Brake booster with one-way valve on centerplate

Claim 1

A brake booster including a center plate which divides the interior of a shell into a front and a rear chamber, a valve body slidably extending through the center plate, a front diaphragm applied to the back surface of a front piston which is disposed on the valve body for dividing the interior of the front chamber into a constant and a variable pressure chamber, a rear diaphragm applied to the back surface of a rear piston mounted on the valve body for dividing the interior of the rear chamber into a constant and a variable pressure chamber, and a seal member mounted on the center plate for hermetically sealing between the center plate and the valve body and for interrupting a communication between the variable and the constant pressure chambers located across the center plate; characterized by a lip formed on the seal member and acting as a check valve which releases the last-mentioned variable pressure chamber any pressure developed in the last-mentioned constant pressure chamber which is to be sealed by the seal member and which rises above the pressure in the last-mentioned variable pressure chamber, an axial portion of the center plate being formed with a cylindrical portion which extends rearwardly, said lip being formed on a front end face of the seal member and contacting the inner peripheral surface of the cylindrical portion to define a space rearward of the lip, and the space communicating with the last-mentioned constant pressure chamber through a channel.