Contaminated oil is the leading cause of pump wear, valve sticking and cylinder seal failure in hydraulic systems. An oil filter installed in the right location, with the right filtration rating and with its element replaced on time, is the cheapest way to extend equipment life.
Three main filter locations
| Location | Function | Characteristics |
|---|---|---|
| Suction filter | Protects the pump from large contaminants | Coarse filtration, low pressure drop to avoid pump cavitation |
| Pressure filter (high-pressure line) | Protects valves and sensitive components | Withstands the system working pressure |
| Return filter | Captures contaminants generated in the system before the oil returns to the tank | Fine filtration, usually mounted on the tank cover |
In addition, the breather filter on the tank cover keeps dust and moisture out when the oil level changes. This location is often overlooked.
Filtration rating and beta ratio
Filtration efficiency is rated by the beta ratio (βx). For example, β10 ≥ 200 means that for particles of 10 µm and larger, at most 1 out of every 200 particles entering the filter passes through, equivalent to an efficiency of 99.5%. Oil cleanliness is usually expressed as an ISO 4406 code. Pump and valve manufacturers recommend the cleanliness level to be achieved.
Magnetic filters
Magnetic filters use magnets to capture iron particles generated by wear before the oil passes through the fine filter element, extending the element’s life. This type suits systems with many moving steel parts, such as presses and rolling mills.
When should the filter element be replaced?
- Replace it when the clogging indicator (differential pressure gauge or switch) is triggered, without waiting for the scheduled interval.
- The bypass valve opens when the element is heavily clogged to protect the filter, but unfiltered oil then flows straight into the system. Do not let the system run for days in this condition.
- Replace the filter element after major repairs, after an oil change or when oil contamination is detected.
- Use genuine filter elements or elements with the correct specifications (filtration rating, media, differential pressure rating).
Dong Tam supplies Leemin hydraulic oil filters and filter elements: suction filters, return filters and magnetic filters for hydraulic power units and industrial machinery.
Need specific advice for your plant? Contact Dong Tam for support from our engineers.