For sealing piston rods, these special U-rings are available for the relatively small installation spaces found in the fields of pneumatics and hydraulics up to100 bar.

Kaco PNI type U-rings distinguish themselves from the standard type U-rings by their unevenly long sealing lips. The external, static sealing lip is longer and often has a larger cross-section in order to guarantee support in the axial direction without impairment of functioning. Therefore, special support rings or similar supports are not necessary.

During installation, PNI U-rings can be snapped by hand into a location groove which can be manufactured easily and cheaply. In order to guarantee good functioning, it is necessary that the U-ring still has an axial clearance of 0.5 to 0.8 mm when installed.

Regarding sealing function, frictional force, and service life, the dynamic sealing lip has an optimum design. Sharp sealing edges are used for sealing liquid media.  Rounded sealing edges, which require no mechanical after treatment after pressing, are predominantly used in aeriform and gaseous media. Because of the pressing skin on the contact surface, especially in the case of lacking lubrication, this version is more resistant to wear and tear and has a longer service life.

The various lip shapes are found as follows in the
designations of the U-rings:

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

Technical data:
Pressure range

hydraulics                                ≤ 100 bar

pneumatics                              ≤ 16 bar
Permissible sliding speed

hydraulics                                ≤  0.3 m/s

pneumatics                              ≤ 1 m/s
Tolerances

dynamic (rod)                      H11

static (housing)                    H11

One advantage of PNI U-rings for application consists of the fact that, during installation, they are compressed by a certain, predetermined dimension. Asa result of this, the relatively large manufacturing tolerances, especially in the case of rod diameters of more than

40 mm, referred to the diameter, can be ignored and the considerably smaller tolerances, referred to the sealing ring cross-section, can be applied during manufacture. In addition, as a result of the smaller tolerances, jamming on the dynamic lip side is also
avoided and it is possible to narrow down the frictional force range.