Tandem pneumatic pressure booster

Claim 1

A tandem pneumatic pressure booster of a type that includes a rear movable wall, a center plate and a front movable wall for dividing the interior of a housing hermetically closed by a front shell and a rear shell into a rear variable pressure chamber, a rear reference pressure chamber, a front variable pressure chamber and a front reference pressure chamber, and a valve body incorporating a control valve therein and adapted to be operated to provide output, characterized in that the booster further includes a reaction disc containing case for accommodating a reaction disc, said reaction disc containing case having a flange clamping said rear movable wall to said valve body, said reaction disc containing case further having a barrel portion, said front movable wall being fixed to said case, a cylindrical passage member fitting over the outer peripheral surface of said barrel portion between said flange and said front movable wall and fitting between said flange and said front movable wall with a fit for avoiding receiving pressure applied to said flange or to said front movable wall, said passage member being provided with a reference pressure chamber communicating passage in communication with said rear and front reference pressure chambers and a variable pressure chamber communicating passage in communication with said rear and front variable pressure chambers.