[Ian Lancaster]

Hi all.  In June last year I fitted a new 40-40 membrane (RO-man MEM 2000)

It was the first replacement for the system that I bought 18 months previously.

It supposedly should give me a rejection rate of about 97% at 70psi which would reduce my incoming tds of 282 to between 008 and 009.  I'm actually getting 022 which is about 92% rejection.

I replaced the last membrane when it was giving 023-025 but this one hasn't lasted anywhere near as long (initially I seem to remember it was giving about 012 which would be just over 96% rejection). 

I'm making about 8000lt a week and my 5lt resin bottle lasts about 9-10 days, so a bag of resin lasts me about a month and a half.

At about £85 a bag delivered, that's £14 a week spent on resin.

Would you risk changing the membrane, hoping to get back to 97% and then maybe spending £5 ish a week on resin, or leave as it is?

Cheers,

Ian

[Spruce]

Hi Ian
I would bite the bullet and replace it now. If you sit out the high TDS for the rest of the year, you have spent most of what a new membrane will have cost you anyway on resin, so save yourself the hassle of changing the resin as often.
My experience with my 450GPD RO is that the membranes always work better with cold water - my TDS is lower than in the summer months - I presume the density of the colder water has something to do with it. I have replaced membranes twice and both times were when we were getting into summer.
I am now expecting the third change in a few months time as they are 2 years old in May/June. So if my gut feeling is right then unfortunately your TDS is going to get higher, hence the reason why I would change it now.
Spruce

[traps7]

omg Ian, 8000 litres a week is a serious amount of water. How many vans have you got? You must clean a lot of windows.

[Sapphire Window Cleaning]

Hi Ian
I would bite the bullet and replace it now. If you sit out the high TDS for the rest of the year, you have spent most of what a new membrane will have cost you anyway on resin, so save yourself the hassle of changing the resin as often.
My experience with my 450GPD RO is that the membranes always work better with cold water - my TDS is lower than in the summer months - I presume the density of the colder water has something to do with it. I have replaced membranes twice and both times were when we were getting into summer.
I am now expecting the third change in a few months time as they are 2 years old in May/June. So if my gut feeling is right then unfortunately your TDS is going to get higher, hence the reason why I would change it now.
Spruce

RO membranes work better in warmer water, this is because the water is slightly more dense due to the water getting closer to freezing (turning into solid)
A lot of people on here are experiencing similar fluctuations with their TDS myself included.
I have a 500GPD with booster pump. producing 300-350litrs per day.
My waste water last Autumn was 780-785, my tap water is 396, my waste TDS at the moment its about 600.
Ian I would wait a couple of weeks for the warmer weather at check it again before going out and replacing a 4040 memebrane.


Matt

[Ian Lancaster]

Good advice both Spruce and Matt - I'll do the cautious thing and wait a week or two - thanks.

Traps: there are 7 vans but one has his own system on board and my van doesn't do a lot :

The other 5 use about 3-400 lt/day each, averages out about 8000/wk.

[D B Services]

My honest advice is to pick up the phone and speak to June at Gapswater.

Those RO-MAN 40 inch membranes varied in quality and performance a lot. I went through 4 of them in a year producing approx 10000 ltrs a week. I spoke to June on someone elses advice and she was very helfull and knowledgeable and have had the same one for over a year now with better output both in water production and lower TDS out.

Cheers

Dan

[Ian Lancaster]

Thanks Dan

I have spoken to June recently, she said my production was about what they would expect, but I wanted to get some more opinions.

[ftp]

Ian, have you got your resin in tandem? Get two bottles - brilliant! Tulsion resin seems to last forever anyway.

[Richard 01903]

why two DIs

[ftp]

First one does the hard work to start with, the second hardly does anything. Resin starts to deteriorate in the first vessel - no problem you can keep it running even if the tds rises past the point where you normally bin it (cos the second is still purifying).
When the resin is really spent in the first, take it off, put No2 in it's place, refill No1 and put in the previous No2 slot and away you go again.

[geefree]

, take it off, put No2 in it's place, refill No1 and put in the previous No2 slot and away you go again.

can i do that with normal membranes on a 300gpd ro-man?

if the bottom one doing all the work and suddenly its slow at producing, rather than buy a new one  .. can i swap them for a while?

[ftp]

Errr dunno only work in series I would have thought.

[Ian Lancaster]

, take it off, put No2 in it's place, refill No1 and put in the previous No2 slot and away you go again.

can i do that with normal membranes on a 300gpd ro-man?

if the bottom one doing all the work and suddenly its slow at producing, rather than buy a new one  .. can i swap them for a while?

Surely they must work in parallel?  The incoming water is split into three and a separate feed goes to each membrane, otherwise as Gazza says the first one would clog up and the last one wouldn't do anything.  Also you wouldn't get three times the water as it still all goes through the same little pipe.

[dd]

Assuming you are in a hard water area your membranes will last a lot longer if you fit a water softener.

Also will last longer if you have a pure/waste ratio of 30/70 instead of 50/50

[Sapphire Window Cleaning]

, take it off, put No2 in it's place, refill No1 and put in the previous No2 slot and away you go again.

can i do that with normal membranes on a 300gpd ro-man?

if the bottom one doing all the work and suddenly its slow at producing, rather than buy a new one  .. can i swap them for a while?

FTP was on about running dual di vessels, when the first di vessel purifies the water the second one doesn't kick in until the resin in the first vessel wears down, lets say once the TDS starts to increase after the first DI vessel the second one will start to purify, the second DI vessel would last longer as the first di vessel is still filtering the water but not as effectively.


Matt

[ftp]

Yes I was on about tandem vessels thanks Matt.

The membrane bit caught me by surprise. I have wondered before though, if your memranes were in series wether the could be swapped about to prolong their life.

[dave0123]

Ian, ask June at gaps abou the ultra low membrane I think it's called I'm on my phone at the gf's at the moment so can't check the name but it's supposed to work great a low pressure with great TDS results .






Dave

[Ian Lancaster]

Thanks Dave

[AJ]

I use a HF5 40-40 from gaps. Takes my 350+ tap tds down to 14tds without pump. used RO Man membranes before, they do not last!!!

[Ian Lancaster]

That sounds more like it