| 摘要 |
A vent valve device having a pair of diaphragm-type piston members forming a pilot chamber therebetween. The one piston controls a vent valve via which brake pipe pressure is vented locally, while the other piston controls a pilot valve to control venting of the pilot chamber. A breather choke between the pilot chamber on one side of the other piston and a control chamber on the opposite side establishes a predetermined pressure differential thereacross only when brake pipe pressure supplied to the pilot chamber is reduced at an emergency rate to thereby actuate the other piston to a position opening the pilot valve. In addition, this other piston operates a cut-off valve to isolate the pilot chamber from brake pipe pressure so that the pilot valve quickly exhausts pilot chamber pressure. The one piston controlling the vent valve is in turn actuated by the exhaust of pilot chamber pressure to positively effect an unrestricted, local reduction of brake pipe pressure via the vent valve when this one piston is actuated.
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