Preventative arrestors?

I'm about to install a new shower valve in remodel. I was looking at a plumbing book from the library and they were installing arrestors on the vertical supply lines on either side of the valve. Is this something I should do now before I seal the wall in? Since the room is torn up I rally have no idea if I'll have a hammer issue, but at least I'd have them installed and wouldn't have to do something after the fact. I mean could it really hurt to install them other than the extra expense?

Old school thought a plain air chamber (stub of pipe capped) worked as a long-term solution for water hammer...it DOES NOT. Some valves specify that they should be installed with arrestors. If yours does, go out and buy some and install them...otherwise, since most don't need them, it'll probably be overkill (but much easier to do now than later, if needed!).

Get an engineered hammer arrestor - typically about $10 each. These keep the water and air separated by a bladder or piston...just an air chamber will have its air absorbed into the passing water and stop working after a short period of time - IOW, a waste of time and materials.

Well can't find anything on the valve instructions about them being required, but I think since I have the chance I'll install a couple of these:

It is not standard to install hammer arresters for a shower valve, and I don't know why you would want to unless you had significant banging because none of your home's piping was strapped properly...

It's not that I want to, I just thought that since I have the room torn up it might be preventative maintenance.

...I am just not a fan of extra leak points and turbulence in the lines. But there is no doubt, putting in proper arresters certainly couldn't hurt, I am just fairly certain they won't help any either...

If he does put in the arrestors, do they have to be accessible?

They should be since they are a mechanical device, and it WILL fail eventually, but unless the arrestor is REALLY needed, and most likely it is NOT, then he would never know even if it were inoperative. This is something, that might not be needed, but at least if he does install them, they may not do any good, but they will also NOT cause any immediate problem.