RO, TDS and DI problem
- Thread starter Gools
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Hi guys. So no one gets confused, let me clarify a few points in this thread that are not spot on.
Although flushing the membrane should help to give you a longer membrane life, its not the first place I'd look to address low rejection from new membranes like we have here.
The rejection rate he's getting is actually 92%. 22/260 = 8% of the TDS is getting through. Factory spec on a 75 Filmtec is 96% to 99%.
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yes but if op wasnt running any kind of flush I suspected one of the membranes developed a hole. Thats why i asked. They are 7 months old after all and those holes dont take long to develope.
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Dr. Reef's comment referring to the optimum placement of the pump is correct, but not likely to be the cause of the low rejection issue here.
This flow restrictor will provide about a 4:1 ratio on a system producing 50 gallons of permeate per day. You have three times that production.
Hopefully your vendor DID NOT sell you an auto flush valve with an integrated flow restrictor.
ASOV valves have an "in" and an "out" port, as do the auto flush solenoid valves.
Pressure switches on the other hand, do not have a designated in/out port or direction of flow.
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Yes - it is critical to know which port is which.
I like to explain things in such a way that people understand the answer, rather than me just giving them something they have to memorize. The easiest way to understand which port is which on a residential-scale RO membrane housing is to remember that RO water exits the RO membrane from the central stem on the end that has two orings. Concentrate (often mis-labeled as "waste water" exits the end of the body (blue part) of the element.
This flow restrictor will provide about a 4:1 ratio on a system producing 50 gallons of permeate per day. You have three times that production.
Hopefully your vendor DID NOT sell you an auto flush valve with an integrated flow restrictor.
I did purchase from brs with the restrictor installed. On there website it says 500ml/min for 75gpd membrane or the 150gpd water saver.
I also have a regular inline restrictor that is 500ml/min that I had received with my original 75gpd membrane.
What restrictor sizing would you recommend?
Thank you
Hopefully your vendor DID NOT sell you an auto flush valve with an integrated flow restrictor.
I did purchase from brs with the restrictor installed. On there website it says 500ml/min for 75gpd membrane or the 150gpd water saver.
I also have a regular inline restrictor that is 500ml/min that I had received with my original 75gpd membrane.
What restrictor sizing would you recommend?
Thank you
RO membranes can fail, but that's really independent from the issue of a system being configured with/without a flush valve.
Ugh. :rolleyes: Well... your situation, which is not uncommon, is a great example of why that is a much less than ideal configuration. Because now you, the customer, are stuck and will have to spend another $50+ (rather than $4) to change that auto flush valve.
On these low pressure systems, unless you have exceptional feedwater, its best to shoot for a 4:1 ratio of concentrate to permeate. Remember that the membranes are spec'ed by the manufacturer with a 5.7:1 ratio.
could you recommend a ml/min flow restrictor for my set up? I'm wondering if I take the auto flusher off and install just a restrictor, what my outcome would be. I have a few restrictors of various sizes lying around
How confident are you in the TDS readings you posted? About half the time when we work through these issues with folks the TDS readings end up being erroneous. The biggest cause of this is people not understanding that you have to let the system run for a couple of minutes before taking readings.
But you are on the right track. First thing to do is figure out why your RO water isn't more pure.
If your readings are accurate, then I'd:
reconfigure the system with the membranes in parallel with the correct restrictors; or leave them in series and use a restrictor that yields something closer to a 4:1
test the output from each membrane independently
Thanks, I do have a 550 kicking around maybe I will just use 1 membrane and see what happens.
If I was to purchase an automatic flusher without a restrictor, how would I use that with the 2 membrane system?
Thanks
If I was to purchase an automatic flusher without a restrictor, how would I use that with the 2 membrane system?
Thanks
That is sort of a loaded question :)
First off, regardless of your system, if you want an auto flush valve, always use one configured with a change-able flow restrictor. The $4 change-able capillary restrictor is in the blue tube in the pic.
if you keep your membranes plumbed in series, then use a flow restrictor inside the blue tube that yields about a 4:1 ratio, assuming you don't have exceptional feedwater.
If you plumb your membranes in parallel, then you'd need TWO auto flush valves.
If you plumb your membranes in parallel, then you'd need TWO auto flush valves.
If you plumb membranes in series, the concentrate from the first membrane is connected to the "in" port on the second membrane.
If you plumb membranes in parallel, the feedwater splits and goes to the "in" port on both membranes and each membrane has its own flow restrictor.
Make sense?
Yes it does. In our experience, and referring here to the residential-scale systems common in this hobby, any feedwater tube longer than about 15 (generally horizontal) feet should be bumped up from 1/4" tube to 3/8" tube. This is not always true, but with your 150 gpd worth of membranes it should apply to your situation.
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