For many, many years, over the road vehicles have encountered severe brake drag problems as a result of residual pressure build-up in the brake system, which problem has been accepted by the trucking industry because of the lack of a satisfactory solution.
In actuality, foot operated brake valves are equipped with either a treadle or a lever connected to linkage for use with a conventional brake pedal or treadle. In operation, when the pedal or treadle, as the case may be, is actuated by the driver's foot, force is applied by means of a resilient plunger acting against a piston. As the piston is moved, the exhaust port is closed and the air inlet is opened. Air pressure from the supply reservoir then flows by the inlet valve and out the delivery ports to the brake chambers which apply the brakes.
When the air pressure in the cavity beneath the piston and the air pressure being delivered to the brake chamber actuators is equal, the mechanical forces on the top of the piston permits the inlet to close, which cuts off any further flow of air from the supply line through the valve and the exhaust remains closed to prevent the escape of air pressure through the exhaust port.
When the pedal or treadle force is removed and the mechanical force removed from the top of the piston, then the air pressure beneath the piston moves the piston to open the exhaust port. The air below the piston and in the delivery lines is then exhausted through the exhaust port.
When quick release valves are used, the quick release valve exhausts the brake chamber air pressure and functions to speed up brake release time by reducing the distance the exhaust air must travel to reach the exhaust port. The quick release valve is operated by air pressure from the brake valve entering the top port on the release valve which forces a diaphragm against an exhaust port seat. This blocks off the exhaust port and permits pressurized air to pass around the edges of the diaphragm and out of each of the side outlets to the brake chambers. As the air pressure is released from above the diaphragm, the air pressure and spring below force the outer edge of the diaphragm to seal on the valve body and at the same time opens the exhaust port seat, opening the exhaust, which opens the brake chambers directly through the exhaust port to atmosphere.
When relay valves are used, the function is much the same as the quick release valves, in that the relay valves are high capacity brake valves which serve as relay stations to speed up application and release time of the brake system.
Therefore, from the foregoing, it would appear that there is no need for the proposed invention, since the brake chambers can be readily exhausted and this is almost true, except for the fact that the exhaust ports in the brake actuating valves, the quick release valves and the relay valves are large and must be immediately closed upon the application of any increased air pressure in the brake system, otherwise the pressurized air escape would be enormous and when the exhaust ports finally closed, the applied brake chamber pressure would be high and the brakes would grab and smooth stops would be impossible, let alone the damage to the equipment.