A HEAVY-DUTY MOBILE ROAD BREAKER.
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A Special Vehicle Built for Work in Connection with the Maintenance and Repair of Gas Service Mains.
ALMOST two years ago—to be precise, in our issue dated June 16th, 1925—we had an opportunity for describing at some length an emergency mobile road breaker which Dennis Bros., Ltd., of Guildford, had supplied to the South Metropolitan Gas Co. Some of our readers may recall that the basis of this special machine was the company's 2-ton chassis, and that its purpose was to transport expeditiously an emergency breakdown gang to any locality Where a leakage or other fault might have occurred in the gas system. The equipment of the machine was most comprehensive and included plant for obtaining the necessary air pressure for operating pneumatic road-breaking appliances in order to reveal a defect in the mains.
The service that a vehicle of this type can give is unquestionably an important one, and that the original machine has proved its merit is indicated by the fact that the company has recently acquired a similar Outfit, although the new machine is built on a much larger scale.
In the first place, the chassis used is the 6-ton Dennis long-wheelbase (15 ft. 10 ins.) model equipped with a Ctype engine developing 47 b.h.p. at 1,000 r.p.m. and capable of giving an output up to 70 b.h.p. The chassis itself is quite standard in all respects, the only modification madenecessary by the particular use to which the machine is put being in connection with the gearbox lid, which is of a special pattern. It carries two separate drives, these being controlled by two levers, which are marked A and B on one of the accompanying illustrations.
As this picture shows, both of these drives are enclosed and run in oil baths. An idle wheel, meshing with the third-speed secondary wheel, transmits power as required to two sliding wheels on shafts connected to the air and water pumps respectively. Each of the final drives is by inverted toothed chain of robust size, the shafts and wheels running on ball bearings.
Power is transmitted to the air compressor by depressing the clutch pedal and manipulating lever A. This is the more important unit and is located on the off side of thefl chassis immediately behind the driver's seat. The compressor itself is a Reavell D.S.A. 6 ins. by 4i ins, vertical, single-stage, two-cylindered pattern, which is water-jacketed. It delivers 85 cu. ft.. of free air per minute at 100-1b. pressure at 800 r.p,m. It is mounted on two steel channels which are fixed at right angles to the frame.
In order to secure efficient cooling, a large-capacity radiator is mounted on the near side of the transverse bearers. Air is forced through this component by a fan
driven through the medium of a Whittle belt from a pulley on a shaft carried on a sliding pinion. Circulation of the water is net dependent on the thermo-siphonic principle, as a sprocket mounted on an extension of the main compressor shaft drives, through the medium of a chain, the water pump, which can be seen in the illustration to which we have already referred.
The compressor is equipped with an unloading device, and this is connected to an air-controlled governor on the engine and regulated in such a manner that when the unloader takes effect the governor closes the butterfly, thus ensuring that the power unit merely ticks over. So soon as the air pressure falls, the governor again begins to operate and the engine is speeded up to its normal number of revolutions per minute.
The air receiver is squated at the rear of the frame and is provided with three delivery cocks, safety valve, two pressure gauges and drain cocks. One pressure gauge is situated at the end of the frame, whilst the other is conveniently located on the dashboard directly in front of the driving position: Another view of the compressor plant which we reproduce shows that on the near side is a water pump, the drive for this being controlled by the lever (B) already mentioned. This pump, which is capable of creating a vacuum, is used for removimb water from mains or flooded trenches. "When engaged on the former work, it will lift from a depth of 22 ft. through suction pipes, whilst flooded trenches can be emptied at the rate of 30-40 gallons per minute. It should be mentioned that the compressor and the water pump can be used simultaneously or independently, according to the requirements of the moment.
Special electrical equipment is employed on the machine. and this has been chosen to stand up to night work and rough usage. The dynamo is a large I2-volt machine, capable of an output of 25-27 amps., supplying a 60-amp. Nife accumulator. The wiring leads to six plug-in points, so that flood lamps can be brought into use. The head, side and tail lamps of the vehicle are also supplied from this electrical equipment.
A large locker at the front of the body encloses all the mechanism of the compressor equipment, but there is plenty of room to the rear of it for enabling gas-pipes 12 ft. 8 ins. long to be carried without the need for the tailboard being lowered. A canvas curtain having clips covers the opening at the front of the body above the driver's cab, so that in the event of extra long pipes having to be dealt with they may be carried without protruding beyond the rear of the body. The position of this curtain can be clearly seen in our illustration of the complete machine, which is reproduced on the previous page.
A large locker is provided at each side of the body in which picks, shovels and other tools and fittings, including electric flood lamps and paraffin hurricane lamps, can be carried, whilst no less than half a ton of additional tackle, such as trestles and poles, can be accommodated on the roof, which is specially strengthened for the purpose and boarded-in all round.