Lift axle suspension

1. A lift axle suspension for a tandem trailer, the tandem trailer comprising at least a first axle and a second axle, the lift axle suspension comprising:

a first suspension air bag mounted to act as suspension for the first axle;

a second suspension air bag mounted to act as suspension for the second axle;

a lift air bag that, when pressurized, applies a lifting force to lift the second axle relative to the first axle;

a first pneumatic circuit that connects the supply of compressed air to each of the first suspension air bag and a diverter valve, the flow of compressed air through the first pneumatic circuit being controlled by a height selector valve that is opened and closed based on the ride height of the trailer, the diverter valve having a first position that supplies compressed air to the second suspension air bag and a second position that supplies compressed air to a pressure regulator that limits air pressure to a predetermined pressure; and

a second pneumatic circuit that connects a supply of compressed air to the lift air bag, the flow of compressed air through the first pneumatic circuit being controlled by a pilot valve that is opened when the diverter valve is in the second position.

2. The lift axle suspension of claim 1 , wherein the pilot valve is pneumatically actuated, and the pilot valve is opened when air pressure is applied to the regulator.

3. The lift axle suspension of claim 1 , wherein the supply of compressed air comprises a pneumatic air cylinder connected to the first and second pneumatic cylinders.

4. The lift axle suspension of claim 1 , wherein the second pneumatic circuit comprises an override switch that closes the second pneumatic circuit.