RODI direct to Auto top off?

[kkegley21]

Can I plumb an RODI directly to the sump with an auto top off controlling it? I have the Neptune ATK and the SV-1 SOLENOID VALVE.

 

[redfishbluefish]

Would not recommend.

Every time the RO/DI turns on, there is breakthrough TDS. Since it's going to turn on and off multiple times each day, you'll chew threw the DI resin real quick.

The second reason is that when you have a failure, you'll have an unlimited supply of water flooding your house.

 

[LowLi]

i built my rodi barrel on a stand.. i added 1/4" quick connect fitting with a ball valve connected to a float switch on a 2g container the gravity auto siphons water into the 2g container and the float valve cuts it off.

but i have my tank in wall so i have the barrel right behind it luckily

 

[fishyguy7]

I have been running like this for nearly 15 years. I do have 4 solenoids Hooke up to the output of the ro for redundancy. I also have a solenoid set to run for 4 minutes that does a DI bypass FOR TDS creep. I would not run it just off of the mechanical float as that is a disaster waiting to happen

 

[Dumaurier7]

Would not recommend.

Every time the RO/DI turns on, there is breakthrough TDS. Since it's going to turn on and off multiple times each day, you'll chew threw the DI resin real quick.

The second reason is that when you have a failure, you'll have an unlimited supply of water flooding your house.

This is not very accurate, I have mine plumbed this way, and have been like this for 2 years without issue. I included a 5 gallon (I think! )pressure tank in my set up so the RODI unit doesn’t always have to turn on every time a top up is required and this is NOT multiple times per day nor every single day . The water is switched by my controller via a solenoid which is backed up with a mechanical float for redundancy, no issues whatsoever.

 

[kkegley21]

This is not very accurate, I have mine plumbed this way, and have been like this for 2 years without issue. I included a 5 gallon (I think! )pressure tank in my set up so the RODI unit doesn’t always have to turn on every time a top up is required and this is NOT multiple times per day nor every single day . The water is switched by my controller via a solenoid which is backed up with a mechanical float for redundancy, no issues whatsoever.

I was trying to avoid having a tank and did watch one of the Neptune videos where they used the solenoid to control with the ato. With the Apex I was hoping to avoid using a reservoir but I am unsure what to do.

 

[chipmunkofdoom2]

This is not very accurate, I have mine plumbed this way, and have been like this for 2 years without issue. I included a 5 gallon (I think! )pressure tank in my set up so the RODI unit doesn’t always have to turn on every time a top up is required and this is NOT multiple times per day nor every single day . The water is switched by my controller via a solenoid which is backed up with a mechanical float for redundancy, no issues whatsoever.

It's absolutely accurate. When an RO unit turns off, you have high-TDS brine on one side of the membrane and clean product water on the other side. The solids tend to want to reach equilibrium, so they move through the membrane until the water on both sides has roughly the same solids. It's also possible that scale on the membrane's surface will dissolve and further increase the TDS. You may not notice the high TDS because your DI resin will pick up the slack. But, it's there.

Now, is this a big deal? Probably not, and it will almost never affect your tank. It'll just hammer your DI resin with high-TDS water for a few minutes every time the unit runs. In your situation as you describe, running your unit for longer periods every few days instead of a few times every day, you're much less likely to see the impact of this. But, if your unit is turning on and off multiple times a day because you plumb it directly to a float switch in your sump, TDS creep will absolutely happen and will burn through your DI resin faster.

If you don't believe us, turn your RO unit on and collect the first few oz of water from the membrane BEFORE your DI resin. It will likely measure around where your tap TDS is, if not higher.

 

[TLeTourneau]

I've have had mine direct plumbed with the ATK and a solenoid valve since I set it up, I've had no issues. I do have a moisture activated automatic shutoff and a LDK sensor as well for peace of mind. TDS creep hasn't been an issue for me as my RO system is whole house and is used several times a day for other things. Also, the ATK on my system activates on average 20+ times a day.

The shutoff I use is:
https://www.amazon.com/Express-Wate...coding=UTF8&psc=1&refRID=8R0CKB7K635X3VDTTX5G

 

[Dumaurier7]

It's absolutely accurate. When an RO unit turns off, you have high-TDS brine on one side of the membrane and clean product water on the other side. The solids tend to want to reach equilibrium, so they move through the membrane until the water on both sides has roughly the same solids. It's also possible that scale on the membrane's surface will dissolve and further increase the TDS. You may not notice the high TDS because your DI resin will pick up the slack. But, it's there.

Now, is this a big deal? Probably not, and it will almost never affect your tank. It'll just hammer your DI resin with high-TDS water for a few minutes every time the unit runs. In your situation as you describe, running your unit for longer periods every few days instead of a few times every day, you're much less likely to see the impact of this. But, if your unit is turning on and off multiple times a day because you plumb it directly to a float switch in your sump, TDS creep will absolutely happen and will burn through your DI resin faster.

If you don't believe us, turn your RO unit on and collect the first few oz of water from the membrane BEFORE your DI resin. It will likely measure around where your tap TDS is, if not higher.

My controller automatically flushes my membrane every day none of this is a concern.

 

[redfishbluefish]

Flushing has nothing to do with breakthrough TDS. It happens regardless of flushing.

Let me show you actual numbers. I made water yesterday. Today, before starting making more water, I flushed for over a minute, and then shut off the flush valve. Breakthrough had already happened...even if I had flushed the day before....and within a minute or two here's what I see on my TDS meter:

(Hard to see....post RO, 43 TDS, post DI, 0 TDS)

So what I do is run the first 4 - 5 minutes of product water to waste to save my DI resin. When RO TDS drops down to 2 or 3, I flip a valve and start collecting. If I didn't do this, this ramp up to some high TDS (43 in this case) would have to be removed by the DI resin. FYI, I get at least a year out of my DI resin.

 

[chipmunkofdoom2]

My controller automatically flushes my membrane every day none of this is a concern.

What @redfishbluefish said. Flushing is not the same thing as discarding the first few minutes of water to get rid of TDS creep.

Also, as I said in my previous post, TDS breakthrough is much less of a problem for you because of the unique way you have your system is setup (where it only runs once every few days for longer periods). This minimizes how much breakthrough gets into your DI resin. But almost nobody does it like you do. Almost everyone who does this type of setup does it the "wrong" way: their RO system is hooked up directly to a float switch/valve and comes on several times a day. This is going to expose the DI resin to higher TDS water multiple times a day. Saying there are no problems with this general approach with regards to TDS creep is at the very least misleading.

Without some pretty fancy controller/solenoid work to make an automated DI bypass, you're going to use resin faster doing it the way the OP proposed. There's just no way around that.