SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

What was the pressure reading last year? How old are the points, and how has your regional rainfall been? Lower water tables drag down performance of perfectly good systems.

40 psi at the pump is no great shakes by the time the water reaches the heads. Since you never measured that pressure before, you are only guessing as to what the pressure was in past years.

Your well point may be clogging up, and in need of back-flushing.

If everything about the well is as it was when it was brand-new, then it is your job to go hunting for leaks. Your eyes. Your feet. Your shovel.

do you have a way to shut off the water to the field via a ball valve,and then open a spigot or vu flow to test water at the pump. you could try fracking the well yourself if your familiar with it. your pretty much just blocking off all ways for the water to go anywhere,besides building up pressure down at the well point, get a hose and shove it down to the bottom of the well let it fill up until it comes out the top,lift the hose up until it is all the way at the top,wait for water then push the hose all the way down,you usually will see sediment comming out around the hose. this is the last thing to do. like stated you need to check for a main line break first, do you have a pressure system with a pressure tank,or a pump start. if its pressure set up,it will cycle constantly with a main break on a pressure system,it wont cycle at all with a zone break or with a pump start,but you wont have the pressure once a zone with a break is on.
it can only be a few things,a clogged vu flow if you have one,a clogged point,low water table,a main or zone break,have you watched what the pressure gauge is doing while the zones are on,you say its happening on multiple zones,a problem with the well would almost always be universal,check for leaking heads,if you never had crazy pressure to begin with,a few leaking seals can make a difference. keep us posted. only details will solve it