R/O Startup TDS Delay Device Thingy

pnosko

pnosko

New member
I don't know what to call this thing, but have been looking for one for years and I think they still don't exist. This is not to be confused with an auto/manual flush kit; there are automatic ones that flush the membrane on startup and at certain running intervals.

What I'm looking for is a device that redirects the product line to waste until the TDS in the product line reaches a certain level.

I have a dual inline TDS meter and can watch as the TDS initially rises on startup then gradually begins to decrease. My tap water TDS ranges from 150-200 on a really good day to 350+ in the late evenings. I've even noticed that it averages 50-100 higher for several days following Winter weather road salt treatments.

I'd like to have my product water discarded until the TDS reaches about 4 or 5 in the product line. This typically take 1-2 minutes when I refill my storage tank.

As a software developer, I'm toying with the idea of building a controller using a Raspberry Pi and some electronic pinch valves. As much as I want to do this, I know this will go into the low hundred$, suffer lots of requirement creep like logging all kinds of stats and eat into my spare time, which is at a premium these days.

Has anyone designed one or come across an existing device that accomplishes this task?
 
How about just running it thru two DI stages. Quick, easy and lots less time and money that a dedicated controller and requirement creep.

1-2 minutes of higher TDS into the DI doesn't seem like that big of a deal.
 
I'm not currently using DI as I don't have a salt water tank running right now. Although I suppose I could. I have half a dozen or so, but they've been stored for over 10 years. Do they have a shelf life?
 
The resin shelf life is only a year or two, IIRC.

Are you using the RO for drinking water? Some other, non salt (oh NO! ) fish?
 
As long as your pre filters are replaced on a regular basis, I wouldn't worry too much. If you use a DI after the RO unit, the water will loose all it's taste for drinking water. I also highly doubt there's anything that will affect a FW tank. You may need to add some things for the fresh water tank.
 
I actually do this exact thing but with my Apex. I use two solenoid valves one going to the drain and one to my storage tank. When my apex turns on my RODI the solenoid connected to the drain turns on then 10 minutes later that one shuts off and the one to the storage reservoir opens.
 
Misled said:
I also highly doubt there's anything that will affect a FW tank. You may need to add some things for the fresh water tank.
Click to expand...
I add SeaChem Replenish to the RO water.

scottwhitson said:
I actually do this exact thing but with my Apex. I use two solenoid valves one going to the drain and one to my storage tank. When my apex turns on my RODI the solenoid connected to the drain turns on then 10 minutes later that one shuts off and the one to the storage reservoir opens.
Click to expand...
Yeah, a dumb timer would greatly simplify and reduce the cost of it. But also some of the development fun...

What solenoid valves did you use? I've been looking at these pinch valves, but they are not cheap.

http://www.biochemfluidics.com/Products/pinch-Valves.asp
 
The solenoid valves I use are from dudadiesel.com they are just heavy duty stainless solenoid valves that I plumbed with 1/4" john guest fittings. I can't get the link to work.
 
pnosko said:
I don't know what to call this thing, but have been looking for one for years and I think they still don't exist. This is not to be confused with an auto/manual flush kit; there are automatic ones that flush the membrane on startup and at certain running intervals.

What I'm looking for is a device that redirects the product line to waste until the TDS in the product line reaches a certain level.

I have a dual inline TDS meter and can watch as the TDS initially rises on startup then gradually begins to decrease. My tap water TDS ranges from 150-200 on a really good day to 350+ in the late evenings. I've even noticed that it averages 50-100 higher for several days following Winter weather road salt treatments.

I'd like to have my product water discarded until the TDS reaches about 4 or 5 in the product line. This typically take 1-2 minutes when I refill my storage tank.

As a software developer, I'm toying with the idea of building a controller using a Raspberry Pi and some electronic pinch valves. As much as I want to do this, I know this will go into the low hundred$, suffer lots of requirement creep like logging all kinds of stats and eat into my spare time, which is at a premium these days.

Has anyone designed one or come across an existing device that accomplishes this task?
Click to expand...

These do exist for commercial systems, but as you suspect its not practical to have a auto DI bypass on the small residential scale RO systems used widely in this hobby due to cost.

