Quick RO/DI question

[LoveReefer]

I'm wanting to add a float switch to my RODI reservoir. When the float switch cuts off the filtered water does the waste water continue to run?

Thanks guys,
Mike


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[BrettDS]

You need an RODI auto shut off valve. That will stop the water from flowing to waste when it's no longer producing water. Some RODI systems come with them and some do not, but they are reasonably inexpensive if you don't have one.

But that said, you probably don't really want to use a float valve with your RODI unit because it can cause you to burn through DI resin very quickly. When an RODI filter is shut off things that would normally be filtered out of the water can pass through the RO membrane. This causes unusually high TDS output from the RO membrane for the first few minutes of water production whenever you start the RODI filter. This is known as TDS creep. The DI resin will remove the extra contaminates and the water will still be clean, but the problem is that if you use a float valve and the RODI turns on and off frequently then it will only run for a few minutes each time and the RO membrane will never get to the point where it's putting out low TDS water, so the DI resin will constantly have to remove a high level of contaminates and will be exhausted much more quickly than normal.

Ideally you should let your RODI reservoir empty completely (or nearly completely) and then refill it to allow the RODI filter to run for a long time.

 

[Tastee]

I use an RODI valve (aka a pressure sensitive solenoid) in my RODI station so that I can turn the water on to refill and walk away. The valve will automatically shut it off preventing any spill and I then turn the water off when I remember. I only refill my reservoir every 2-3 weeks as needed.

They are also a little noisy during shutoff so I prefer to ensure this happens during the day to avoid annoying my neighbours.


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[wrott]

https://premiumaquatics.com/products/aquafx-high-pressure-auto-shut-kit.html

 

[ROB2005]

To prolong the life of your DI resin if you use it for small batches, you can add a tee and a ball valve after the the tee on the line from your membrane to your DI. Add another ball valve on the line from the tee going to the drain, this way you can drain the excess TDS that has built up in the line rather than letting your DI have to filter it out.

Hope this helps.

 

[BrettDS]

To prolong the life of your DI resin if you use it for small batches, you can add a tee and a ball valve after the the tee on the line from your membrane to your DI. Add another ball valve on the line from the tee going to the drain, this way you can drain the excess TDS that has built up in the line rather than letting your DI have to filter it out.

Hope this helps.

That will definitely work if you are manually operating the RODI filter and is a great idea for small batches. But the OP was looking to install a float valve which will start and stop the RODI without manual intervention, so there would be no way to manually bypass the DI resin for the first few minutes.

 

[Tastee]

That will definitely work if you are manually operating the RODI filter and is a great idea for small batches. But the OP was looking to install a float valve which will start and stop the RODI without manual intervention, so there would be no way to manually bypass the DI resin for the first few minutes.

With a controller such as an Apex you can make this work. The below would give you an automated weekly fill. Obviously change days and times to suit your needs.

1. Incoming water line to 24V solenoid controlled by Apex (S1).
2. Output of S1 to Pressure Sensitive solenoid (PSV aka RODI float valve kit). Normal configuration of the PSV.
3. Tee between RO membrane and DI resin.
4. 24v solenoid on the Tee line connected to waste.

Program the Apex to open S1 and S2 at 7 am on a Saturday. Program S2 to then close after 2 mins, and S1 to close after 10 hours.

The RO unit will turn on automatically at 7 am on Sat and for the first 2 mins waste all water being produced to stop TDS creep. When S2 closes the unit will start producing RODI water. When the reservoir fills the PSV will shut off the system. The Apex will then turn off the inlet supply some time after.


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[mcgyvr]

These answers are assuming you are wanting to use the float switch to keep that reservoir topped up so that whenever the water level drops "some" that the float turns the water back on.. And their comments about problems with "short cycling" are certainly a potential issue..

However if you just want to use that float because you drain your reservoir down all the way often and then turn the water back on to completely fill it and often find yourself forgetting and come back to an overflowing bucket then yes a mechanical float is an excellent way to prevent those floods and won't be a problem at all..

And yes.. Closing the float "should" stop the flow of waste water assuming you have an ASOV valve.. Sometimes though there doesn't seem to be enough backpressure and the waste water will continue to flow for a short while or indefinitely.. Each system is slightly different.. It "should" cut off the waste water though..

 

[LoveReefer]

These answers are assuming you are wanting to use the float switch to keep that reservoir topped up so that whenever the water level drops "some" that the float turns the water back on.. And their comments about problems with "short cycling" are certainly a potential issue..

However if you just want to use that float because you drain your reservoir down all the way often and then turn the water back on to completely fill it and often find yourself forgetting and come back to an overflowing bucket then yes a mechanical float is an excellent way to prevent those floods and won't be a problem at all..

And yes.. Closing the float "should" stop the flow of waste water assuming you have an ASOV valve.. Sometimes though there doesn't seem to be enough backpressure and the waste water will continue to flow for a short while or indefinitely.. Each system is slightly different.. It "should" cut off the waste water though..

This.

I should have been a little more specific as to how I wanted to use the float valve. I'm afraid to leave it on too long while filling and flood.

With that being said I think this turned into a really informative thread and I definitely learned a few things from it. Thanks guys

Mike


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[Kevin Guthrie]

The amount of evap doesn't change much from day to day. What we've done for a couple of decades:
Float valve on reservoir shuts off RO/DI input. RO/DI feeds the reservoir.
Once a day I top off a 5 gallon water jug on the floor from a tap on the reservoir. The water jug feeds a Pulsatron pump which feeds a kalk reactor which feeds evap makeup water into the sump. The Pulsatron is on a timer and runs during lights off, which equalizes pH. I adjust the timer or the Pulsatron when the level in the sump goes up or down - couple times a year. The system goes thru about 3 gpd evap in the winter and 2 gpd in the summer.
I also fill a water change jug from the reservoir tap, and fill our drinking water containers. Contrary to some posts here drinking it doesn't explode our guts.