| 摘要 |
A pneumatic booster comprising a housing, a power piston separating the inside of the housing into a constant pressure chamber and a variable pressure chamber, a valve body attached to the power piston, an output shaft, a plunger slidably received in a bore in the valve body, an input shaft and a valve mechanism in the bore for selectively communicating the variable pressure chamber with a negative pressure source or the atmospheric pressure, the valve mechanism including a valve member mounted on the inner wall of the bore, a first valve seat formed on the inner wall of the bore and a second valve seat formed on the plunger. The booster further comprises a hollow chamber formed within the bore and adapted to communicate with the variable pressure chamber when the valve member rises from the second valve member, a means for detecting actuation of the input shaft, a second valve mechanism adapted to be changed over depending upon a result of detection of the detecting means so as to selectively communicate the hollow chamber with the negative pressure source or the atmospheric pressure. The valve member and the second valve seat are designed to be spaced apart from each other by a predetermined distance when the input shaft positions in its initial or non-operated position.
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