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Flow Meters for RO and Water Plants: Types, How to Read Them and Why They Matter
- Rotameters for RO lines
- Read at the float mark
- Recovery = permeate ÷ feed
- Log readings daily
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Why Flow Meters Matter
An RO plant's output, membrane life and water quality depend on flows staying in the designed range. Without meters you cannot tell whether a membrane is fouling, a pump is weakening or someone has changed the reject valve. A few inexpensive meters prevent costly membrane replacements.
Instruments at H-TECH
Flow Meters panel mountedKSh 2,900
TDS Handheld MeterKSh 6,500
Conductivity Monitor – Model: CCT3320V (CM230)KSh 12,000
Conductivity ProbeKSh 3,000
Panel Mount RO Controller (RO-2015)KSh 15,000
Pressure SwitchKSh 4,500| Product | Price |
|---|---|
| Flow Meters panel mounted | KSh 2,900 |
| TDS Handheld Meter | KSh 6,500 |
| Conductivity Monitor – Model: CCT3320V (CM230) | KSh 12,000 |
| Conductivity Probe | KSh 3,000 |
| Panel Mount RO Controller (RO-2015) | KSh 15,000 |
| Pressure Switch | KSh 4,500 |
Current listed prices incl. VAT (updated 19 October 2026).
Types of Flow Meters
| Type | How it works | Use |
|---|---|---|
| Panel rotameter (variable area) | A float rises in a tapered tube | RO permeate and reject lines; no power needed |
| Paddle / turbine digital | Rotor speed measured electronically | Totalising, dosing control |
| Water meter (totaliser) | Counts total volume | Billing, daily production (see prepaid meters) |
How to Read a Rotameter
- Check the units on the scale (LPH, GPM).
- Read where the float's reading edge (as marked by the maker, often the top or the widest part) lines up with the scale.
- Read at eye level to avoid error.
- Note the reading when the plant is at normal operating pressure.
Calculating RO Recovery
| Permeate | Reject | Feed | Recovery |
|---|---|---|---|
| 250 LPH | 500 LPH | 750 LPH | 33% |
| 500 LPH | 500 LPH | 1,000 LPH | 50% |
Illustrative numbers. Run at the recovery the system designer specifies for your water; pushing recovery too high scales and fouls membranes.
What Changing Flows Tell You
- Permeate dropping at the same pressure: fouling or scaling; plan cleaning (RO maintenance).
- Reject rising, permeate falling: check the reject valve setting and membrane condition.
- All flows low: pre-filters blocked or pump problem; check the cartridges (sediment filter guide).
Installation Tips
- Mount rotameters vertically, flow from bottom to top.
- Choose a range so normal flow reads in the middle of the scale.
- Keep glass or acrylic tubes out of direct sun and clean them so the float is visible.
- Log permeate, reject, pressures and TDS daily.
Watch: RO purifiers and water ATMs
Frequently asked questions
What is a flow meter used for in an RO plant?
To measure permeate and reject flow so you can check output and recovery.
How do I read a rotameter?
Read the scale where the float's marked reading edge lines up, at eye level.
How do I calculate RO recovery?
Recovery = permeate flow ÷ (permeate + reject flow).
Why is my RO permeate flow dropping?
Usually membrane fouling or scaling, blocked pre-filters or low pressure.
Do panel flow meters need electricity?
No, rotameters work mechanically.