Tractor trailer brake system

Claim 1

IN A TRACTOR TRAILER BRAKE SYSTEM HAVING TRACTOR BRAKE AND TRAILER BRAKE ACTUATORS, A PEDAL CONTROLLED VALVE FOR SUPPLYING PRESSURE TO THE TRACTOR BRAKE ACTUATORS, AND A SERVICE LINE CONNECTED TO SAID VALVE, IN COMBINATION, AN EMERGENCY RELAY VALVE HAVING A FIRST CHAMBER CONNECTED TO SAID TRAILER BRAKE ACTUATORS AND A SECOND CHAMBER CONNECTED TO SAID SERVICE LINE, AN AXIALLY MOVABLE STRUCTURE IN SAID RELAY VALVE MOVABLE BY PRESSURE IN SAID SECOND CHAMBER TO CONNECT SAID FIRST CHAMBER TO A SOURCE OF PRESSURE TO OPERATE THE TRAILER BRAKES, SAID EMERGENCY VALVE HAVING A THIRD CHAMBER, A PRESSURE MOVABLR ELEMENT SUBJECT TO PRESSURE IN SAID THIRD CHAMBER TO OPERATE SAID AXIALLY MOVABLE STRUCTURE, AND ELECTRO-MAGNETIC MEANS FOR ESTABLISHING PRESSURE IN SAID THIRD CHAMBER, SUCH MEANS COMPRISING A SOLENOID, A CIRCUIT ADAPTED TO BE CLOSED UPON INITIAL OPERATION OF SIAD CONTROL VALVE FOR ENERGIZING SAID SOLENOID, SAID SOLENOID HAVING TWO ARMATURES OPPOSITELY MOVABLE UPON ENERGIZATION OF SAID SOLENOID, AN EXHAUST VALVE CONNECTED TO ONE ARMATURE AND NORMALLY OPENING SAID THIRD CHAMBER TO THE ATMOSPHERE, A NORMALLY CLOSED PRESSURE INLET VALVE CONNECTED TO THE OTHER ARMATURE WHEREBY ENERGIZATION OF SAID SOLENOID WILL CLOSE SAID EXHAUST VALVE AND OPEN SAID INLET VALVE TO SUPPLY PRESSURE TO SAID THIRD CHAMBER, AND MEANS, INCLUDING A PRESSURE REGULATOR, FOR DETERMINING THE PRESSURE SUPPLIED THROUGH SAID INLET VALVE TO SAID THRID CHAMBER IN ACCORDANCE WITH THE LOAD ON THE TRAILER.