[edd]

how long will 25ltr Di last at 280 ppm or how many litres of water will it make
my ro and van are going in for repair at last and will off the road for 2 weeks
so I'm hiring a van putting an ibc inside Di battery and pump I hope this will operate 2 of us with just 1 pump!!but need to know how many litres of water it will make as mine lasts about a year with  the ro .....Edd

[john tomkins]

The calculations are
20000 multiplied by litres of resin, divided by TDS into resin = Litres of pure

For you with 25ltr containers of resin and 280 TDS into resin (from RO)
20000 x  25/280 = 1785 ltr of pure

[michael papworth]

Very interesting formula, John. Where did you get it from?

[cbcs]

Don't know where it got that from!? I use 25 of resin every 8 weeks. At a TDs of 076 ppm I can produce 35000-40000 litres of pure.

[michael papworth]

Sorry about this - I LOVE maths!!!

Now this is very interesting and could be very useful to a lot of people. Of course, the work may already have been done and (as someone recently and very kindly pointed out, I'm a newbie, so) I simply don't know about it.

The formula is going to look something like:

k x (mass of resin/tds of input water) = volume of 000 water produced.

It might not be a perfect formula, but it should give at least a rough idea of the quantities involved.

The problem is to find the value of k.

Another complicating factor is that k is very likely going to be different for different manufacturers of resin. However, knowing a rough value for k is going to be a terrific measure of the quality of resin from any particular source.

We need to gather figures from as many people as possible to get the data to calculate k.

As I'm a newbie, I don't have much data to work from, but my first lot of data is: 700 ml of resin gave me about 5000 litres of water and the tds from my ro unit is usually about 006.

So, I calculate k as being:

k = volume of 000 water x (tds of input/mass of resin)

= 5000 x (6/0.7)

= 43000 - which is about double the figure quoted by John

Putting Chris's data into the formula we get:

k = 40000 x (76/25)

= 120000 - which is six times the figure quoted by John

Does anybody else feel like looking over their records and coming up with a figure?

So far, empirical results between 43000 and 120000 suggest that there is still some research needs to be done!

Putting v8edd's figures into the formula and using the lower value of k gives:

volume of water = 43000 x (25/280) = 3800 litres

and using the higher value

volume of water = 120000 x (25/280) = 11000 litres

Assuming each guy uses about 300 litres per day, two guys working for two 5-day weeks is going to be 6000 litres.

So you will get away with it if the higher value is true. If the lower value is true, you'll need about 40 litres of resin!

Having said that - DON'T RELY ON THESE FIGURES!!!

(Shouting is appropriate here!!!)

Thanks for the question. It certainly gave my mathematical neurons a bit of a work out.

[steve.ternent]

  Wow Wally what are you doing being a window cleaner?
I read the first two line and then shot myself!
No it looks great, but I still jumped to the bottom of the page!
Brilliant pure brilliance! regards steve

[edd]

wally  wow dude that waz the best reply`Ive ever seen so I will need 2 bags for 2 weeks then???
2 guys on 600 a day di only

[michael papworth]

Hey. v8edd. Take it easy. It's just an estimate.

All I said was, "maybe it will be enough, maybe it won't," which is probably not much better than anyone else could say without all the complex mathematical stuff.

It's only based on two sets of data (only gives a confidence level of plus or minus 70%) which is nowhere near good enough and there is no guarantee that the data used was accurate.

What you CAN say is that it will probaby be more than one full bag and less than two, so you've got a ball park figure to aim for. You can be pretty certain that it's not going to be a bag a day.

What will be really interesting is if you keep a really careful record of (i) the tds of the input water and (ii) how much water you use before the first bag starts to give a reading of 001/002 and then we can calculate a fairly accurate value of k.

If lots of us did that, we could do some really useful research and get concrete results.

[TennetClean]

yeah gotta hand it to ya this time wally, that was pretty cool

[russ_clark]

You certainly ain't a Wally- Wally   

[john tomkins]

Very interesting formula, John. Where did you get it from?

