I don't know which type my is. I've had 3 in use, and had one fail once. It didn't "hammer", it just stopped shutting off the flow. On the other hand, I've had the system "hammer" before, but I can't remember what the problem was.
This is the type I've been using:
Not much info, but I did find this:
http://www.reefcentral.com/forums/sh....php?t=1293478