Need advice on how to replace a Watts Series 8 Model 8A non-removable vacuum breaker.
There is a repair kit available for that part. Since it is designed to be non- removable, I would assume you can repair it in place.
Your other option, depending on what's wrong with the first one, could be to just screw another vacuum breaker onto the existing one without removing it.
If all else fails, I think you're going to be cutting it off with an angle grinder, dremel, or similar.
You do know the meaning of non-removable, right? That being said, you'll need to replace the spigot. Those fittings have a brake-away threading system that allows you to tighten them for installation but breaks away the sleeve from the threads if you try to turn it counterclockwise. Something like the safety caps on pill bottles. Now, I have removed them with a Dremel drill with a cutoff wheel and carefully cut the breaker off of the spigot but it was a slow process so I wouldn't damage the threads on the spigot. the next time I came across one that had to be removed, i just replaced the spigot and added a new breaker.
You absolutely do NOT need to replace your spigot everytime your vacuum breaker fails (which may need replacement as often as every 5 years). Despite being "non-removable" they can actually be removed fairly easily:
A) VB type one screws on and then has a break-off set screw/bolt that snaps off. To remove this type take a dremel with a small metal cutting disk and cut a diagonal line into the top of the screw. It is fine to also cut into the side of the VB while doing this. You are essentially creating a slit for a standard screwdriver tip. Put a small screw driver into the slit you cut and rotate the broken bolt out a few millimeters. The VB will then unscrew normally. You can also just drill the screw out but this can be more difficult because the screw is steel and the body of the surrounding VB is softer brass. It is easy to slip off the harder screw into the softer brass while drilling. There are numerous videos on YouTube showing both methods. You can get it off in ten minutes.
B) Older vacuum breakers (VBs) may lock on using an internal spring and have no screw hole on the side. For these (I had one) take a dremel with a cutting disk mounted on it. Cut the VB top to bottom on the left and right side of the spigot with the dremel. Be attentive to your depth so you don't damage the threads on your spigot with the cutting disk. When you have cut down both side stick a big screwdriver in and just pry the VB body apart like a clam shell. You can do this in about 15 minutes.
Finally, if you are going to put new VBs on your hose bibbs, take out the break away screws and throw them away. Replace them with stainless steel M5 hex head bolts of the same length. That way when they fail again you can simply loosen the bolts with an Allen wrench and unscrew the VB normally.
It is idiotic to replace your entire hose bibb every single time a vacuum breaker fails. Your hose bibb can last 40 years and replacing it yourself will cost you $20 to $40 (plumber much more). Your VBs can fail as often as every 5 years and they cost $6 to $8.
This vacuum breaker is titled "non-removable" for good reason.
The unit is secured by a set screw that is snapped off through tightening. If you need to remove it the only way I see to do it is to completely drill out the set screw with a metal drill bit. I believe the only other option is to replace the entire spigot.
I would try drilling it first.