Thanks to their flexible uses, modern mini excavators perform a wealth of important tasks in construction and rehabilitation projects, up to and including clearing work after natural disasters and much more, around the world. They often handle a Herculean workload in harshest conditions which pose a challenge particularly to the hydraulic cylinders and the sealing systems inside them. A tandem sealing system developed by Parker-Prädifa now helps ensure that the mini excavators meet the high demands made on them in terms of service life, performance and efficiency, as well as ease of maintenance and eco-friendly operation.
The tandem sealing system features a special design in combination with hydrolysis-optimized and wear-resistant polyurethane compounds and consists of the following components:
As a result of increasingly sensitive elements within the hydraulic circuit the wiper function becomes ever more important as well because contaminated fluid systems are a frequent cause of total system failures that lead to high consequential costs. To prevent this, Parker-Prädifa has developed the special AV wiper profile with an integrated dirt shield. It is available in a wide range of materials and exhibits improved wear resistance and low compression set (standard version: Parker compound P5008).
Bulletin “AV Wiper”
Pressure peaks of up to 1,000 bar (approx. 14,504 psi) are not uncommon in the cylinders used in mini excavators. To isolate the load from the secondary seal, the BU rod seal is installed in front of it. It returns the pressure that can build up between the primary and the secondary seal under certain conditions to the hydraulic working system like a check valve. This prevents damage to the secondary seal due to excessive intermediate pressures and the resultant reduction of service life.
Catalog “Hydraulic Seals”, Page 92-93
The HL profile “secondary seal” utilized in this tandem sealing system typically operates as a non-pressurized seal. Due to the cascading dynamic sealing lips the seal is automatically controlled by the system pressure. In non-pressurized conditions, it latches on to the mating surface only with the “tip” of the first sealing lip, thus ensuring optimal ease of movement.
Brochure "HL Rod Seal"
The design of the OK piston sealing set and profile properties superbly fit the requirements and operating conditions in mobile hydraulics. In addition to its extreme wear resistance, this sealing set exhibits further positive properties such as insensitivity to extreme pressure peaks, maximum extrusion resistance in the case of high pressures and large gaps, short axial installation length (dimensions according to ISO 7425-1) and easy installation.
Catalog “Hydraulic Seals”, Page 115-117
In mobile hydraulics, Parker-Prädifa prefers guide rings based on duroplastic synthetic resins with fabric reinforcements. This corresponds to the FR and FK guide rings using the Q5038 compound. The low guidance lash and the higher permissible surface compression of the guide materials ensure reliably centric guidance of the piston rod. As a result, neither the surface of the piston rod nor the sealing elements are affected.
Catalog “Hydraulic Seals”, Page 57-66
The Parker tandem sealing system has proven its viability in diverse applications and ambient conditions. Due to the continuous further development of the seal design and sealing materials the sealing systems are continually modified to meet the end user’s requirements.
An extensive version of this article with further product details and background information can be found here:
EMG Report, April 2015, Page 10
Article contributed by Fabio Bueti,
Engineered Materials Group,
Packing Division Europe