If we're warning about valves, be sure that your gate valves are fully open (or fully closed), otherwise the gate will erode and may erode to the point where it can no longer close.

For those that do not know, Practical Engineering has video on it: https://www.youtube.com/watch?v=xoLmVFAFjn4

Less of an issue for area shutoff valves (e.g. under-sink) , since most of the time they are used before doing maintenance and there is little flow at the time.

We did have a plumber (!!) damage our pressure regulator by turning the whole-house shutoff valve (inches away from the regulator) too quickly; that was a bit annoying.

It would be extremely difficult to cause water hammer with a ball valve. They're just too difficult to close quickly.

Water hammer is a huge issue with faucets, which can be closed quickly, and with electrically actuated valves such as in washing machines, which close very quickly.

Is this actually a thing? I know there are videos of watwr hammer on youtube (US centric)

There are no regulations afaik in Europe in domestic = no-industrial plumbing and sure we have quarter valves which you can quickly turn off. I never ever heard of a bursting pipe because of water hammmer.

I am a plumber and sprinkler tech (nyc) and literally have never seen a broken pipe that could reliably be traced to water hammer damage.

Really would only be concerned if you are building fire safety systems. Now those sudden GPMs need some support.

I had a problem just this past summer hooking up a pressure washer to a hose outlet. After two hours of constant on-off cycling, had the pipe leading to the hose bib burst. You could hear the water hammer quite clearly (and violently!) after I repaired it, so I went back and added a hammer arrestor.

To me what I hear: your pipes weren't supported and your pressure is too high if it can be described as violent. I can hear my old office's script telling me to sell you a PRV or two.

I hear what you’re saying but isn’t it a bit of six of one and half a dozen of the other? The high(er) pressure relative to what the pipes could withstand exacerbates the effects of water hammer induced by the pressure washer’s solenoid constantly slamming open and shut in the matter of milliseconds, no? Lower pressure (via a PRV or otherwise), higher-rated pipes, slowly opening and closing valves, or strategically installed hammer arresters are all (theoretically and to various extents) viable solutions, no?

Because you are fixing symptoms (w/ another failure point) with local solutions and not the disease (high pressure, bad or unsupported pipes) and good plumbers do not do that because A) ethics B) liability

If your question is can those gas piston water hammer arrestors protect fixtures-- sure, I mean that part is just physics. Whether it's worth it before a hosecock is a completely different matter -- also as per the OP you're far more likely to break a toilet valve just from handling than from water hammer.

I use quarter turn ball valves everywhere and slam the crap out of them. If a pipe bursts from that, it needs to be fixed, and I’d rather it happen while I’m there slamming valves around than when I’m not home.

But it has never happened.

Ah yes, the chaos monkey approach to plumbing. I buy it. The best time to have a leak is during or immediately after doing plumbing work. The worst time is when you are asleep, out of the house, or on vacation.

Isn't it code nowadays to have water hammer arrestors that trap air and create a cushion?

Plastic piping (if equipped) functions as a water hammer arrestor. An expansion tank will as well, though a picky inspector may insist that the automatic valve location must have a water hammer arrestor if you are piped with metal supplies.

I know expansion tanks are required by IRC these days and those can help with hammer a bit too, as they're doing a similar function.

It happened to me once, now I turn off the water when I go on vacation.

you don't have embedded copper water lines in concrete slabs I assume? sure a little drywall damage is nothing but having to jackhammer that up is a bigger ask.

I've seen people just abandon those lines in favor of running pex through the walls rather than fix them.

When I lived in South Africa and the power went off frequently, the water went off because it couldn't be pumped. It absolutely was a thing in the water came back on. I could totally hear it in the roof.

And/or stick a hammer preventer in your piping in multiple places.

A timer sprinkler system kept water hammering, and I bought a little device that completely stopped it.