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Waste RO TDS reading


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Hello. I’ve been using a pumped 200GPD RO system I’ve just got. Flushed it through for a couple of hours yesterday when I installed it. My water pressure is bad, about 30psi, which is why I bought a I pumped version. The pure water coming out is fine and at 0, but it’s quite fast, about a litre of pure a minute, and the waste TDS is high. My tap is about 260 but the waste  is at over 490. I know it’s going to be higher but thought this might be very high. I was very careful installing everything and all seems ok visually. I also thought that id it was a 40/60 pure to pure ratio would mean that waste would come out quicker than pure - ie 40 litres of pure would be produced in the same time as 60 litres of waste, but my waste is actually coming out a tiny bit slower than the pure at about a litre of waste in 1 minute 10 seconds. Have I made any mistakes anywhere here please? Any advice is much appreciated, thanks.

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You need to open your waste valve a bit more to get the balance right. You should have a higher percentage waste to pure than you have.

If you leave it the way it is your membrane longevity will suffer and you will use more resin.

Edited by spruce
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@spruce should the valve be part open all the time? I thought it was closed apart from when flushing. Apologies for the questions, some of what I’ve read up on is so confusing. 

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Your waste valve should be partially open. How much will depend on membrane, input psi and desired output TDS as well as temperature.

if your input TDS is 260 I would expect and output of maybe 5-13 TDS or ppm based on 98-95% efficiency. Open the waste valve a little at a time until you achieve in that range perhaps.

do you have a service type valve with two parts? By this I mean that there is two parts to the valve.  One adjustable valve that stays put. This controls the waste to pure ratio. And then another valve you just use to fully open or close which is used for flushing. This setup allows you to flush without having to reset your waste to pure ratio each time.

re waste TDS. Just think of it like maths. 260 in which then goes out at 50-50 waste to pure and the pure is 10 then..

Then 250 TDS has been removed for the pure which will carry in the waste making around 510. Gives an example. The dissolved solids don’t disappear. They are just redistributed in a way of speaking. 

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Thanks @Omega. There’s just one manual waste tap/valve. I opened it fully to flush it yesterday and left it for about 2 hours. The TDS was about 13 or 14 after that. The unit has a resin vessel after the membrane so I then put in the resin cartridge which took the TDS down to 0 and turned the tap valve to the off position. The instructions say it should be closed in normal use, and then opened occasionally for a few minutes to allow the pump to flow through the waste which will flush the membrane. It’s confusing being a window cleaner sometimes lol.

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So 13-14 after RO seems about the right range. 0 after resin I take it from what you are saying. If so all sounds spit on.

a tip that I do with ours. After each use flush With waste open for 5-10 mins. When you want to produce pure again disconnect after RO before resin with it open. I.e not using a hose lock or insert a male to male fitting if you do.

allow the water out the RO to reduce to 13-14- TDS before reconnecting back to resin.

reason is

after flushing it takes a minute or so for output pure from RO to drop to the desired level. If you keep testing it with a TDS tester you will see it drop not by bit until the target.

its a small thing but for us with high tap TDS it limits a bit of 40-50 TDS water going into the resin. 

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4 minutes ago, Omega said:

So 13-14 after RO seems about the right range. 0 after resin I take it from what you are saying. If so all sounds spit on.

a tip that I do with ours. After each use flush With waste open for 5-10 mins. When you want to produce pure again disconnect after RO before resin with it open. I.e not using a hose lock or insert a male to male fitting if you do.

allow the water out the RO to reduce to 13-14- TDS before reconnecting back to resin.

reason is

after flushing it takes a minute or so for output pure from RO to drop to the desired level. If you keep testing it with a TDS tester you will see it drop not by bit until the target.

its a small thing but for us with high tap TDS it limits a bit of 40-50 TDS water going into the resin. 

Should do the above every time before filling as well. We can get anything up to half a bucket full of water before we connect to the DI vessel.

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Posted (edited)

@Omegabrilliant. Yes it was 0 after the resin cartridge was installed . Thank you very much for your help.

Edited by wgwindows
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3 hours ago, wgwindows said:

@spruce should the valve be part open all the time? I thought it was closed apart from when flushing. Apologies for the questions, some of what I’ve read up on is so confusing. 

