| 摘要 |
<p>The invention relates to a valve unit for use in a pneumatic braking system for a tractor, of the type with two pipes, a supply pipe and an operating pipe respectively, to control the braking of a trailer. The valve unit includes two coaxial pistons (110, 120), opposite ends of which are exposed to the pressures supplied to first and second operating chambers (C, D) respectively. In the event of a loss of or a reduction in the pressure supplied to the second control chamber (D) during service braking, the pistons (110, 120) are adapted to move a control piston (101) to a position in which it closes a stop valve (93, 68) and opens a seat (64) of a relay valve (84, 90, 64) so as to cause the the automatic braking of the trailer. <IMAGE></p> |
