As a matter of fact, I do have the Irritrol valve. I have the conventional valve. My 1200gph pumps do not produce enough pressure to open or push up on the diaphragm to let the water through. Now when I took the spring out, the water flowed like a champ when the pump was on. Now on the sown side, the water still flowed even when the pump was off. I ordered a different type of valve without a spring. It has a plunger and it is a low pressure valve. I hope it works if not, I hope your system works. I am running out of ideas.
this is the one that I used
http://www.irritrol.com/valves/valves_205s.html