Electro-hydraulic Platform Offers Quicker Lamp Servicing
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DEVELOPED by the Midlands Electricity Board, Mucklow Hill. Halesowen, a new street-lamp servicing vehicle enables the man-hours for lamp servicing to be reduced by 40 per cent compared with the time taken when conventional vehicles are employed. The platform-elevating mechanism is of the telescopic-boom type with a number of novel features and of particular importance with regard to time-saving, the platform (or aerial workshop) is lockted adjacent to the one-man cab in the lowered position, the operator gaining access to it without leaving the vehicle. if necessary direct from the cab through a sliding door.
On a typical day's run the vehicle travels about 10 miles, and operations could include servicing 21 class-A lanterns at a height of 35 ft. and 28 class-B types at a height of 14ft. Insulation of the platform frame from the main structure provides a high safety factor.
The prototype vehicle is based on a standard Albion underfloor-engined Claymore 4-5-ton chassis having a wheelbase of 12 ft. 3 in., whilst the body is of aluminium construction with a plastics roof supplied by Holmes (Preston) Ltd. Simon Engineering (Dudley) Ltd., built the elevating gear.
The boom is mounted on a turntable above the rear axle and can slew through 1200. Battery-operated electric motors drive the three variable-output hydraulic swash-plate pumps which feed the rams of the stewing, elevating and boomextension mechanisms, d.c. current being supplied for charging by a Lucas-C.A.V. 24-v. alternator with an output of
60 amp. at tick-over Speed, all three pumps being operable simultaneously. The lead-acid batteries have a capacity of 232 amp.-hr. and are mounted behind the boom to act as a counter-weight.
Safety devices include limit-switch control of boom movements, which prevents contact with the vehicle body, and switches are incorporated in the footand hand-brake linkages which immobilize the boom unless both brakes arc applied, the foot brake remaining hydraulically locked by key operation. A spring-loaded "dead-man's foot" master button in the floor of the platform is connected hydraulically to a solenoid on the turntable which breaks the electrical circuits if pressure on the button is released. The need for stabilizing jacks is eliminated by fitting a torsion bar transversely in front of the rear axle.
Of 12-in. by 10-in, steel box section, the main boom has a length of 17 ft. 9 in.. whilst the telescopic member is of plastics construction and gives an extension of 7 ft, Connected to the various hydraul cally-operated solenoids of the operatic mechanisms by flexible nylon pipes, th master and slave actuators of the pla form control panel give infinitely-variabl speed control of both forward an reverse movements, the use of nylon pip( being of importance because, combine with the use of a boom extension r plastics material, they provide electric insulation from the main boom membe The platform is of rigid glass fibre wit steel reinforcing.
Theboom mechanism is designed t provide vertical angular movements ( 72° above the horizontal and 10° belov Underslung from the boom extension, th platform is automatically maintained i a level position by a closed hydrauli system. again using nylon tubes. All th hydraulic cylinders are equipped wit lock valves to prevent creep. Provisio is made for fitting a bleed valve t enable the boom to be lowered in th event of mechanical or electrical failure