, is to weld each of the individual sections in the flat, then pass the completed skin through a programmed set of rollers which turn it into the required shape. Baffles, bulkheads and end plates are then added in the usual manner.
After welding has been completed, a water-pressure test certifies the vessel's soundness before it is passed on to the final fitting-out shop where it is mounted onto the vehicle chassis, or in the case of a semitrailer, matched to the running gear.
Following the fitting out of all ancillary equipment, each machine is prepared and functionally tested in a separate test house set apart from the main assembly areas. Kerosene is pumped through into the tank and the full operational sequence pursued.
Although petrol is always discharged under gravity, most road trankers purchased by oil companies are equipped with either a mechanical or hydraulically operated pump to accommodate the discharge of oils.
When the vehicle leaves the test house it goes immediately into the coach painting shop, after which it is available for service in the field.
At the time of my visit to Gloster, production was concentrated on a batch of airfield refuellers, part of an export order destined for the Middle East. These vehicles are designed to conform to both Ministry of Defence and NATO specifications, which require that the vehicle be able to be carried in three different types of transport aircraft and have a limited rough-terrain capability.
Mounted on a rigid 6x4 Leyland chassis and equipped with a self-priming centrifugal pump, the tank has a capacity of just 13,640 litres (3,000gal). But a further 20,500 litres (4,500gal) can be made available if used in conjunction with a drawbar trailer.