| 摘要 |
A microprocessor controlled valve system is used with an EOT unit on a railcar remote from the locomotive of the train. The system includes a pressure transducer, a microprocessor, a valve device, a motor drive and a pneumatic drive. The microprocessor receives from the transducer an electrical signal indicative of actual brake pipe pressure and from the locomotive a brake command signal indicative of desired brake pipe pressure. The microprocessor issues a drive signal when the brake command signal requires a service brake application and an actuating signal when the brake command signal requires an emergency brake application. The valve devices defines an elongated bore, a primary passage, a branch passage, an exhaust passage and an elongated valve body able to move reciprocatingly in the bore according to the operation of the drives. The primary and branch passages communicate with the brake pipe, and all of the passages communicate with the bore. The valve body feature (A) a first valve that when opened allows at least partial communication between the primary and exhaust passages and (B) a second valve that when opened allows communication between the branch and exhaust passages. The motor drive opens the first valve in response to and to the extent dictated by the drive signal. In response to the actuating signal, the pneumatic drive fully opens the second valve thereby fully opening the first valve so that pressure in the brake pipe flows through the valves and vents via the exhaust passage.
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