The chamber’s pressure and the opening of check valve is two factors have the highly influence on the pressurization process which created by using the piezoelectric-hydraulic pump. In this study, the extension of O-ring which lead to the change of chamber’s volume will be consider. The volume change could reduce the chamber’s pressure more than 50% compare to the constant volume case. Related to the opening of the check valve, due to the bending of plate valve, the load area will be change overtime. With this change, the time when the check valve start opening have to found to determine when pressurization process begins after every cycle.