Issues with hose vacuum breaker assembly

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Hi all,

What is supposed to be such a "simple" thing is turning into a daunting house has two outdoor hose bibs (in Minnesota) attached to the front and back of the house. They are McDonald non frost proof regular hose bib - almost positive they are 72014 model. They each have Watts N9-CD backflow preventer/vacuum breakers? attached. They both leak. At first I didn't know what the device was, so after a little struggle I removed one by hand (later to find out these are supposed to be non removable). I bought a replacement and when I try to thread it onto the hose bib, it never full connects to the gasket inside and I can turn it forever and won't tighten, and leaks everywhere. I tried pushing while threading, pulling while threading, wiggling the breaker side to side while threading. I'm not sure what the magic touch was, but at ONE point it threaded on fully, but then I turned it counterclockwise slightly and gave it a tug per the field testing instructions. After that, it would not tighten again (which it should per instructions), so I pulled it off the hose bib again. Called Watts several times and their tech guy had no ideas and acted like I'm stupid because it should just screw on with the self locking spring inside. So I assumed it was defective and bought a second new one to replace it....same problem of not threading on! this time I rolled some of the hose bib threads getting the N9-CD off, and the new N9-CD is damaged in the process... For the life of me I cannot get a replacement to thread on, even though it's the same model! What am I doing wrong? To add - I removed the locking inner spring from the one good N9-CD that I have left to see how it fits in the hose bib threads, and it threads onto the hose bib just fine when it's not in the N9-CD... So I don't understand why it won't fully tighten.

Also, I don't understand the difference between this dual check N9-CD compared to the NF8 single check hose vacuum breaker, for example. It appears the N9-CD is ASSE 1052 where the single checks are ASSE 1011. When I look at the ASSE descriptions the only difference is 1052 protects against "rated working pressure back pressure". I'm not sure what that is in regards to a garden hose. Watts can also not clearly articulate the benefit of the dual check either, even though tech support is a plumber....can anyone help me understand why one would buy a dual check hose vacuum breaker vs a single check? The N9-CD is significantly more expensive.


N9-CD - Watts
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