14 and the wheel cylinder conduit 21 the pressure acting in the expansion chamber 36 will at this time be sufficient to cause the expansion chamber plunger 37 to move to the left and increase the volume in the expansion chamber 36 this increase in volume relieves the pressure on the wheel cylinders 17 and 18 and in effect will release the brakes it should be noted that at this time the expansion chamber plunger 37 will have moved away from the plungers 33 and 34 of the check and bleed valve 29 at a predetermined condition the electric module 26 will send a signal to cause reapplication of the brakes in the illustrated embodiment this is done by dicontinuing the electric current flow to the solenoid winding 66 the valve plate 62 is then urged upwardly by the spring 63 to close the valve seat 67 and open the valve seat 61 power steering pump pressure will then be reapplied to the power piston 42 which in turn urges the expansion chamber plunger 37 to the right to decrease the volume in the expansion chamber 36 at this time the combined check and bleed valve 29 will still be closed thus the wheel cylinders 17 and 18 are gradually reapplied first by the action of the expansion chamber plunger 37 it should be noted that unless the operator has removed his foot from the brake pedal wheel master cylinder pressure will still be experienced in the conduit 14 and chamber 28 after the expansion chamber plunger 37 has moved sufficiently it will engage the bleed valve plunger 34 to open it from its engagement.