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For those who don't know, Dunlop produced full
air suspension systems for
several British commercial vehicle manufacturers, the most popular manufacturer
to use
Dunlop's full
air suspension kit was the Birmingham based LDV. These were
generally used on ambulances an public authority vehicles.
The
Dunlop system consists of a live axle supported on
air Dunlop springs,
these are inflated from an on board
compressor feeding a reservoir tank. The
system was then controlled from an electronic control unit (ECU) which took
information from an electronic height sensor linked between the chassis and the
axle. There are other inputs from brakes etc. for safety features. Naturally the
system maintained its own ride height, but was able to kneel when required for
easy loading.
Basic layout of the original Sherpa/LDV full air suspension system
Like all technical systems, the
Dunlop
air suspension system was great when
new. However we're a number of years down the road and some LDV's are feel their
age and don't warrant the expense to repair a failed system. The most expensive
item to fail and replace is the ECU system. Unfortunately Dunlop have not spares
stock available for this system. If anyone enquires for
spares with
Dunlop
Systems and Components in Coventry, they'll refer you to us at
Marcle Leisure as
we already handle a lot of their retro fit
air suspension systems for light
commercial vehicles and
motorhomes.
Marcle Leisure does have the where with all to restore a failed ECU system
with a semi automatic system which will as before maintain a suitable ride
height, regardless of the load carried.
To move forward to a semi automatic system the airlines need to be change
around to accommodate new
pneumatic fittings such as a
height sensing valve
mounted on the chassis and linked down to the rear axle. The original
compressor
feeds the original reservoir tank via a
non return valve. The
compressor is fed
via a relay from the vehicles electrical system. The relay is activated via a
pressure switch on the reservoir tank and ignition switch, so the
compressor
will only run when the ignition switch is on. The
compressor runs until the
pressure reaches a certain cut-off pressure, then when the pressure drops to a
certain point and cuts in again. No driver interaction for the
compressor is
required. Compressed air is fed to the
height sensing valve on the rear axle via
a
flow restriction valve. From the
height sensing valve controlled compressed
air is fed to the
air springs (air bellows) supporting the chassis off the rear
axle. The
height sensing valve can also exhaust air from the
air springs to
lower the chassis. The system described above with give you a height maintained
system, however simple improvements can be made using existing
pneumatic valves
already fitted to the vehicle. Using a standard one port in, one port out
solenoid valve, plumb this between the
height sensing valve and the
air spring,
then feed the solenoid from the ignition. This solenoid valve will then
effectively stop the
height sensing valve making any changes to the chassis
height when the ignition is off, thus not draining the reservoir tank when the
compressor is not running.
The
height sensing valve is shown outline below.
Above was mentioned the use of a
flow restriction valve on the
height sensing
valve. This item is required to limit the air flow between the
air springs and
the height sensor valve to limit the reaction of the height sensing valve,
otherwise the system can easily use more air than the
compressor system can
deliver.
As mentioned earlier, some vehicles were fitted with a kneel feature to lower
the chassis for easier loading. This feature is possible with the semi automatic
system above. For this another solenoid valve is required, but with three ports,
one in (port A) and out of one of two other ports (ports B and C) a sort of Y
port valve. This valve is fitted between the
air springs and the 2 port valve
mentioned earlier, or the height sensing valve if not fitted. When the valve is
not powered, the air must flow between the
air springs and the height sensing
valve freely. Activation of this valve will then release air from the
air
springs to lower the chassis. This 'kneel' valve needs to be energised from a
spring return switch (so that the driver doesn't leave it activated and then
wonders why the rear suspension fails to lift). The switch feed can be live, so
that the ignition is not required to lower the suspension. Depending on the port sizes, it may be necessary to fit a
flow restriction valve on the
exhaust of this solenoid valve as its not safe to drop the chassis too quickly as damage may occur to
air springs or occupants of the vehicle.
Marcle leisure can offer an extensive range of
pneumatic fittings for all
vehicle air suspension systems from
Marcle Leisure's online store
here
For LDV enthusiasts, there is a very helpful forum -
http://www.ldv-sherpa.co.uk - Tell them we sent you along
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