Abstract: An automatic shut-off valve for a fire hydrant or other device that is vulnerable to breakage, which is attached to a straight-walled fluid carrying pipe, the valve having a pair of separated mounting rings (20 and 22) positioned in the pipe near the breakable device. A cylindrical rod (36) having a frangible end (40) is slideably retained in the middle of the pipe by the rings and a disc (48) is positioned over the rod. A hub (66) is rigidly connected to the rod add a spring over the rod (72) forces the hub away from the ring. A link (60) connects the hub to the disc and the rod is pulled away from ring compressing the spring and opening the valve by positioning the disc parallel to fluid flow within the pipe.