Wet Processing
A part-filled jet does not use less liquor. It holds its minimum volume and raises the liquor ratio instead, and every gram-per-litre chemical follows.
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What this batch actually runs at, not what the machine is rated at
Minimum circulating volume is a machine property and the number that makes this calculation worth doing, so take it from the manufacturer or from the level gauge at the point the pump cavitates, never from the nominal ratio multiplied by some fraction. Modern low-liquor jets hold their ratio down to a much lower fill than older winches and overflow machines, which is precisely the case this tool is built to let a dyehouse quantify before it replaces anything. The chemical overdose figure applies only to auxiliaries dosed in grams per litre; dyes are dosed on fabric weight and do not scale with the bath, so a part load wastes salt and alkali without wasting dyestuff - which is why the loss hides from a costing built on dye consumption alone. Energy follows liquor rather than fabric too, so the heating cost per kilogram carries the same penalty as the salt, and on a full-cycle reactive dyeing it is usually the larger of the two. The tool says nothing about whether a batch will run well: a machine loaded far below capacity can rope, tangle or crease for reasons of fabric transport that have nothing to do with liquor ratio, and a batch far above nominal will do worse.
Dyeing Machine Fill Ratio & Part-Load Penalty — free, with the formula and a worked example, at Textile School.