Abstract: A pressure relief valve for exhausting pressure from a pressurized device, includes a valve body that has a first end and a second end, a chamber extending through the valve body, and a valve seat located within the valve body. A valve member comprises a piston and a stem, with the piston shaped so it can be mounted adjacent the valve seat. A spring is mounted within the chamber so as to bias the piston toward the valve seat. In one embodiment a valve cap includes a sidewall shaped to fit around the outside of the second end of the valve body and has a hole through which the stem extends. The valve cap is connected to said valve body in a manner that renders the valve substantially inoperable at the preselected pressure once the valve cap's position is changed. In another embodiment, the stem is a formable wire that extends through the valve body and stem is bent to enable the valve member to move within the valve body.