The Parker Prädifa rod sealing set profile M3 consists of 5 chevron rings (3 fabric-reinforced and 2 rubber seals), 1 header ring, and 1 back-up ring. The header ring may be manufactured of hard fabric material or of plastic. The back-up ring is only manufactured in hard fabric. For rod diameters of 80 mm and larger we supply these sets with 4 fabric reinforced chevrons and 1 rubber seal. For diameters of 14C mm and larger the sets contain 5 fabric reinforced chevrons. In case of dimensions different from those mentioned in this leaflet please choose a packing set combination from our MO-programme. Our sales department will inform you of the respective order code.

The main advantages of these rod sealing sets are:

• Adjustability to different fluids and temperature ranges by proper choice of suitable compounds
• Adaptability to exceptional working conditions by changing or adjusting the axial preload (shims or screw rings).
• Not sensitive to high-pressure peaks on account of form stability.
• Not sensitive to contamination of the medium, or slight damages to the sliding surfaces in comparison with one-piece seals.
• It is possible to split the seals to facilitate the installation. Thus it is not necessary to fully dismantle the cylinder in the case of maintenance or repair.
• Excellent sealing performance due to long contact area and several sealing lips.

The Parker Praedifa chevrons are manufactured with radial preload, which provides close contact of the sealing lips at the inside and outside diameters achieving a good sealing performance with low friction. The operating pressure is effective in providing a close fit between the sealing set and the mating surfaces. An optimum adaption of the relative friction to tightness may be achieved by an adjustable housing (screw rings or shims). Due to this adjustment facility, it is possible to achieve a longer working seal life.

Field of application:

Working pressure:                   ≤ 500 bar

Working temperature:           —40 to +100 °C

Surface speed:                          ≤ 0,5 m/s

Chevron sealing sets are well suited for the sealing of plungers, piston rods of presses, cylinders, valve shafts, and spools, even in difficult working conditions. Thus they can be recommended for use where the actual conditions are difficult to predict.

Compounds:

Back-up ring:  Hard fabric, NBR-based (Q5021/ Q5022).

Chevrons: Fabric reinforced rubber material, NBR-based (05018/Q5019) resp. NBR elastomer
(N3578).

Header ring: Polyacetal (POM-W5001) or hard fabric, NBR-based (Q5021/Q5022).

For special requirements (pressure, temperature, speed, etc.) please contact our Consultancy Service, so that suitable materials and/or designs can be recommended.

Installation:

Due to the relatively low elasticity of the fabric chevrons and the required axial preload of these sealing sets, an installation groove, which is open on one side has to the provided. The actual height of the set is normally in accordance with the length
“L” of the housing. Manufacturing tolerances of the seals and the metal parts (especially in case of large dimensions) may be compensated for by screwrings or shims in order to achieve an optimum function. (Adjustability at least 5 `)/0 of the length “L”).

When strongly squeezed the flexibility of the sealing set may be substantially reduced. Thus it could be transformed to act as rod guidance with excessive friction and high wear. Due to the adjustability, it is possible to use these sets for special applications: For example in case of high speed, exceptionally large temperature range, strongly varying pressure, or a combination of these parameters. The various components of the set must be installed individually according to their sequence within the set. Oiling or slightly greasing will facilitate the assembly. Fabric chevrons with relatively large cross-sections can be made more flexible by slightly kneading them in warm oil. This will facilitate the installation considerably. For easier maintenance, the sealing sets may also be slit. The chevrons and the back-up the ring are cut at a 45° angle, the header ring with a 90° angle. The cuts of the components must be staggered by 120° at installation, which will not alter the length of the housing.