Present invention makes it possible to discharge the air in suspension bellows (6) of a trailer used in intermodal freight transportation, when it is being loaded on a train, without the need for operator input, incorporating pneumatic roller valves (1) that are connected to each other in series, activating the system that will discharge the air in suspension bellows (6) by sending a signal once they are connected to the hooks of the crane lifting the trailer to be loaded on the train, a pneumatically induced valve (2), keeping the air discharge system that is activated by connecting both of the pneumatic roller valves (1) to the hooks of the crane, to be active continuously, a solenoid pneumatic valve (3) to deactivate the air discharge system that is kept active continuously and an air induced pneumatic valve (4) allowing the air that is compressed in the bellows to be discharged to the atmosphere.