Twin-engined sweepers face threat from environmental legislation

In a special contribution to LAWE's Millennium 2000 Preview Issue, Roger Hoadley, the founder and Managing Director of Scarab, sets out his view on the potential impact of Government legislation on the design of road sweepers.

Environmental legislation could bring about the demise of twin-engined sweepers. The effective subsidy of rebated red fuel will surely become an area for the UK Government to investigate, particularly if the income could help finance solutions for environmental issues elsewhere.

Any road suction sweeper requires engine power for propulsion, and for their brushes and vacuum fans. Machines in the 1960s had mechanical drive from the prop shaft. When the vehicle stopped so did the fan, and as it took several seconds to spin up to speed again, a long uncleaned strip was left each time the vehicle moved off.

The industry found the solution was a second, smaller engine to power brushes and fan, which require some 50-60bhp.

Lorry engines of the early 1970s did not have that much power to spare, so by 21 years ago, when I was working for Blaw Knox, there were half a dozen makes of sweeper, all using two engines. But engine efficiency had been increasing greatly, so that even a small lorry had enough power for the sweeping services.

Alternative solution
With the launch of the Scarab Major range we tackled the problem from another direction, using a Scarab hydrostatic drive to move the vehicles at low speeds so that the truck engine rpm could be maintained for fan brushes. Between sites the hydrostatic drive is disengaged and the truck driven in the normal way.

More recently came the Scarab Maxim, which uses the normal clutch and gearbox with a mechanical PTO for the fan, but still using the single chassis engine principle.

Maintaining Scarab's technical advances is the latest hydrostatic drive machine, the Scarab Monic, with infinitely variable road speed for city work.

Initial development has been based on an Isuzu chassis cab which is only two metres wide, saving 200mm over most 7.5 tonners. The engine drives a pump which supplies sweeper services and the hydraulic motor which replaces the gearbox and clutch.

I am convinced that any investigation into the use of rebated fuel will spell the end for the twin engine sweeper. Other advantages of the single engine include one tonne greater payload, and more space in the hopper, because you have no donkey engine, cooling system or extra diesel tank.

Meeting targets
The Scarab philosophy indeed translates directly the task that Government has set manufacturers to ensure that operators have available vehicles that are:

  • more fuel efficient
  • less polluting
  • quieter
  • less resource intensive
With exhaust emissions being the predominant source of air pollutants from road transport, and with the main thrust of measures being to cut down on pollution from vehicles directed to improving exhaust emission performance of new vehicles, it is surprising that the retention of 'auxiliary engines' has remained for so long. The setting by Government of mandatory vehicle emissions has only applied in principle to the 'chassis' and not to the total vehicle operation.

It is an important fact that the majority of road sweepers individually have more impact on local urban air quality as their operating pattern is focused on towns and cities.

Given that air quality problems are concentrated locally the case for operating 'single' engined sweepers is very strong, particularly when the units can be used predominantly in urban areas.

Scarab has established a complete range of truck-mounted road sweepers that have low environmental impact, particularly in respect of exhaust emissions, without any compromise in their roadsweeping performance.


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