Another water hammer question

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???
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Sounds like you may have greater water pressure than your other system. How about a small expansion tank? That should stop the banging.
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Actually, that was a problem that I dealt with, with a pressure regulating valve. I don't remember what it is set at now, but it is what the Rain Bird tech recommended. It was 105.
Thanks for your thoughts Bill.
Bill wrote:

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105 what? Not PSI..?? The expansion tank is like on your hot water heater. Small tank, about 1 or 2 gallons in size. Has a bladder inside with air in it to prevent an expansion problem on hot water tanks, and it helps well pumps with less on, off cycling. Absorbs the water pressure differential.
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Yep,,, 105 PSI. This system was too high.
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"I don't remember what it is set at now, but it is what the Rain Bird tech recommended. It was 105."
How many heads are on that 105psi zone? You must have an excellent water supply system.
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PS What is an expansion tank, and how do I install one?
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