Reliability that pays for itself

(Werdohl, June 2013)

Offline filters increase the productivity of hydraulic machines and systems

For the trouble-free and low-maintenance operation of hydraulic and lubrication systems, the cleanliness of hydraulic media is of utmost importance. 70 to 80 percent of all machine downtime is caused by impurities due to inadequate oil maintenance. Because precision hydraulic and lubrication systems work with gap dimensions in the micrometre range, even the smallest particles can lead to increased energy consumption due to friction, a reduction in the performance capacity or often costly downtime. It is not unusual for this to be caused by an unscheduled oil change or the replacement of sensitive components.

Contamination in hydraulic media can be the result of a variety of circumstances: Basically, a differentiation is made between existing contamination, caused by production, storage and installation of system components, subsequent secondary impurities, e.g., caused by damaged tank or cylinder seals or incorrectly dimensioned tank filler breathers, as well as contamination created within the system. Along with cavitation wear and particle jet erosion, this also applies to mechanical, biological and chemical mechanisms. Even fresh oil can usually not be classified as pure, because it is rarely micro-filtered during production and processing, and particles can be added during filling and transport (e.g. in refillable containers). Therefore, it is always recommended to fill a hydraulic system using an appropriately designed and dimensioned filter unit.

When replacing hydraulic meda it has to be considered, that a particular amount of contaminated oil will usually remain within the system (e.g. in the pipelines), while a complete cleanout by flushing the system would mean a substantial effort and thus would not be economically advantageous. Depending on the situation, it might be therefore recommended to filter the contaminated oil as well before emptying the hydraulic reservoir. This way, the cleanliness of the mix of used oil and fresh oil will stay on a resonable level.

The purity of hydraulic media is usually determined by the assessment of the number and size of the contamination particles found in 100 ml. No differentiation is made between the shape and composition of the particles. For the purpose of arriving at a reliable and comparable assessment of the impurity level, a so-called cleanliness class is assigned, which is defined in ISO 4406 (1999) and NAS 1638 among other regulations. The manufacturers of specific system components (such as pumps, motors, valves and cylinders) require binding compliance with the stipulated cleanliness classes, or they recommend them, whereby the components most sensitive to contamination are extremely important to the design of the filtration concept.

In addition to conventional full-flow filters which usually remove only the particles larger than 3 micrometres, the strategy at Stauff is to rely on a slow but continuous, and therefore very effective filtration of the so-called bypass flow of the system. The OLS offline filters with a built-in motor-pump unit that are used for this purpose can be subsequently integrated into the hydraulic system, and they function independently from the system cycle, even during scheduled machine downtimes. The fine, specially-developed cellulose filter medium removes even the tiniest impurities that are smaller than 1 micrometre.

At a renowned manufacturer of plastic caps and packaging systems, the purity level as per ISO 4406 (1999) improved by several levels within a period of just 6 weeks, thanks to the widespread use of offline filters on the injection moulding machines. In one case, for example, it changed from purity class 22/18/15 (corresponds to more than 2,000,000 particles cumulatively larger than 4 micrometres per 100 ml) to purity class 14/11/8 (corresponds to less than 16,000 particles cumulatively larger than 4 micrometres per 100 ml).

Picture 1:

Optional: OLS bypass flow filters with twin housing length
and pre-installed particle measuring unit LPM II

(Courtesy of Walter Stauffenberg GmbH & Co. KG)

Download picture (JPG, 10x10cm, 300dpi)

Picture 2:

A subsequently installed OLS offline filter on an injection moulding machine

(Courtesy of Walter Stauffenberg GmbH & Co. KG)

Download picture (JPG, 10x10cm, 300dpi)

Background Information

Walter Stauffenberg GmbH & Co. KG was founded in the 1950s in Werdohl, in the German province of North Rhine-Westphalia, and was initially a contract turning shop. Today the company operates under the trade name STAUFF, developing, producing and marketing fluid technology components for use in plant construction and mechanical engineering. In the fields of tube, pipe and hose clamps, measuring technology and hydraulic filtration, STAUFF is one of the world’s leading organisations in a growing industrial segment.

Meanwhile, more than 1200 employees (12/2012) in 18 companies generate an annual turnover of more than EUR 190 million (12/2012) worldwide. Additional distribution subsidiaries have recently been opened in Ireland, Malaysia and Vietnam. Besides the group headquarters in Werdohl Ehrenfeld, the company has production and logistics facilities in the German cities of Plettenberg-Ohle and Neuenrade-Küntrop.

Press Contact

Mr Boris Mette
Head of Marketing Communications
Tel.: +49 (0) 2392 / 916-154
Fax: +49 (0) 2392 / 916-270154
E-Mail: b.mette@stauff.com

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