When to Change Membranes etc...

[Tuffers]

So, about 3 weeks ago I got my first ever RO setup. It has 2x 20" pre filters and a 20" HF4 membrane. My water TDS is about 220 and it's coming out of the RO at 007. I'm doing a 10 minute flush once a week. I'm making about 300/350 litres of water a day. How will I know when to change any of the filters and membrane?

 

[Part Timer]

I've just changed both pre filters and resin today, last time was a year ago. TDS had gone up to 8, coming out of RO @ 12. Only ever changed the membrane once after 3 years, no particular reason, just worried it might pack in if I left it any longer.

 

[Dave B]

When your tds creeps up too high

I change all 3 pre filters when the sediment filter is completely brown

Got my ro off damo and the membrane is already old but still going strong

I only make about 300l per day myself but put it on flush every day for 5 minutes before i make pure

Good for the membrane to flush regularly

 

[Dave B]

Thinking of switching to fibredyne carbon block and sediment so will only need 2 filters

 

[AGlassAct]

I've always flushed my membrane before and after production. All the new autoflush systems flush every hour so the method in my madness isn't that far off. I've had my 4040 for two years so far and it's still going strong - start TDS 280ish down to 10ish. Spruce has made some good references to RO replacement guidelines in the past - if you use the manufacturers recommended rejection rate minus 10% or so. Or when the TDS before resin impacts on resin consumption to the point of it being more cost effective to replace the membrane - personally I have a figure of 50ppm, that's the cut off when I will replace my RO.

Daveyboy - I've just replaced my ridiculous Ionics 30" linear filters for the fibredyne and single sediment, I've saved so much room and it seems to be producing water faster for me too. I'll be doing a step by step guide soon hopefully for a cheapish 4040 trolley mount system in the DIY when I can actually get in my shed again. RO seems to come up a lot on the forum so hopefully I can make something simple for everyone to follow.

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[spruce]

So, about 3 weeks ago I got my first ever RO setup. It has 2x 20" pre filters and a 20" HF4 membrane. My water TDS is about 220 and it's coming out of the RO at 007. I'm doing a 10 minute flush once a week. I'm making about 300/350 litres of water a day. How will I know when to change any of the filters and membrane?

At the moment your membrane is running at 97% efficiency. That is to spec although I would have thought it would have been around 98%. However, it is a HF4 and if your water pressure isn't high, then this could be a factor.

When to change membranes? This is up to you but the rule of thumb used to be when the efficiency of your membrane drops to below 94%. Someone with low tap water tds won't see much of an increase in resin costs if they let it drop to below 94%, but my take is that the membrane is on its way out so you might as well bite the proverbial bullet and change it sooner rather than later.

How often is another question which no one can answer. Mines been in 4 years and still performs as it did when new. The previous 150GPD membranes lasted 6 years. But if your water has a high mineral content then one can't expect the membranes to last as long.

If you have a fiberdyne carbon block prefilter then that's good for 75700 liters according to manufacturers specifications. I would take that figure as gospel although the manufacturers will be giving figures for the worst case situation. The amount of chlorine you get at your tap may be a lot less than the maximum chlorine allowed so you could find your fiberdyne lasts longer - but you maybe wrong.

The 75700 liters includes all the water that goes through your prefilters, waste, pure and flushing.

If you are using 350 liters of pure a day then 5 days a week = 1750 liters.

If your pure to waste ratio is 1 to 1 then you are going to use approx 3500 liters.

Flushing at 15 lpm for 10 minutes = 150 liters

Total water used = 3650 liters per week

Total water used per month = 15700 liters

If your waste to pure ratio is 2 to 1 then you will use 5400 liters per week and 22700 liters per month.

In the first example your Fiberdyne prefilter will last nearly 5 months

In the second example it will last just short of 3.5 months.

The reason why I bang on about Fiberdyne prefilters is that the normal carbon block prefilters don't last as long as the Fiberdyne ones do. I still have a GAC 20" carbon block prefilter in my box. Its service life is good for 2500 gallons. Pretty good chance its US gallons which will be 10000 liters.

.

 

[Tuffers]

Thanks for the reply @spruce

 

[Duncs]

If you change your pre filters regular then you will save your membrane and resin

i,m changing my pre filters every month £30 ,cheap if you let it go cost in resin and membrane

 

[Duncs]

not sure what make the pre filters are must check