Retainer in valve mechanism of booster

In a valve mechanism for booster including a first valve seat formed on a valve body, a second valve seat formed on a rear portion of a valve plunger connected to an input shaft, a valve element formed of an elastic member and adapted to be seated upon either the first or second valve seat, and a retainer for securing a rear end of the valve element in tight contact with an inner peripheral surface of the valve body, the valve body having a terminal end;

• the retainer comprising a tubular holder supporting an inner peripheral surface of the rear end of the valve element and urging an outer peripheral surface of the rear end of the valve element into tight contact with the inner peripheral surface of the valve body, a securing portion disposed rearward of the tubular holder and extending radially outward to be secured to an inner peripheral surface of the terminal end, an anti-withdrawal portion disposed forward of the tubular holder and projecting radially outward, and a tapered portion disposed forwardly of the anti-withdrawal portion and extending radially inward and axially so as to be narrowed into a conical configuration;
• and
• the tapered portion of the retainer comprising an inner tapered portion which continues forwardly from the tubular holder and extends radially inwardly and axially, and an outer tapered portion which is formed by folding from a distal end of the inner tapered portion upon itself to overlie the inner tapered portion on the front side thereof, the anti-withdrawal portion continuing from the distal end of the outer tapered portion and projecting radially outward beyond an outer peripheral surface of the tubular holder.