RODI Issues

I purchased a 150gpd 1.5:1 unit from PureWaterClub.com. Plumbed everything in yesterday and wasn't impressed with the results. I'm generating 40 gallons of product a day and 120 gallons of waste in a day running at 45psi using cold water. I've checked the pressure before the membrane and it's running great. As soon as it hits the membrane, I lose most of the pressure. It seems even less after the DI filter. Do you have any more ideas on what I can check or do to make this thing more powerful? Seems to be generating a ton of waste.

 

Forgot to add, my starting water is 198ppm. The product produced is 0ppm.

 

you can add a pump to increase your pressure. 45 PSI is pretty low. These things normally want closer to 60 psi (give or take).

Unless the waste is an issue of some sort... sounds like it is running normally to me.

 

yes 45 is too low--60-65 is nominal

 

RO/DI units are made to produce the stated GPD at optimum conditions, a water temp of 77 degrees and minimum PSI of 50 pounds pressure. The colder the tap water the lower the water production you can expect.

I would talk to thefilterguys.biz. the # is 218-724-8000 great to deal with and they have anything you need to fix your issue.

 

lol im glad I get free water in my condo, mine run at about 40 psi and produces right under about 40-50g per day, im ok with it since i only do 10g water changes. Unless your desperate I wouldnt worry those fuggin pumps are expensive and think what else you could do with that money

 

A 150 GPD membrane system needs an absolute minimum pressure of 60 psi and more is better. Unfortunately they don't have a clue and their systems will fail at a waste ratio of 1.1-1.5:1 like the claim. Legitimate brick and mortar RO vendors have tried this for years and its just not possible long term, membranes soon foul and plug with particulates and no amount of flushing in the world will ever restore them short of chemical treatment which is not available in household units. You MUST keep the waste ratio in the 3:1 or better yet 4:1 range for them to last, the waste is what flushes the contaminants away from the membranes surface, without the velocity at 4:1 they collect on the membrane and harden. If you have never seen what happens, it looks like salt caked around the membrane, I have seen them cut apart and its like table salt pouring out of everywhere. So called "flush valves" have no proven benefit either, unless you make water manually, start from day one and never ever miss flushing the membrane manually each and every time you shut the membrane off the damage has been done and is irreversible. Once salts build up it continues to get worse no matter what you do for flushing. You need that 4:1 waste ratio to carry stuff away period.

What people don't realize is when you reduce the waste ratio you concentrate the TDS surrounding the membrane more and more until its double or more what the tap water was, you need to keep it moving. at 4:1 waste ratio the TDS surrounding the membrane is only 20-25% higher than the tap water TDS , not 100% higher so its is managable. 120% vs 200% is a big difference. It also changes the osmotic pressure which effects how well the membrane works.

The two best things you can do are get a booster pump to raise the incoming pressure up to at least 60 but I run mine at 90-100 with even better results. The other is get a capillary tube flow restrictor and trim it for an exact 4:1 waste ratio to fit your water conditions.

 

I don't think it's correct to use the phrase "absolute minimum pressure of 60 psi" - though I agree w/the post as a whole.

I mean, you have 45psi and you are getting 0 TDS water... so I wouldn't say 60 is the absolute minimum... but it is needed for efficient use and for better life of the expensive membranes, filters, etc.


But I'm sure DRats point is that you need better pressure to get better life out of the membranes.

If I'm misrepresenting you DRat, my apologies. Good info!

 

The 0 TDS water is coming from the DI resin not the membrane which is underperforming. DI won't last worth a hoot since it is doing the job of the membrane too.

To demonstrate this all he needs to do is take a TDS reading from the RO only not from the RO/DI. You will find its way below 96-98% where it should be.

Pressure has a big effect on membrane performance, the higher the better, the only limiting factor is the hosuings and fittings which should if they are ANSI and UPC approved should have a working pressure of 125 psi. The membrane will operate all the way up to 300 psi and get better and better the higher you go.
The 150 GPD membrane gets its 150 rating at 65 psi and 77 degrees water temp with a softened water TDS of 250. They do not perform well at lower pressures.

I see people all the time saying 0 TDS and are tickled pink. What they don't realize is the DI is doing all the work and costing a mint to replace. A very good rule of thumb says for every 2% you increase the RO membranes efficiency, you DOUBLE the life of your DI resin. A 4 or 6% increase in RO rejection has a huge effct on DI life.

 

Wow, great info DRat & Peredhil. Now to find an inexpensive 60psi+ pump...