without an extra large piston and cylinder in order to prevent interference with the normal air brake system 39 s operation by air flowing back into the brakepipe from air bellows 34 when brake pipe pressure is reduced within its normal operating service pressure range of 50 110 psi the air bellows 34 can be connected to the brake pipe 10 by a simple interlocking valve 60 as illustrated in fig5 the interlocking valve 60 prevents feedback of pressure from the air spring into the brake pipe which would extend the time needed to exhaust the brake pipe 10 and could also cause release of applied train brakes the interlocking valve 60 includes a housing 62 with a brake pipe port 64 handbrake actuator port 66 and vent port 68 a charging check valve 70 interconnects the brake pipe port 64 and the handbrake actuator port 66 a charging restriction or orifice 21 is provided in the hand brake actuator port 66 an interlock piston 72 has a 20 psi spring 74 biasing the piston 72 on one side to open the charging check 70 the other side of the piston 72 is responsive to pressure at the brake pipe port 64 when the brake pipe is charged the interlock piston 72 is moved to the left against a 20 psi biasing spring 74 in its left most position it allows the charging check valve 70 to seat this check valve 70 permits flow of air from brake pipe to the actuator and will assure a release of the handbrake a the brake pipe 10 is charged however when brake pipe pressure is reduced.