rodi flowrate

[mizimmer90]

Is having too high of a flowrate a cause for concern with an rodi system?

I bought a 5 stage rodi from BRS and see that the flowrate is higher than expected. It should be 75 GPD but based on the rate its filling my containers, it's coming out at ~120 GPD. The TDS is 20 coming in and 0 coming out though.

Is this within normal ranges or should I be requesting a new membrane/filters?

 

[Aaron75]

What's your psi?

 

[mizimmer90]

Fluctuating around 70 psi

 

[mizimmer90]

I also noticed that the resin chamber doesn't fill all the way while running. Is this normal?

 

[Buckeye Hydro Verified Sponsor]

If you use the calculator on our website you'll see that at 60F (assumed) and 70 psi, a 75 gpd membrane should put out about 79 gpd. So yes, there is something wrong.

You have 20 ppm RO water or 20 ppm DI water? What is the TDS of your tap water?

BTW - your pressure gauge is leaking.

Russ

 

[mizimmer90]

If you use the calculator on our website you'll see that at 60F (assumed) and 70 psi, a 75 gpd membrane should put out about 79 gpd. So yes, there is something wrong.

You have 20 ppm RO water or 20 ppm DI water? What is the TDS of your tap water?

BTW - your pressure gauge is leaking.

Russ

Thanks for the reply, Russ! Coming off of the RO, it's between 20-50 ppm, and 0 ppm coming off of the DI resin. I don't know the TDS of my tap water but I assume it's high.

I've measured the rejection rate by comparing rates of filling a measuring cup for the DI and reject streams. It should be 4:1 but I'm seeing 2:1, consistent with the increased flow rate.

I've tried contacting BRS multiple times but they're insisting that it's all within normal operating parameters. Is this enough evidence for being more insistant?

 

[Gtinnel]

Coming out of the permeate side of the membrane at 20-50 is really high and a very broad range. I would guess that you are possibly leaking around the membrane causing some of your water to bypass the membrane completely.

Also, rejection rate usually refers to the drop in tds across the membrane. You really need to know your supply water tds to prove there is a problem.

 

[mizimmer90]

Coming out of the permeate side of the membrane at 20-50 is really high and a very broad range. I would guess that you are possibly leaking around the membrane causing some of your water to bypass the membrane completely.

Also, rejection rate usually refers to the drop in tds across the membrane. You really need to know your supply water tds to prove there is a problem.

Thanks for the info!

I will try and reconfigure my RODI to have tap go straight into the DI to use that TDS meter.

My understanding of rejection rate is that it is the fraction of water rejected from the membrane compared to the fraction of water that passes through. i.e. my rejection rate of 2:1 means that I'm rejecting 2 parts for every 1 part that goes through.

 

[Gtinnel]

Thanks for the info!

I will try and reconfigure my RODI to have tap go straight into the DI to use that TDS meter.

My understanding of rejection rate is that it is the fraction of water rejected from the membrane compared to the fraction of water that passes through. i.e. my rejection rate of 2:1 means that I'm rejecting 2 parts for every 1 part that goes through.

I only have the two probe tds meter also, so when I want to check my supply tds I usually swap the probe out with a coupler and then put the probe into the supply line. If you put your supply water directly into the di you will deplete the di quickly.
Rejection rate is the percentage of tds that gets removed by the membrane. For instance if your supply was 100tds and after the membrane it was 2tds then your rejection rate is 98%.

 

[Buckeye Hydro Verified Sponsor]

Thanks for the reply, Russ! Coming off of the RO, it's between 20-50 ppm, and 0 ppm coming off of the DI resin. I don't know the TDS of my tap water but I assume it's high.

I've measured the rejection rate by comparing rates of filling a measuring cup for the DI and reject streams. It should be 4:1 but I'm seeing 2:1, consistent with the increased flow rate.

I've tried contacting BRS multiple times but they're insisting that it's all within normal operating parameters. Is this enough evidence for being more insistant?

Almost... but not quite. It also looks like there's some confusion re the jargon here.

