Heres a little hydraulic problem I am having and I would like some opinions. POC, downstream of the double check pegs my 100-PSI gauge in static pressure. 120 feet downstream are the 5 or 6 valves for the system. I have about a 10-foot elevation change upward here so I should lose about 2 or 3 PSI. Static pressure at the manifold is 72 PSI. I realize that the static pressure at the POC should be the same as at the manifold, plus or minus the elevation change. When I turn on the large rotor zone I drop to about 26 PSI and I get 22 PSI at the rotor. When I turn on the large field of 15-foot full heads my pressure at the manifold drops to 22, which fits with the 18 PSI I get at the first head of the zone. I have a zone 50 feet away that had a lot less heads on it than the 15-foot full zone and they are half heads with varying radiuses. With this zone my pressure drops at the manifold to 10 PSI and they spray poorly. When I shut off the valves the pressure goes to around 50 PSI and slowly creeps upward to 72. I have more investigation to do, but wonder what the collective wisdom here is? I may have a main leak and/or lateral leaks (there is no evidence of this) or I may have an obstruction in the mainline (rocks, crushed line, etc.) What are your thoughts and any guidance would help.