The basic demand on piston seals for hydraulic cylinders under the operating conditions, for which they have been chosen, is to maintain a high level of sealing performance during their service life. The choice of the type of piston seal is to a great extent depending on the way in which the cylinder operates, i.e. in single-acting or double-acting operations. For a cylinder, which is exclusively single-acting, it is always best to choose the type of seal designed to provide optimum sealing qualities for single-acting functions with e.g. the thinnest possible lubrication film that can pass through the contact area between the seal and the cylinder tube surface. The best sealing capacity of a double-acting cylinder is achieved by choosing a double-acting seal. A piston design where two single-acting seals on the piston for a double-acting cylinder are used can easily give rise to a breakdown. The reason is that a very high pressure can be trapped between the seals. Contact your local SKF representative for more details. | 
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