Rejection Rate: The percentage of TDS removed by the RO membrane. So if your feedwater is 100 ppm, and your RO permeate is 7 ppm, that's a 93% rejection rate. The higher the rejection rate is, the lower the permeate TDS is, and the longer the lifespan of the DI resin.

Recovery: The percentage of the feedwater that becomes RO permeate. So if you run your RO and you end up 4 gals of concentrate ("waste water") and 1 gal of permeate ("RO water"), we know you started with 4+1=5 gals of feedwater. 1/5 = 20% recovery.

You want to know TDS in THREE locations:
1) feedwater
2) permeate
3) DI water

If you know #1 & #2 you can calculate the rejection rate and know when you need a new RO membrane(s).
If you know #3 you can tell when it's time to change the DI resin.

THAT's why we typically recommend the TRM1 - a 3-probe TDS meter for those with an RODI system. If a vendor recommends the 2-Probe DM1 or DM2, I'd question that recommendation. In all likelihood they either don't know any better or they are trying to keep costs down.

TRM1 Tri Inline TDS Meter

At Buckeye Hydro we specialize in providing the highest quality water filtration systems and accessories for every potential need.

www.buckeyehydro.com

DM1 Dual Inline TDS Meter

At Buckeye Hydro we specialize in providing the highest quality water filtration systems and accessories for every potential need.

www.buckeyehydro.com

DM2 Dual Inline TDS Meter

At Buckeye Hydro we specialize in providing the highest quality water filtration systems and accessories for every potential need.

www.buckeyehydro.com

Russ

 

[Buckeye Hydro Verified Sponsor]

With these inline probes, you don't want to make a habit of removing them and reinserting them into the tee fitting. The probe is easy to scratch with the stainless steel "teeth" inside the fitting... and then you'll have trouble with leaking where the probe goes into the tee.

If you already have a DM1 (dual probe) and want a third probe:

SM1 In-Line Single TDS Meter

At Buckeye Hydro we specialize in providing the highest quality water filtration systems and accessories for every potential need.

www.buckeyehydro.com

Russ

 

[mizimmer90]

I only have the two probe tds meter also, so when I want to check my supply tds I usually swap the probe out with a coupler and then put the probe into the supply line. If you put your supply water directly into the di you will deplete the di quickly.
Rejection rate is the percentage of tds that gets removed by the membrane. For instance if your supply was 100tds and after the membrane it was 2tds then your rejection rate is 98%.

Almost... but not quite. It also looks like there's some confusion re the jargon here.

Rejection Rate: The percentage of TDS removed by the RO membrane. So if your feedwater is 100 ppm, and your RO permeate is 7 ppm, that's a 93% rejection rate. The higher the rejection rate is, the lower the permeate TDS is, and the longer the lifespan of the DI resin.

Recovery: The percentage of the feedwater that becomes RO permeate. So if you run your RO and you end up 4 gals of concentrate ("waste water") and 1 gal of permeate ("RO water"), we know you started with 4+1=5 gals of feedwater. 1/5 = 20% recovery.

You want to know TDS in THREE locations:
1) feedwater
2) permeate
3) DI water

If you know #1 & #2 you can calculate the rejection rate and know when you need a new RO membrane(s).
If you know #3 you can tell when it's time to change the DI resin.

THAT's why we typically recommend the TRM1 - a 3-probe TDS meter for those with an RODI system. If a vendor recommends the 2-Probe DM1 or DM2, I'd question that recommendation. In all likelihood they either don't know any better or they are trying to keep costs down.

TRM1 Tri Inline TDS Meter

At Buckeye Hydro we specialize in providing the highest quality water filtration systems and accessories for every potential need.

www.buckeyehydro.com

DM1 Dual Inline TDS Meter

At Buckeye Hydro we specialize in providing the highest quality water filtration systems and accessories for every potential need.

www.buckeyehydro.com

DM2 Dual Inline TDS Meter

At Buckeye Hydro we specialize in providing the highest quality water filtration systems and accessories for every potential need.

www.buckeyehydro.com

Russ

I appreciate the clarifications! So, I think I am mixing up rejection rate and waste water recovery.

I played around with the connections of the system and plugged the inlet directly into the TDS meter that then goes only into the DI. My tap water is reading ~300 ppm and after the DI resin its 1 ppm.

