[rb4no]

Hi guys, OK I'm getting a TDS reading of about 360 PPM at the tap, after my RO I'm getting low to mid teens, my first DI vessel would get that to zero, but then once that reading started to creep up to about four I purchased another DI vessel about four months ago and got it down to zero again. Now the past week, my TDS reading has gone to one/two, I've just checked this morning's reading's along the line and they go as follows: After RO 11 PPM, first DI vessel, 9PPM second DI vessel 2PPM. Now I guess the first DI vessel needs to be replaced but still between the two DI's it should be able to deal with 11PPM right, especially since the resin in the second vessel hasn't even done 20,000 litres right? Please advise..

[Simon Trapani]

My understanding of double di is when your tds after  second di gets to 1 ppm or more, it’s time to ditch the resin in the first vessel & put the second vessel where the first was. Then refill what was the first vessel & put it where the second vessel was. Make sense? That’s what we do anyway.

[p1w1]

Your first vessel is spent now, just do as above, also might be worth giving the vessels a shake now and again just to mix the resin about. Also you dont state what size vessels you are using so impossible to say how long they should last.
This would give you a rough idea https://gardinerpolesystems.co.uk/Resin_Calculator.htm

[rb4no]

i've got two 11 litre vessels, I'm using a 4040 RO which has only done about 70,000 litres... my concern being is that only after a few months the DI's are struggling to deal with like 11 to 15 TDS...

[andyM]

When you start up your 4040 are you disconnecting the DI vessel or diverting the water away until the tds settles down?

[Ian Lancaster]

Resin has a fixed capacity for removal of ions.  Hence the various 'calculators' available on the web.  Having one, two or a dozen cylinders won't extend the life of resin, it will still only be able to absorb the same finite amount of dissolved solids.  If water is passing through resin and still has dissolved solids in it then (a) the resin is 'spent' - i.e. it no longer has any 'space' left on the surface of the beads to attract ions or (b) the water is passing through the resin too quickly for the absorption process to complete.

There is also a tendency for water to create 'tracks' through the resin which will become 'lines of least resistance' so water passes more easily through them than through the undepleted resin elsewhere in the cylinder.  A really good daily shake can dramatically increase the effectiveness.

[rb4no]

I don’t tend to disconnect the Di vessels to start with cos if the Tds is high it only stays like that for a few minutes., and to be honest it’s a bit of a faff given the way my van system is mounted etc. I will take your advise and give it a good shake and see how it goes. Thanks everyone.....

[andyM]

I don’t tend to disconnect the Di vessels to start with cos if the Tds is high it only stays like that for a few minutes., and to be honest it’s a bit of a faff given the way my van system is mounted etc. I will take your advise and give it a good shake and see how it goes. Thanks everyone.....

I do reckon that is why your resin is depleting quickly.
I used to disconnect the hose from the DI vessel but have since plumbed in a diverter hose system using two 1/2" JG ball valves and JG tubing.
It works well.   

[nathankaye]

He makes a valid valid point as tds creep can certainly kill your resin.
Check it out on you tube etc.

But basically when your RO isn't under pressure the two side will mix so your first lot of water can be extremely high, close even to your starting point and do that a couple of times and your resin will be spent.
To reinforce the point, take a reading after your RO but before your Di and see for yourself when you first turn it on and you'll have your answer

[֍Winp®oClean֍]

Resin has a fixed capacity for removal of ions.  Hence the various 'calculators' available on the web.  Having one, two or a dozen cylinders won't extend the life of resin, it will still only be able to absorb the same finite amount of dissolved solids.  If water is passing through resin and still has dissolved solids in it then (a) the resin is 'spent' - i.e. it no longer has any 'space' left on the surface of the beads to attract ions or (b) the water is passing through the resin too quickly for the absorption process to complete.

There is also a tendency for water to create 'tracks' through the resin which will become 'lines of least resistance' so water passes more easily through them than through the undepleted resin elsewhere in the cylinder.  A really good daily shake can dramatically increase the effectiveness.

With respect, you clearly don't understand the multi DI vessel process.

