| 摘要 |
The system comprises a control unit, manually operated actuating devices, a relay valve interposed between the pneumatic main pipe and the brake pipe and provided with two control inlets, an electropneumatic control unit connected to the main pipe and operable under the control of the said unit to supply a variable braking control pressure, pneumatic back-up devices connected to the main pipe and operable under the control of the actuating devices to supply at their outlet a pneumatic back-up pressure which can be used to control the braking, and an enabling valve which can be switched between a normal operating condition and a back-up operating condition in which it can connect a control inlet of the relay valve selectively to the outlet of the electropneumatic unit or to the back-up devices. There is also provided a valve unit for controlling the pressure overcharge and its discharge, interposed between the outlet of the enabling valve and a further control inlet of the relay valve, and operable selectively when the enabling valve is in the back-up operating condition.
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