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Dunlop LDV Air Suspension?

Dunlop Systems & Components available from Marcle Leisure LDV & Sherpa Air Suspension Components From Marcle Leisure

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
Sherpa LDV Pneumatics Diagram of their 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.
Height Sensing Valve For Full Air Suspension Systems

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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