RO/DI - Are all equal?

[Otrips]

People are still confusing the purpose of a flush valve vs a DI bypass valve.

Not sure who this is directed at but the purpose of a flush valve is to flush the membrane before/after use...
Flushing by bypassing the DI as well also helps to flush the other side of the membrane (TDS creep) which is the best option as your not sending unnecessary "dirty" water through the resin.

I have the 6 stage Fountanhead 150gpd $169 system. It is identical to BRS's 150gpd $339 system minus the add on 2nd RO membrane, dual TDS & a couple extra connectors. I compared the 2 side by side.
The closest I could compare it to the systems you sell is the $209.52 150gpd 4 stage system. Yours does include a pressure gauge but doesn't include the GAC filter and only has one DI cartridge. It does appear to use the same housings.

I do agree the horizontal DI cartridges specific to his system are not ideal. But please don't bash other vendors for offering an economical option. personally I'd pay the $30 more for the 6 stage vertical system. At least they offer it.

 

[Otrips]

I hope it ain’t me. I’ve tried to explain it the way AZDesertRat explained it to me many years ago. Any additional insight?

I agree with your explanation.

 

[JoshH]

Not sure who this is directed at but the purpose of a flush valve is to flush the membrane before/after use...
Flushing by bypassing the DI as well also helps to flush the system bypassing the restriction caused be the DI resin which is the best option as your not sending unnecessary water through the resin.

Flush Valve = Bypasses the membranes FLOW RESTRICTOR to flush the surface of the membrane which helps prevent build up on the membranes surface which can prolong the life of the membrane itself. This can be done before and after production but should be done at a minimum immediately after water production. The flush valve does not technically bypass the DI stage and the DI stage does not form any type of restriction in the system. I will also add running a flush valve alone does absolutely nothing to prevent high TDS from entering your DI stage.

DI Bypass Valve = A three way valve placed between the RO membrane and the DI stage that bypasses the DI stage of the system and allows excessive TDS in the initial product water present due to TDS creep (discussed in detail earlier by @Water Dog) to be directed to the "waste" line. This valve is used on initial start up to prevent high TDS water from entering the DI stage and depleting it unnecessarily quick.

These two valves provide VERY different functions and both are required for a long lasting system to keep performing at it's best.

 

[Buckeye Hydro]

This unit does a small back flush before it supplies any water, it does another large flush periodically.

Fun fact to know and tell: There's no such thing as a "BACKflush" of an RO membrane. There's no reversal of the direction of water flow when a flush valve opens. Sending water through a membrane in the wrong direction will ruin the membrane.

Russ

 

[Buckeye Hydro]

Residential and Commercial Reverse Osmosis-How it works to give you great drinking water. Installation and Systems Guide

One thing I noticed is your waste drain flows up. It should always flow downwards.

The concentrate flowing to an outlet above the membrane is not something that would concern me in nearly all situations.

 

[siggy]

Fun fact to know and tell: There's no such thing as a "BACKflush" of an RO membrane. There's no reversal of the direction of water flow when a flush valve opens. Sending water through a membrane in the wrong direction will ruin the membrane.

Russ

Thanks Russ, Than what am I really doing, flushing the membranes input surface?

 

[Buckeye Hydro]

You're temporarily taking the flow restrictor out of operation - when you do this feedwater rushes through the membrane and through the membrane housing. You're accelerating the flow of concentrate.

 

[Otrips]

Thanks Russ, Than what am I really doing, flushing the membranes input surface?

The Flow restrictor essentially creates back pressure forcing water through the membrane. Flushing the unit by opening the "flush valve" by-passes the flow restrictor allows more water out the "waste" tube which would otherwise be trying to force itself through the membrane. This creates a higher stream of water over the surface of the membrane which flushes any loosely attached particles off & out the "waste" tube. Also anything that may have passed, or now be able to pass through the pre filters. Organics and other material that may have broken down since last using or loosely gotten hung up on the pre filters. Or anything the may have grown. It extends the life of the membrane and possibly the DI resin.

 

[Otrips]

The reason why you open either the DI valve or RO if you have a DI bypass, when flushing is to open the auto shut off valve & get the water flowing. The Auto shut off valve uses the back pressure created after the membrane (between the shut off valve and your manual valve) to stop the flow of water entering the membrane housing and right out the drain tube.

 

[HouseofStark]

I am trying to add a DI bypass for 2 mins... but I use a booster pump. I am having an issue with "auto shutoff" pressure switch seeing enough pressure to shut off the waste water side. I have the pumps on/off pressure switch after the ro membrane and before the TDS bypass tee....which does see pressure and shuts down the pump off after production has reached full level, but then I can see/hear the 4 way diaphragm pressure switch still letting water run down waste side off the RO membrane. Any suggestions ideas? The only way I can get the system to stop is, leaving the DI production solenoid open 1-2 mins past the full RO storage tank shut down....which will let water pressure build back to pump switch which turns off the pump and then back to the 4 way diaphragm that closes of water flow. Is that the way it should be? Most setup/write ups don't show or have a booster pump involved.

