[Ian Lancaster]

Hi all.  Following on from my thread asking for opinions on my membrane, I've fitted a bypass with a stopcock so I can divert the pure side into the waste while I'm flushing and a flow meter on both the pure and waste lines.

This means I can monitor the performance of the membrane very accurately.

So:

I was running at 2.5:1 ratio (waste to pure).  The pressure at the membrane was 60psi.  Incoming water is around 300ppm (varies slightly) water out of the membrane (before DI) was 24ppm.

Supposedly if the pressure is higher, you should get lower tds out.  If you reduce the volume going to waste by closing the flush valve slightly this will increase the pressure at the membrane (less water to waste=more water through the membrane=higher pressure).  I reduced to a ratio of 1.5:1.  The pressure increased to 90psi but the tds out of the membrane almost doubled to 48ppm

This was the exact opposite of what I expected - I thought that increasing pressure would reduce the tds but probably shorten the life of the membrane.

I increased the waste gradually and the tds came down as the pressure reduced and the waste increased.  By trial and error I found that the best tds I could get was the 24 I had been getting originally, but at about 65psi and a ratio of slightly less than 2.5:1.  Reducing the pressure (and increasing the waste) beyond that made no difference so I am assuming I have found the optimum performance setting for my membrane.

Working out the percentages, I am getting 92% rejection which still means the resin has a lot of work to do to get the 24tds down to 001 (000 seems unattainable)

I'm going to buy a new membrane, probably the HF5 but I'll wait till I can talk to June at Gapswater.

My old RO-man 300gpd used to produce water at 3-4ppm before DI so the performance of my current 40-40 leaves a lot to be desired.

I'm changing resin now about every 8 days (when the tds reaches 009) so I'm hoping I will get less than 009 from a new membrane and then I won't need to use DI, or if I do, it should last a good deal longer.

[ftp]

Ian, put your di in tandem with another. It saves loads on resin it really does. Oh, and get some Tulsion resin - it's the best I've found so far.

Interesting results though. I suppose every membrane has a limit it's only material with holes in it after all. Maybe too much pressure forces particles through that would normally become trapped?

[SherwoodCleaningSe]

For a 4040 those results are shocking.  How about running a softener and seeing if that improves things.  To be honest I'd wonder if your membrane is a little up the creak.

The increased pressure improves efficiency in flow rate not removed solids.

Simon.

[Londoner]

I've just changed the membranes on my RO and boy what a change in output. I reckon its worth the money.
Another point, I have done away with the carbon filters on the pre- filters and it doesn't seem to have any adverse effect on the TDS, its still 000. A thread a while back said they were only used for drinking water to add to the flavour but it took me a while to build up the confidence to try it without. Has anyone else tried running without?

[Lee GLS]

I'm going to buy a new membrane, probably the HF5 but I'll wait till I can talk to June at Gapswater.

What membrane do you have at the moment?

[AJ]

Another point, I have done away with the carbon filters on the pre- filters and it doesn't seem to have any adverse effect on the TDS, its still 000.

The carbon block filter is to remove the chlorine/chloromine. Most membranes have zero tolerance to chlorine, so I would put the pre filters back or risk seriously reducing the life of your membrane.

[Window Washers]

I cant wait to see the results on this.

I also would like to know who said membranes have zero tolorence to chlorine and why.


Question for Ian Lancaster, did you flush your membrane for a long while with booster pump added as it sounds like it needs it, 24 tds is quite poor froma  4040 I have 13 to 11 un pumped and a tds of 470+ if I put on the softner it comes down add a pump and it goes down to 6/7 tds with a high pure to less waste.

[David Kent @ KentKleen]

hi Ian, i have a 40 40 system with similar tap tds to you, booster pump @40 psi and my tds after 40/40 is around 14.
What resin are you using?
Polishing down to 000 mine is lasting 2 month!! Tuslin!!
Are your 40/40 membrane housings all ok, sounds like they might have a fault, i.e leaking waste water into your filtered. I had this with a housing Araldite rapid sorted this out, sealed up a crack in one of the threads. Give em a good check over!!
hope any of that helps!!
regards
Dave 

[ftp]

http://www.accepta.com/industry_water_treatment/reverse_osmosis_ro.asp

Bit of info there. Membranes don't like chlorine.

[AJ]

I also would like to know who said membranes have zero tolorence to chlorine and why.

http://www.osmotics.co.uk/hf54040-commercial-extralow-pressure-membrane-p-531.html

At the bottom of the page it gives the cholrine tolerance.

[ftp]

http://www.water.siemens.com/en/applications/industrial_process_water/Pages/pw_cs_carbon_filters_to_ro.aspx


Maybe some membranes are ok with chlorine but for the price of a filter I can't see why anyone would leave it off?

[Roy Harding]

I put a new 40 x 40  ro and complete system in someone's van Friday & Saturday.

When I set mine up Stream wfp company said to set it up with a 50 x 50 rejection rate.

However Gaps water 0n there site say's that rejection is 98% we rang June and she said it was right, as if set less the membraines wont last as long.

Roy

[craig21t]

Ian, by restricting the waste water too much from the ro, you are artificially raising the system pressure. Depending on what ro membrane you you have to have different water pressures. eg for a HF4 membrane you need to have a minimum of 100psi @ the correct manufactures waste to product ratio. For a HF5 membrane the minimum is reduced to 80 psi. Again this is the minimum pressure, so if your tap only produces 50 psi @ the correct waste/product ratio it would not give you as good a rejection rate (product tds), by closing the waste you are artificially raising the system pressure(by the gauge) and therefore forcing waste through the membrane layers as it has no where else to go. Well thats the way I understand it anyway.

[AJ]

I put a new 40 x 40  ro and complete system in someone's van Friday & Saturday.

When I set mine up Stream wfp company said to set it up with a 50 x 50 rejection rate.

However Gaps water 0n there site say's that rejection is 98% we rang June and she said it was right, as if set less the membraines wont last as long.

Roy

50 -50 is the flow rate, waste to product. i.e 1 litre of waste to 1 litre of product exiting the RO.
98% rejection rate is the amount of TDS that is taken away from raw tap water. A certain amount of water is required to wash these contaminants away. so, the 50% waste water is used to wash away 98% of the contaminants, the other 50% is product water.
(I know what I mean anyway )