25 are connected with guide or push rods 72 and 73 which supported by springs 74 and 75 are actuatable by the brake pedal 21 via a crosspiece 76 the supply pressure exerted by the brake force of brake pedal 21 via the travel imparting spring 22 and the control valve 6 reaches the primary chambers 70 and 71 of the main cylinders 7 and 8 via channels 49a and 69 and simultaneously reaches the work chamber 57 of the barrier piston 58 via channel 68 under this effective pressure on barrier piston 58 which is opposite to the brake force direction the barrier piston 58 performs a slight movement counter to the force of the plate spring 59 this slight but frequent movement helps to prevent seizing due to corrosion and actuates the brake light switch 66 the pistons 24 and 25 are moved within the main cylinders 7 and 8 toward the left the secondary chambers 26 and 27 are separated from the refill chambers 34 and 35 by movement of rods 31 and 32 which pass through the ring seals 32 and 33 and brake pressure is sensed via channels 28 29 by pressure transducers not shown which generate signals to brake circuits i and ii via the channels 28 and 29 braking occurs when full brake pressure is exerted the movement of switches 39 and 42 from an open position to a closed position is not permitted by the movable plugs 37 and 38 that is only if a defect in the braking system is not present the cutoff assembly which includes barrier piston.