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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"dave" wrote in message
ups.com...
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:
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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"dave" wrote in message
oups.com...
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???