A pressure relieve valve for cardio pulmonary bypass responsive to abnormal pressure changes due to kinks in conduits used with the valve. In this situation, a principal flow path through a duckbill valve can be bypassed by positive and negative secondary flow paths for pressure relief. The secondary flow paths exist using umbrella valves of opposite orientation blocking holes in a flange separating inlet and outlet extensions of a tubular central body housing the duckbill valve. Each umbrella valve is throttled with a nipple that moderates flow in each of the secondary flow paths for slowing pressure equalization.