Auto-levelling vehicle trailers are a great idea, so long as the driver
the consequences of not doing so can be anything from ripped check-straps
to chassis weld failure! However, thanks to a new joint development, that
momentary lapse of driver concentration is no longer a problem
Vehicle trailers that utilise air suspension systems are capable of
pneumatically raising or lowering the trailer deck height to match that
of a loading/unloading bay - a feature that is particularly useful if
wheeled or tracked handling equipment is used in the loading operation.
Hitherto, manual raise/lower valves, which act directly on the air
springs, bypassing the vehicle's levelling valve, have been the norm in
this type of application; however, they have one major drawback - they
are not foolproof. If the driver forgets to reset this manual valve,
allowing the levelling valve to resume control over the suspension before
driving off, he could be looking at anything up to £1,000 worth of
damage! The sort of problems that arise as a result of this simple lapse
of concentration include damage to shock absorbers and shock absorber
attachments, ripped off check straps and damaged bump stops, ruptured air
springs and even damage to the welds attaching the air suspension to the
chassis. These problems were very much the concern of the design team at
heavy vehicle brake and suspension system specialist, Meritor HVS, which
has successfully brought to market a device that automatically resets if
the driver forgets to do so before driving off. This is Levelride II, an
IP66 sealed unit, with simple 'raise', 'lower' and 'reset' pushbutton
controls, that is installed in-line between the levelling valve and the
air springs. The thing that separates Levelride II from its manual
counterparts, however, is the automatic reset, initiated by the slightest
depression of the vehicle's brake pedal. Levelride II is a joint
development of Meritor and Parker Pneumatic (a division of Parker
Hannifin). The original product marketed by Meritor involved a cabinet
style enclosure housing around 14 valves and all the associated pipe
work; Parker's brief was to translate this into a single, compact
multifunctional unit that would be lightweight and effectively sealed
against the hostile environment of a trailer's underbelly. The final
design solution is a single compact, flange-mounting plastic valve
(pictured), replicating the function of five separate pneumatic valves,
with two of the valve functions sharing a common spool as an additional
space-saving measure. Three of these valves provide the main raise/lower
functions, while the remaining two are for the all-important manual and
automatic reset functions. Push-in fittings (10mm) are used throughout to
simplify installation. The choice of auto-reset actuation - pneumatic or
electric - was largely governed by the need to avoid 'notifiable
alteration' regulations. Breaking into the brake service line would have
affected the brake system response and such an installation would
certainly have come under these regulations. Instead, an electric signal,
taken from the brake rear warning light circuit, is used to activate the
auto-reset valve and a special low wattage solenoid is deployed to
minimise the current drain on this circuit. Parker Pneumatic project
engineers, Rod Blackshaw and Tony Gem drew on the company's Europe-wide
expertise to fulfil the needs of this project, with main spool technology
coming out of Parker's operation in Sweden, and the reset solenoid,
manual reset valve and push-in fittings all sourced from separate Parker
plants in France.
If you'd like more information on Levelride II, which can also be
retrofitted to existing vehicle suspension systems with an appropriate
kit of parts, call Meritor on 01978 852141