Desalination & Membrane Water Treatment Equipment worked example

Spare Membrane Buffer with average membrane element demand of 3,000 elements / day: a worked example

What does the result look like when average membrane element demand reaches 3,000 elements / day? The full calculation is worked below with real intermediate numbers. Use it when spare membrane buffer in desalination and membrane water treatment equipment is being sized for a buffer or safety stock review.

The inputs for this scenario

  • Average membrane element demand: 3,000 elements / day (raised for this scenario; the documented default is 1,200)
  • Membrane replenishment lead time: 85 days (unchanged)
  • Spare membrane safety stock: 1.1 elements (unchanged)

Working through the calculation

  • Applying the documented formula (Lead-time membrane demand = average membrane element demand × membrane replenishment lead time) to the inputs above produces each figure below.
  • At this operating point the engine returns 32.09 days for protected days of supply, the number this scenario is built around.
  • At this operating point the engine returns 35.29 days for unprotected days.
  • At this operating point the engine returns 3,000 pieces for inventory.
  • At this operating point the engine returns 85 pieces / day for daily usage.

How this compares with the baseline

  • Against the tool's baseline example, where average membrane element demand sits at 1,200 elements / day and the headline result is 12.83 days, this scenario comes in 150% above the baseline at 32.09 days.
  • A figure at this level is achievable when average membrane element demand is genuinely sustained, not just peaked for a shift. It assumes steady daily element demand, but real replacement is lumpy; a chlorine excursion or scaling event can consume a season's worth of elements in days, outrunning any average-based buffer.

Results at a glance

  • Protected days of supply: 32.09 days (headline result)
  • Unprotected days: 35.29 days
  • Inventory: 3,000 pieces
  • Daily usage: 85 pieces / day

Run it with your numbers

  • Every input above is editable in the live Spare Membrane Buffer calculator, which recalculates instantly and can be shared with the inputs intact.

Last reviewed 2026-05-12.