why does adding another membrane increase twice the speed?

[Johnb123]

how does this work exactly?

[Johnb123]

bump!

[shifty51008]

Your basically running 2 units but useing the same prefilters and di for both as long as your not running them one after the other

[seamonster124]

Originally Posted by Johnb123

how does this work exactly?

If you are talking about the BRS upgrade; it takes your waste water and filters it again.

[Johnb123]

i know but how does going through another membrane suck water out faster?

[shifty51008]

It doesnt, it just saves waste water.

[lawdog75]

The membranes reduce the throughput, so two membranes in parallel allow a higher rate of throughput essentially doubling the output.

Must water feed lines are (in Aus) about 250g per hour allowing plenty of head room for two membranes. The only thing to watch is reduced pressure which will reduce output and efficiency. In some setups you may require a booster pump.

In essence you could run 4 membranes in parallel given enough head pressure and make a massive amount of water.

For those systems that are in series or utilising the waste water from the RO you will find membrane life on that line will be significantly less as it is handling a far higher amount of impurities compared to the original feed water.

HTH

[daquan44]

Essentially, water is pushed through the RO membrane, but dissolved solids and a lot of the water is unable to flow through. The rejected TDS water is sent to the waste water line. If you add another membrane, that water has a second chance to be forced through a membrane to be cleansed. As a result, less water is rejected, and more clean water is produced. If one membrane can do 75 gallons per day, two can do 150 gallons per day. You are still wasting a lot of water though. the 150 gallon systems do a 1:1 ration. So for every gallon of water you make, it rejects 1 gallon as well. 150 gallons flushed straight down the drain. Without the upgrade your rejecting a lot more water than that.

[Logzor]

It is true that you can achieve nearly a 1:1 ratio with the dual water saving membranes. However I was told that I'm prematurely frying my DI and Membranes since all that extra waste is now being trapped in the system. I may be installing flow restrictors to increase my waste water so I can increase the lifespan on my filters.

[outy]

Originally Posted by Logzor

It is true that you can achieve nearly a 1:1 ratio with the dual water saving membranes. However I was told that I'm prematurely frying my DI and Membranes since all that extra waste is now being trapped in the system. I may be installing flow restrictors to increase my waste water so I can increase the lifespan on my filters.

DI will only be exhausted quicker because you double production. If you have decent incoming TDS


If you have high TDS incoming its not a good idea because your second membrane is getting higher TDS then normal. Thus spitting out higher TDS then normal.

TDS needs to be checked outgoing behind membranes to make sure your not getting sill high output numbers.

Dual membranes are not wise for everyone.

[SNAKEMANVET]

I have thought about adding another 150 gpd to produce more water.My water pressure without a booster pump is 105 psi.My tds going in is 14.Could I do another 150 membrane with that pressure.

[outy]

Originally Posted by SNAKEMANVET

I have thought about adding another 150 gpd to produce more water.My water pressure without a booster pump is 105 psi.My tds going in is 14.Could I do another 150 membrane with that pressure.

Your a ideal for it. Crazy not to with low of TDS and pressure.


I like the ebay cheapo membranes, and have great success with them.

I use 2 x 75gpd with a 50gpd restrictor in the winter. I have 27tds incoming and 0 out of my membrane before DI.

[SNAKEMANVET]

thanks outy.

[Buckeye Hydro]

Realize that if you add membranes, and increase the flow through the prefilters, you need to be careful not to push water through the carbon block faster than it can pull out the chlorine. Most 10" x 2.5" blocks are rated at a max flow of 1 gpm, but you'd be better off keeping the flow considerably slower than that. Remember that all your "waste" water and your purified water go through the block.

Russ

[BigDave]

If you add a second membrane such that it is being fed by the waste water of the first membrane, then your flow through the first two filters is still the same. Only the flow through the DI is increased.

[Buckeye Hydro]

Yes - if you plumb the membranes in series. Not my favorite configuration on these little residential units.

[Big E]

I'm not sure I'm getting how this all works...........

In the configuration where membrane 1 waste goes to membrane 2 input I see how you are saving water but how does the output of clean water double?

You still have a 75gpd restrictor on the at the end of membrane 2 waste.

What am I missing??

I'm asking because I hooked my upgrade kit and my output was the same. I believe everything is hooked up correctly just like the BRS video.

[Buckeye Hydro]

Originally Posted by BigDave

If you add a second membrane such that it is being fed by the waste water of the first membrane, then your flow through the first two filters is still the same. Only the flow through the DI is increased.

Nope - that's not the way it works...

You have twice the membrane surface so you get twice the amount of waste water and twice the amount of RO water. If you use the wrong flow restrictor as a certain popular vendor suggests, you'll get less than twice the waste.

[Buckeye Hydro]

Originally Posted by Big E

I'm not sure I'm getting how this all works...........

In the configuration where membrane 1 waste goes to membrane 2 input I see how you are saving water but how does the output of clean water double?

You still have a 75gpd restrictor on the at the end of membrane 2 waste.

When you "Y" connect the membrane outputs you lose the doubling...............don't they need seperate outputs?

What am I missing??

When you plumb two low pressure residential membranes in series, you should use a flow restrictor that yields about 4x the amount of RO water produced. With two membranes you have twice the membrane surface and get about twice the RO water.

[Big E]

Originally Posted by Buckeye Hydro

When you plumb two low pressure residential membranes in series, you should use a flow restrictor that yields about 4x the amount of RO water produced. With two membranes you have twice the membrane surface and get about twice the RO water.

Ok, that makes a lot more sense to me, but now I can see how you stated the watch out about the carbon block.

I think I need to call someone

[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]

Originally Posted by 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

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]

Originally Posted by 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.


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