Please Help Me to Understand Something About RODI Systems

[Dom]

So I am using a 5 stage RODI system. Included in this system is a flush valve and another component (I don't know the name) which automatically stops the flow of water as pressure builds up from the float valve slowly closing as the water level reaches the top of the container.

Typically, I will run the system with the flush valve open to get the TDS reading down to zero. Once TDS reaches zero, I close the flush valve and divert the water to the collection container. Once full, I turn off the source water and start the process over again when I'm running low on RODI water.

I decided to keep the source water on all the time since the pressure valve stops water flow once the float valve closes. I thought that by doing this, I would always have a full 40 gallon reservoir.

But today, when I removed some water from the reservoir, it began to refill. But when I looked at my TDS meter, it gave a reading of 16.

What is the purpose of that automatic cut off, if I have to flush the system every time I make water? SHouldn't the water still be zero TDS?

Thanks,
Dom

 

[RobB'z Reef]

I might be mistaken, but i think they make auto flush systems as an add on. Like most things, you have your entry level effort and then automation costs more.

 

[flourishofmediocrity]

So I am using a 5 stage RODI system. Included in this system is a flush valve and another component (I don't know the name) which automatically stops the flow of water as pressure builds up from the float valve slowly closing as the water level reaches the top of the container.

Typically, I will run the system with the flush valve open to get the TDS reading down to zero. Once TDS reaches zero, I close the flush valve and divert the water to the collection container. Once full, I turn off the source water and start the process over again when I'm running low on RODI water.

I decided to keep the source water on all the time since the pressure valve stops water flow once the float valve closes. I thought that by doing this, I would always have a full 40 gallon reservoir.

But today, when I removed some water from the reservoir, it began to refill. But when I looked at my TDS meter, it gave a reading of 16.

What is the purpose of that automatic cut off, if I have to flush the system every time I make water? SHouldn't the water still be zero TDS?

Thanks,
Dom

The way I heard it explained was if you let water sit in the RO, the product and waste sides of the membrane seek equilibrium and essentially stuff you don't want will migrate slowly from the waste side to the product side. I've watched several BRS videos explaining this is why you want to flush your RO membrane before and after you make water for at least a minute. They also sell booster pumps that will increase the efficiency of your water production, and works with the auto flush valve that will do this for you automatically.

 

[ying yang]

This ?

 

[MaxTremors]

The whole point of the auto shut off switch/valve is that it’s a fail-safe in case you forget to check it so that it doesn’t overflow the container you’re filling and flood your house. I can’t tell you how many times I have forgotten or not gotten to it in time and had a giant mess to clean up. The float switch solves this. I don’t think it’s meant to allow you to just leave it on and work as an auto-too off.

 

[ZoWhat]

"Dang it Harry, you should have listened to the man and bought an auto-shutoff-thing-amiga. I oughta beat you with this mop"

 

[Dom]

The way I heard it explained was if you let water sit in the RO, the product and waste sides of the membrane seek equilibrium and essentially stuff you don't want will migrate slowly from the waste side to the product side. I've watched several BRS videos explaining this is why you want to flush your RO membrane before and after you make water for at least a minute. They also sell booster pumps that will increase the efficiency of your water production, and works with the auto flush valve that will do this for you automatically.

That makes so much sense to me. And this is called TDS Creep?

 

[Dom]

The whole point of the auto shut off switch/valve is that it’s a fail-safe in case you forget to check it so that it doesn’t overflow the container you’re filling and flood your house. I can’t tell you how many times I have forgotten or not gotten to it in time and had a giant mess to clean up. The float switch solves this. I don’t think it’s meant to allow you to just leave it on and work as an auto-too off.

Yes... and that is what I was shooing for; auto-top off.

 

[Matt L.]

Pressure is used to drive the stuff we measure as TDS out of the source water in reverse osmosis. Applying a booster pump can lead to more efficient reverse osmosis. The reverse osmosis membrane, however, is like a door that can swing both ways. When pressure is removed, some of the stuff we removed can creep back through the other way. It's not pressure, but a gradient in concentration. All the stuff on the other side wants to dissolve itself back in the pure water. So when a RO/DI unit sits, the water in the RO filter can be high in TDS, and should be discarded on startup. For the price of a booster pump, I recommend a programmable TDS switch. In the photo below, this triggers the lower pair of solenoids (I have a NO/NC pair, but a 3-way solenoid would also work) to divert water. The TDS controller is the little green box top center.

