Before I get too many descriptions of a water hammer,,, I'm a
firefighter, so I know allll about water hammers. And, I am aware of
the 'water hammer arrester'. I have one.

This is a little different story. When I bought this house 5 years
ago, all 6 valves would bang when closing. As you can imagine it drove
me crazy. I called Rain Bird, with zero luck.

Finally I thought that I would just dig up the old valves and replace
them, and as I got ready, I realized that it is just the guts that need
changing, so I replaced the old diaphram with new ones. It worked!
Absolutely blew me away, but I was so pleased that I didn't question
why.

About two years later I started getting the banging again, but this
time, I found a supply place that sold diaphram kits.

Now I am starting to ask questions. I still have one valve (the last
one in line) that bangs when closing if it doesn't get a new kit every
year.
Why would this be necessary? I went 16 years in my old house with the
same valves and I never changed the diaphrams. It is a simple fix, but
it shouldn't happen this often.

I have two adjusting valves (screws) on top. One lets me turn the
system on to test it, but for the life of me I don't know what the
other one does. I'm not talking about the large manual valve at the
top. These are both smaller.

Any thoughts???