RODI newbie and need advice!
- Thread starter glb
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The membrane is flushed when your rejection rate is between 96 and 98%. To calculate the rejection rate take your tap TDS, subtract the RO only TDS, divide that number by the tap TDS and multiply by 100. For simplicity sake lets use a tap TDS of 100 and a RO only TDS of 3.
100-3 = 97, 97/100 = 0.97. 0.97x100= 97% rejection rate.
To calculate the waste ratio use a measuring cup and a clock or watch for exactly one minute, first from the waste line then from the treated line. If you have normal tap TDS in the 200 or higher range and non softened water you want around 4:1 waste to good. If you have softened water and lower than normal tap TDS then you can waste closer to 3:1 and in very rare situations with very soft wate rand very low TDS as low as 2:1 but that is not often the case.
You can buy a capillary tube flow restrictor for $5-$6 and trim it to fit your exact water conditions so you don't have to rely on a fixed type that is rarely correct.
100-3 = 97, 97/100 = 0.97. 0.97x100= 97% rejection rate.
To calculate the waste ratio use a measuring cup and a clock or watch for exactly one minute, first from the waste line then from the treated line. If you have normal tap TDS in the 200 or higher range and non softened water you want around 4:1 waste to good. If you have softened water and lower than normal tap TDS then you can waste closer to 3:1 and in very rare situations with very soft wate rand very low TDS as low as 2:1 but that is not often the case.
You can buy a capillary tube flow restrictor for $5-$6 and trim it to fit your exact water conditions so you don't have to rely on a fixed type that is rarely correct.
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glb
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My rejection rate seems to be stuck at 94% for the last three gallons. Is this normal? I've made 6 gallons so far. I do one at a time in a milk jug, measure it, discard and continue. I'm using a 5g jug for waste water. It is picking up speed though. It's closer to 13min/gallon now.
Your membrane may only get to 94%. 98% is not a guarantee, only a guideline based on manufacturers testing. Spectrapure is the only vendor I am aware of who guarantees a rejection rate in writing with their 99% SpectraSelect Series membranes and systems that use it.
The longer the unit runs the better it gets up to a point so always try to make a minimum of 3-5 gallon or larger batches so the effects of TDS creep are reduced and the membrane stays well flushed. Short runs kill a membrane and DI. It is better to make 5 gallons every 10-14 days than to make a half gallon every day.
The longer the unit runs the better it gets up to a point so always try to make a minimum of 3-5 gallon or larger batches so the effects of TDS creep are reduced and the membrane stays well flushed. Short runs kill a membrane and DI. It is better to make 5 gallons every 10-14 days than to make a half gallon every day.
You can but its not necessary as long as you keep the tubing up higer than the housings so it doesn't all siphon out. You should be using the system at least every 10-14 days so what is inside will not evaporate out in that time.
