A rotary union adapted to be used for transferring a fluid in a machine between a fixed part and a rotary shaft ; the rotary union comprises: - a rotary manifold provided with at least a first fluid passage ; said rotary manifold being defined by the shaft or being suitable for being coaxially mounted on the shaft in angularly fixed position relative to the shaft ; - a stationary manifold provided with at least a second fluid passage and coaxially mounted on the rotary manifold by means of bearings ; - fluid communication passages to establish a fluidic communication between the first fluid passage and the second fluid passage ; and - an intermediate manifold arranged between the stationary manifold and the rotary manifold , mounted coaxially on the rotary manifold by means of bearings , and provided with at least one third fluid passage fluidically communicating with the first fluid passage and the second fluid passage through said fluid communication passages ; rotary union characterized in that it comprises: a gear train arranged between the stationary manifold and the rotary manifold in such a way to cause the rotation of the intermediate manifold at a speed lower than the speed of the rotary manifold during operation. a fixed part and a rotary shaft ; the rotary union comprises: - a rotary manifold provided with at least a first fluid passage ; said rotary manifold being defined by the shaft or being suitable for being coaxially mounted on the shaft in angularly fixed position relative to the shaft ; - a stationary manifold provided with at least a second fluid passage and coaxially mounted on the rotary manifold by means of bearings ; - fluid communication passages to establish a fluidic communication between the first fluid passage and the second fluid passage ; and - an intermediate manifold arranged between the stationary manifold and the rotary manifold , mounted coaxially on the rotary manifold by means of bearings , and provided with at least one third fluid passage fluidically communicating with the first fluid passage and the second fluid passage through said fluid communication passages ; - a rotary manifold provided with at least a first fluid passage ; said rotary manifold being defined by the shaft or being suitable for being coaxially mounted on the shaft in angularly fixed position relative to the shaft ; - a stationary manifold provided with at least a second fluid passage and coaxially mounted on the rotary manifold by means of bearings ; - fluid communication passages to establish a fluidic communication between the first fluid passage and the second fluid passage ; and - an intermediate manifold arranged between the stationary manifold and the rotary manifold , mounted coaxially on the rotary manifold by means of bearings , and provided with at least one third fluid passage fluidically communicating with the first fluid passage and the second fluid passage through said fluid communication passages ; rotary union characterized in that it comprises: a gear train arranged between the stationary manifold and the rotary manifold in such a way to cause the rotation of the intermediate manifold at a speed lower than the speed of the rotary manifold during operation. <EOS>