Description & Operation (page 20 of 26)

Pilot Exhaust Valve  

A solenoid operated pilot exhaust valve is connected to the air delivery gallery, downstream of the air dryer. The pilot 
valve, when opened, operates the main compressor exhaust valve. This allows the air springs to be deflated when 
required.  
 
When the solenoid is energised, pilot air moves the exhaust valve plunger, allowing pressurised air from the air springs 
and/or reservoir to pass via the reservoir control valve to the air supply unit.  
 
The solenoid has a resistance value of 4 Ohms at a temperature of 20 °C (68°F).  
 

Exhaust Valve  

The exhaust valve has three functions. It operates in conjunction with the pilot exhaust valve to allow air to be exhausted 
from the air springs and/or the reservoir as described previously.  
 
The valve also protects the system from over -pressure. The valve is connected into the main pressure gallery which is 
always subject to the system pressure available in either the air springs or the reservoir. The valve is controlled by a 
spring which restricts the maximum operating pressure to between 333.5 to 370 lbf/in

2

 (23.0 to 25.5 bar).  

 
The minimum pressure in the system is also controlled by the exhaust valve to ensure that, even when deflated, the air 
springs contain a positive pressure with respect to atmosphere. This protects the air spring by ensuring it can still 'roll' 
over the piston without creasing.  
 

Electric Motor  

The electric motor is a 12V dc motor with a nominal operating voltage of 13.5V. The motor drives a crank which has an 
eccentric pin to which the compressor connecting rod is attached.  
 
The motor is fitted with a temperature sensor on the brush PCB assembly. The sensor is connected to the air suspension 
control module which monitors the temperature and can suspend motor operation if an overheat condition occurs.  
 

Compressor  

The compressor comprises a motor driven connecting rod and piston which operate in a cylinder with a cylinder head. 
The motor rotates the crank moving the piston up and down in the cylinder bore. The air in the cylinder is compressed 
with the up stroke and is passed via delivery valve, through the air dryer into the system.  
 

Air Dryer  

The air dryer is an integral part of the air supply unit. The air dryer contains a desiccant which absorbs moisture. 
Pressurised air is passed through the air dryer which removes any moisture in the compressed air before it is passed to 
the reservoir and/or the system  
 
When the air is exhausted from the system, the returning air is passed through the air dryer, regenerating the air dryer by 
removing moisture from the desiccant and expelling it to atmosphere via the exhaust.  
 
The air dryer is an essential component in the system ensuring that only dry air is present in the system. If moist air is 
present in the system, freezing can occur, resulting in poor system operation or component malfunction/failure.  
 

AIR RESERVOIR