RO flow rate questions

[tom]

Replace the filters often? Tom

[tom]

And realize that you're dumping 3 to 4 times the water that's filtered for drinking. Tom

[Mike Hartigan]

I've had an RO system installed in my home for the past 15 years and have always been happy with the water. One thing that's always bothered me, however, is the flow rate at the faucet - about 1 gal/min. How can I increase this without adversely affecting the water quality?

I have a pretty generic auto shutoff valve that stops at about 40psi which as expected, is about 2/3 of my input pressure (60psi). There are valves available that shut off at 90% of input pressure, or about

54psi, in my case. Would this help? What would be the downside, if any? Would I need a check valve with this in case of a drop in supply pressure? (would it be wise to have a check valve anyway?)

My system is about 25' from the faucet. Does that length of 1/4" line reduce the flow? If the unit was closer to the faucet, would that help? (not that that's an option). Would it help to use 3/8" or 1/2" line with suitable reducers even though the ends are only

1/4? I'm using 2 tanks. Could I feed a bigger line more efficiently from two tanks, each with 1/4" fittings and get better flow even though the faucet is only 1/4"?

Any other suggestions?

Thanks, Mike

[Paul Franklin]

The 1/4 inch line is killing you. Raising the pressure would help a bit, as would increasing the line size for as much of the line as you can. (it reduces the pressure drop across the line) Also, what is the change in elevation (head) between the tanks and the faucet? Lowering the head (by raising the tanks?) would help increase the flow as well, since you don't have to work as hard to overcome gravity.

HTH,

Paul

[Mike Hartigan]

That's irrelevant. The waste goes through a separate line so it wouldn't have any effect in the flow to the faucet.

[Mike Hartigan]

Is the length of the line significant? In other words, does the length of the line dictate bigger tubing? Would a bigger line help even though all the connectors are 1/4"?

The tank is on the basement floor, so we're looking at about 12 ft. I could hang the tanks between the ceiling joists to save about 8 ft. Wouldn't that increase the pressure on the clean side of the membrane, though?

[Paul Franklin]

In a word, yes. A pipe is a series circuit; reducing the resistance to flow anywhere will increase the flow. All else being equal, you would expect on the order of twice the flow through a .375 tube as a ..25. Having short sections of .25 at start and end will put you somewhere between what you have now and twice what you have. Now you may not see as much improvement as that statement would lead you to expect because your tanks and faucet fittings may not be full .25 bore; fittings often are more restrictive than straight pipe. But you will still see improvement.

Do a quick test. See how much flow you get right at the tank outlet... (but keep in mind that right at the outlet you also aren't working against 12 feet of head, so even with a 2" pipe you won't get the same flow at the faucet).

Yes, you're absolutely right, my mistake. Raising the tanks would help if the tank pressure stayed the same, but it won't because the valve fixes the pressure down at the RO, so the total head remains the same. Now if you could raise the whole RO....

So you could add another quick test. After you check the flow right at the tank outlet, add enough tubing to get you to ceiling height and measure the flow there. That will give you an idea of how much flow you're losing just from the head v.s. from the tubing run.

HTH,

Paul

[tom]

Mike Hartigan wrote:That's irrelevant. The waste goes through a separate line so it wouldn't have any effect in the flow to the faucet. Maybe to the subject at hand, yes. But I live in Southern Arizona. I collect the brine and use it to flush toilets, do laundry, and other non-potable uses. Just trying to help the OP (and the rest of you) to be aware of the wasteful aspect of RO treatment. HTH. Tom

[Mike Hartigan]

While I can appreciate your sentiment, I live in the Great Lakes drainage basin. As such, water conservation *for the sake of water conservation*, while noble, is a meaningless effort here. Granted, there are other considerations, such as treatment, etc, but the water, itself, is simply not going to run out.