The present specification discloses a brake actuation system for a vehicle, which is applicable to both hydraulically or pneumatically operated/spring released brakes and spring operated/hydraulically or pneumatically released brakes. With such brakes it is often necessary to have secondary means for brake operation or release. Such braking systems thus have primary and secondary means for brake operation or release.
The present invention provides a fail-safe system which can provide at least an indication of impending failure. The brake actuation system of the present invention comprises a cylinder (1) within which two axially aligned pistons (3,5) are axially slidable, the space (7) between one end of the cylinder (1) and one piston (3) being connected to a primary power system (13,11,25,9) and the space (15) between said pistons (3,5) being connected to a secondary power system (13,21,19,17). When such an actuation system is used in a spring operated/hydraulically released braking system, the primary power system (13,11,25,9) of the present invention is the primary brake release and the secondary power system (13,21,19,17) is a secondary or emergency release which may constitute a handpump (19). By providing suitable flow detection means (21,25) in the primary and secondary power systems, leakage past piston seals (53,57) can be monitored and detected before the seal failure is sufficient to dangerously affect brake performance.