US Patent 7159839 Control device

Booster means 11 for transmitting a force acting on a piston 10 to a valve stem 9 on amplification comprises pivotal members 25 each supported by casings 7, 8 so as to hold an outer end and an inner end thereof in contact with an outer peripheral portion of the piston 10 and a flange portion 22a formed on the valve stem 9 respectively from below and to be pivotally movable about a horizontal rod 26 positioned closer to the inner end. Metal bellows 16 are provided between an outer peripheral portion of the casing top wall 8a and the outer peripheral portion of the piston 10 for sealing off a compressed air admitting space.