Idea: Is running 2 4040 membranes worth it?

I just bought myself a new Axeon HF5 membrane and installed it and happy with the results I'm now getting. This made me wonder though when I pulled out my old membrane if that membrane could be useful for anything or maybe it's worth something to someone. Then I got to thinking what if I used 2 membranes. My old membrane was producing pure water at 115PPM down from 335PPM at the tap.

I could buy an IBC tank and fill it up using my old membrane so that water would be 115PPM. I bought a booster pump that I'm currently using to boost my pressure to 80PSI on my new membrane, I can just suck the water out of the IBC tank straight into my pre filters and new membrane. My thinking is that if my membrane is currently taking 335PPM water down to 10PPM (97% efficient) why can't it take 115PPM water down to like 3.5PPM. Therefore saving me tons in resin costs.

The only downside I'm seeing is double the amount of wasted water from 2 membranes. The cost to run the pump doesn't count as I'm using it anyway to fill my van. The only costs are for me to buy an IBC tank a couple of pipes for the old membrane input/output and a new membrane housing.

Am I missing something? Why can't I find any other posts about using 2 membranes... just my bad searching skills?  :crazy:

Could even advertise it as double filtered R/O water!!!!  :1f609:  Lol just kidding 

This is interesting! The thing is how would you push through the water that's 115ppm through the new membrane to make it work efficiently if the water was lying in an IBC? I wonder if you could have the two membranes inline so that the pressure is there for the second membrane to work off 115ppm?

Calling @spruce, @Alex Gardiner, @doug atkinson

I’ve seen double Ro set ups before (same as double Di) but wouldn’t have a clue how to plumb it up!!


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I did test this by filling up a old kitchen bin full of water and then put my pump inlet in the bin simulating an ibc tank. It then connects up to my pre filters and membrane in my van. It was only able to produce 45PSI compared to 83PSI with the mains pressure and booster pump though. I just added up the costs to do it and come up with these numbers... IBC tank £50, hose pipe £15, membrane housing (2nd hand) £50, pipe/fittings £20 

Total = £135 roughly 

Would it be unreasonable to expect the new membrane to last twice as long in this setup do you think? If the PPM is lower as well then should save on resin. 

Problems I see are the lower pressure at 45PSI making my new membrane work less efficiently at producing pure water bringing the PPM up, therefore cancelling out everything.

Old membrane steadily creeping up in PPM to the point where it's not really doing anything

AGlassAct said:

I’ve seen double Ro set ups before (same as double Di) but wouldn’t have a clue how to plumb it up!!


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I'm thinking something like this... I made a little drawing, gave me an excuse to use my tablet and pen lol

I think rainwater harvesting could be a better option. But your system will work, it'll just use 1.5 times as much water. So if you are on a water meter you have to calculate if the extra resin cost would be lower.

Then again, building stuff is always fun, so go for it.  :1f609:

Nudel said:

I think rainwater harvesting could be a better option. But your system will work, it'll just use 1.5 times as much water. So if you are on a water meter you have to calculate if the extra resin cost would be lower.

Then again, building stuff is always fun, so go for it.  :1f609:

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I looked into rainwater harvesting and after some napkin math I figured it wouldn't be worth it might have to look back into it. Luckily I'm on no meter, can't imagine how annoying it would be to have 335TDS water and being on a meter.

anyone tried this without a pump, would be interested to see if it works

Why would you want to go to all these lengths? You've got too much time on your hands @HazelwoodWindowCleaning.  :1f602:

I doubt anyone has tried this so any replies would be theoretical. So lets see how this goes. Firstly, the prefilters need to be on the first 'old' membrane rather than on the second new membrane. If you felt better you might add another sediment filter to the second membrane. Its not necessary, but you don't need a carbon filter as you have already removed the chlorine from the water and you aren't introducing any more.

Simply stated, a membrane is material with microscopic holes. What you want to do is use 2 membranes in the same way as some cleaners use double di. In our case a membrane working at 97% efficiency will remove 97% of the dissolved solids from the water its filtering. This means that the remaining 3% are so small that they pass through the membrane pores. Adding another membrane after the first (say in series) isn't going to reduce that 3% as those dissolved solids are just going to pass through the next membrane.

