New RODI question

[gryffandor]

Just got a new Pure-Flo II 50 gpd 3 canister system. Seems to be operating ok, about 2.5 gph output. The 3rd canister, DI does not seem to get more than 1 or 2 in. in it. I expected it to fill like the others. Is it working correctly?

[neanderthalman]

Mine does this as well. I don't know your setup, but mine is a refillable DI canister in a vertical chamber. The water pools in the outside chamber, and can only enter the DI canister from the bottom, and exits the top of the DI canister. How I see it is that the RO entering the chamber has to develop sufficient pressure to be forced up the DI canister. To do so, the trapped air necessarily becomes slightly compressed, and the bottom inch or two fills with water.

 

As for whether or not it's a problem, I do not know. I do know that you're not supposed to let your DI resin dry out, and my intuition tells me that, once the RO unit shuts off, the air decompress and empty the chamber, but it should not empty the DI canister. Regardless, I wasn't sure, so I vented the trapped air by cracking the outer chamber open a 1/2 turn and ran the system. Now the air was unable to compress and force the water through the DI canister, and instead forced the air out through the threads that seal the outer chamber. Once filled with water, I retightened the outer chamber. Now I know that the resin cannot dry out.