Abstract: An improved centrifugal pump protected against reverse rotation injury. The pump has an impeller mounted upon a pump shaft within a casing. The impeller has a central hub mounted over a threaded portion on the shaft and seated against a shoulder. A tubular nut mounts onto the threaded portion of the shaft and within the hub of the impeller. A flange on the nut seats on the hub. Offcenter axial pins are secured in the hub and extend into openings in the flange to interconnect drivingly the impeller and pump shaft. Upon undesired reverse rotation of the pump shaft, the nut unthreads from the pump shaft until the pins withdraw from openings in the flange. Then, the nut spins off the shaft. Now, the pump shaft can rotate safely within the stationary impeller.