It is time for the municipal sector to examine the advantages of hydrostatic single engine sweepers, says Andrew Farley, Branch Manager (Domestic Sales & After Sales) at Scarab Sweepers.

Driving down emissions with the intention of combating climate change is one of the key prevailing issues of our time. In the municipal industry, these days the emphasis is on the use of greener fleet solutions, with electric vehicles and hydrogen power ostensibly at the forefront of the movement. Whilst many manufacturers are jumping on the bandwagon, do these kinds of vehicles really offer the solution in the short to medium term? Electrical power is still primarily generated via the burning of fossil fuels; whilst electric vehicles themselves may be carbon-neutral, carbon emissions are instead given off at the point of production at power plants. In addition, whilst hydrogen technology will likely be the long-term solution, as it stands today the safety concerns have not yet been sufficiently addressed.

The issue is even more complicated when it comes to truck-mounted road sweepers. Conventional twin-engine truck-mounted road sweepers may use a truck engine which has been manufactured to the latest emissions standards for the vehicle’s movement, but the power for the sweeping equipment comes from a secondary engine which is one or more stages behind the latest legislation. In effect, this means that the energy-rich sweeping function is emitting dirty air, far more than the truck itself which is after-treated. EN-15429 fuel tests show that the truck engine in a twin-engine vehicle consumes 2.55 litres of fuel per hour, when compliant with the latest emissions legislation. However, the sweeper engine consumes a significantly larger amount of 7.70 litres of fuel per hour. Together, this means total fuel consumption is a massive 10.25 litres per hour. Is there an alternative? The answer is yes.

Revolution on the roads

For 30 years, Kent-based Scarab Sweepers have provided the hydrostatic truck-mounted sweeper. This model utilises a hydrostatic gearbox positioned in the driveline of the truck, which harnesses the full extent of the truck engine’s power to drive both the vehicle itself and the sweeping equipment. This means only one, single engine which is accredited to the very latest emission standards is being used.

“Our company founder Rodger Hoadley was the driving force behind the development of the Scarab hydrostatic gearbox in the 1980s,” said Andrew Farley, Branch Manager (Domestic Sales & After Sales) at Scarab Sweepers. “He saw the opportunity to design a system using some of the available power from the truck engine to also power the sweeping equipment, thus enabling the ‘single engine’ sweeper concept.” Tests were initially carried out to prove the concept using a proprietary gearbox, but Scarab subsequently designed their own gearbox in-house to better enable fitment of the sweeping equipment and to allow fitment into vehicles of differing power and payload.

“The hydrostatic gearbox is fitted to the vehicle driveline using anti-vibration mounting to ensure a smooth driving experience,” explained Andy Duncan, Sales Support Manager. “This entails ‘splitting’ the propshaft on the truck and remanufacturing it in two pieces, fitting suitable joints to mate to the Scarab gearbox.

“When in ‘Normal Drive’ the gearbox drives straight through, meaning the truck can be driven between sites completely normally, with no effect whatsoever on the standard driveline. On-site, the vehicle is stopped, top gear is engaged, and the hydrostatic transmission is enabled. This shifts the gearbox into hydrostatic, transferring the power from the engine through a hydraulic pump and motor. This means that the vehicle can be driven from 0-20mph completely hydraulically, with no requirement for using the clutch or brake, as the hydraulic pressure ensures that when lifting off the throttle there is a braking effect. “When the driver has completed his sweeping, he can dip the clutch, disengage the hydrostatic and the vehicle will revert to normal status.”

Long list of benefits

Whilst the advantages are numerous, the two primary benefits of opting for a hydrostatic sweeper model are reduced emissions and fuel consumption. The same EN-15429 tests for a hydrostatic truck-mount, with the same performance as the twin-engine vehicle previously described, reveal a total fuel consumption of just 6.12 litres per hour at the latest emissions standard. “With just a single engine in operation at the optimum rev-range, the improvements in fuel consumption and emissions are vast,” said Andy Duncan. “But the benefits do not stop there.”

• Reduced servicing and maintenance The hydrostatic gearbox allows for a constant slow speed to be maintained without clutch slip or brake usage. This consequently leads to reduced clutch, brake and driveline wear. This extends component lifetime and subsequently minimises both vehicle downtime and repair costs. Moreover, the hydrostatic gearbox is a sealed system that simply needs an oil change at prescribed intervals – it does not require the servicing that a secondary engine does, nor does it have the complexity or likelihood of faults that can be experienced with an engine-driven solution.

•  An easier ride – There is no slipping of the clutch, dabbing of the brakes or feathering the throttle to maintain the optimum sweeping speed, which creates a more seamless driving experience for the operator. Furthermore, the hydrostatic sweeper model has its own cruise control meaning that the optimum sweeping speed is maintained automatically, without input from the driver.

•  Improved payload to water carrying and hopper capacity ratio – A traditional twin-engine sweeper has a large engine mounted directly behind the driver, meaning the water tank has to be fitted into the bottom of the hopper to enable wheelbase to be kept to a minimum. However, on the hydrostatic vehicle, the space that the secondary engine occupies is replaced by the water tank, meaning that as well as increased water capacity, the hopper can also have a larger volume with no increase in height, whilst remaining at the shortest wheelbase possible. This has the added advantage that the water capacity and payload capacity is spread more evenly across the vehicle’s axles, improving stability.

•  Keep it quiet – Cutting the engines from two to one in number turns operational volume down significantly. There is therefore no requirement for the integration of extra sound-deadening material, which saves on weight in comparison to a twin-engine vehicle.

Consider your options

Many municipal vehicle fleet operators in the UK are yet to adopt hydrostatic sweeper models – and it is about time they considered this solution, according to Andrew. “Most EU customers, particularly in France, will not buy sweepers with secondary engines,” said Andrew. “They are fully committed to hydrostatic and have been for some years.

“UK operators must ask themselves; will any twin-engine road sweeper be compliant with Clean Air or Ultra Low Emission Zones? Are they really committed to cutting emissions and being more environmentally friendly? Now is the time for local authorities and private contractors here in the UK to not just accept the standard and instead assess the myriad benefits of the hydrostatic gearbox. I can guarantee they will not be disappointed.”

For more information: 01622 831006 or