FREIGHT BRAKE CONTROL VALVE HAVING LAP LEAKAGE PROTECTION

摘要

A service valve piston assembly for a freight brake control valve device in which the graduating valve is configured to cooperate with the associated slide valve to close off the application port via which auxiliary reservoir pressure acting on one side of the piston assembly feeds the brake cylinder prior to opening of the stability port via which the brake pipe pressure on the opposite side of the piston assembly is communicated with auxiliary reservoir pressure on the one side of the piston, thereby preventing the piston valve assembly from finding a quasi-lap position in which the brake cylinder continues to be pressurized.