Clean, green, sweeping machines

With the battle to prevent climate change heating up, Scarab Sweepers’ single-engine vehicles provide an efficient clean alternative for its customers

Scarab Sweepers pioneered the single-engine sweeper in the UK. While the technology is by no means a new innovation, single-engine sweepers are coming into focus as a more environmentally friendly vehicle than traditional double-engine sweepers.

The world is focusing more and more on environmental issues. The UK government aims to bring down CO2 and NOx emissions to safe levels. To do this, less efficient vehicles are in the firing line. Clean air zones to be introduced in Bath and Bristol and the expanded ULEZ in London will make it difficult and expensive for more polluting vehicles operating in city centres. It is likely that additional cities will bring similar policies into force in the near future.

Traditional road sweepers use one engine to power the vehicle and another engine to power the sweepers. Most dual-engine sweepers use modern, efficient diesel engines to run the vehicle, ensuring that they are compliant with the majority of road-worthiness legislation. However, the auxiliary ‘donkey’ engine is generally of a lower quality, producing far more pollution. The donkey engine is not covered by the same laws as the main engine, meaning it can operate in areas where a similar engine powering the vehicle would be banned. Furthermore, the donkey engine generally consumes more fuel than the vehicle engine, so it contributes far more CO2 and NOx than the sweeper’s main engine does.

Scarab Sweepers offers a range of single-engine road sweepers. These run both the vehicle and the sweeper from a single engine using Scarab’s hydrostatic drive system. This means that the road-standard main engine is running the sweeper, bringing down pollution and using less fuel overall. This potentially reduces the amount of unused hydrocarbons in the exhaust, the chemicals responsible for diesel engines’ characteristic smell.

FACTS spoke with Scarab Sweepers’ Domestic Sales & Aftersales Manager Andy Farley and Sales Support Manager Andy Duncan about the advantages of single engine sweepers and the company’s long-standing commitment to the environment and high standards for its vehicles.

“We attended a Transport for Scotland seminar where the message was the time to act is now,” Andrew Farley said. “We have this decade to make a difference. If we do not make any changes, then that is going to affect the climate.”


The hydrostatic drive system simplifies driving the vehicle. When placed in sweep mode, one pedal accelerates and reverses the vehicle. When neither pedal is in use, the transmission enters neutral.

The hydrostatic drive unit works in tandem with the conventional drivetrain and gearbox. The vehicle can be driven in conventional mode when in non-sweep mode. Once the vehicle has stopped, the hydrostatic drive unit can be activated.

This also gives the driver far greater control as the speed can be changed in far smaller increments. The hydrostatic system is also simpler and less prone to wear and tear, as there is no requirement to slow the vehicle by means of a clutch or brakes.

An automatic gearbox is also a solution on a twin-engine machine, but the hydrostatic system provides the benefits of an automatic gearbox, but without the additional cost.

Scarab has evolved the hydrostatic design, which it pioneered in the 1980s. These innovations and higher engineering standards not only have increased the sweepers’ reliability, but also increased their performance.

“Compared to what we had in the 80s, we have a much better engineered hydrostatic system,” Andy Farley said. “We have a stainless steel suction path, while the fan, the impeller, the screens, the hopper, they are all constructed at industry spec.”

Andy Duncan added: “The high speed fan has a 25-30% increase in suction. You do not need to upgrade the engine as it is a different gearbox that harnesses the hydraulic power and a differently designed fan that moves the air in a different way to provide such great suction.”

The two-engine model has been the long-standing favourite across many markets and operators. The majority of sweepers in service are currently twin-engine so the design is familiar to most operators and maintenance staff. But is a twin-engine the right choice today?

“If there is any concern from customers when changing from a twin engine to a hydrostatic, we have warranty and training packages to alleviate any anxiety that customers may have.”

Though, Andy Duncan noted that “it takes a couple of seconds to get into hydrostatic. To put the sweeper into hydrostatic mode, you have to stop to let the CAN bus read your road speed.”

Andrew Farley said that the environmental benefits of using hydrostatic make it worthwhile. “To activate the sweeper does means you initially have to stop, but please take five seconds to consider the environment and you will then be in hydrostatic drive, it’s as simple as that.”

The future

New technology is often touted as being key to preventing climate change. Electric vehicles are frequently promoted as the technology of the future. However, there are still doubts over whether the technology will be ready in the next two decades. Producing and transmitting enough electricity and creating efficient batteries are some of the problems that still need to be solved. In the meantime, refining existing fossil fuel technology can help meet demand up to and potentially beyond the 2035 deadline.

“Not everybody can afford an electric solution yet,” Andy Farley said. “A lot of people are saying that they are two or three years away from having municipal electric vehicles at an affordable price, if at all. Everybody is talking about what the manufacturers must produce, but nobody is talking about the infrastructure.”

Andy Duncan also noted that Scarab has “investigated the electric solution with a number of different service providers. At the moment there is no commercially available OEM chassis to build an electric sweeper.”

One promising fossil fuel technology currently on the horizon is using twin-cylinder two-stroke direct injection engines. “The efficiency of a two-stroke direct injection engine is basically double that of a four stroke because the four stroke has a wasted stroke for every power stroke. On a two stroke, you get power from every stroke,” Andy Duncan said.

“Fossil fuels are not dead. We will use them but we will use them a lot more efficiently. The internal combustion engine is not dead, but we will not be able to have the internal combustion engine in the form we have it today. We will still power the majority of our transport once the development is put into these engines. It would appear that the two-stroke direct injection engine is now on the test benches, providing significantly more efficient figures using synthetic fuels.” This is coupled with the benefits of using alternative fuels such as HVO and GTL.

Andy Farley added: “If this decade is a pivotal moment in our climate change crisis, then everybody has to evolve and change their buying behaviours. The government and the economy provide direction on everything that we do. However, we have to make small changes in the way that we buy things.

“If we think about right now, people cannot afford to buy electric – they cannot afford to buy something that is four times the price. An alternative is needed and the answer has been there for 30 years.”

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