why does adding another membrane increase twice the speed?

[Buckeye Hydro]

Worked with someone recently who had frankenstein-ed a system together with a single 10" x 2.5" carbon block and two 150 gpd membranes in parallel, each with a needle valve flow restrictor carefully tuned to a 4:1.

So for sake of discussion let's say he had factory spec pressure (65 psi) and temperature (77F).

Membrane 1 would produce 150 gpd RO and (150x4)=600 gpd concentrate ("waste") = 750 gpd total. Multiple that by 2 because he had two membranes and you get 1500 gpd being pushed through a 10" x 2.5" carbon block. 1500 gpd = 1.04 gpm - that's just too much flow through that size of carbon block - even when it is brand new.

Russ

 

[ericarenee]

Sorry if this thread stealing...

Sorry if this thread stealing...

Worked with someone recently who had frankenstein-ed a system together with a single 10" x 2.5" carbon block and two 150 gpd membranes in parallel, each with a needle valve flow restrictor carefully tuned to a 4:1.

So for sake of discussion let's say he had factory spec pressure (65 psi) and temperature (77F).

Membrane 1 would produce 150 gpd RO and (150x4)=600 gpd concentrate ("waste") = 750 gpd total. Multiple that by 2 because he had two membranes and you get 1500 gpd being pushed through a 10" x 2.5" carbon block. 1500 gpd = 1.04 gpm - that's just too much flow through that size of carbon block - even when it is brand new.

Russ

You have my interest here..

My Setup . I have a pleated Pre Filter. then a .5 micron then a .1 micron. then two carbon block filters.. at this point 5 pre filters ..

then i have dual 75 gpd membrane first membrane waste goes into second membrane (to save water ) Then both clean water out of membranes have a y connector then into my Dual DI/ RESIN. My waste line has a 75 gpd restrictor /backflush valve..
of course there is a auto shut off installed .
Since i added the two extra canisters.. extra micron and extra carbon block my tds before membrane is much lower.. and i use way less Di resin..

I do NOT get 150 gpd more like 120 ish at 75 lbs of water pressure

-------------To my Comment and Question----------------------

The second R/O Membrane is bringing the waste of the first membrane down to acceptable levels for DI to finish polishing it.. My assumption is that this second membrane will not last as long as the first ? But at the same time I am still just pushing the same amount of water thru the Carbon blocks But I HAVE less waste water ?

Is the above true... If NOT I am interested to know if there is a better way.
my system is mixed and matched with dow membrane. parts if it actually came from you guys some from brs some from local pool place that also do RO/ DI Systems.

Erica

 

[Buckeye Hydro]

If you follow our posts you know that plumbing these low pressure RO membranes in series should NOT be thought of as a was to "save water." Use a flow restrictor that gives you a 4:1 ratio of waste to purified.

If all you want to do is cut the waste from one membrane in half, spend $4 and use a different flow restrictor. But I don't recommend you do that...


5 prefilters - that's a lot. You have me wondering why you selected the array you did. Remember that you lose some pressure with each prefilter.

Do you have your pump plumbed in AFTER the prefilters?

You mention a "backflush valve." Remember that there is no "back" about it - there should be no reversal of the flow direction when you flush a membrane.

Sediment filters and carbon blocks don't really affect TDS - so if your TDS is lower something else is going on.

My assumption is that this second membrane will not last as long as the first ?

Correct

With the way you have your system set up you have greater permeate flow, but the same waste water flow you had with one 75 membrane - not really a good idea.

Why don't you call in - if you can tell me what you want to accomplish (less waste? faster production? cleaner RO water?) we can tell you how to do it.

Russ

 

[ericarenee]

If you follow our posts you know that plumbing these low pressure RO membranes in series should NOT be thought of as a was to "save water." Use a flow restrictor that gives you a 4:1 ratio of waste to purified.

If all you want to do is cut the waste from one membrane in half, spend $4 and use a different flow restrictor. But I don't recommend you do that...


5 prefilters - that's a lot. You have me wondering why you selected the array you did. Remember that you lose some pressure with each prefilter.

Do you have your pump plumbed in AFTER the prefilters?

You mention a "backflush valve." Remember that there is no "back" about it - there should be no reversal of the flow direction when you flush a membrane.

Sediment filters and carbon blocks don't really affect TDS - so if your TDS is lower something else is going on.


Correct

With the way you have your system set up you have greater permeate flow, but the same waste water flow you had with one 75 membrane - not really a good idea.

Why don't you call in - if you can tell me what you want to accomplish (less waste? faster production? cleaner RO water?) we can tell you how to do it.

Russ

The Reason i am asking is because in the past (just added the extra carbon and micro filters... I would only get about a year from a membrane before my tds would go thru the roof and after membrane pressure would drop well below 40 .. I have 90 psi coming into my system . no booster pump. its connected to the main water supply in basement. out of membrane i have about 70 psi...
i change the micron filters once a month and carbon block every 3 months. I am going to rotate changing the dual carbon blocks one every 3 months. I have only had it setup like this for maybe 2 months.

I Really was not asking to get anything more out of it. Was just kinda asking for confirmation to how its setup....

but as i said before the added pre filters i was only getting year on the membrane . I am hoping they help resolve this issue ...

I found the setup info on a water filtration site somewhere. but not necessary a aquarium forum... one of those survival type sites ..

Thanks for the reply

 

[Buckeye Hydro]

I'n not clear on why you would be measuring pressure OUT of the RO membrane. The critical place to know the pressure is right before it goes IN to the membrane. If you want to be able to monitor the pressure loss at each prefilter stage I guess you could put a gauge after and before each, but that would be overkill IMO.

What was your indication that the membranes needed to be changed after a year?

You could probably get more use out of your prefilters than you are now - but that is up to you.

Russ

 

[gus6464]

So I downloaded the water quality report from my local water company and in it they stated that they treat with chloramines. I added another stage to my RODI with one of those fx chloraguard filters. My booster pump is installed after the sediment and carbon filters. This is the path.

0.5 sediment -> 0.5 carbon -> 1.0 chloraguard -> booster pump -> ro -> di

The TDS out of my ro membrane before the chloraguard was 12-14. Now with the added chloraguard stage it's 2. Is it normal for that much of a drop? I have my booster pump set to 90 PSI.

 

[Buckeye Hydro]

Nope - something else is going on.

 

[FirstContact]

Hey Russ,

This is a hard choice for me. I have the BRS supplementation kit to go from 75gpd to 150gpd. If I want to save water as a resource, I run the waste water from the first membrane to the second membrane and use the 75gpd restrictor in the second membrane and limit the life of the second membrane filter. If I am doing that, how many resources am I wasting by shortening membrane life compared with water sent down the sewer or backyard?

Also, if I don't want to shorten the life of the membrane and want the 4:1 waste to product ratio which size flow restrictor am I going to use? Right now I'm running a single 75 GDP membrane with a single 75gpd flow restrictor.

Thanks,
Gary

 

[Buckeye Hydro]

75 gpd x 2 = 150 gpd. So if you have 50 psi and 77F water, you'd use the 150 gpd restrictor. You can use the calculator on our website to see how much one of the membrane will produce given your pressure and temperature, and then just double that. You might be able to use the 100 gpd restrictor and get something less than a 4:1 but more than a 2:1.

Flow restrictors are cheap - $4, so it doesn't hurt to have one around for summer, and a different one foe winter.

Russ