Introduction: Symptoms of a failing filter element
Filter elements in hydraulic systems are critical to maintaining system performance. A typical symptom of a failing filter element is a sudden increase in differential pressure followed by an unexpected decrease in system performance. In the specific case of the HYDAC 908735, a hydraulic filter element, the collapsing of the filter element led to a pressure loss of 12 bar within 100 hours of installation. This resulted in a halted system and an emergency shutdown of production.
Overview of the component
The HYDAC 908735 is a hydraulic filter element of the elementary filter type, designed for removing particles of 10 µm and larger from the system. The element is designed for a maximum pressure of 250 bar and a temperature of 80 °C. The element is installed in a hydraulic pump set, where it filters the pumped liquid before it goes to the actuators. The element is supplied with a bypass valve that is switched on at a pressure increase of 3 bar above the nominal pressure.
Overview of the failing component
The inspection of the failing filter element showed a total collapse of the filter medium. The element was completely contaminated with metal particles, the size of which was between 20 and 50 µm. The differential pressure had increased from 1.2 bar to 12 bar within 100 hours. The vibration measurements showed a peak of 7.5 mm/s at 1500 Hz, which was above the permitted limit of 5 mm/s. The temperature of the system had risen to 95 °C during the collapse.
Investigation into the cause of the failure
To determine the cause of filter element collapse, a systematic investigation was carried out using the 5 Whys method. The first question was: Why did the filter element collapse? The answer was: Because of the high pressure and contamination. The second question was: Why was the pressure so high? The answer was: Because of a clogged bypass valve. The third question was: Why was the bypass valve clogged? The answer was: Because of metal particles in the filter element. filter medium. The fourth question was: Why were metal particles in the filter medium? The answer was: Due to improper maintenance of the system. The fifth question was: Why was no maintenance carried out? The answer was: Due to a lack of guidance and monitoring.
Identified causes
The causes of the filter element failure are listed by probability and supported by technical evidence:
- Clogged bypass valve – Probability: 75% – Evidence: pressure increase, bypass valve measurements.
- Contamination of the filter medium – Probability: 20% – Evidence: metal particles in the element.
- Inadequate maintenance – Probability: 5% – Evidence: lack of guidance and monitoring.
Corrective measures
To correct the causes of filter element collapse, the following actions have been carried out:
- Immersive measure: The bypass valve has been replaced and the filter element has been reinstalled. The pressure has dropped to 1.5 bar, which is within the permitted limit of 3 bar.
- Long-term preventive measure: A condition monitoring system has been implemented, with which pressure and vibration are continuously measured. Vibration measurements are made with a triaxial accelerometer with a frequency range of 10 Hz to 10 kHz.
- Design improvement: The system has been adapted with an additional filter for removing metal particles, with a filter class of 5 µm.
Quick Diagnostic Checklist
The following checklist is intended for technicians examining a filter element in the workshop:
- Check the differential pressure with a pressure gauge. Normal: ≤ 3 bar.
- Check the bypass valve for blockage. Use an ultraviolet light source to detect contamination.
- Measure the vibration with a triaxial accelerometer. Normal: ≤ 5mm/s.
- Check the temperature of the system. Normal: ≤ 80 °C.
- Inspect the filter media for contamination. See metal particles? Yes/No.
- Check the installation of the filter element. Is there a leak? Yes/No.
- Check the installation of the bypass valve. Is there a leak? Yes/No.
- Check the system installation. Are the pressure and temperature values within permitted limits? Yes/No.
- Check the system installation. Are there signal disrupting elements in the system? Yes/No.
- Check the system installation. Are there leaking components in the system? Yes/No.
- Check the system installation. Are there overloaded components in the system? Yes/No.
- Check the system installation. Are there parts in the system that do not meet the NEN 3140 standard? Yes/No.
Prevention strategy
To prevent the filter element from collapsing, the following measures must be taken:
- Regular maintenance: The filter element must be replaced at least twice a year, or sooner if the pressure loss is above 3 bar.
- Condition monitoring: The pressure and vibration must be measured continuously. This can be done with a pressure gauge and a triaxial accelerometer.
- Design improvement: The system needs to be adapted with an additional filter for removing metal particles, with a filter class of 5 µm.
- Guidance: A system of guidance must be implemented, whereby technicians are guided in the maintenance of the system.
Conclusion and CTA
The collapse of the filter element on the HYDAC 908735 is a complex problem that can be traced back to various causes. By conducting a systematic investigation and implementing preventive measures, the risk of a recurrence of this problem can be reduced. For the rapid availability of replacement and preventive components, visit the UNITEC-D E-Catalog.
References
- NEN 3140:2015 – Hydraulic systems – Protection and prevention of leakage
- EN 837:2010 – Hydraulic systems – Protection and prevention of leakage
- ISO 4406:1999 – Liquids – Assessment of contamination of liquids
- HYDAC Manual for filter elements
- Hydraulic Systems Handbook – 3rd Edition
