Permeate flow is not pump flow
In reverse osmosis, recovery is the ratio of permeate flow to feed flow. Always identify which flow is being specified when discussing the pump duty. “We need 8 m³ of water per hour” is insufficient for selection: does it mean feed or permeate? The calculation below is an illustrative selection worksheet, not an installed project or a performance promise for a particular product.
Illustrative example: a flow balance
Assume a permeate target of 8 m³/h and design recovery of 75%. For continuous operation without recirculation, feed flow is 8 / 0.75 = 10.67 m³/h and concentrate flow is approximately 2.67 m³/h. The 75% figure is a calculation assumption, not a recommendation for every water or membrane. Recirculation, flushing or a different arrangement requires a separate calculation of the flow through the pump. Do not order from permeate capacity alone.
Separate the pressure added by the pump
Assume a membrane inlet requirement of 12.0 bar(g), pump suction of 1.5 bar(g) and 0.5 bar loss between pump and membrane. Neglecting elevation and velocity differences, the pump must add 12.0 + 0.5 − 1.5 = 11.0 bar. For water at an assumed 1,000 kg/m³, this is approximately 112 m head. The 12 bar requirement is a placeholder to be supplied by membrane design; actual pressure must follow water analysis and the membrane calculation.
Move from a series name to an actual selection
Lowara includes reverse osmosis among e-SV applications. This does not mean every e-SV or other multistage pump can deliver the example duty of 10.67 m³/h at 112 m. Select model, stages and speed using the manufacturer curve. Ask the proposal to show the target duty, selected curve and assumptions together. Verify suction conditions, material compatibility and sealing suitability in the same selection file.
What should the application file contain?
Provide water analysis, temperature range, target permeate quality, membrane design output and available upstream pressure. State the flow used to calculate pipe loss. Describe normal production and other operating scenarios separately to expose the limits of a selection that looks suitable at one point. Keep unknowns as explicit questions in the enquiry instead of presenting assumptions as site measurements. Complete selection by checking pump and process requirements together.
Let’s select the right product.
Your contact information and a short description are enough to start. Add flow, head, fluid and quantity if known; we can clarify the rest together.