A method of actuating a subsea tree comprising opening a valve assembly by transferring a first volume of fluid into a first chamber and closing the valve assembly from the open position to a shear position via a gas charged valve actuator in response to the transfer of fluid out of the first chamber. Shearing a workstring positioned within an axial bore of the valve assembly with the valve via the gas charged valve actuator. Closing the valve from the shear position to a closed position with one or more gas charged push rods to isolate the wellbore above from the wellbore below the closed valve. The shearing force generated from the gas charged valve actuator is greater than the closing force of the one or more push rods.