Predictive Maintenance
A nozzle 10% oversize passes 21% more air for a weaker jet — and every nozzle wears together, so nothing looks wrong.
— mm
After erosion at the pick count given
A negative picks-remaining means the nozzle is already past its threshold, which is the common finding — relay nozzles are cheap and rarely tracked, so they are usually changed on a stoppage rather than on wear. Uniform linear erosion is assumed and real wear is directional, biased toward the side the weft strikes, so the jet loses coherence and aim before the diameter figure suggests. Flow is taken as proportional to area at constant pressure, which holds for choked flow through a sharp orifice and less well once the edge has eroded round. Measure a sample of nozzles with pin gauges before acting on any of it.
Air-Jet Relay Nozzle Wear & Airflow Drop Calculator — free, with the formula and a worked example, at Textile School.