The flush valve should be fully open when flushing the membrane and partially closed when producing pure water. 

There are different valves in the market. Some have been modified to allow some water to pass through them when fully closed. These valves may still have to be opened fractionally to allow more waste water to be let through to match the best waste to pure water ratio - start at 60 waste to 40 pure.

Others have to be left open a little to restrict the water going to waste as they haven't been modified.

There was a youtube video around once from Purefreedom on how to set up a Ro-Man type ro. I'll have a look tomorrow and see if it's still there.

 

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6 hours ago, wgwindows said:

@sprucethanks very much 

As you should be able to see PF use a flush valve that, when closed, still lets some water through it. If your flush valve completely switches the flow to waste off, then you have to open the valve a little until you get roughly the 60/40 waste to pure ratio.

You must never completely stop the flow of water to waste when producing pure. This waste water is what flushes the impurities away that the membrane is filtering out. If you close that tap then the membrane will block up and have to be replaced.

Just a word about this. You will notice that the TDS meter read 23ppm when the pure water was first tested. The di vessel was then connected up and a further test showed a tds of zero. I'm sure this was to show the viewer the di vessel working. Water with a tds of 23 will eat up the resin in that tiny di vessel very quickly. You need to get that pure tds reading down as low as possible before connecting your di vessel in.

As @Omega has commented, with a tap water tds of 260 you want to get the pure output from the membranes down to 5 or 6ppm. If you don't you are going to be forever changing the resin in the di vessel.

Now here's the thing. You don't say where you purchased the r/o, but if you can't get that tds down in the next few days then you need to focus in on the r/o you purchased. Some of these r/o's sold cheaply contain poor performing membranes made in China. They are good enough for aquatic purposes and purifying water for coffee machines and general household drinking water requirements from the kitchen tap. But they aren't efficient enough for window cleaning as we need to best quality available to keep overall running costs down. In other words, what you saved on buying a cheap membrane will cost you more in resin over a period of time.

 

Edited by spruce
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doug atkinson

You have made no mistake it's just the company who have sold this to you the set up is wrong. Something they should know before supplying the product.

This is something we cannot fix but for you to advise to the company you have purchased it from and ask if the outputs are correct. They then should spot the problem straight away and advise you.

Please do not quote me, thanks.

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Posted (edited)

@spruce thanks for this. Waste comes out regardless of whether the valve is open or closed. You do hear a slight adjustment in speed when you turn it from open to closed and vice versa. The RO cartridge I will probably remove when the resin is spent, and then connect the RO to a DI vessel separately and then into my tank. That way I can flush as I turn the unit on and when turning it off. When I’m flushing I’ll disconnect from the DI vessel and let the first bit go into a bucket, hopefully prolonging the resin in the DI vessel even longer. Thank you also  @doug atkinson. I wouldn’t want to name the company as I want to make sure I’m not making an error before I do anything. Can you advise on what may have been a better system for me please? My low water pressure pushed me into getting a pumped unit.

Edited by wgwindows
Spelling mistake
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1 hour ago, wgwindows said:

@spruce thanks for this. Waste comes out regardless of whether the valve is open or closed. You do hear a slight adjustment in speed when you turn it from open to closed and vice versa. The RO cartridge I will probably remove when the resin is spent, and then connect the RO to a DI vessel separately and then into my tank. That way I can flush as I turn the unit on and when turning it off. When I’m flushing I’ll disconnect from the DI vessel and let the first bit go into a bucket, hopefully prolonging the resin in the DI vessel even longer. Thank you also  @doug atkinson. I wouldn’t want to name the company as I want to make sure I’m not making an error before I do anything. Can you advise on what may have been a better system for me please? My low water pressure pushed me into getting a pumped unit.

A pumped unit is fine. You may just need to replace the membranes with more efficient ones.

Waste valve lets water pass open or closed. Great. Your water to waste is too little when the tap/valve is closed. You need to open it slightly more to get a better ratio: ( more waste than pure).

Edited by spruce
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3 hours ago, spruce said:

A pumped unit is fine. You may just need to replace the membranes with more efficient ones.

Waste valve lets water pass open or closed. Great. Your water to waste is too little when the tap/valve is closed. You need to open it slightly more to get a better ratio: ( more waste than pure).

Thanks very much for your help @spruce

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