 

[mrlavalamp]

so your RO tank fills and the booster shuts down, but the diaphragm does not?

Diaphragm stays open unless you leave the DI line open for 2 minutes after the RO tank fills? If you leave the line open then how is it building pressure to shut things off?

The diaphragm on my setup does not "open" and "close" like you think of a normal valve. It is very soft and functions partially. I leave my DI resins chambers off and disconnected from the system and allow them to "dry" between making DI water for the aquarium. I have a pressure tank for RO drinking water. Once my tank is full i can hear the flow slowly decrease until I can barely see a trickle coming out of the waste line, maybe a couple of minutes of running slowly/silenty and then it stops.

I bought a SUPER cheap RO unit, but it is brand new and had zero issues so far.

 

[HouseofStark]

Correct, right above the storage tank (not in picture) I have a "fill" solenoid that controls the whole production (all connected to my Apex controller)

Make water command is given, bypass solenoid opens for 2 mins to remove high TDS, then closes; DI solenoid opens and RODI water is send into storage tank.

Once the tank is filled (or "max run time") is reached. I have the DI solenoid closed. (Bypass has been closed since the first 2 mins of make water started)

My thought was....it then pressurizes back to pump pressure switch, which it does, and pump turns off. Then waste water continues to run.

Does it have to due with my house water being at 55psi and the pump running its at 80?

You can hear pump cut off at 7 seconds, that's when it was suppose to stop, but instead it send all water down RO waste, the only way I can stop it is...….to reopen the di valve, it will then build pressure back and system will shut down (about 20-30 seconds) to do that

 

[Buckeye Hydro]

You need a solenoid https://www.buckeyehydro.com/shut-off-latching-solenoid-valve-1-4/
on the feedwater tube that runs on the same circuit as the pump. Both the pump and the solenoid would be controlled by the presssure switch. Get rid of your ASOV

 

[HouseofStark]

So I need a 2nd https://www.buckeyehydro.com/shut-off-latching-solenoid-valve-1-4/ ??? I have one on it now...labeled in pic as pump switch....that seems to work, it powers down the pump once I close the product water.

I've had a ASOV behind the 2 RO units since I put it together 2-3 years ago and working fine (before I added the TDS flush).....I did have the pressure switch for the pump right above the outgoing check valve. I moved it before the tee, thinking when both of them were off, the switch would see pressure and shut down. Not sure why my ASOV is passing water when system is pressurized?

 

[Buckeye Hydro]

Not sure I'm following you... but ASOV's can by problematic when also using an electric pressure sensitive switch. The better configuration as a pressure switch controlling 1) the pump, 2) any other items such as a flush valve, and 3) water flow to the system via a solenoid valve.

 

[HouseofStark]

Not sure I'm following you... but ASOV's can by problematic when also using an electric pressure sensitive switch. The better configuration as a pressure switch controlling 1) the pump, 2) any other items such as a flush valve, and 3) water flow to the system via a solenoid valve.

So your saying completely remove the ASOV, and add a solenoid on the house water (incoming to unit) side to control flow.

 

[Buckeye Hydro]

Correct!

 

[Jason777]

Go with what Water Dog said. Use TDS probes before and after the DI stage so you will know what your resin is doing and not relying only on color change. Use the third TDS probe to monitor inlet of the membrane so you will know the efficiency of your membrane by comparing inlet to outlet TDS, this will tell you when the membrane needs to be replaced. The biggest thing we need to know is TDS going into the DI stages.

I use a 2 stage DI section and when my TDS goes above zero I move the downstream canister of DI to the upstream and change out the upstream to new and move it to downstream. This has saved me a ton of money because the resin isn't completely done just because it lets your TDS go above zero. This way your water comes from the membrane into partially used resin which will decrease it some before going to the second canister where it will be reduced to zero. My water is very poor here and I'm lucky if I can get it down to 20 TDS with 95-98% membrane rejection. By using the 2 stage and swapping canisters my resin changes have been less than 1/2 what they previously were.

TDS creep is also real and I bypass my resin for about 5 minutes prior to each run with the 3 way valve Water Dog showed.

 

[HouseofStark]

I do use probes... I have 5 TDS probes, incoming water, between RO/DI, between Cation/Anion, between Anion/mixed bed and finally product water. I moved from 3 mixed beds in series to separate beds, to save the "musical chairs/beds" and a lot of the mixed bed wasted/not used, because its exhausted at different rates.

Will do @Buckeye Hydro, I originally planned to add a 110v apex controlled solenoid for input side, but pig-tailing off pumps power harness will save me from all that! Thanks

 

[Buckeye Hydro]

3 way valve: https://www.buckeyehydro.com/3-way-valve/

Kit: https://www.buckeyehydro.com/tds-creep-bypass/

Russ