Nomadman;
I had the same problem with my soaker system that is fed off a spigot, not on its own dedicated line. After much trial and error I just went to an RV supply store and bought a brass regulator they are easily adjustable and very hard to overload. Since then I've had no problem.
Hope this helps.
J.R
P.S.
The thingy Yardenman is talking about is called a backflow preventer.
