A wellhead assembly made up of a wellhead housing, a production tree mounted on the wellhead housing, tubing suspended into a wellbore from within the wellhead housing, and an annulus between the tubing and the wellhead housing. A shuttle valve is provided within a tubing hanger that supports the tubing from within the wellhead housing. An accumulator is disposed in the annulus that is in fluid communication with a closed position port on the shuttle valve. Pressure is maintained in the accumulator for closing the shuttle valve when a force for opening the valve is removed.