A basic idea of how an RO/DI filter works and how to set it up

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An RO filter is a membrane. The membrane is partially permeable so it removes unwanted ions and molecules. Applied pressure is used to over come osmotic pressure. How an RO works





Inside an RO membrane


D772E27A-09D4-4AF6-97A6-4C3A63128B23.jpeg 1AC1357B-733B-4615-A873-8FC8C0C2C5E8.jpeg

Basic RO filter C8BEE0FB-DCF8-4FE3-A0AE-BAA570B16A27.jpeg
 
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They run prefilters before the RO. A sediment filter and a carbon filter. They call the filters stages. So the more filters you have the more stages. For example you can run two carbon filters to make them last longer. You can also run two sediment filters. The reason for the prefilters is to avoid clogging the membrane which is the most expensive filter to replace.
 
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The over all layout of an RO/DI filter is like so


FA1C720E-776D-4E65-9FA8-56168BE110F3.jpeg
 
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An RO doesn’t quite take take every thing out of your tap water so we use Di filter to finish it off. That’s the very last filter. You can put a pressure gauge after the carbon filter a drop in pressure tells you the prefilters are starting to plug and should be replaced. You can test chlorine after the carbon filter as well which will tell you you need to replace the carbon filter.
 
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We can use a hand held TDS meter to make sure our DI is good or you can use an inline meter. You measure TDS after the RO and after the DI. TDS stands for total dissolved solids. It’s a measure of the dissolved combined content of all inorganic and organic substances present in a liquid.


0097FAB0-4EDB-435C-A1F6-EB17416737FE.jpeg
 
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We check how well the RO is doing by calculating the rejection rate. We do this by checking the TDS of the tap water and the TDS after the RO. Let’s say our tap water has a TDS of 350 and after the RO we are getting a TDS of 40.

40/350=0.1143

0.1143x100=11.43

100-11.43=88.57

When you start getting a rejection rate around 95% it’s probably time to start thinking of replacing the membrane.
 
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TDS calculator

 
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An RO membrane splits the water so you have one stream of good water and one of waste water. The amount of waste water your filter will produce is given in a ratio. So if your filter says it has waste water ratio of 4:1 that means for every 1 gallon of good water you will produce 4 gallons of waste water for a total of 5 gallons ran through the filter.
 
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There are some things we can do to make the RO last longer and produce less waste. We can buy a flush kit and flush the water before we start filtering and after we are done. After the water sits for a while in the lines of the RO filter it will end up with a high TDS we can flush this out so it doesn’t go through the membrane. RO filters use flow restrictors on the waste water line to create pressure we can bypass that and flush the high TDS water out. There are two different types of flow restrictors

32017630-1857-45F6-8FE4-9B4057DE6384.jpeg 2652E26E-88DD-4F5F-A021-57DC02D21DDF.jpeg

Flush kit

BF916906-7A51-4298-A556-BEFE95B69DFC.jpeg

Auto flush kit

BBD3F6D5-595F-4D93-A558-4BF18E2A30AC.png

How to install

 
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We can change the waste water ratio by adding a 2nd membrane in line like so

 

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RO joke.jpg
 
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You can also run a booster pump on an RO/DI filter which will lower your waste water. You add the booster pump after the tap and before the whole filter. If your tap water is less then 50psi then your going to want to run a booster pump no matter what. RO membranes are designed to run at a minimum of 50psi.

How to install



Booster pump

4F6566B7-337F-4999-AC48-8904466D65E7.png

Booster pump and auto flush B671C2CA-C873-48E3-B39D-EACE3ECDCF46.png
 
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RO’s are rated in GPD gallons per day. The higher the rating the faster the water production.
 
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We can also run two inline DI filters. Normally when you get a TDS of 1 off the DI resin you would replace it but if we run two DI canisters we can replace one and continue to run the other using up more of the DI resin then we would have. If I remember right you run the old DI first then the new stuff last.

RO/DI filters with more then one DI canister

C562AE1C-0A46-4D1D-A3FE-0FEFB0E667F5.png 4212EE27-4B62-472E-B26A-FF42AF15A697.png
 
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There are several companies to choose from and everyone has their own opinion on who best so I will leave that up to people to recommend what they like.

How to install an RO/DI filter


 
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Last I am by no means an expert and I’m sure more and better detail can be given. I used information from the internet, things I was told or read and YouTube. I hope this gives people an idea of what’s going on that have no idea how to set up an RO/DI filter. Let me know if there is something I should add.

Thanks
 

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I like the detail and references! I just recently been researching the subject and updating my system as well as the whole house filter... they're simply complicated Haha but luckily companies have done the research and set up for us!
 

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