| 摘要 |
Fluid pressure braking system (10) for supplying fluid pressure to actuate the service brake actuators (26) and to supply hold-off pressure to release the spring brake actuators (22) of the trailer portion of a tractor-trailer combination vehicle includes a spring brake relay valve (32) having a delivery port (38) communicated with the spring brake actuators (26), a control port (34) communicated with the trailer supply line or conduit (12), and a supply port (36) communicated with the supply line (12) through a bypass passage (40). Accordingly, hold-off pressure can be supplied directly to the spring brake actuator (26) before the reservoir (44) is fully charged. The reservoir (44) is charged through the supply line (12) and a pressure protection valve (54) which opens to permit charging of the reservoir (44) only when the pressure in the system exceeds a predetermined level.
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