Water pressure drops when changing zones and wont come back up to normal

I have a eight zone sprinkler system. It is ran off my drilled well. I have a submersible pump. My water pressure switch has a cut in of 40 and a cut off of 60. Recently noticed my rainbird 5004's weren't spraying out as far as normal. Started watching my pressure gauge by my water pressure tank. I noticed that when the system switched from one zone to the next pressure would drop to 23psi and it only comes back up to 30psi. Normally it would stay at 40 or 41 psi. It doesn't seem to matter what zone you start on it drops when going on to the next zone. Also the first zone you start on will read 41psi. My valves are rainbird dv-100's. Any help would be greatly appreciated.

You may be running near the limits of your well/pump, and when changing zones, the fact that two zones are simultaneously open, is a drag on your supply. There might be some sense to seeing if you can't change rotor head nozzles to a smaller size, which will reduce flow, and raise pressure.

By the way, you might be better off with the DVF-100 valves, with the flow controls throttled down, which speeds the closing of the valves, and minimizes the overlapping.

Some controllers have a capability to program a delay between zones, and if yours is one of those, you might be able to program your way out of the problem.

There is a characteristic of all pumps that the pressure they can deliver is lower as the flow increases. You should know that characteristic (it's a curve of GPM on the bottom and pressure on the left) when you design a sprinkler system. The pressure (head) on the curve must be adjusted to reflect depth to water and pressure losses in the pipe.

The irrigation system zones should have enough sprinkler head flow rate at the middle of your switch setting range to keep the pump running constantly.

If your pressure is dropping below where you need it for spray range you should install smaller (lower flow) sprinkler heads on that zone and let the zone run longer to get the same amount of water on your lawn.

Is it possible the submersible pump is plugged or near the end of its life? The pump is 9 years old and we have rusty water. When the sprinkler system was put in 5 years ago it ran great. Is it also possible that the spray nozzles have opened up thru years of use and actually putting out more than originally. Thanks!!!

I ran into a similar situation where the fix was a control clock with a Zone / Zone delay. You are using a lot of water to fill empty pipes when a zone opens, and sometimes a slow closing valve will stick open and not close.

The solution was set a 20 minute "rest" period between zones, to allow the well to refill the pressure tank, and for the slow closing valves to close completely before the next one tried to open. This allowed the full tank to charge the lines and then the pump would keep up with the full usage of the system, with a little help from the reserve left in the tank.

update

This weekend I changed the nozzles on my rainbird 5004's. I went from 3gpm nozzles to 2gpm nozzles. My pressure is great and have finally got proper distance back. My next question is should I have our well driller come back out to check the condition of our pump. Five years ago when the sprinkler system was put in it easily handled five heads on a zone with 3gpm nozzles. We have iron in our water-could the inlet screen of our submersible pump be plugged or the pump near the end of its life.Thank-You for your help!!!!