In the fields of hydraulics and pneumatics, Kaco U-rings are most often used for sealing purposes on longitudinally moving pistons and rods. These are manufactured with various lip versions as has already been explained in more detail in the section on “structure and operation”.

The gap width between the housing and rod or between the piston and cylinder has a decisive influence on the useful life of U-rings. As a rule, this should normally not be more than 0.15 mm. Only in the case of pressures below 20 bar can a larger clearance be permitted. In the case of an excessively large gap, the sleeve rear deformed by the pressure gives way in the intermediate chamber. As a result of this, rubber particles are sheared off and the useful life of the seal is reduced.

The field of pneumatics is the main field of application for U-rings of the PNN…N and PNN …A series. These can have a sharp or rounded sealing edge. The design the nation provides information on the design of the sealing lips:

PNN…N  sharp sealing edge (trimmed)
PNN…A  rounded sealing edge (completely molded).

PNN…N series U-rings are also used for special hydraulic applications (e.g. water) (figure 26 shows an installation example). Support rings are necessary as the sealing lips must be removable in all cases and the edges may not come into contact in the axial direction. The height of the support ring must be such that approximately 0.5 mm space remains between this and the U-ring.

Technical data:

Pressure range                                  ≤  100 bar

Permissible sliding speed               ≤ 0.3 m/s
Tolerances

dynamic (rod)                    h 11   (cylinder)            H11

static (piston)               h 11  (housing)           H 11