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Auto Shut off valve question


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I've been having trouble with my ATO system and have finally decided to address it.

My Auto shut off valve (ASOV) is installed between my RO membrane and DI cartridge, which is where BRS recommends installing it. I've got a check valve in there as well.

When I first installed it, you could hear the ASOV whoosh on and off as needed in normal operation, and any time the ATO kicked in there was a little bit of extra pressure at first then it would go to its normal state of a fast dribble of water.

Then the ASOV started making a kind of stammering whoosh sound, and got quite a bit louder. The functionality was the same, but it seemed to be having problems. Then it seemed my ASOV failed completely because it no longer made ANY noise, and there was a much greater amount of pressure building up in the line if the outlet was closed off. At one point one of my cartridge filter housings cracked, I assume from the pressure. From then until now I've been shutting off the water supply to the RO system when not in use to prevent pressure build up.

I replaced my ASOV and the new one is doing the exact same thing, no sounds, lots of pressure build up.

Now I'm wondering what I should look at next...if the check valve has failed would that be the culprit? What else might it be?

Another general question...should there be any air in the DI filter housing? Since putting my most recent DI resin cartridge there has been a layer of air between the cartridge and the housing wall. I just tonight got around to removing the air, but I'm worried it might somehow return, I don't really know how it got there to begin with. There are currently no water leaks anywhere.


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I am not sure what type of ASO you have but if it is a float valve type, they recommend that you don't keep pressure to it all the time. The guy at spectra pure told me that it messes up the membrane and that ASO are typically so that you can fill up a reservoir and not worry about it overflowing but should turn it off until the reservoir needs to be filled again. In my case, I was going through DI cartridges like crazy and couldn't figure it out and it turned out to be because I left the water supply on. Hope it helps.

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  • 1 month later...

If the ASOV is working - meaning that it is stopping the flow of waste water when the flow of purified water is stopped, then your check valve is working.

When the ASOV's stop working, it is typically one of 3 things:

1. Float valve leaking

2. Check valve leaking

3. Bad ASOV

The ASOV's "compare" the pressure in the high pressure side of the system to the prssure on the low pressure side of the system. When the low pressure side reaches about 66% of the high pressure side, the ASOV cuts off the high pressure side and stops frow to the RO membrane. The ASOV doesn't add pressure in any way.

Regarding your DI housing - you just have some air trapped in there. With the system running, unscrew the housing a quarter turn and you'll be able to burp the air out of the housing and you'll see the water level start to rise. Just as the water leavel reaches the black oring, cinch the housing tight.


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