| 摘要 |
<p>Compressed air braking apparatus of a tractor vehicle capable of controlling secondary and parking brakes of a towed trailer has driver operable service brake control valve means (10) and parking and secondary control valve means (20, 27) moveable over a range of positions to control tractor brake pressure and the pressure in a trailer brake control line (28) and said control valve means having a parking position in which it causes parking brakes to be applied on the tractor vehicle and causes a predetermined pressure to be applied to the control line (28) which predetermined pressure is chosen such that subsequent loss of the control line pressure results in the application of spring brake actuators to maintain overall parking brake force without significant depletion thereof.</p> |
