This invention relates to rotating seals for continuous flow centrifuges.
Continuous flow centrifuges provide a continuous flow of fluid into and out of a spinning rotor. This is accomplished by the use of rotating seals having a rotating disk and a stationary disk in face-to-face contact. Typical of rotating seals used in centrifuges of this type are those described in U.S. Pat. No. 4,011,972 issued to Pederson, British Pat. No. 925,677 and German Offenlegungsschrift No. P 19 10 576.1 filed by Heraeus Christ of Germany.
In the rotating seals described in these prior art patents, the rotating disk is coupled by a flexible shaft to the rotor while the stationary or nonrotary disk is spring mounted to the rotor housing. While the rotating seals used in these prior continuous flow centrifuges have certain advantages, they also have many drawbacks. Among these drawbacks are that the rotating seal causes the nonrotating disk to "toss" because of misalignment induced vibrations between the contacting disk faces. Also, vibrations of the rotor are amplified by the shaft coupling the rotor and seal.
To alleviate some of these problems, the prior art sought to isolate the seal from the system vibration by the use of spring pressure to maintain good contact between the disk faces. Unfortunately, too strong a spring pressure causes undue wear of the seal faces. Vibrations in the system tend to cause leakage between the seal faces, particularly in situations where the rotor is not perfectly balanced.
This vibration induced leakage becomes a particular problem in sedimentation field flow fractionation (SFFF), a technique described in U.S. Pat. No. 3,449,938 issued June 17, 1969 to John C. Giddings and U.S. Pat. No. 3,523,610 issued Aug. 11, 1970 to Edward M. Purcell and Howard C. Berg. Sedimentation field flow fractionation uses a long, thin annular belt-like channel which is rotated about the axis of the channel annulus. Because the belt-like channel has a significant mass located at extreme radial distances from the axis of rotation, vibrations induced in this system can be severe. Under these conditions, existing seals have been found to be not entirely satisfactory. As noted, even small vibrations of the rotating system are amplified by the rotating shaft which connects the rotating seal and rotor. This serves only to increase the leakage.