9. Magnetic liquid vacuum seals

Abstract

Summary Magnetic liquids have been used as sealants in various devices over the last 20 years. There has been steady development in attaining more stable magnetic fluids and also several developments in the devices themselves, especially in shaft seals. The present seals and Ferrofluids used are described in the paper. Two 120 mm diameter 3000 rpm seals have been designed and made at Oxford University, and have proved successful in sealing a vacuum of 10−6 torr. More recent work with a static model has demonstrated the operating mechanism of a magnetic liquid seal and explains how a multistage seal adjusts itself to exactly contain the sealed pressure applied to it. The model was studied visually with a high speed cine camera and film is available to show a multistage seal in operation. The paper contains diagrams and still photos from these studies. The general operating characteristics of magnetic fluid seals are explained, which demonstrate the attributes and limitations of the seals. The paper concludes that present multistage magnetic liquid seals are ideally suited for sealing high speed shafts to vacuum with negligible leakage and long life.