Four signals
① Falling impact: residue appears at the same pressure and flow. ② Pattern distortion: wider fan, split or tail. ③ Flow drift: larger spread between nozzles of the same model. ④ Surface defects: longitudinal streaks, local over-cooling.
Why measure instead of eyeballing
An orifice change of a fraction of a millimetre can visibly cut impact — invisible to the eye. Periodic flow or impact checks are far cheaper than chasing a quality complaint later.
Material sets life
Tungsten carbide inserts outlast plain stainless under high pressure and particulates — but everything wears; the point is knowing when to replace.
General industry knowledge; confirm parameters against your process and measurements.