| 摘要 |
<p>A proportioning control valve (10) for heavy duty fluid pressure braking system includes a proportioning piston (52) which is normally held in engagement with an abutment by control pressure. A tare pressure spring (104) urges a caging member (100) into engagement with a stop (102) which is spaced a predetermined distance (g) from the end of the proportioning piston, which is less than the distance between the valve engaging member carried by the proportioning piston in the proportioning valve member. Upon loss of pressure at the control pressure port (80), the proportioning piston is urged toward the caging member. The proportioning piston moves between the gap defined between the end of the proportioning piston and the caging member without opposition from the tare pressure spring, thereby permitting the full force of fluid pressure to break seal friction between the seals (90, 98) carried by the proportioning piston and the wall of the housing.</p> |
