RODI Issues since moving to the area

[Buckeye Hydro]

There's some mis-information in this thread I want to address - no offense intended - just want to avoid confusion.

A 2% increase in rejection will double the DI life

Not really. You have to do the math. For example - not true if you have an old 90% 100 gpd membrane.

...going past 80 psi you risk membrane perforation

This common max pressure limit has nothing to do with the RO membrane. The membranes can handle much more pressure. The idea is to avoid over-pressurizing other components in the system. The weakest link, in terms of ability to withstand pressure, is typically the clear housings.

Flushing doesn't provide enough pressure to void the membrane of stagnant water.

Remember when you open a flush valve - it allows water to rush through the RO element and RO housing - ON THE WASTE WATER side of the RO membrane. TDS creep however is a situation where higher TDS water has made it through the RO membrane to the low pressure (permeate) side of the membrane. So flushing (temporarily bypassing the flow restrictor) doesn't remove the TDS creep water.

Russ

 

[HowManyClowns]

RODI Issues since moving to the area

Thanks for the info. Might as well post an update. Since this thread I ended up buying a booster pump and a spectrapure select membrane. I am running my pressure a little high but it is working much better for me. I am pushing around 130gpd and consistently getting 11-12 TDS after the membrane. My DI is lasting well over a month now! Thanks for everyone's help

 

[frogg21]

Add a T and a valve right after your membrane. Flush and then purge the first minute or two of water this way you also clear the water in the membrane.

I use a 12v solenoid valve controlled by Apex which has float switches. I can change the frequency with a few clicks on the Apex. Currently letting it top off every hour except during peak lighting (kalk dosing topoff to counter night pH swing) if the floats switch is calling for it. DI is burning up too fast and I suspect its what has been identified in the thread, simple TDS creep compounded by many cycles a day.

So here's the conundrum: I could just limit top off sessions to 1 or two a day. (Would a 1-2 gallon cycle vs. a 5 oz cycle help much with TDS creep?)

Problem is, top off doses kalk. A few ounces every hour or two at night is perfect. 1 gallon of kalk ATO might be bad news on the pH. (Probably need to test this assumption) (tank evaporates 1-2 gal/day). This is also assuming 1-2 gallons of fresh water isn't too much for a 200 gal tank. But even if its tolerable, I'm sure its not ideal as the goal with these parameters is stable as possible.

I'm NOT into manual top off, one of the many reasons for the Apex. Has anyone out there got their Apex (or Arduino or whatever controller method) to delay their top off pump/switch and open a flush valve to flush the TDS creep water out. In other words, anyone get a controller to flush the way people are doing manually?

 

[aguila88psi]

Those are a couple reasons to not have an RO system be your auto top off. Best bet is to get an ro container and use that to ato the tank and just fill up the container once or twice a week or once it reaches a low set point with your RO system.

To combat the pH issue you can always use two solenoid valves, one going straight to your tank and the other to a kalk reactor/stirrer, this way you can program whichever one you want to fill your tank with. Say pH is ok or higher then a certain level so then apex keeps solenoid to kalk off, if pH is low then apex closes the ato valve off and turns on the kalk valve and if ph ever gets too high then apex would shut down the solenoid to kalk and open the other valve. You could essentially have this running during the day and keep pH maintained indefinitely.

My RO system auto flushes the membranes prior to startup and every hour or two, each flush has a duration of 15s. Just use two t's and two lines where one line has the restrictor and another line a solenoid valve, then whenever you want to flush the valve will bypass the restrictor and membranes will automatically flush.

Hope I helped.

 

[rEeFnWrX]

This common max pressure limit has nothing to do with the RO membrane. The membranes can handle much more pressure. The idea is to avoid over-pressurizing other components in the system. The weakest link, in terms of ability to withstand pressure, is typically the clear housings.

Russ

having been a victim of this first hand would force me to partially disagree as your point is valid but you cannot state that the membranes are not subject to perforation.

This came directly from spectrapure. You can run it higher but risk chance at membrane perforation. The main reason to boost higher is to increase production rate when instead you could just buy a higher gpd membrane.

you may recall a thread of mine having issues with two new membranes... after giving up and knowing it had to be the membrane and not my system I bought a 99% from spectrapure and then sent the two bad ones back to BRS. They confirmed the bad rejection rate and stated the membranes were perforated.

I now get 99.7% rejection. 1 TDS post membrane before DI with 340 TDS source water running at 68psi the lowest my pressure pump will perform. Besides production rate there is no reason for me to increase the pressure.

 

[rEeFnWrX]

I use a 12v solenoid valve controlled by Apex which has float switches. I can change the frequency with a few clicks on the Apex. Currently letting it top off every hour except during peak lighting (kalk dosing topoff to counter night pH swing) if the floats switch is calling for it. DI is burning up too fast and I suspect its what has been identified in the thread, simple TDS creep compounded by many cycles a day.

So here's the conundrum: I could just limit top off sessions to 1 or two a day. (Would a 1-2 gallon cycle vs. a 5 oz cycle help much with TDS creep?)

Problem is, top off doses kalk. A few ounces every hour or two at night is perfect. 1 gallon of kalk ATO might be bad news on the pH. (Probably need to test this assumption) (tank evaporates 1-2 gal/day). This is also assuming 1-2 gallons of fresh water isn't too much for a 200 gal tank. But even if its tolerable, I'm sure its not ideal as the goal with these parameters is stable as possible.

I'm NOT into manual top off, one of the many reasons for the Apex. Has anyone out there got their Apex (or Arduino or whatever controller method) to delay their top off pump/switch and open a flush valve to flush the TDS creep water out. In other words, anyone get a controller to flush the way people are doing manually?

If I were you. I would switch your setup to fill an ATO contajner with a float switch mounted at the bottom. Make sure it's a quality sealed switch or just use silicone to seal it more.

Install a T right after your membrane. Get another solenoid that your APEX would open first and purge RO water. How long depends on your source water, I typically wait to 4 TDS before switching flow to the DI. This is about 30 seconds of purging for me. Then have that solenoid close and open the solenoid to your DI. buy a top off pump pump and switch to perform your ATO.

The line that you would T off after your membrane. Add another T right after your flow restrictor and connect that line. This way you only have one waste line and your RO purge line will not be restricted.

 

[Buckeye Hydro]

having been a victim of this first hand would force me to partially disagree as your point is valid but you cannot state that the membranes are not subject to perforation.

This came directly from spectrapure. You can run it higher but risk chance at membrane perforation. The main reason to boost higher is to increase production rate when instead you could just buy a higher gpd membrane.

Any membrane can develop leaks for a number of reasons. But the pressures we are talking about here are well withing the specs on brand name membranes.