This invention is a cylindrical rotary power device, usable as and convertible to a rotary internal combustion engine, pump, and/or compressor. The device incorporates an ingenious design and composition utilizing bilateral symmetry to minimize power losses and maximize efficiency. It operates with a minimum of moving parts which can be manufactured at relatively low cost and readily maintained. Also, the power device of the present invention is readily converted to an internal combustion engine by merely removing the external power source and providing fuel flow and ignition charge to the cylinders.