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The basic demand on piston seals as well as on rod 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 overall demands on both these function-determining main seals in the hydraulic cylinder are meanwhile very different in many respects. In this section, we feature both single- and double-acting piston seals.
The choice of the type of piston seal is to a great extent decided by the way in which the cylinder operates. 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, for instance, 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.
Piston seals, both single- and double-acting, can be designed for and used with integrated or separate back-up rings and guide rings. The ultimate choice must be based on the operating conditions of the cylinder.