[Smudger]

who doesn't ? Ian you mean ??

if so please enlighten the rest of us as that is exactly what i understand things to be

Darran

[֍Winp®oClean֍]

who doesn't ? Ian you mean ??

if so please enlighten the rest of us as that is exactly what i understand things to be

Darran

"Spent" resin is used to pre-filter new resin. My input TDS is 70ppm so my pre-filter resin isn't "spent" untill it hits 70ppm. This is the whole point of a twin DI system- it facilitates the extended use of resin that would otherwise be "spent".

[Simon Trapani]

who doesn't ? Ian you mean ??

if so please enlighten the rest of us as that is exactly what i understand things to be

Darran

"Spent" resin is used to pre-filter new resin. My input TDS is 70ppm so my pre-filter resin isn't "spent" untill it hits 70ppm. This is the whole point of a twin DI system- it facilitates the extended use of resin that would otherwise be "spent".

Spot on Peavey.

[Smudger]

On that basis my resin isn't spent until it reaches my water TDS of 375 - thats not a lot of cop to anyone

i understand your point but at a certain level used or 'spent' resin is just doing nothing to help the second di bottle

Darran

[֍Winp®oClean֍]

On that basis my resin isn't spent until it reaches my water TDS of 375 - thats not a lot of cop to anyone

i understand your point but at a certain level used or 'spent' resin is just doing nothing to help the second di bottle

Darran

Any normal, particularly experienced person would understand that the resin isn't spent untill either- it reaches the input TDS or the freshest vessel begins to rise anyway- the latter is obviousley dependant on the input TDS!

It's not rocket science boys

[Smudger]

thats my point - my ads  after ro is 006 - so at that its spent - yet i could pass it onto you and it's not spent


Darran

[֍Winp®oClean֍]

thats my point - my ads  after ro is 006 - so at that its spent - yet i could pass it onto you and it's not spent


Darran

 Like I said the scope of extended resin life is dependant on the input TDS. I would not even bother with twin vessels after RO.
So, again, it's not a given/definite point as to when resin is "spent' or "clearly" we would all be throwing it away at 001ppm.

[nathankaye]

So if someone's start(input) tds is 050 their Di resin is spent when it reaches 050.
But someone else's tds input might be 015 and if their di reaches 015 its spent.
That reasoning doesn't make sense.

There has to be a factual answer as to what level tds will effect the working life of resin or is it also dependant upon the tds particles and so there is no definitive answer perhaps

[֍Winp®oClean֍]

So if someone's start(input) tds is 050 their Di resin is spent when it reaches 050.
But someone else's tds input might be 015 and if their di reaches 015 its spent.
That reasoning doesn't make sense.

There has to be a factual answer as to what level tds will effect the working life of resin or is it also dependant upon the tds particles and so there is no definitive answer perhaps

Yes- as a pre-filter vessel to a fresh vessel. OBVIOUSLEY you can only pre-filter up to the input TDS ........ or you are not in fact pre-filtering at all. For this reason, a twin DI system becomes more effective with a higher input source but is most effective within certain parameters. Too low and the pre-filter efficiency is negligible- too high then RO pre-filter is required. On the higher boundaries of the optimum parameters other factors may come into play like water meters, waste water ratio etc. to determine the most efficient method.

[dazmond]

So if someone's start(input) tds is 050 their Di resin is spent when it reaches 050.
But someone else's tds input might be 015 and if their di reaches 015 its spent.
That reasoning doesn't make sense.

There has to be a factual answer as to what level tds will effect the working life of resin or is it also dependant upon the tds particles and so there is no definitive answer perhaps

Yes- as a pre-filter vessel to a fresh vessel. OBVIOUSLEY you can only pre-filter up to the input TDS ........ or you are not in fact pre-filtering at all. For this reason, a twin DI system becomes more effective with a higher input source but is most effective within certain parameters. Too low and the pre-filter efficiency is negligible- too high then RO pre-filter is required. On the higher boundaries of the optimum parameters other factors may come into play like water meters, waste water ratio etc. to determine the most efficient method.

spot on peavey......my input tds is usually in the 025-030  range so when my single DI starts to creep up(say 005)i put a second fresh vessel in front of it until the first one reaches 025-030 then throw that "spent" resin away.......this way im making the most of my resin.....and i go back to a single DI until the same happens to that one....

i dont know why people get so confused about it TBH......