Haldex provides a technical overview of its reinvention of the double-diaphragm spring brake actuator: LifeSeal+.
Double-diaphragm spring brakes offer simple mechanical brake actuation, and an emergency failsafe. The units, also known as foundation brakes, consist of two chambers.
Each one is divided in two by a large rubber diaphragm, behind which sits a coiled spring. On the other side of the diaphragm is a pressure chamber with air inlet and outlet. When compressed air enters the pressure chamber, it pushes on the surface of the diaphragm and overcomes the spring’s force, compressing it. That also drives the brake pushrod backward, releasing the brake.
To apply the brakes, the compressed air is released out of the chamber, allowing the tensioned spring – and pushrod – to extend, applying the brakes. In event of a pneumatic system failure, such as a cut or leaking line, the chamber also empties, applying the brakes: this is a failsafe.
Conventional actuators contain vent holes on the chambers’ spring sides, to expel air forced out when the spring is compressed. But that also means that when the spring is released, a vacuum is created in the spring side, which draws air in.
As the actuators are mounted at or near wheel-end, (in rainy conditions) moisture can enter the spring chamber either directly, or entrained in incoming air. Over time, that means the spring will rust and, as it is constantly under high tension, can lead to failures.
By contrast, the parking brake chamber of the LifeSeal+ has no vent holes but one-way check valve. When the brake is released, air is exhausted out of the spring chamber into the air side of the service brake chamber.
Installation also differs from conventional spring brakes, because the caging tool is permanently integrated; technicians simply wind it down to apply the parking brake. As the tool remains in place, a plug is no longer needed, and technicians can release the brakes in case of a pneumatic air failure by turning the caging nut with a normal spanner, without needing a special tool.
Having been launched in 2018 at the IAA exhibition, LifeSeal+ is a proved product for the trucks and trailers in North America, but the actuator has not been sold in Europe, until now.
