| 摘要 |
A pneumatic brake servo using two air pressure sources and including a rigid shell (3) divided by a movable sealing wall (4) into at least two chambers (3a, 3b). The movable wall may be actuated by a pressure difference, caused by the actuation of a valve, between pressures supplied to the chambers to drive a pneumatic piston (5) supporting a control valve (7), the inside (50) of said piston being separated from the second source by a cleaning filter (14). The brake servo comprises controlled-opening sealing means (16, 51) arranged between the second pressure source (A) and the inside (50) of the piston for controlling an air intake channel (15) linking the second chamber (3b) to the second pressure source (A) while by-passing the filter (14) and the valve (7), and resilient means (17) reacting to a pressure difference between the inside of the piston and the second pressure source to selectively enable the sealing means to be opened when said pressure difference exceeds a predetermined threshold.
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