a neutral buoyancy auto - balancer eliminates the need for complex manipulation and operation in accordance with a change in diving depth . the auto - balancer automatically follows , rapidly and precisely , the change in diving depth by natural breathing during diving , and resolves the risk of failure of air - trapping not only in the vertical position but also in a slanted position to automatically follow a working posture of the diver . the neutral buoyancy auto - balancer comprises a weight 4 which radially outwardly extends from a shaft 14 which is rotatably supported at central holes 121 , 131 of a cylinder 11 body . a nozzle 22 of an inlet duct 2 is fixed in the opposite direction to the projected weight 4 . an inlet port 32 of an outlet duct 3 for both air evacuation and feed and drainage of water radially outwardly opens in the same direction as the weight 4 . an angular displacement adjusting means 6 of the outlet port is provided for operably adjusting the direction of the outlet port with respect to the weight at any desired angle , and an initializer means 5 is provided for initializing a water level of the cylinder .