Do RO filters need a large pressure differential

[Torps]

This isn't a fish question, but you fish folks are by far the most knowledgeable on this topic. Will an RO filter pressurize a pressure tank to equal or close to input pressure? My house water pressure is 60psi. Will a standard RO system (SpectraPure Eliminator 4) pressurize the tank to 60 psi or will it stop at like 30-40 psi?

My intent here is to supply a pot filler above the stove. I'd like 3 gallons available from this ~1 gpm faucet every couple days. Below are the specs of an Amtrol 14 gal tank I'm eying. If I can fill the tank to 50 psi, That looks like it'll be plenty.

empty precharge = 15 psi
2.0 gal = 20 psi
4.7 gal = 30 psi
6.4 gal = 40 psi
7.6 gal = 50 psi
8.4 gal = 60 psi

 

[KrisReef]

Don't know about the pressure, but I think the table suggests that you should get 8.4 gallons from the tank with your 60psi house pressure. I have had smaller ro tanks, 60 psi house pressure and I upgraded to 4 or 5 gallon tanks so I could get more water in one sitting. I would expect a 14 gallon reservoir to easily provide 3 gallons of water with another 3 gallons still available.

But, as far as pressure, not sure what the tank side is at, always presumed it was also 60?

 

[Torps]

Don't know about the pressure, but I think the table suggests that you should get 8.4 gallons from the tank with your 60psi house pressure. I have had smaller ro tanks, 60 psi house pressure and I upgraded to 4 or 5 gallon tanks so I could get more water in one sitting. I would expect a 14 gallon reservoir to easily provide 3 gallons of water with another 3 gallons still available.

But, as far as pressure, not sure what the tank side is at, always presumed it was also 60?

That's what I assumed till I did more reading and found fairly vague references to RO output pressure being <2/3 the pressure of the input. I'm not sure how RO actually works beyond the dumbed down explanations. I'm wondering if the RO membrane acts as a sort of a pressure gate that allows zero flow if the differential is less than something like 20 psi.... meaning 60 psi in gets 40 psi out, 50 psi in gets 30 psi out, etc.

 

[irischan]

the larger of the inlet water pressure, the faster ro water production and lesser waste water.

 

[Torps]

It looks like the RO system CAN produce the same outlet pressure as supply, but it becomes very inefficient once the pressure drops below 40 psi. While reading about permeate pumps, I've found that the auto-shut-off valve activates once the output pressure is 2/3 the supply pressure. In my case that would be 40 psi, which is only a 20 psi pressure difference so the membrane will not be very efficient.

A permeate pump solves this. It isolates the product water discharge of the membrane from the pressure tank. The product water fills the pump on one side. Once it's full, the brine side of the pump opens and the pressurized brine water pumps the product water into the tank.

 

[Reefering1]

Keeping it simple... if you only want a few gallons every few days, that membrane will last well over a year(maybe 2)- regardless of if it's operating at peak efficiency or not

 

[Torps]

Keeping it simple... if you only want a few gallons every few days, that membrane will last well over a year(maybe 2)- regardless of if it's operating at peak efficiency or not

Well I suppose the main reason I'm stressing over this is cause I'm so annoyed that the RO sellers don't seem to know squat about this stuff. My OCD won't let me drop a few Benjamins without knowing about it

Then the other reason is I need plenty of pressure to get the water thru 20' of pex including 7' vertically into the attic. I also need to maintain 30+ psi to keep the ice maker happy.

 

[Reefering1]

My rodi goes through about 50ft of tubing, including about 8 feet climb. Can't tell the difference in output vs 10ft outlet..