I then connected my inlet directly into the membrane and got 20 ppm coming off of the RO, giving me a rejection rate of ~93%. Is this too low?

 

[mizimmer90]

With these inline probes, you don't want to make a habit of removing them and reinserting them into the tee fitting. The probe is easy to scratch with the stainless steel "teeth" inside the fitting... and then you'll have trouble with leaking where the probe goes into the tee.

If you already have a DM1 (dual probe) and want a third probe:

SM1 In-Line Single TDS Meter

At Buckeye Hydro we specialize in providing the highest quality water filtration systems and accessories for every potential need.

www.buckeyehydro.com

Russ

Thanks, I think I'll buy that one!

 

[Gtinnel]

I remove the whole tee fitting (without removing the probe) and put into the supply line. I agree that moving it around isn’t ideal but in a pinch will work.

 

[Gtinnel]

I appreciate the clarifications! So, I think I am mixing up rejection rate and waste water recovery.

I played around with the connections of the system and plugged the inlet directly into the TDS meter that then goes only into the DI. My tap water is reading ~300 ppm and after the DI resin its 1 ppm.

I then connected my inlet directly into the membrane and got 20 ppm coming off of the RO, giving me a rejection rate of ~93%. Is this too low?

I would definitely wait on Russ (he truly is the expert on anything rodi related) to reply but it seems a little low to me for a new membrane. There are several things that effect rejection rate including pressure and water temp, but I usually see around 97-99% on mine.

 

[Buckeye Hydro Verified Sponsor]

Yes... 93% is too low, especially for a new 75 gpd Filmtec at 68 psi. And we still have the issue that you're getting too much permeate. I'd pull the membrane out and inspect the two orings on the central stem. Make sure they are in good shape. Then put a very light coat of food grade silicone grease https://www.buckeyehydro.com/oring-lubricant-food-grade/ on them, and reinsert the membrane. You can slide it in with just two fingers. When you feel it hit the far end, push hard with the heel of your hand and you should feel it go in about a 1/4". It's that last 1/4" that is critical. Then check your permeate flow and your permeate TDS.

If flow is still too high and permeate tds still too high, I'd suspect that you have an internal crack in your RO membrane housing, or you have a bad membrane.

 

[Buckeye Hydro Verified Sponsor]

Also - the issue of your DI housing not filling up all the way. You just have some air trapped in the housing. With the system running, unscrew the DI housing about a 1/4 turn - just enough to break the seal at the black oring up near the housing threads. Have a towel handy - you're burping the air out and you'll get a few drips with it. You'll see the water level start to rise immediately. When the water level approaches the oring, cinch the housing tight and you're done.

Russ

 

[Floyd-]

When my BRS 4 stage is running my DI stage is never "full" in the container. Maybe 1-2" on the bottom.

 

[mizimmer90]

Yes... 93% is too low, especially for a new 75 gpd Filmtec at 68 psi. And we still have the issue that you're getting too much permeate. I'd pull the membrane out and inspect the two orings on the central stem. Make sure they are in good shape. Then put a very light coat of food grade silicone grease https://www.buckeyehydro.com/oring-lubricant-food-grade/ on them, and reinsert the membrane. You can slide it in with just two fingers. When you feel it hit the far end, push hard with the heel of your hand and you should feel it go in about a 1/4". It's that last 1/4" that is critical. Then check your permeate flow and your permeate TDS.

If flow is still too high and permeate tds still too high, I'd suspect that you have an internal crack in your RO membrane housing, or you have a bad membrane.

Also - the issue of your DI housing not filling up all the way. You just have some air trapped in the housing. With the system running, unscrew the DI housing about a 1/4 turn - just enough to break the seal at the black oring up near the housing threads. Have a towel handy - you're burping the air out and you'll get a few drips with it. You'll see the water level start to rise immediately. When the water level approaches the oring, cinch the housing tight and you're done.

Russ

Thanks so much, Russ! This is incredibly helpful information!

I quoted all the numbers to BRS and they're sending me a new membrane. I'll fiddle with it in the meantime amd get some of the lubricant to see if it can fit in there better!