Here's my situation... Newly constructed home [entirely finished] with a dedicated line that was installed for a future irrigation system. Well, the future has arrived, and had an irrigation specialist over for a bid. He ran some gpm tests, and upon checking the water pressure with the test being run, he shuts off the line valve and we get an Extreme water hammer [only when it was shut off abruptly]. if he slowly shut the valve...no hammer. His opinion that was there was a problem with the dedicated supply line (which was the new 1" plastic line) and that it wasn't large enough to handle the 18 gpm flow that he said was running thru the line. And, he had a concern that he said at that rate, the valves would probably close quickly causing the hammer. So, had the plummer over today and only real suggestion that he could give was that he didn't think the irrigation valves would close that quick to create the hammer, but if they did, that he would install an arrestor. My fear is having an irrigation system installed, along with an arrestor, and the water hammer continues...then what??? My house is completely finished, so an increased 1 1/4" line option is probably not viable. What options do i have? I realized that many of you experts may need more info to help me out, so ask away. thanks much in advance for all the advise. [signed] "A guy who REALLY wants an irrigation system."