A valve body is provided defining housing a moveable valve spool having a first end and a second end. The valve spool forms a gas balance chamber within the valve body. The valve spool has an end for closing an opening in the valve body. A channel running through the valve spool provides communication with the second end of the valve spool and the gas balance chamber. The second end of the spool valve is adapted to have an effective surface area greater than the effective surface area of the gas balance chamber.