Lets look your first membrane. Its bringing your water down from 335 to 115ppm. So its removing 220ppm atm. Your new membrane is bringing your water down to 10ppm. On paper using your system should  bring the tds down further to 3 or 4ppm. Lets say 3 so a saving of 7ppm.

Now lets say you are using 400 liters of pure a day and you use 1500 liters of pure a week or 6000 liters a month. Resin costs per month for polishing off 3ppm for 6000 liters is £2.62 per month using Alex's resin calculator. Polishing of the same amount of water at 10ppm is going to cost £8.73 in resin. Then we have to take into consideration the time you have to spend 'managing' system which is saving you £6.11. We also haven't considered the cost of electricity running a booster pump, and neither have we considered the cost of all these additional pieces of kit needed to achieve this saving of £6.11. (Alex's resin calculator is 'set' at 4000 liters per month. If that is more like the amount you are using then your saving is £4.07.) You will be using more water so you will need to replace your prefilters more regularly. That extra water will just be going to the drain.

So for me I'd put all the extra energy I've used up toward cleaning one or two extra houses a month to save me all the hassle.

Now what could be interesting is to link 2 x 4040 membranes in series. So first you have your prefilters, then the first housing with the failing membrane. The pure from the first membrane would connect to the inlet of your second membrane  and you would join the 2 wastes together and fit a restrictor valve after the join on the pipe going to waste. I would think you would need to add a booster pump in the equation. So the cost of this experiment just isn't worth it IMHO. It doesn't make good business sense.

Haven't you got a garden? :1f602:

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Haha @spruce I had a conversation with my brother just last night about exactly what you described about having to much time to do stuff like this. I guess I find it interesting even though in the long run it probably causes more hassle than it's worth. It makes you think about possibilities that you would otherwise not of even thought off and if you apply this to everything in your life than hopefully you see some benefits in the end.  :1f609:

I hadn't thought of the membranes in the way you explained how they would probably work. It's logical though. I'm tempted to put my old membrane in my housing again and fill up my kitchen bin and then switch the membranes back and actually test what would happen. If I don't it will haunt me in my sleep and I will always wonder what if. :1f602:  

What else better have I got to do on a Sunday!

HazelwoodWindowCleaning said:

Haha @spruce I had a conversation with my brother just last night about exactly what you described about having to much time to do stuff like this. I guess I find it interesting even though in the long run it probably causes more hassle than it's worth. It makes you think about possibilities that you would otherwise not of even thought off and if you apply this to everything in your life than hopefully you see some benefits in the end.  :1f609:

I hadn't thought of the membranes in the way you explained how they would probably work. Sounds logical though.I'm tempted to put my old membrane in my housing again and fill up my kitchen bin and then switch the membranes back and actually test what would happen. If I don't it will haunt me in my sleep and I will always wonder what if. :1f602:  

What else better have I got to do on a Sunday!

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The old saying says; "neccessity is the mother of invention."

Not sure if this one fits that or not. :1f602: . But that could change if the world ran out of resin. We (me) could clean windows with pure of 3ppm (just) but not 10ppm.

If you do decide to try this then it would be interesting to see how the theory works in practice. So please report your findings. It would be interesting to know how far apart the theory and the practice are. 

If it wasn't for @H MAN would we have the Gardiner Quickloq? It wasn't necessary as we screwed our brushes on, but its introduction has made changing brushes so convenient and easy.

TBH I doubt that you will get a response from @doug atkinsonor @Alex Gardiner. :1f602:

In fact I would be seriously concerned if Alex did reply. He needs all the spare time he can find to keep us windies going with stuff we actually need to keep us working and earning.

There are severaL company’s that supply twin ro systems as standard figment on there larger systems I have two on mine and it makes fill times shorter especially if it’s used in conjunction with a booster pump 

So I tested it out for myself. Put my old membrane in tested with my booster pump off mains water and filled up my kitchen bin with 99PPM water this time (water went through pre filters before membrane). I then put my pump inlet hose into the 99PPM water and used the pump only(obviously no mains pressure) with my pressure at 45PSI going to my pre filters then membrane. My resulting PPM was no different stayed on 10PPM for 10 minutes while I emptied my kitchen bin full of water. So now I know that the end pure water wont be reduced in ppm. I don't know whether the drop down from 335ppm to 99ppm water would save a lot of life on the new membrane, my guess would be yeah but not really worth it. Still nice to know