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kruse_alan
08/16/2009, 01:28 PM
Would your permeate pump be worth while purchase to increase productivity on a 75 gpd membrane with 40 psi. ?

Thanks

Brad

Buckeye Hydro
08/16/2009, 01:35 PM
Hi Brad - It would, but permeate pumps are designed to improve production on systems with a pressurized RO (not DI) storage tank. A better choice would be a booster pump.

Russ

kruse_alan
08/16/2009, 02:18 PM
Thank you for the reply. I have a storage tank with my unit. I run my storage water through a add on DI unit .

Would this be Ok?

Buckeye Hydro
08/16/2009, 02:47 PM
For a number of reasons, you should not run RO water from a pressure tank through a DI stage. If you really want to do this, a permeate pump would help substantially in keeping the TDS in the tank water down and decreasing the time necessary to fill the tank w/ RO water, and increasing the life span of your resin.

Russ

johnlvs2run
08/21/2009, 08:45 PM
<a href=showthread.php?s=&postid=15539343#post15539343 target=_blank>Originally posted</a> by BuckeyeFS
For a number of reasons, you should not run RO water from a pressure tank through a DI stage.
Could you elaborate on the reasons.

I am planning to do this too, as there is considerable tds creep from the 85 gpd membrane, i.e. 13 to 37 tds.

Perhaps I should have gotten a 50 gpd membrane and will do so the next time.

Buckeye Hydro
08/22/2009, 04:52 AM
<a href=showthread.php?s=&postid=15571749#post15571749 target=_blank>Originally posted</a> by johnlvs2run


I am planning to do this too, as there is considerable tds creep from the 85 gpd membrane, i.e. 13 to 37 tds.

Perhaps I should have gotten a 50 gpd membrane and will do so the next time.

"TDS creep" is something you'll see with any RO membrane. A couple of ways to deal with it:
minimize the number of on/off cycles your system goes through over the coarse of a day.

Install an auto-flush flow restrictor that flushes upon being energized.

Russ

Buckeye Hydro
08/22/2009, 05:23 AM
<a href=showthread.php?s=&postid=15571749#post15571749 target=_blank>Originally posted</a> by johnlvs2run
Could you elaborate on the reasons.



Because of the back pressure on the membrane supplied by a pressure tank, you'll find that the tds in a full pressure tank will (significantly) exceed the tds in your RO water if it is supplied to an atmospheric (non-pressurized) storage tank.

Additionally, a pressure tank will serve to force this higher tds water through the di resin faster...


Russ

johnlvs2run
08/22/2009, 04:34 PM
<a href=showthread.php?s=&postid=15573184#post15573184 target=_blank>Originally posted</a> by BuckeyeFS
Because of the back pressure on the membrane supplied by a pressure tank, you'll find that the tds in a full pressure tank will (significantly) exceed the tds in your RO water if it is supplied to an atmospheric (non-pressurized) storage tank.
Thus the slower water passes through a given membrane, the higher the tds will be.
a pressure tank will serve to force this higher tds water through the di resin faster.
Thus the faster water passes through the di resin, the higher the tds will be, i.e. the less the tds reduction from the tank.

I have not seen any stats on "how much" the greater pressure would affect tds reduction through the resin.
At least one person posted that the reduction was still excellent.
I am wondering about whether to get a permeate pump instead of resin for drinking, or else both.

johnlvs2run
08/22/2009, 04:39 PM
<a href=showthread.php?s=&postid=15573164#post15573164 target=_blank>Originally posted</a> by BuckeyeFS
"TDS creep" is something you'll see with any RO membrane. A couple of ways to deal with it:
minimize the number of on/off cycles your system goes through over the course of a day.

Install an auto-flush flow restrictor that flushes upon being energized.

I would like to minimize the number of on/off cycles but don't know how that would be possible. It would seem that some type of a control in the tank would do this, for example where the system only turns on when the tank is 1/2 empty. How would an auto flush flow restrictor reduce the number of cycles?

My previous system (aquasafe) gave me 9 to 15 tds after the pressurized tank for five years, from input water of 330 to 400 tds. The current system (filtersdirect) which I got three months ago and am not happy with at all, gives 15 tds from the membrane, and 27 to 40 from the pressurized tank. However the tds was never lower than 50 for the first two months of use. Then it dropped to 30, and I removed the post filter at the same time, which had no further effect. Water use and number of on/off cycles have been consistent, and the same brand of tank is used with each system, in fact I am currently using the old tank, which has not made any difference.

Considering there was some creep with the first system, (1) the post membrane tds with the current system is much higher, and (2) the tds creep with the current system is even higher and of significant concern. If the 1st membrane tds was 7, then the creep was 2 to 8; however the 2nd membrane tds is 15 and the creep is 12 to 25. This is a major difference. It looks to me that this membrane is not good, and that I need to get a better membrane from somebody else. Is this right?

The 1st membrane was Applied Membranes M-T1812A100 100 gpd (good), and the 2nd is GE Osmonics Desal TFC-75/TFM-75 75 gpd (not good). I have read that 25 to 50 gpd membranes, in general, have lower tds output and lower creep. It would be interesting to see an explanation of this, based on use with pressurized tanks.

Buckeye Hydro
08/22/2009, 05:43 PM
John - its sometimes hard to have complicated discussions via these posts or email. If you'd like to discuss, please feel free to give us a call at 513.312.2343

Russ @
Buckeye Field Supply

johnlvs2run
08/22/2009, 06:00 PM
Russ,
Thanks for your reply.

I didn't realize my question was that complicated but perhaps it is.

My aim is to improve the drinking water quality (lower tds) of this particular system,
with (1) much improved membrane, and/or (2) di cannister, and/or (3) permeate pump.

Buckeye Hydro
08/22/2009, 06:23 PM
OK. I'd go for the permeate pump.

Russ