Abstract: Apparatus and method for reducing the effects of draft tube pressure fluctuations acting on a runner in a hydraulic reaction turbine or the effects of suction tube pre-rotation acting on the impeller in a centrifugal pump. A closed surge suppression chamber is mounted about the exterior of the turbine draft tube or pump suction tube. A plurality of openings are provided about the exterior of the draft tube or pump suction tube communicating with both the interior of the draft tube or pump suction tube and the interior of the chamber near its bottom thereof. An air inlet is provided leading into the chamber at the top thereof. In operation, and during operation of the turbine or pump where a rotating helical vortex of water has formed in the draft tube or pump suction tube, water flows from the draft tube or pump suction tube through the openings and into the bottom of the chamber while air is injected into the top of the chamber.