RO/DI System

[fishsticks4sale]

i just purchased a 7 stage ro/di system dual membrane system, with booster pump. i get roughly 80-85 psi with the pump and my water waste to good is 1:1. i was wondering what will happen if i add another membrane??? will i have more good water being produced compared to waste? will i have like
.5 gallon waste to 1 gallon good??

[TheFishTeen]

80-85 PSI is usually a little much...dontcha' think?

[fishsticks4sale]

not really considering when running dual membrane its required to have a minimum of 65psi to be most efficient. im avg 80, some reviews customers stated getting 90 psi with their pumps. as long as u have the 1:1 ratio and your not over 90 your good. im just trying to find out what if i add another membrane how will i benefit, if i benefit at all?

[coralreefdoc]

Only real benefit, as far as I can think of atm, would be less frequent DI resin changes

[fishsticks4sale]

I'm willing to do 3 membranes just to save water but I gotta be sure its Gunna work.

[Buckeye Hydro]

First - remember that what folks call "waste water" really would be better thought of as "flush water" in that this water serves the important purpose of internally flushing the surface of the semipermeable membrane to keep the membrane from fouling/scaling.

When you configure a system with two membranes in series (the waste from the first membrane going to the "in" port on the second membrane), for this discussion let's say it's two 75 gpd membranes, the system behaves like you have a single long (75 gpd x 2) 150 gpd membrane.

Now - if you use a proper flow restrictor, that is, one for a 150 gpd membrane, you'll have about a 4:1 waste to product ratio. Sounds familiar, right?

If however you don't change the flow restrictor - meaning you keep using the same restrictor you were using when you just had one 75 gpd membrane, then you'll see a waste to product ratio much lower than 4:1. But remember that the recommendation for a ~4:1 ratio comes from the membrane manufacturer. They are telling you that you need about a 4:1 ratio to keep the membrane flushed and keep the membrane from fouling or building up scale. Run the system with a lower ratio and you will foul/scale the membrane(s) quicker than would have otherwise been the case.

Instead of adding a second membrane to lower that ratio, you could have just changed out your flow restrictor ($4) instead. A much less expensive approach to get you to the same endpoint in terms of saving on waste water.

Now, to confuse things just a bit. Filmtec specs call for the 4 to 1 ratio on the basis of assumptions about the water that will be supplied to the membrane. If you have very soft water you MAY be able to get a decent service life from the membrane running at a ratio lower than 4 to 1 (e.g., 3 to 1). Remember that the waste water from the first membrane is about 25% harder than your tap water.

Bottom line: If what you are after is reduced waste water, experiment with a different flow restrictor for $4 instead of messing around with a second membrane plumbed in series.

As a side note, you can also lower the ratio by increasing the pressure delivered to the membrane (with a booster pump), because flow restrictors are sized assuming you are providing factory spec conditions (50 psi and 77 degrees for Filmtec membranes). Increase the pressure and you'll drive more water through the membrane and viola - less waste water. But as I mentioned above, if you do this (just like over-restricting a membrane) - the lower the waste to product ratio, the shorter the lifespan on the membrane.

Makes sense?

Russ

[fishsticks4sale]

damn russ u broke it down lol, thanks man. where can i purchase flow restrictors?? is the restrictor the small plastic piece that sits inside the waste line coming out of the membrane?

[fishsticks4sale]

i found this stuff...

vhttp://www.spectrapure.com/St_replac_p3.htm

now i just get a flow restrictor thats lower than 75gpd correct?
for example i would replace the one i have now sitting in my single membrane that has a 3:1 ratio 75gpd with the (FR-40) in the link so it makes it 40gpd? = more restriction?
also i do have a booster motor on order, should put me up to 90psi.
since i already ordered my 2nd membrane can i still add the flow restrictor ex: FR-40 and maybe get better than 1:1. maybe .5:1

[Buckeye Hydro]

Originally Posted by fishsticks4sale

where can i purchase flow restrictors??

RC doesn't like us to make commercial posts...

[Buckeye Hydro]

Originally Posted by fishsticks4sale

is the restrictor the small plastic piece that sits inside the waste line coming out of the membrane?

Yes sir.

[Buckeye Hydro]

now i just get a flow restrictor thats lower than 75gpd correct?
for example i would replace the one i have now sitting in my single membrane that has a 3:1 ratio 75gpd with the (FR-40) in the link so it makes it 40gpd? = more restriction?

Correct. However, remember that in most cases "...the lower the waste to product ratio, the shorter the lifespan on the membrane."

also i do have a booster motor on order, should put me up to 90psi.
since i already ordered my 2nd membrane can i still add the flow restrictor ex: FR-40 and maybe get better than 1:1. maybe .5:1

Sure - you could do this, but "...the lower the waste to product ratio, the shorter the lifespan on the membrane." So we really can't recommend the kinds of ratios you refer to here.

[snorvich]

Originally Posted by BuckeyeFS

RC doesn't like us to make commercial posts...