Russ
 
I have this on my list of things to do, and have most of the parts purchased already. I am going on vacation for 2 weeks in June, so this may get moved to the top of the list (to get automated RO replenishment based on the sensed level).

The only thing I have left to source, are the various Murlok fittings I will need. For valves I will be using Echotech 12V solenoid valves. I plan on having 4 valves in various parts of the RO system.

  1. in my fishroom in front of the manual float valve in my reservoir.
  2. after the membrane, but before the DI, which will be for dumping startup water for a fixed period of time.
  3. parallel to my existing manual flush valve for flushing on startup/shutdown.
  4. before the system, but after my manual off valve.

Originally I planned on putting a BBB at the RODI system, but after thinking about it, I am now planning to run an ethernet cable with breakout boards at each end to control the 3 remote valves at the system using a relay board in my fishroom. The valves are NC, so any loss of connectivity will fail safe.

Another improvement I have added is a TDS meter between my DI stages so that I can tell when the first DI canister has reached the end of its life. When that happens I move the second DI canister into first position and add a refilled canister into the second position.

I have been toying with the idea of adding a dual membrane upgrade, but I have not worked it out in my head yet how the plumbing needs to change to support it, so that is on hold.

Dennis
 
I have been toying with the idea of adding a dual membrane upgrade, but I have not worked it out in my head yet how the plumbing needs to change to support it, so that is on hold.
Click to expand...

If you are thinking about this as a way to produce less waste water, don't do it! Happy to explain if anyone is interested.

Russ
 
Buckeye Hydro said:
If you are thinking about this as a way to produce less waste water, don't do it! Happy to explain if anyone is interested.

Russ
Click to expand...

I am interested! There is a company that sells a second membrane to go from 75gpd to 150gpd with less waste water... can you please explain with this is a bad idea? Thanks!
 
We get this question a lot - I think we need to add this to our FAQ list: http://www.buckeyehydro.com/faq/

We feel it is misleading to tell people they can cut down on waste water by adding a second membrane. Here's why.

First - remember that what folks call "waste water" really would be better thought of as "flush water" in that this water serves the important purpose of internally flushing the surface of the semipermeable membrane to keep the membrane from fouling/scaling.

When you configure a system with two membranes in series (the waste from the first membrane going to the "in" port on the second membrane), for this discussion let's say it's two 75 gpd membranes, the system behaves like you have a single long (75 gpd x 2) 150 gpd membrane.

Now - if you use a proper flow restrictor, that is, one for a 150 gpd membrane, and have something near the factory spec water pressure and temperature, you'll have about a 4:1 waste to product ratio. Sounds familiar, right?

If however you don't change the flow restrictor - meaning you keep using the same restrictor you were using when you just had one 75 gpd membrane, then you'll see a waste to product ratio much lower than 4:1. But remember that the recommendation for a ~4:1 ratio comes from membrane manufacturers. They are telling you that you need about a 4:1 ratio to keep the membrane flushed and keep the membrane from fouling or building up scale. Run the system with a lower ratio and you will foul/scale the membrane(s) quicker than would have otherwise been the case.

Instead of adding a second membrane to lower that ratio, you could have just changed out your flow restrictor ($4) instead. This is a much less expensive approach to get you to the same endpoint in terms of saving on waste water.

Now, to confuse things just a bit. Filmtec specs call for the 4 to 1 ratio on the basis of assumptions about the water that will be supplied to the membrane. If you have very soft water you MAY be able to get a decent service life from the membrane running at a ratio lower than 4 to 1 (e.g., 3 to 1). Remember that the waste water from the first membrane is about 25% harder than your tap water.

Bottom line: If what you are after is reduced waste water, experiment with a different flow restrictor for $4 instead of messing around with a second membrane plumbed in series.

As a side note, you can also lower the ratio by increasing the pressure delivered to the membrane (with a booster pump), because flow restrictors are sized assuming you are providing factory spec conditions (50 psi and 77 degrees for Filmtec membranes). Increase the pressure and you'll drive more water through the membrane and viola - less waste water. But as mentioned above, if you do this (just like over-restricting a membrane) - the lower the waste to product ratio, the shorter the lifespan on the membrane in most cases.

Makes sense?

Russ
 
Thanks for explaining the dual membrane theory Russ. That simplifies my decision (and plumbing) greatly.

Dennis
 
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