Positive Action seals have been known and used in Europe for more than 20 years. Early designs used the “Threaded Bush” principle, but this was developed into the “Spiral Groove” principle in order to achieve the advantages of economic production along with positive action sealing. The paper presents a historical survey of these developments and outlines the current situation. Reference is also made to “Duo-Positive” seals (i.e. Positive Action seals which operate equally effectively for both directions of shaft rotation).

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