Hi all. In summation. Replaced a 2 handle bath / shower faucet with a one handle Pegasus. Made water hammer sound since that time. Tried hammer absorber off union, then into regulator (extra elbow now). Fired it up and knock gone, but shower won't activate ( vacuum from shower tap). Removed absorber setup and replaced with elbows, no help. Will go back to original config I guess. A couple more days and I'm calling a plumber. Too much stress! All this over a damn knock. I bet if I bought a Moen, Delta, or even Pfister, I'd prob be OK. Either this valve has a sensitive pressure balancer, or the plumbers a dope ( me ) LOL... Any advice would be appreciated.

I thnik Moen is you answer. Usually we can get rid of hammer with a shock arrester but your have could be slamming shut and that's hard to combat. How large of an arester did you install and both lines, right?

First, make sure you installed that valve "right-side-up". It has 4 identical outlets and it is easy to get confused during installation. Please, check it out and let us what you found out...

The regulator is right side up. It's the first thing I checked. Actually I was hoping I had messed that up. I installed 8" arrestors on both hot and cold supplies. I wish I had recourse with Pegasus or Home Depot. $180 when I bought it... Clearance rack... discontinued now $99.00. Might have to look for Moen. At least I have all the PEX now. Easy to use. Bummer is faucet wall reconfigure. New rock... panel. U bend shower head. Damn!!

Can you remove trim plate, take a photo of it and post it ?