Pump replaced, new distributor installed, system filled with fresh oil. The machine returns to the battlefield, but after a week of work, it loses power again, and an ominous grinding sound comes from the vicinity of the pump? In 8 out of 10 such cases, the culprit is one – dirt that was not caught by the system's "kidneys," i.e., hydraulic filters.
Replacing the pump without replacing filters and flushing the system is like taking a shower in dirty clothes. BRhydraulic experts have prepared a guide that will help you organize your knowledge about filtration once and for all, choose the right microns, and stop throwing money down the drain.
1. The Holy Trinity of Filtration – Which Filter Does What?
Modern hydraulic systems rarely use only one filter. Depending on how valuable and sensitive the hydraulics in your machine are, different lines of defense are used. See how they differ:
| Filter Type | Mounting Location | Main Task and Accuracy |
| Suction Filter | Inside the tank, directly on the pipe leading to the pump. | Catches the largest "debris" (pieces of seals, large metal shavings) so they don't tear the pump apart. Usually, it's a coarse metal mesh (60-90 µm). A filter that is too dense will lead to cavitation! |
| Pressure Filter | After the pump, and before the most expensive components (e.g., proportional distributors). | Protects the most sensitive components from contamination generated by the pump itself. Must withstand enormous pressure (up to 300 bar). Very accurate (10-25 µm). |
| Return Filter | At the end of the system, on the return line just before the oil enters the tank. | The system's "cleaner." Catches metal shavings from wearing cylinders and motors before the oil returns to the tank. Standard accuracy is 10-25 µm. |
2. The Magic of Microns (µm), or How Clean is "Clean"?
Many customers simply look for "a filter for an excavator" without paying attention to the accuracy of the cartridge. This parameter is expressed in micrometers (microns). To realize the scale: a human hair is about 70 µm thick. The most dangerous for valves and pumps are particles invisible to the naked eye – those between 5 and 15 µm!
-
Too fine a filter (e.g., 1 µm in a standard tractor): It will clog up instantly, and by creating enormous resistance, it will slow down oil flow and raise its temperature.
-
Too coarse a filter (e.g., 90 µm on return): It will allow fine metal dust to pass through, which will act on cylinder surfaces like the sharpest sandpaper.
-
The golden mean: In standard power hydraulics (agricultural and construction machinery), for return filters, glass microfiber or cellulose cartridges with an accuracy of 10 µm or 25 µm are most commonly used.
3. The Silent Killer – What is the By-Pass Valve for?
"I don't change the filter because the oil keeps flowing, and the machine works" – this is the biggest myth in workshops! Return and pressure filter housings have a built-in bypass valve.
When the filter cartridge becomes clogged with dirt, the pressure before it drastically increases. To prevent the filter housing from rupturing, the by-pass valve opens. The result? Oil bypasses the filter and flows sideways, carrying all the accumulated mud and metal shavings directly to your distributor. The machine continues to work, but in reality, it is destroying its most important components with every passing minute.
BRhydraulic tip: Always choose filters equipped with a clogging indicator (visual manometer or electrical sensor). This tells you exactly when the cartridge needs to be replaced, before the bypass valve opens.
4. Golden Rules for Filter Replacement
-
Always after a breakdown: If you replaced a seized bearing, a damaged pump, or a ruptured cylinder – the old filter cartridge absolutely goes into the bin. Otherwise, metal shavings from the old pump will destroy the new one.
-
Schedule: In intensively operating machines, replace the return filter at least once a year or every 500-1000 operating hours (according to the machine's DTR).
-
Bleeding: After replacing the cartridge, don't forget to bleed the system, especially if you replaced filters on the suction line!
Summary
A filter cartridge costs a fraction of a new gear pump or an advanced spool valve. Regular replacement of filtering elements is the cheapest and most effective insurance for your machine.
