[samdog]

I've had the GE Merlin for a while and it's been a pretty good unit. Every once in a while it won't shut off and runs to drain when the pressure happens to be a bit low.

So I did some research and found that GE recommends the Merlin have either a post-filter cartridge or an auto shut-off cartridge in the product line. They say that both of these cartridges have an additional shut-off valve in them to correct the common run-to-drain problem.

OK great, so I put a post-filter cartridge in the product line (genuine GE part, installed correct flow direction, yadda, yadda). Now the unit shuts off very reliably and makes even better water with the polishing filter.

But here's what's different: when the faucet is opened, the unit builds pressure for about a second and then the ASO in the base snaps loudly as flow starts. This is definitely the ASO in the base, not the ASO in new post-filter. The snap is quite distinct, can be felt in the base and it even causes a miniature water hammer -- you can see the 1/2" feed line jerk.

So obviously the new post-filter with the built-in ASO is having an effect on the ASO in the base. It's working, but holy bovine...should it snap like that on opening?

ps, this is marked "revision D" on the post-filter.

[samdog]

Well, I think I figured it out. The unit can take several hours of running to evacuate all of the air. I let it run a while longer and the snapping ASO is getting quieter and less forceful. It's almost gone now, and I can tell it's just air by the more familiar sound as it bleeds out.

It never bled air so loudly before without the post-filter, so the ASO built into the post-filter has a very positive shut-off. If your Merlin is sensitive to low water pressure (running to drain after closing) this inline post-filter may fix it for you.

[samdog]

Final update.

It's not an ASO in the post-filter, it's a bladder. (Sort of a miniature pressure tank.)

Merlin shut-off is reliable now.