Single-acting piston seals
UNP profiles (fig. 1) are single-acting U-cup seals made of thermoplastic polyurethane (TPU). They are suitable for pressures up to 350 bar (5 075 psi) and are available in metric (→ Size list [pdf]) and inch sizes (→ Size list [pdf]). For additional information, refer to UNP profile data.
In case of higher pressures, SKF provides full-face anti-extrusion rings on request. For additional information, contact SKF.
Single-acting piston seals in double-acting cylindersTwo single-acting U-cup profile seals, facing in opposite directions, can be used in a doubleacting cylinder. It is important to select seal designs which can relieve reverse pressure for such arrangements to prevent build-up of pressure between the two seals. UNP profiles are suitable for such double-acting arrangements because the dynamic seal lip can flex to relieve reverse pressure.
Rod seals used as single-acting piston seals
Some rod seal profiles are designed with similar inside and outside sealing geometry and, therefore, can also be used as single-acting piston seals in single- or double-acting cylinders (fig. 2). PTB, STD and DZ rod seal profiles (→ Rod and buffer seals) can be used for those applications.
Rod seals with loaded-lip U-cup profiles may not relieve reverse pressure, but it is possible to remove their energizer (X-ring) from one of the seals to allow reverse pressure relief (fig. 2).