Abstract: A method and device are disclosed for fitting a shaft-butterfly valve unit in a pipe formed by a butterfly valve body. The device comprises a frame receiving the pipe with its unit. It also comprises a first thruster for moving the shaft in a first direction as far as the first abutment position and a second thruster for moving the shaft in the opposite direction as far as the second abutment position. A sensor detects the abutment positions, and the gap (j) between the abutment positions is computed. The first or second motor is controlled for moving the shaft from the first or second abutment position by a distance equal to a predetermined fraction of the gap.