RODI and water pressure

[braddo]

I've had my RODI unit for about two months now and I've notice production of clean water has dropped of drastically. To start troubleshooting I picked up a pressure gauge and measured water pressure in two locations. Water pressure out of the faucet measures 36psi. I then moved the pressure gauge between the carbon filters and the RO membrane; here pressure measures only 26psi.

Air Water & Ice state that the RO membrane needs a minimum of 30psi to produce clean water. My question for you all is has anyone measured their water pressure like this in multiple locations? Is it expected that restriction through carbon filters would cause a 10psi drop or is this a sign of dirty\damaged carbon prefilters?

 

[Scooterman]

Most recommend 45 to 55 minimum pressure, In your case your wasting more water than normal production at higher water levels. I would recommend you purchase a booster pump which will pay off in way more production water.
My inlet water is usually around 76 psi, yours seems to be low. To answer the other part yes you will drop pressure as it goes through the filters.

 

[braddo]

Thanks Scooterman.
I agree my pressure is low, the recommended minimum pressure is what you list and a booster pump is on my shopping list. 30psi is the minimum stated threshold for any clean water to make it through the membrane. At or below 30psi you get 100% waste water.

Can you comment on whether 10psi seems like an excessive pressure drop?

Just trying to determine why I went from slow output to no output in such a short time. I am on Seattle city water which is soft (about 2dGH) and 22tds so I wouldn't expect filters to clog that quickly.

 

[Scooterman]

How much water did you make in the two months?

I would suspect that the carbon block may be reducing your pressure, is it a .5 micron or a 1 micron?

 

[braddo]

I haven't made much water, my guess is somewhere between 30 and 50 gallons.

The unit has an inline .5 micron sediment filter and inline .5 micron carbon filter.

 

[Scooterman]

If you have an extra sediment replace it & see, then the carbon, if your output goes up then you know what causes it. Being so low in pressure the water probably can't pass through them enough.
That is my guess, taking for granted everything else was hoopked up right & working well until it started producing less water. Was this change gradual or sudden?

 

[braddo]

Thanks, I think I will just go ahead and order all new filters and a booster pump. Once I get thew new filters I can do some comparisons to track down the issue.

 

[Scooterman]

I would just replace the first two, really If you get the pump then I wouldn't' change a thing until you put it on the system.

 

[braddo]

I figure the filters are cheap enough and I will need them eventually. A replacement pack with sediment and carbon filter is only $18. This way I can do some comparisons and have baseline numbers to work from in the future.

 

[braddo]

Hmm, apparently water pressure fluctuates quite a bit in our small apartment complex. I measured pressure out of the faucet today at 50PSI and I am making clean water like a champ.... or at least about as fast as I would expect a 50gpd RO unit to make water.

 

[Slate]

Some apartment buildings can be a huge pain on water pressure since a large number of them are fed off one large line from the city. So if you start getting a few hot water heaters filling along with other uses at peak hours you can really see a drop in psi.

 

[braddo]

Grrr, today I went to make more water, pressure is still at 50PSI but I am back to almost no clean water output. Anybody have any idea what could cause day to day output fluctuations?

 

[Scooterman]

Have you replace any filters yet?
Check pressure after carbon block to see what your getting out it, you can do a simple disconect the line and squirt it in a bucket or something. Visually you should get decent water pressure there. If that isn't it the either the membrane or the restrictor may be damaged. Make sure the restrictor is in properly, otherwise it may be a membrane issue. Assuming your do indeed have 50 psi out. I'd replace that restrictor first but make sure you have constant pressure that booster pump would solve that issue.