Booster

A booster for boosting an input force applied to an input member in order to output the same through an output member after having boosted by means of gaseous pressure comprising:

• a power piston disposed in such manner as to divide a chamber inside an air-tight casing into two chambers and operated due to the pressure difference in the two chambers situated on opposite sides of the power piston;
• a control piston slidably fitted in a through-bore axially formed in said power piston;
• spring means for biasing said power piston and said control piston to be restored to respective original positions thereof;
• said power piston being allowed to advance relatively to said control piston leaving the latter at said original position;
• limiting means for limiting the relative advancing of said power piston to a predetermined distance so as to make said power piston and said control piston advance in unison after said predetermined distance has been reduced to zero;
• a control valve disposed between said control piston and said input member, and operated by a relative movement between said control piston and said input member for controlling the pressure difference in the two chambers on opposite sides of said power piston;
• an intermediate mechanism for transmitting a force imparted from said input member;
• and
• a power lever, abutting at one end thereof on an output portion of said intermediate mechanism, abutting at the other end thereof on an output portion of said power piston, and abutting at the middle portion thereof on an input portion of said output member, for transmitting, while allowing relative movement between said intermediate mechanism and said power piston, the output from the former and the latter to said output member;
• whereby when said input member is shifted by a slight stroke in the intial operation stage of said booster to actuate said control valve, said power piston is advanced in relation to said control piston, independent of the stroke amplitude of said input member, instantly by said predetermined distance, and after that said power piston is advanced together with said control piston.