RO membranes

[reefermadness]

I find the best flow restrictor to be a ball valve. With a PSI gauge on the input of the membrane you can adjust the ball valve so that the pressure on the membrane is to spec.

The 150gpd may have good rejection rate but needs 65psi to the membrane in order to acheive this. Most city homes will not have this kind of pressure and a booster would be needed. The 75gpd is the most popular membrane because it also has a high rejection rate that only needs 50psi to acheive which is great for most city homes and you would not need a booster to reach 50psi.

[mike31154]

Originally Posted by reefermadness

I find the best flow restrictor to be a ball valve. With a PSI gauge on the input of the membrane you can adjust the ball valve so that the pressure on the membrane is to spec.

The 150gpd may have good rejection rate but needs 65psi to the membrane in order to acheive this. Most city homes will not have this kind of pressure and a booster would be needed. The 75gpd is the most popular membrane because it also has a high rejection rate that only needs 50psi to acheive which is great for most city homes and you would not need a booster to reach 50psi.

Restricting the flow before the membrane is unlikely to correct a problem of mismatched membrane/flow restrictor downstream of the membrane. I could be mistaken, but I'm not sure a ball valve will lower the psi that the membrane sees either, all you do with that is restrict the volume of water available by making the opening in the line smaller, the same psi will still be present. If you're on city water and wish to adjust the water pressure, you may be better off locating the PRV (pressure reducing valve) in your home's plumbing. These are requred by code in most municipalities and I believe the default setting is 50 psi. They are adjustable though, and I've adjusted mine to provide around 80 psi.

[reefermadness]

I never said I restrict the flow before the membrane. The ball valve goes on the waste end of the membrane and the PSI gauge on the input. When adjusting the ball valve you will see the PSI on the gauge go up and down.

Never heard of the PRV before...I will look into that.

[mike31154]

Originally Posted by reefermadness

I never said I restrict the flow before the membrane. The ball valve goes on the waste end of the membrane and the PSI gauge on the input. When adjusting the ball valve you will see the PSI on the gauge go up and down.

Never heard of the PRV before...I will look into that.

Ah so, sorry, I made an incorrect assumption there when I saw the part about the PSI gauge on the input. My bad.

PRV should be fairly near your water meter, just downstream, although mine is quite a ways down and my outdoor tap is plumbed in before it to take advantage of full city pressure for the garden.

http://www.plumbersurplus.com/images...-5734-3809.jpg

[StirCrazy]

Originally Posted by mike31154

Ah so, sorry, I made an incorrect assumption there when I saw the part about the PSI gauge on the input. My bad.

PRV should be fairly near your water meter, just downstream, although mine is quite a ways down and my outdoor tap is plumbed in before it to take advantage of full city pressure for the garden.

http://www.plumbersurplus.com/images...-5734-3809.jpg

hmm so you are using a PRV as a flow restrictor after your RO? to me that doesn't make sence as an adjustable PRV is about 75 bucks where a ro restrictor is 1.00.

I spent 5 bucks on a needle valve and used it to adjust my inlet PSI but I run two membrains in parallel

Steve

[reefermadness]

NO he mentioned the PRV as something someone could adjust to get your house plumbing at a higher PSI. The PRV is located near you main shut off I guess (still havent went looking for mine).

As for the GPD ratings being multiple on Dow membranes, when I look at the dow filmtec membranes are not sold like this. I believe that virtually any ro membrane will produce more GPD when higher pressure is applied. The problems with doing so is that the rejection rating will be affected. If you want rejection ratings similar (I actually find them better) then advertised then you should run them to spec.

[StirCrazy]

Originally Posted by reefermadness

NO he mentioned the PRV as something someone could adjust to get your house plumbing at a higher PSI. The PRV is located near you main shut off I guess (still havent went looking for mine). .

ah, ok.. I never had one in my houses. I had to install one in the first house as they jacket the PSI, but my PSI in the second house sucked so I had to buy a booster pump.

Originally Posted by reefermadness

As for the GPD ratings being multiple on Dow membranes, when I look at the dow filmtec membranes are not sold like this. I believe that virtually any ro membrane will produce more GPD when higher pressure is applied. The problems with doing so is that the rejection rating will be affected. If you want rejection ratings similar (I actually find them better) then advertised then you should run them to spec.

DOW never sold them this way, it was a company who was buying dow mwmbrains and relabling them as so many GPD@60PSI and so many @ 90 PSI. the rejections rates are constant through out there operating range as Dow is giving a minimum operating spec. I installed several systems over the last 8 years (comercial and non comercial) so I have had to talk to DOW directly on a few of the aplications and what I got from there engineers was that the rejection rate won't change untill the membrain starts to break down. so if you operate it in a way the is dammaging then you will get degraded preformance. operating at 100 PSI wont cause this, operating at 150 might start to as that is its upper end. at any rate I was confadent running my own at 120 PSI with a high volume pump to suply the water (only had 40 PSI at the second house) so after two years the output was still "0".

Steve

[StirCrazy]

Originally Posted by reefermadness

I find the best flow restrictor to be a ball valve. With a PSI gauge on the input of the membrane you can adjust the ball valve so that the pressure on the membrane is to spec.

The 150gpd may have good rejection rate but needs 65psi to the membrane in order to acheive this. Most city homes will not have this kind of pressure and a booster would be needed. The 75gpd is the most popular membrane because it also has a high rejection rate that only needs 50psi to acheive which is great for most city homes and you would not need a booster to reach 50psi.

the 150 your talking about is that the Dow 100/160? I run two of these in my RO unit, they put out 100gpd at 60psi, or 160 gpd at 90 psi. exelent membraines.

Steve

[reefermadness]

Yes I'm talking of the dow filmtec membranes (the best IMO).

How ever I only know of the 50,75,100 and 150gpd membranes. Never head of the 100/160?

[StirCrazy]

Originally Posted by reefermadness

Yes I'm talking of the dow filmtec membranes (the best IMO).

How ever I only know of the 50,75,100 and 150gpd membranes. Never head of the 100/160?

almost all of them are variably rated, one rating at 50 psi a few years.
back unsaviory vendors were using this to there advantage and not telling people, so they would sell the 75@60 as a 90/160 , as at 60 PSI it is a 90gpd and at 100 PSI it was 160 GPDand it was cheeper than buying the 100 which would give you a true 100@50psi. then they would blame the lower output on the temp of your water.

since the membrain is rated for up to 150 PSI this wasn't a problem as long as people knew what they had and that at 50 PSI they only had a 75 gal membrain. another company started relabling dow 75 and 100s as 100/160's at 50 and 90 psi, but it was a dow membrain just relabled. mine are dow 100's which I run at 120 PSI giving me a total output of more than 360 GPD when I measured it last. I ran them this way for 2 years and did a 5 min backflush after every use, but they have been dry since I moved now so I will have to buy new ones.

Steve