Dyehouse High-Temperature Pump Cavitation & NPSH Margin

Vapour pressure is computed for pure water by the Antoine equation, and dyebath liquor is not pure water — dissolved salts raise the boiling point and lower vapour pressure slightly, which is conservative, while any entrained air or solvent does the opposite and is not. Good practice keeps a margin of at least 0.5 to 1 m over NPSH required rather than merely a positive number, because the published requirement is defined at 3% head drop, by which point cavitation damage is already occurring. Friction loss must be taken at the actual flow with a dirty strainer, not a clean one. **Pressurised high-temperature systems are hazardous**: changes to pressure, temperature or pump duty are engineering decisions for a competent person.