Abstract: A rotary rock bit with passageways for conducting air or other gaseous fluid to cool the bearings and flush cuttings from the borehole includes valve means for controlling the entry of water into the bearings. The stream of air or other gaseous fluid is directed through a valve system that prevents water from reaching the bearings. In one embodiment a truly positive backflow shutoff valving arrangement through both the nozzle and bearing passageways provides a means for more effectively preventing water and cuttings from entering the bearings and bearing passageways of the bit.