Every hose bib vacuum breaker that I can find comes with either a set-screw designed to snap off after it's tightened, or some other mechanism that prevents removing the breaker. Why is that necessary? AFAICT all it accomplishes is to force you to spend hours trying to remove it, or have to replace the entire spigot, if/when the breaker malfunctions.
1The main reason for the set-screw is to prevent the device from coming loose when the hose is removed. Many people would just regard as part of the hose.– Hot LicksJun 17, 2022 at 12:57
If you replace the entire spigot once with the right thing, vacuum breaker maintenance after that is trivially easy. Most of the VBs with set-screws we see in questions here didn't snap off, they just rusted in place for the want of $0.001 in grease or anti-sieze applied when they were installed.– EcnerwalJun 17, 2022 at 20:55
They are made hard to remove simply to discourage people from removing them. It is a public safety issue (the possibility of contaminated water getting back into the general water supply). And so they are made to be "tamper proof".
It is normal for the vacuum breakers to spit a little bit of water sometimes.
The way it's supposed to work is the valve is deep inside the house, and the blue area in this diagram is supposed to automatically drain when not in use. That way, the hose bibb doesn't take freeze damage.
However, people regularly destroy them by making one of two mistakes.
First, they leave a hose attached through a night frost, which can be more subtle than they realize, and can happen a month before or after you'd expect, and can happen even in temperate "doesn't freeze" areas like Seattle, Sacramento or L.A. The flow resistance of the hose prevents the blue area from draining fully. Freeze damages the valve, worst on the outdoor part of course, and you notice the only really vulnerable thing outside is the vacuum breaker.
Second, people leave the valve open and pressurized 24x7, because they want to feed other valves or a splitter, run automatic sprinklers, etc. Frost proof sillcocks are not for that application. This continuous service damages the vacuum breaker. For such applications, use a regular faucet, with a shutoff valve on the interior to manually drain it in winter.
2The question appears to be about the add-on vacuum breakers that go inline with the hose on a "boiler drain used as sillcock" or ancient sillcock that lacks a built-in vacuum breaker. The style illustrated here are dead easy to remove and replace the vacuum breaker on as it's not between the original hose threads and the place the hose threads on to it, and if you just remove it, you have a huge leak encouraging you to replace it with a working one, not "siphon-city" from your kiddie pool or pond back to the municipal supply.– EcnerwalJun 17, 2022 at 20:52