| 摘要 |
A brake booster includes a key member coupled to a valve plunger. When the booster is inoperative, the key member is brought into abutment against an inner wall surface of a shell to limit a free retracting movement of a valve plunger and its connected input shaft so that a lost stroke of the input shaft can be reduced when the brake is operative for the next time. According to the invention, a shell includes a cylindrical extension which is circumferentially and integrally formed with an annular bulge which extends radially inward, with a seal member disposed on the rear side of the annular bulge.
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