Valve member 1 is linked by its stem to diaphragm 2 which is held down by spring 3 to the valve housing. Spring 4 tends to lift diaphragm 2 and valve member 1 to their upper position. The upper and lower guides of valve member 1 have orifices through which air can pass. Compressed air from the tank of the truck is delivered under diaphragm 2. Compressed air from the brake valve is delivered to the upper port of the acceleration valve above diaphragm 5. Chamber a of the acceleration valve is connected through port d to the auxiliary tank. Chamber b of the emergency valve is connected through port f to the brake chambers of the rear wheels of the trailers. When the brakes are not applied, compressed air from the main tank raises valve member 1 and the edge of diaphragm 2, pressing the diaphragm against annular projection c. At this, air passes through chamber a and port d into the auxiliary tank. Chamber b is connected to chamber e of the acceleration valve. When the brakes are applied, compressed air from the brake valve, acting on diaphragm 5, opens valve member 6. This admits air from chamber a into chambers e and b, and, through port f, to the brake chambers of the wheels. Chamber a is replenished by air, first from the auxiliary tank through port d and then, when the pressure in this tank drops to a definite value, from the main tank. In releasing the brakes, when the air pressure in the upper part of the acceleration valve drops, air from the brake chambers is discharged through chambers b and e, lifting diaphragm 5 slightly. If one or all the trailers break away from the truck, they are braked to a full stop by the emergency valve. Rupture of the pipeline leads to a drop in pressure under diaphragm 2 of the emergency valve. Then the pressure of the air of the auxiliary tank in chamber a bends diaphragm 2 downward, moving valve member 1 onto its seat. Chamber b is connected to chamber a, i.e. the braking action is performed by the supply of air from the auxiliary tank. Closed valve member 1 prevents the air from passing out through diaphragm 5 into the atmosphere. This stops the trailers that have been broken away. The emergency valve operates in conjunction with the acceleration valve.
$4046$EHP,Va$