Most hydraulic failures trace back to contaminated oil, and the filters are the only thing standing between contamination and the valves. Yet both “change it on schedule” and “change it when it alarms” get the timing wrong — the differential pressure itself is the only reliable signal.
Three circuits, three maintenance logics
Suction side (tank → pump). Protects the pump with a coarse element and minimal pressure drop. Signs of a clogged strainer are pump noise and cavitation. Mesh elements can be cleaned and reused; paper elements are replace-only.
Return side (system → tank). The net that catches system wear debris. Return filters such as the MP Filtri MPF / MPFX series carry a clogging indicator: when the needle enters the yellow zone, order the element; at red, replace immediately — once the bypass opens, everything it caught flows straight back to the tank.
Pressure side (pump outlet / upstream of key valves). Direct protection for servo and proportional valves, with little pressure-drop headroom. Pressure filters such as the MP Filtri FHP / FMP series use stronger, costlier elements — which is exactly why the clogging indicator should set the schedule, not the workshop calendar.
Cleanliness management
- Define a target ISO 4406 cleanliness class (servo systems typically one or two classes cleaner than general circuits) and sample periodically.
- New oil is not clean oil — filter every top-up, and put the breather and air filter on the maintenance list too.
- When changing oil, clean the tank sump; otherwise yesterday’s contamination re-enters the system within hours.
Common mistakes
| Mistake | Consequence |
|---|---|
| Calendar-based element changes | Wasted elements, or months running in bypass |
| Opening the bypass to keep running | Contamination straight into servo valves, wider failures |
| Replacing elements without finding the source | Cleanliness never stabilises, cost keeps climbing |
| Choosing a finer rating “for better protection” | Higher pressure drop, bypass cycling, cavitation risk |
Indicators and sensors
Clogging indicators come as visual, mechanical and electrical versions; the electrical type feeds the pressure signal into the PLC for remote alarming. Check the indicator itself when replacing the element — a filter with a dead indicator has no early warning at all.
Replacement and spares
Send us the part number on the filter head and we will match it directly. Cross-reference across the MP Filtri suction, return and pressure ranges is straightforward, with common elements partly stocked and the rest sourced through the original channel with documentation.
- Browse the MP Filtri hydraulic filtration range we carry.
- Or go straight to the inquiry form.