Strip the component and clean the parts by immersion in a heated ultrasonic tank with a detergent that suits the soil and the metal. Load each part so the galleries flood and trapped air can escape. Filter the bath, rinse the galleries, dry with blow-off and protect steel parts from flash rust. Then prove it with a particle count or a flow test. A part that looks clean at the mouth of a gallery is not proven clean inside it.
What has to come off
A hydraulic part on rebuild carries three kinds of soil:
- Oil and grease. Hydraulic fluid, assembly grease and preservative on every surface.
- Varnish. Oxidised fluid that has set into a film inside valve blocks and cylinders. Abrasives cannot reach it there.
- Particles. Swarf from machining rework, wear metal and dirt. One retained chip in a hydraulic gallery is a warranty claim waiting to happen.
The soil that matters most is the soil nobody can see: inside cross-drillings, blind holes and galleries.
The steps
- Strip and identify. Take the component apart. Note the metals, including anything plated, aluminium or soft in the assembly. The metal decides the chemistry and the temperature.
- Pick the detergent for the soil. Oil and grease: FX Degreaser, or AquaVantage 1696 GD where the metals are sensitive. Heavy grease and tenacious soil on steel or aluminium: AquaVantage 815 QR-NF. Baked varnish and sludge on ferrous parts: Desludge at 10 to 20% v/v and 40 to 60 °C.
- Heat the bath. Oil thins as it warms, so the same detergent at 60 °C does work it cannot do at 25 °C. Keep aluminium parts at or below 60 °C. Above about 70 °C cavitation weakens.
- Load for the galleries. Orient each part so the galleries fill and the air can get out. Cavitation cleans wherever the liquid reaches. An air pocket in a blind gallery is a dry spot that stays dirty.
- Run the ultrasonics. 20 to 28 kHz for heavy soil on robust steel and cast parts. 40 kHz for general precision work. The higher bands suit gallery-dense valve blocks with fine detail.
- Filter the bath. Swarf flushed out of the galleries falls into the bath. Without filtration it goes back into the next part. A weir skims the released oil off the top.
- Rinse, dry and protect. Rinse so the galleries flush clean. Dry with blow-off for blind holes and galleries. Dip steel parts in Anti-Rust at 2 to 5% v/v for 1 to 2 minutes if they will wait before assembly.
- Prove it. Flow-test or borescope the critical galleries against a known-good part. For a drawing that calls up a cleanliness level, count the particles to ISO 16232.
Hydraulic cleaning methods compared
| Method | What it reaches | Watch for |
|---|---|---|
| Spray washer | Outside faces and open bores | Stalls at the mouth of a gallery |
| Soak tank | Loose oil and grease | Varnish and packed swarf stay |
| Brush and air gun | What you can see | Pushes swarf further into cross-drillings |
| Ultrasonic immersion | Every surface the liquid reaches, galleries included | The part must be loaded so air can escape; the bath must be filtered |
Our article on blind holes and galleries covers the loading and the residue figures by method.
Which frequency for hydraulic parts?
Heavy rebuild work on steel and cast iron runs at 20 to 28 kHz. The large bubbles at that band shift heavy grease and varnish, and hard ferrous parts tolerate it. A 130 kHz tank on mining hydraulics does very little. Precision valve blocks with fine galleries and soft or polished faces climb the bands. See choosing the frequency.
How do you prove a hydraulic part is clean?
| Test | What it measures | When it fits |
|---|---|---|
| Flow test or borescope | Galleries open and clear | Every rebuild, on the critical galleries |
| Gravimetric residue | The weight of soil washed off | Specifications that call up a residue limit |
| ISO 16232 particle count | Particles by size on the part, as a cleanliness code | Hydraulic, fuel and engine components to a drawing |
| ISO 4406 | Particles per millilitre of the fluid | The assembled system, after flushing |
More on each test: clean is a number.
Clean parts, then a clean system
Clean parts can still go into dirty pipework. Weld spatter, mill scale, sealant and assembly grit leave a hydraulic system through the first pump or valve that fails. The fix is to flush the assembled system at high velocity through staged filtration until the fluid reads the target ISO 4406 code.
The HFU 600 does this at 10 to 600 litres a minute, through up to seven filter stages with a 5 micron final stage. An in-line particle counter ends the flush, and the printout is the record.
The machines that do it
- MSX benchtop (MSX 15 and MSX 30): brake and hydraulic parts, small valves and fittings.
- Ultrasonic parts cleaners (MSX 50 to MSX 240, EvoSonic): pump and valve bodies and manifolds.
- Large industrial ultrasonic cleaners: cylinders and heavy assemblies from mining and plant.
- Filtration: bag filters and housings for the bath.
- HFU 600: flushing the assembled system.
Questions we are asked
Can you clean a hydraulic valve block in an ultrasonic cleaner?
Yes. Cavitation works wherever the liquid reaches, so it cleans inside galleries and cross-drillings that a brush or spray cannot reach. Load the block so the galleries flood and the air can escape, then rinse and dry with blow-off.
What detergent cleans hydraulic oil off parts?
A surfactant detergent in a heated bath. FX Degreaser covers oil and grease on mixed metals. AquaVantage 1696 GD suits sensitive metals. AquaVantage 815 QR-NF takes heavy grease off steel and aluminium. Baked varnish on ferrous parts needs hot alkali such as Desludge.
What frequency should I use for hydraulic parts?
20 to 28 kHz for heavy soil on robust steel and cast parts. 40 kHz for general precision work. Higher bands for fine galleries and soft or polished surfaces.
Will ultrasonic cleaning damage seals or soft parts?
Strip the component first and clean the metal parts. Check each material against the chemistry before it goes in. Soft alloys erode faster at the low, aggressive bands, which is why aluminium work moves up the bands.
How do I know the galleries are clean?
Flow-test or borescope the critical galleries against a known-good baseline. Where a drawing calls up a cleanliness level, count the particles to ISO 16232 or weigh the residue.
Is cleaning the parts enough before commissioning?
No. The pipework and the rest of the system also carry debris. Flush the assembled system until the fluid reaches the ISO 4406 code the component maker specifies.
Related: Mining equipment cleaning · Matching chemistry to the soil · Parts washers · Hydraulic flushing
Send us a part
Tell us what the component is, what it is made of and what is on it. We clean it and send back the result.