Abstract: There is described herein an apparatus for charging a fluid line through a coupler such as a penetrator. The apparatus comprises a body formed from a sidewall defining a bore positioned along the longitudinal axis and extending therethrough. The first end of the body forms a substantially flat face. There is a stem positioned within the bore of the body and being movably mounted in the body for movement from a first position to a second position with respect to the body. There is a valve means attached to the apparatus for filling the body with hydraulic fluid. The substantially flat face of the body is fastened to a coupler. There is also an adjustment means attached to the stem for adjusting the position of the stem within the body. A method for charging a downhole hydraulic system is also described. There is also a method for installing a tubing hanger having a production string depending therefrom in a subsea wellhead while maintaining a hydraulically actuated downhole valve in an open position.