One micron-scale particle at the compensation valve is enough to make bleeding impossible. Cleanliness is measurable — ask for the report.
Those who say Chinese parts are dirty and those who say local parts are dirty are usually describing the same thing. A single micron-scale particle can hold a compensation valve open: the pedal misbehaves immediately, and the circuit becomes almost impossible to bleed.
Why one particle is enough
- The compensation valve seals at micron precision.
- A grit particle trapped at the valve seat stops fluid returning correctly, and the pedal changes feel straight away.
- Worse, it makes bleeding very difficult, so the technician blames the cylinder body and replaces a part that was never the problem.
Where the reputation comes from
- The impression that Chinese parts are poor usually traces back to a few early batches with unclean internals.
- Local parts are criticised by technicians for exactly the same thing — dust out of the box.
- Same root cause on both sides: an assembly environment and a cleanliness check that were never taken seriously.
Making it verifiable instead of arguable
- Cleanliness is measured per batch, with the particle grade reported.
- Assembly environment control runs alongside port plugging and internal dividers, so the part is not recontaminated in transit.
- The report is available on request, and it is worth comparing against whatever else you are buying.
The conclusion is one line
Ignore the country of origin and read the report. A per-batch cleanliness report is the first sieve — if a supplier cannot produce one, the rest of the conversation is guesswork.