Ro/Di Initial Startup Water Flush

I decided to add a "emergency shutoff valve" to my water storage tank. My ro system does not have a auto shut off and I dont really need one since I make relatively small batches of water at a time. But I decided to add a valve just in case I forget it sometime so as not to flood the basement. The problem I ran into is being able to flush the system for the first few minutes while I get my 1-3 tds water on startup since I cant just easily pull the hose out of the valve. So I came up with this simple design that I can bleed off water to the drain then open the valve to the tank, and shut off the bleed off valve. Hope that makes sense. Anyways seemed like a good idea to me. Has anyone else done this?

 

Explain more clearly please.
What you need to be doing if you are trying to eliminate or reduce teh effects of TDS creep is to break into the line between the RO membrane and the DI cartridge and send that to waste for 30 seconds or so. By flushing the membrane to waste you reduce the TDS that hits the DI resin thus extending its life and giving you a lower long term cost of operation and better water quality.

If you have installed the tee on the final treated water line you are reducing the TDS in the water storage vessel but you have not helped the DI life. I can't really tell from your photo quite how it is plumbed.

 

Ah ok. I thought I was just preventing a normal start up problem. I used to just drain the first few ounces into the sink. I will try to change my setup around to the ro output before di

 

Can you explain in more detail please? A diagram would be awesome if you know where one can be found.. I also just run my rodi for about 5 min and it def seems wasteful. Thanks

 

You should only get maybe 6-8 ounces of TDS Creep or elevated TDS water upon start up in most cases, its basically the water sitting inside the RO membrane housing which has osmosed or travelled from the tap water side of the membrane to the treated side due to RO water being agressive and trying to get back to its natural "dirty" state. Once you have flushed those few ounces away it should drop rapidly back to its normal rejection rate. The highest the TDS creep should be is maybe 1/2 your tap water TDS and probably much lower than that so its not going to kill resin overnight or in a week and since its just a few ounces its really not a huge issue.

Personally I don't worry much about it since I make water in infequent, larger batches so it does not happen often and the amount is slight. If I had a float valve which has limited travel so cycles frequently then I might consider something but that is an automated system and would require something automated to flush the TDS creep away too. There are systems that do this but I'm not sure you would recoup the investment in DI savings?

The so called "flush valves" or flush kits do nothing for TDS creep since all they are doing is flushing the water on the brine or waste side of the membrane and do nothing for the TDS creep which is on the treated side of the membrane. All they do is give you a warm fuzzy feeling and lighten your wallet.

 

Ok so the "flush valve" that some places sell is not going to make or break a system? My ato is only 5 gal and I need to replenish every 3 days or so. The process I use is annoying to evacuate the higher tds.
In your above post, you're suggesting a "tee" between ro membrane and di cart. And basically run it for a few min without di?

 

The purpose of my initial design is not to flush the membrane as I do not think pushing dirty water through the clean side of the RO membrane is a good idea in my opinion, but instead to be able to bleed off the first few ounces of water on start up that have collected TDS in the RO membrane after the last shut down. Usually on initial start up my TDS readings are apx 2. Obviously this isnt terrible or anything but I would prefer to keep all water going into my storage container at 0 TDS. My initial design was on the RO/DI output (blue line) but I was unaware that the TDS buildup came from the RO membrane and had thought it may be from the DI. Anyways I changed my design so that I can "purge" the system from the RO membrane on start up straight to the drain. Then closing the drain off valve and opening the valve to my storage container allows for 0 TDS water. The reason I wanted this is because my "emergency shut off valve" prevents me from easily just taking the clean water line out of the storage tank for the initial purge and then putting it back in.

I will try to make a drawing so that you may be able to understand my intentions and design more.

 

Ok hopefully this color coding may help explain.

Green- The green line is CLEAN water coming out of the RO membrane (on start up the TDS coming from the membrane are momentarily above 0 TDS)

Blue- The blue line w/ valve is the water from the RO membrane to the DI stage of filtration. This allows me to shut off water going to DI while the initial start up TDS are elevated and prevents my water storage container from having any water above 0 introduced.

Yellow- (the painted yellow line) This yellow line is the valve I open on initial start of the system which allows the water that has slight TDS creep to be purged out to the drain.

 

By installing a tee and ball valve between the RO membrane and DI filter you are flushing the treated side of the membrane just as the membrane is designed to work. The "flush valves" you buy are basically a bypass valve around the flow restrictor so you slightly increase the flow and velocity of the waste, supposedly removing accumulated solids. In theory this sounds good but in reality it does little if anything and does nothing for the treated side.

By flushing or wasting the first few ounces or gallons or whatever after the DI cartridge, you are still drawing the TDS creep water surrounding the membrane into the DI resin and doing nothing to extend its useful life. Its not a huge deal breaker but serves little benefit. If you are going to go to the small expense and time to flush something, get the most bang for the buck and flush it between the membrane and DI to get the most benefit.

Membranes by design "push dirty water through the clean side of the RO membrane", this is how they operate always, you draw tap water through the membrane fabric by reverse osmosis. Thats what they do.

 

My initial reasoning was not to prevent the use of DI to extend its life, although that IS part of the reason now that AZ explained TDS creep a bit more. The main reason is since I added the shut off valve I have no way of easily disconnecting the clean water line from the barrel to run the system for a few minutes on start up.