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MDA Technologies 2/2015

MDA Technologies 2/2015

Dynamic sealing system

Dynamic sealing system for mini excavator actuators Fabio Bueti Thanks to their flexibility and versatility 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. They often handle a Herculean workload in harshest conditions. A tandem sealing system developed by Parker-Prädifa helps ensure that the little ‘heavy-duty diggers’ meet current and future demands in terms of loads, service life and eco-friendly operation. Fabio Bueti, Application Engineering Fluid Power, Parker Engineered Materials Group Europe, Packing Division, Parker-Prädifa, 74321 Bietigheim-Bissingen The service life of sealing systems in mini excavator applications today plays a much greater role than it did in the days of the so-called ‘disposable excavator.’ That was the expression coined at the time for the mini excavators that were frequently utilized in landscape gardening. The reason for calling them ‘disposable’ was their much shorter lifespan compared with large excavators, as a result of which they would either be scrapped right away or disappear in the second-hand market where they would often be used for non-commercial purposes. Today, in the light of increasingly constrained space conditions, mini excavators play an increasingly important part in diverse projects such as new residential construction, rehabilitation work on existing buildings and facilities, as well as in clearing work following natural disasters. In contrast to large excavators, they can be utilized in tight spaces or hard to access areas and, due to their low weight and small size, they can be loaded on trucks for fast and easy transportation to the project site. Increasing demand meets with increasing requirements As a result, mini excavators, thanks to their practical and flexible uses, have been in increasing demand around the world. This demand is being met by a large number of 48 MDA Technologies 2/2015

CASE STUDY 01 Parker tandem sealing system 02 AV wiper product features manufacturers offering a wide range of models and sizes. At the same time, however, the extended range of uses and harsher operating conditions lead to higher demands being made on these excavators in terms of service life, performance and efficiency, as well as ease of operation and maintenance. The resulting high design requirements particularly affect the manufacturers of hydraulic cylinders – typically guard, swing, shovel and boom cylinders – and thus the sealing systems used in them. The requirements for longer service intervals in the face of consistently increasing service pressures and significantly changed ambient conditions are fully transferred to sealing performance as well. This also applies to the increasing demand for leak-free cylinders under the heading of ‘clean hydraulics.’ Optimal pairing of seal design and material The sealing and materials specialist Parker- Prädifa began to address the progressively higher demands made in the field of hydraulics several years ago and developed a solution that has since been proven in numerous applications. This solution, which also satisfies the increased requirements in mini excavator actuators, is a tandem sealing system featuring a special design in combination with hydrolysis-optimized and wear-resistant polyurethane materials as described in detail below.(Figure 01). Wiper with Integrated dirt shield The wiper is the major element on the hydraulic working cylinder to prevent dirt ingress. It protects the entire hydraulic system against dust, dirt, moisture and other environmental influences. 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. The AV wiper profile developed by Parker-Prädifa MDA Technologies 2/2015 49

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