A valve assembly for adjusting the flow of bodily fluid from one part of a human body to another includes a body portion having a flow inlet and a flow outlet. A valve located in a flow path from the inlet to the outlet includes a valve seat and a closing element that is adapted to seal against the valve seat. A carrier element is mounted within the body portion and has a plurality of pockets. Each pocket houses a respective preload element, wherein each preload element is of a different weight from that of the other preload elements. The carrier element is moveable relative to the body portion so as to align a preload element of a desired weight with the closing element. The self weight of the chosen preload element applies a preload to the closing element dependent on the orientation of the valve assembly.
