A valve assembly 20 operable to selectively control a flow or passage of a fluid. The valve assembly may be applied to any appropriate mechanism such as a hydrocephalus shunt, fluid draining sewage system, or tank holding system. The valve assembly disclosed may include a selected profile for various applications. The valve assembly comprises a valve member 140, a valve biasing member 160 and a rotor 100 having at least two regions of different diameters to adjust the pressure on the valve biasing member and valve member.
