| 摘要 |
<p>The trailer pneumatic brakes are supplied with air via a flow control valve. This has a spring loaded control piston held in the open position by the relative pressures of the brake circuits in the towing vehicle and the trailer. If the trailer brakes fail, then the valve closes and allows the trailer brakes to vent rapidly and apply the safety brake. The piston is also fitted with a smaller spring above the piston. This holds the piston downwards. If the parking brake is applied then the pressure above the piston, corresponding to the normal brake pressure, is vented and the piston is pressed upwards against the small spring. Every time the vehicle is parked, the piston is moved. This prevents it from seizing through long inactivity.</p> |
