I have a marginal system that I am trying to fix. Pressure is ample and there are not too many sprinklers, at least according to the tables I've seen. All the pipe is 1" heavy wall PVC. The sytem has 1" Orbit Jar Top valves. These valve do NOT have as large an inside diameter (ID) as the 1" pipe. Thin or thick wall pipe matters not, the valves inlet and outlet ID are visibly smaller. This undersize ID at both the inlet and outlet must be creating an orifice and restricts flow. Stupid valve design. Question: What valve brand (if any) has a flow capacity (same ID and flow annulus) the same as the 1" pipe? I only need to replace 6 valves, so cost is not much of an issue. Thanks for loaning out your experience and expertise.