Brake pressure proportioning valve with an additional valve

A vehicle brake pressure porportioning valve subject to the load of a vehicle and controlled fluidically, comprising a piston sliding in a stepped bore in a body and carrying a normally open shutter arranged between a source of fluid under pressure and an associated brake circuit, said piston being movable counter to a spring under the effect of the pressure of said fluid which tends to close said shutter, and a sealed control chamber connected to a vehicle load sensor, said pressure proportioning valve further comprising a normally open additional valve arranged between said sealed control chamber and said vehicle load sensor in order that the additional valve operates to interrupt communication between said sealed control chamber and said vehicle load sensor at the beginning of a braking operation and enable the proportioning valve to operate continually, during said braking operation, according to the load of the vehicle present before an occurrence of a vehicle load transfer attributable to the braking operation.