Here Wally....
www.cleantech.co.uk/tdscalc.htm
You just input your TDS and check how much you'll get out of a sack (25ltrs)

[john tomkins]

Don't know where it got that from!? I use 25 of resin every 8 weeks. At a TDs of 076 ppm I can produce 35000-40000 litres of pure.

Who you calling "it" ..... cheeky git
Anyway what are you cleaning if you are using 5000 ltrs of pure per week

Most the calculator says you should get is 6579 ltrs out of a 25 ltr sack, so you either need a new TDS meter or you let the TDS from DI get up to 76 before you change resin

[michael papworth]

Yep. Checked the calculations and John is right about the value of k = 20000 if the cleantech calculator is correct. Thanks very much for that link, John.

If that is right, v8edd is in for a VERY nasty shock as it gives 1800 litres of 000 from a 25 litre sack. That's going to be expensive - about 4p per litre.

Still, there is much to be learned here from people's actual results.

(Not wishing to be cynical, but it IS in cleantech's interests to quote the highest possible cost of using resin alone since the calculator is there to convince customers to buy an RO unit. I wouldn't argue with them there, it is more economical for most people. They might, however use rather more egg in their cakes than is strictly necessary.)

[Clive McDonald]

The factor k is 20,000 divided by tds.(the first post said this)

If used as a polisher after the ro it lasts a long time. It's also been said running it in tandem is better.

The answer is check tds after a week and if it's okay carry on.

[Paul Coleman]

The factor k is 20,000 divided by tds.(the first post said this)

If used as a polisher after the ro it lasts a long time. It's also been said running it in tandem is better.

The answer is check tds after a week and if it's okay carry on.

Obviously it breaks down to the same result but, as I imagine most people buy resin in 25k sacks, I have always found it easier to do the 500,000/TDS = litres of pure water per sack of resin.  20,000 x 25 being 500,000 of course, so the same maths.
I've just recently changed the resin in a vessel.  It's about 12 litres in the vessel (half a bag say).  The RO has been producing anything from 006 to 012 with a much higher TDS for a few litres after startup.  The resin lasted a bit over 6 months.  Not much help though as I've no idea how much pure water I've used in that time.  Assuming an average of 10 TDS (for easy calc), that would indicate 50,000 litres per bag so that would give 25 litres from a half bag vessel.  That's around 1,000 litres per week average.  Well I'm sure I've used a lot more than that in the 6 months.  Maybe it's high because, as it's from an RO, it's only been trickling through the resin.

[steve m]

got to the second line and me eyes glazed over and I couldnt read anymore

[Clive McDonald]

Yes that's a better way of understanding and being able to do it in your head shiner.
The reason I posted was that the mathematician was trying to crack it  from first principles and empirical observation. The mysterious k was not a mystery because it had already been given, but k varies from place to place dependant on the tds.

In other words k is not a constant,

[michael papworth]

No! k is NOT 20,000 divided by tds. k is independent of tds and is a property of the resin.

The value of k is 20,000 - according to cleantech.

Discount might be right, of course, k might not be a constant. It might vary from one manufacturer to another and possibly with temperature and even flow rate.

We don't need to know the value of k with any great precision. But it might be useful to know if the value is 20,000 or 40,000 or somewhere in between.

It isn't going to change the nature of window cleaning, and it isn't going to change the way that we clean windows. It isn't going to change the cost of resin and it isn't going to make any difference to the rate at which you use resin. In fact, it isn't going to make any difference at all to anybody or anything.

Some people will find it interesting and others will find it boring and pointless - and all that is OK.

However, if we could find that k for one particular manufacturer was very much higher than for another, for example, now THAT might be useful. It would be evidence that one manufacturer made more effective resin than another.

And if we find that k is 20,000 for all resins from all manufacturers, that's useful as well, because the prices aren't all the same and it would make perfect sense simply to buy the cheapest.

If you enjoy this type of analysis, that's good. If you don't, please don't knock it or criticise it. A bit of thought went into it and it was for a good reason and hopefully might be of benefit to all.

At the very worst, it shouldn't hurt or cause offence to anyone.