To expedit the driving of a valve assembly and satisfy the requirement of a production line by forming a piston multiplier assembly having a ball valve part arranged in the bottom of a piston stem opening/closing a discharge or supply orifice for the valve assembly.

A second top piston 166, a second top piston rod or stem arranged in the top air cylinder housing 161 is provided and a center air cylinder housing 122, a first bottom piston 152, a first bottom piston rod or stem 116 and an air channel 174 for 'opening' the inside are included in the range of a structural arrangement. As a result a plurality or double type piston multiplier is effectively and integrally incorporated or provided in a valve assembly 110. This constitution can improve the driving speed of the valve assembly 110 in the both open/close driving states or stages.