There’s more to specifying specialist trucks than meets the eye05 January 2010

NMS Civil Engineering in Wigan, Lancashire, reports success with its first Volvo truck – an FH-480bhp tractor with sleeper cab, chassis-mounted Palfinger crane and integrated stability control (ISC) deployment system. The unit is in use on the motorway network in the North West, installing temporary barriers for road reconstruction, and NMS contracts director Peter Law says it's handling restricted access and uneven surfaces well.

Thomas Hardie Commercials supplied the Euro-4- 6x2 tractive unit, which is plated for 44 tonnes gcw and equipped with a tag axle, 14-speed gearbox and Volvo's EBS High electronic braking and stability control, under a five-year repair and maintenance contract. The crane, specified and fitted by TH White of Devizes, is a Palfinger PK42502c, with 12.1 metre reach and a lifting a capacity of 3,140kg at maximum radius. The truck replaced a MAN 6x4, plated at 80 tonne gcw, also equipped with a Palfinger, which, in its day, was also had to haul 38tonne road plating machines on oversize King trailers.

So much for the bare facts. Law explains that he specified the tag axle to maximise manoeuvrability and minimise the truck wheelbase, while the low sleeper cab meant the crane would also be able to reach across the front. He also wanted to improve mpg over NMS' earlier 6x4 tractor, because the new unit was required to work further afield round the motorway network. All of which is easy to request "but you need to be very careful," he adivses.

Why? "At 6.6 tonnes, you're talking about a big lump of crane, so you've got to watch the axle loadings. And, because of the tag axle, there were also concerns about where to site the fifth wheel to keep the weight on the drive axle, but still provide enough space for the crane, with clearance for the trailer swing. You've got to get everybody talking on a job like this."

In fact, TH White's technical department handled most of the engineering, liaising directly with Volvo in Sweden. THW's Doug Wright says the weight issue was easily solved, using a 9 tonne front axle and bolting on a bespoke twin-plate subframe, with all welded construction, spanning the width of the chassis, to carry the crane. However, the coupling was a different story.

"Normally, we fit this type of crane on a 6x4 tractor, but NMS wanted the tag axle, and that meant putting the coupling beyond the usual limit, behind the drive axle. So we did the usual calculations to prove overall vehicle stability and axle loadings, with and without the trailer] but then went back to Volvo for sign-off on the fifth wheel."

Beyond that, Wright explains that the crane had to be specified not only for operation over the cab and sides of the truck, but also with four hydraulic boom extensions to provide a reach capable of lifting materials off and onto the trailer. That, in turn, meant going for Palfinger's ISC (these systems are now mandatory under European legislation, as of 1 January), which senses the location of the crane's stabiliser legs and automatically de-rates the crane to prevent the operator from slewing the crane into an unstable situation and tipping the truck over.

Additionally, because the truck works mainly on motorways TH White fitted a 180/180/360 degree key switch slew interlock to prevent accidental movement of the crane into the live line of traffic. And Wright also specified swing-up legs in transit. "In this case, it wasn't a case of clearing chassis ancillaries, but to enable NMS to extend the stabiliser legs over a crash barrier, for example, to get full stability and so full capacity from the crane," he says.

Author
Brian Tinham

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