when the vehicle operator would like to convert to the dump operation the switch is activated to provide a signal along line 200 to relay 202 once the tabs controller 132 indicates that vehicle speed has been reduced to a velocity under ten 10 miles per hour a signal is then provided on line 204 to energize the solenoid this in turn provides a control signal from port 144 of the solenoid valve to the control port 152 of the inversion valve and the inversion valve then exhausts air that it would have otherwise delivered to the relay valve through the pressure protection valve 210 the pressure protection valve is designed to only partially exhaust the air to a certain predetermined level for example 10 psi and thereby cause the relay valve to exhaust the rear suspension 116 118 to the same level in this manner the rear suspension air bags are maintained at a reduced level relative to the air bags of the front suspension and the check valves maintain this pressure differential an alternate solution using a commercially available r 12 relay valve available from bendix commercial vehicle systems llc the assignee of the present application is shown in fig7 more particularly the leveling valve 160 delivers air directly to supply port 174 of the relay valve in addition the pressure.