Hand-Pump Cup-Seal Wear Priced per Cubic Metre: The Sand Content at Which a Seal Design Change Is Forced

For a hand pump with a 75 mm cylinder and 350 mm stroke, delivering a computed 1.31 litres per stroke at 85% volumetric efficiency, this paper counts 761 strokes per cubic metre and applies an abrasive wear model in which leather cup-seal life falls from 400,000 strokes in clean water as sand content rises. Seal life falls from 525.7 m³ in clean water (cost 0.019 dollars per m³, seal plus labour at 10 dollars) to 47.8 m³ at 500 mg/L sand (cost 0.209 dollars per m³, about 76.4 replacements per year at 10 m³/day). At 500 mg/L the replacement interval falls below about a month and the cost per cubic metre exceeds ten times the clean-water figure: that is the stated threshold at which changing the seal design or removing the sand is forced, rather than simply replacing seals more often. SIMULATED, NOT MEASURED.