<p>A valve assembly comprises a body and a passageway defined through the body. The passageway has a first end and a second end. A valve arrangement is positioned between the first end and the second end. The valve arrangement is movable between an open position in which the passageway is open and a closed position in which the passageway is closed. The valve arrangement is adapted to close the passageway in response to at lease two modes of failure.</p>
