Disclosed is a differential pressure valve comprising: a valve body, the valve body having at least one flow inlet and one flow outlet: at least one shutter, the shutter being movable between an open position and a closed position under a differential pressure across the valve; at least one flow passage from the flow inlet to the flow outlet; at least one biasing member configured to bias the shutter towards a closed position so as to block the flow passage through the flow inlet. The biasing member is a non-linear biasing member.