ON CERTAIN AERIAL DEVICES MOUNTED ON GMC C7500 TRUCK CHASSIS AND EQUIPPED WITH AN ALTEC ELECTRIC-AIR/MANUAL TRAILER BRAKE CONTROL, THE TWO-WAY CHECK VALVE COULD BE INSTALLED IN EITHER THE FRONT OR REAR BRAKE SYSTEM IN SUCH A MANNER THAT STOPS AIR FLOW TO THAT PARTICULAR PART OF THE CHASSIS BRAKE SYSTEM.