RO/DI question
- Thread starter Billycaicedo
- Start date
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Let me introduce another wonky RO system term: TDS Creep.
TDS Creep is the movement of dissolved solids across the membrane (to the RO water side) while the system is turned off. This results in relatively high tds RO water for a short period of time when you first deliver pressure to the membrane by turning the system on. What do I mean by "high", and what do I mean by "short period of time?" Here's some data from two test runs on a system with one 75 gpd RO membrane
You'll see that at startup, the TDS of the RO water (not DI water) was about 20% that of the feedwater, and over about 60 seconds, the TDS of the RO water came down to where we'd expect it to be.
This is why we always want folks to run the RO system for a couple of minutes before they test the RO water TDS.
Also - think about the repercussions here of having your system plumbed directly into a float valve in your sump. Every time the sump level drops just a tiny bit, the system would kick on and refill the sump quickly and then shut off. And on again, and off again, all day every day. We call this "short-cycling," and you should configure your system to avoid this. It causes your DI resin to repeatedly be hit by high TDS RO water, and shortens the useful life span of your DI.
Russ
TDS Creep is the movement of dissolved solids across the membrane (to the RO water side) while the system is turned off. This results in relatively high tds RO water for a short period of time when you first deliver pressure to the membrane by turning the system on. What do I mean by "high", and what do I mean by "short period of time?" Here's some data from two test runs on a system with one 75 gpd RO membrane
You'll see that at startup, the TDS of the RO water (not DI water) was about 20% that of the feedwater, and over about 60 seconds, the TDS of the RO water came down to where we'd expect it to be.
This is why we always want folks to run the RO system for a couple of minutes before they test the RO water TDS.
Also - think about the repercussions here of having your system plumbed directly into a float valve in your sump. Every time the sump level drops just a tiny bit, the system would kick on and refill the sump quickly and then shut off. And on again, and off again, all day every day. We call this "short-cycling," and you should configure your system to avoid this. It causes your DI resin to repeatedly be hit by high TDS RO water, and shortens the useful life span of your DI.
Russ