Matt

 

[Dom]

Pressure is used to drive the stuff we measure as TDS out of the source water in reverse osmosis. Applying a booster pump can lead to more efficient reverse osmosis. The reverse osmosis membrane, however, is like a door that can swing both ways. When pressure is removed, some of the stuff we removed can creep back through the other way. It's not pressure, but a gradient in concentration. All the stuff on the other side wants to dissolve itself back in the pure water. So when a RO/DI unit sits, the water in the RO filter can be high in TDS, and should be discarded on startup. For the price of a booster pump, I recommend a programmable TDS switch. In the photo below, this triggers the lower pair of solenoids (I have a NO/NC pair, but a 3-way solenoid would also work) to divert water. The TDS controller is the little green box top center.

Matt

Nice. But way too complicated for me. LOL

 

[redfishbluefish]

Your flush valve only flushes the back side (waste side) of the membrane. Leave the flush valve open for a minute or so on startup (and if you wish, for a minute or so when you're shutting down.) Flushing really has nothing to do with TDS readings....it's just to extend the life of your membrane. Now, if you wish to minimize break-through TDS, then you need to run the first couple minutes of RO water to waste on startup. Break-through occurs when the membrane sits and TDS "creeps" through the membrane. Flushing the waste side does not eliminate that TDS on the product side. That's why you need to do that with another valve. I use a three way valve right before my DI resin.

On startup, I flip the valve and run the RO water to waste. This flushes out the TDS that has broken through the membrane. I actually have inline TDS meters that tell me when the RO water has dropped to a steady rate.....for me, around ten minutes. I then flip the valve which directs the RO water through the DI resin. By doing this little step, I extend the life of my DI resin considerably.

 

[flourishofmediocrity]

That makes so much sense to me. And this is called TDS Creep?

Yes, and I also learned recently that these flush valves don't shut off the flow completely, they either just restrict it enough to provide the backpressure needed or wide open (when flushing). So if you do ever end up replacing it, or getting an auto flush, you have to get the one rated for the GPD of your RO membrane(s).

 

[redfishbluefish]

I am old school and have a manual flush valve that bypasses the flow restrictor...that completely shuts off directing all water through the restrictor.,

 

[JGT]

Your flush valve only flushes the back side (waste side) of the membrane. Leave the flush valve open for a minute or so on startup (and if you wish, for a minute or so when you're shutting down.) Flushing really has nothing to do with TDS readings....it's just to extend the life of your membrane. Now, if you wish to minimize break-through TDS, then you need to run the first couple minutes of RO water to waste on startup. Break-through occurs when the membrane sits and TDS "creeps" through the membrane. Flushing the waste side does not eliminate that TDS on the product side. That's why you need to do that with another valve. I use a three way valve right before my DI resin.

On startup, I flip the valve and run the RO water to waste. This flushes out the TDS that has broken through the membrane. I actually have inline TDS meters that tell me when the RO water has dropped to a steady rate.....for me, around ten minutes. I then flip the valve which directs the RO water through the DI resin. By doing this little step, I extend the life of my DI resin considerably.

Love this idea. So in the pic above, the canister is your DI, the top white tube is coming from your RO and the clear tube on the left is going to waste?
I have a RODI unit with an auto flush switch which kicks on at startup and periodically when the RODI runs for a while which is great but I still get high TDS on startup. I put a container under the float switch to catch the water until my TDS goes down but that is a pain. Your idea is much more elegant. Thanks.

 

[ying yang]

Nice. But way too complicated for me. LOL

If you find out what parts to buy and just connect/ install each piece one at a time it be easy ( just break it down to you installing one piece not several/then after installed one.then install another) ovbiously need to see diagrams over where the water starts and which way it flows.
I started out as a commercial/ industrial plumber working in factories/ offices/ prisons/ schools then as a sole trader working for myself in a domestic setting ( peoples houses) so could bought all the parts and installed myself,but i decided to just buy it pre- plumbed/ wired.in the picture is the flush valve circled


Edit: £ 183.00 for complete rodi set up and inline tds meter and spare membrane,pre filters and resin

 

[ying yang]

I did want find video of someone explaining how the water flows through EVERY step of the rodi unit,this one only explains how it flows through each chamber,but then thought its same rodi unit i got and how easy it is getting it all set up for you and you just attach few bits pipe,tds meter and you ready to go basically.if its to daunting for you to install it all yourself.

