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Dump air then tip, warns SAF
Page 5
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• German axle manufacturer SAF has issued a warning to any tipper operator using a trailer with it's air suspended running gear to dump the air out of the suspension before tipping.
The "operating recommendation" follows recent tipper safety trials involving three major trailer manufacturers competing for the Lafarge contract (see Vehicle Sews. p16-17).
The bulletin, issued via Its UK distributor IMS, says the practice "._ofters a greater stability and also, lowering the trailer lowers the centre of gravity". It adds: 'if air is retained, and the tipped body is tilted, the airbag on the 'unladen' side acts downwards, pressing the tyre to the ground. This causes an equal reaction at the ground which magnifies the tilt effect. When 'fast discharge' loads like barley are tipped without releasing the air, the leveling valve can't exhaust the air from the inflated airbags quickly enough. the stored energy is released quickly and 'bounces' the trailer up. This is not only potentially very dangerous, but can damage shock absorbers, air bags and body fittings.
"The ideal design combination is a valve which is activated when the ram is operated. This valve automatically exhausts air from the suspension to coincide with the ram lifting. it is acceptable to operate the tipper at up to 20 km/h on reasonably level surfaces leg in combination with road pavers] in this condition."
The bulletin is likely to further stoke the controversy over what constitutes "normal practice" among operators when discharging loads.
But Andrew Smith, director of Stas Trailers' UK importer Newton Commercials, has welcomed the bulletin. "It is SAFs recommendation that tipping trailers should be tipped with the air dumped—no ifs and buts."
He adds that SAF has plenty of test data on its air suspension and stability to underpin the recommendation. If anyone wants to contradict the SAF recommendation we would like to see their research data."