Abstract: A pressure relief valve for positive pressure pump systems in which fluid is displaced from the inlet to the outlet of the pump. The pressure relief valve includes a bypass tubing member interconnecting the outlet and a lower pressure area such as the inlet. Pressure limiting means normally occlude the bypass tubing to restrict flow when the outlet pressure of the pump is below a predetermined level and responds to pressure above a predetermined level to shunt fluid from the outlet to the inlet. In the preferred embodiment, the pressure limiting means consists of bar-like members which engage the exterior of the tubing and are biased to compress the bypass tubing to a flow restricting position by elastic bands extending around the bar-like members.