 

[redfishbluefish]

Love this idea. So in the pic above, the canister is your DI, the top white tube is coming from your RO and the clear tube on the left is going to waste?

Yes. And the valve handle shows the current direction of water flow, so in the picture, water is now going through the DI canister. And that valve is available from BRS. Again, used to clear TDS creep on startup.

.....
I have a RODI unit with an auto flush switch which kicks on at startup and periodically when the RODI runs for a while which is great but I still get high TDS on startup. I put a container under the float switch to catch the water until my TDS goes down but that is a pain. Your idea is much more elegant. Thanks.

Again, flush valves have absolutely nothing to do with TDS, or clearing TDS on startup. They are used to supposedly extend the life of your membrane by flushing the waste side of the membrane. The product side of your membrane will still have the break through TDS that occurred while sitting unused. You will always have break-though TDS on startup. The only way to get rid of startup TDS is to run that water to waste before it gets to your DI resin. By not doing this, you will eat through your DI resin much quicker.

 

[Raheel-82]

H

Pressure is used to drive the stuff we measure as TDS out of the source water in reverse osmosis. Applying a booster pump can lead to more efficient reverse osmosis. The reverse osmosis membrane, however, is like a door that can swing both ways. When pressure is removed, some of the stuff we removed can creep back through the other way. It's not pressure, but a gradient in concentration. All the stuff on the other side wants to dissolve itself back in the pure water. So when a RO/DI unit sits, the water in the RO filter can be high in TDS, and should be discarded on startup. For the price of a booster pump, I recommend a programmable TDS switch. In the photo below, this triggers the lower pair of solenoids (I have a NO/NC pair, but a 3-way solenoid would also work) to divert water. The TDS controller is the little green box top center.

Matt

Pressure is used to drive the stuff we measure as TDS out of the source water in reverse osmosis. Applying a booster pump can lead to more efficient reverse osmosis. The reverse osmosis membrane, however, is like a door that can swing both ways. When pressure is removed, some of the stuff we removed can creep back through the other way. It's not pressure, but a gradient in concentration. All the stuff on the other side wants to dissolve itself back in the pure water. So when a RO/DI unit sits, the water in the RO filter can be high in TDS, and should be discarded on startup. For the price of a booster pump, I recommend a programmable TDS switch. In the photo below, this triggers the lower pair of solenoids (I have a NO/NC pair, but a 3-way solenoid would also work) to divert water. The TDS controller is the little green box top center.

Matt

Hello Matt,

Pls help me. I am getting so stressed. I have autoaqua auto shut off installed on a timer. Everything is perfect but the problem is whenever the rodi unit starts it is having the initial tds. I don’t want tds going in my auto top off. Pls let me know what I should do for 0 tds as I don’t want to manually flush every time. I know you have shown in the diagram but I am so new that I need some guidance. I await. Thanks.

 

[Raheel-82]

Pressure is used to drive the stuff we measure as TDS out of the source water in reverse osmosis. Applying a booster pump can lead to more efficient reverse osmosis. The reverse osmosis membrane, however, is like a door that can swing both ways. When pressure is removed, some of the stuff we removed can creep back through the other way. It's not pressure, but a gradient in concentration. All the stuff on the other side wants to dissolve itself back in the pure water. So when a RO/DI unit sits, the water in the RO filter can be high in TDS, and should be discarded on startup. For the price of a booster pump, I recommend a programmable TDS switch. In the photo below, this triggers the lower pair of solenoids (I have a NO/NC pair, but a 3-way solenoid would also work) to divert water. The TDS controller is the little green box top center.

Matt

Hello Matt,

Sorry for the trouble but after reading your post over and over again. I think I can install the 3 way solenoid valve to the di line and then after diverting the water for a few minutes till the tds becomes 0 I can then start filling the ato reservoir. I think I will again have to put this on a timer so once the tds is 0 the solenoid can push water to my ato reservoir. Am I correct, pls guide.

One last question, should I order the 3 way normally closed solenoid valve or the 3 way directional solenoid valve.

Thanks again.

 

[Raheel-82]

Hello Mat,

I also wanted to know as you mentioned a 3 way solenoid valve would work so I wanted to know that if I install the 3 way normally closed solenoid valve on the di output line so once the 0tds is achieved and when I power on the solenoid will the water flow from the cavity port to thr orifice port because in the diagrams they show the flow happens from thr orifice port to the cavity post. Pls advice because the water should flow from the cavity port to the orifice port and from there on my auto top off reservoir.
Pls guide.

Thanks.