But he is an excellent supplier of all equipment associated with RO/DI.

[fishsticks4sale]

Originally Posted by snorvich

But he is an excellent supplier of all equipment associated with RO/DI.

yea no lie, i finally kinda understand how ro/di systems work. i would ask on forums about how systems work and really didnt get a good answers, but now i understand how the ro membrane works.
also i wanted to post a quick pic of my set up, dont mind the garage its terrible lol.

[Plato]

No, I get 120psi on two 100 gpd membranes with 350 gpd.

Originally Posted by TheFishTeen

80-85 PSI is usually a little much...dontcha' think?

[fishsticks4sale]

hot damn lol is that a 3/4 hp motor???? that thing is a monster.
i meant over 90 for the 8800 motor, but for yours i dont know 120 psi man u must have good water production? what is your ratio with that dual membrane?

[PurdueWaterGuy]

Since y'all are posting pictures of your RO systems, here's mine at work. 20,000 gallons per day of 800 k-ohm-cm permeate, 5 and 7 HP pumps, 30 Filmtec BW30-4040 membranes, 80% recovery ratio, net driving pressure of 160 psi in the first pass and 210 psi in the second pass.

Yeah, I know, I'm evil. Just couldn't resist. :-)

[fishsticks4sale]

lmao jesus.

have a question for you guys what maintenance is needed before and after use of my ro/di unit??? also when should i flush after certain gallons produced? or by time table? monthly weekly?

[Buckeye Hydro]

Originally Posted by Plato

No, I get 120psi on two 100 gpd membranes with 350 gpd.

Yeow. I know you haven't had problems yet, but...

120 psi on the clear housings is something to avoid. If you can move the pump inlet/output to after the prefilter housings that would be a good idea.

Russ

[PurdueWaterGuy]

+1 on moving the pump to after the clear polycarbonate filter cannister. Not pretty when they fail. Been there, seen that, had to clean up after others. :-(

Noticed that your pump doesn not have the built-in pressure relief valve, watch your pressures.

Check the pressure ratings on all the components, plan for the worst, hope for the best.

[fishsticks4sale]

+++2

[AFU]

Originally Posted by PurdueWaterGuy

Since y'all are posting pictures of your RO systems, here's mine at work. 20,000 gallons per day of 800 k-ohm-cm permeate, 5 and 7 HP pumps, 30 Filmtec BW30-4040 membranes, 80% recovery ratio, net driving pressure of 160 psi in the first pass and 210 psi in the second pass.

Yeah, I know, I'm evil. Just couldn't resist. :-)

WOW. that is the real deal. I want one. haha.

[PurdueWaterGuy]

Originally Posted by AFU

WOW. that is the real deal. I want one. haha.

Running the 460 VAC 3-phase for the pumps into your house might be a bit of a problem ;-)

[Buckeye Hydro]

Originally Posted by PurdueWaterGuy

Check the pressure ratings on all the components, plan for the worst, hope for the best.

Plato - Can't say for certain as that's not one of our systems, but guess what the weak link in the chain typically is concerning abilty to withstand high pressure on a system like yours. You have to consider the tubing, fittings, prefilter housings, RO membrane, membrane housing...

It's the clear housings. If you have any chips, scratches, etc, in those housings, their ability to handle pressure is even lower.

Russ

[PurdueWaterGuy]

All this talk of failing filter cannisters conjured up a flashback - once upon a time I came into work to find my ion implanter (sort of a giant mass spectrometer mated to a particle accelerator) shut down. The 20" tall DI cannister had gotten dirty and was restriciting flow, and the positive displacement pump (made by Procon, like the one in your picture) kept on pushing, until it split the cannister in two, leaving a ring with the top threaded part attached to the machine, and bounching the bottom half and IX cartridge across the lab.

Ahh, the bad old days.... :-)

[Plato]

Originally Posted by fishsticks4sale

hot damn lol is that a 3/4 hp motor???? that thing is a monster.
i meant over 90 for the 8800 motor, but for yours i don't know 120 psi man u must have good water production? what is your ratio with that dual membrane?

I thank its only a 1/4 hp motor with a 50 or 60 gpd pump head. The pump is in my apartment garage. It is gravity fed by a vat, so all pressure is supplied by pump. My product rate, well I fill a two hundred gallon vat that when toped off holds 220 gallons. I turn the pump on and the waste on the ro is 1 to 4 but the waste water goes back into the 200 gallon vat. My water that I fill the vat with starts at 50 ppm and after the ro its 0. By the end of the 200 gallons it goes up to 300 ppm and the ro goes up to 2 or 3. Its all controlled by float valves to shut the pump off if the feed vat goes empty or the product vat gets full. So out of 220 gallons I get 200 gallons if ro/di water to 20 gallons waste. At the start of every 200 gallon cycle I flush the membranes for 5 minutes and after I run ro/di water through the membranes for 5 minutes to prevent scaling and buildup.