Augie, that's the first time that I have heard of a 3/4" or 5/8" line freezing up. Send me a PM with your mailing addy and I'll send you price on a pop off valve. When I DIY a system I put it on the PVC manifold that has the ball valves/gauge on it. I just glue a threaded adapter in the "T" that is at one side of the manifold to put the valve in.