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

That may work, but it sounds like not much thought was put into the sizing of the pump and this is a critical part of the design process. There are very powerful pumps that you won't be able to put on a residential system. The life of a pump and sprinkler valves and piping depend on velocity of water through the pipe and pressure on the valves and If you don't figure it in correctly the system that should last 20 years will not last a season.

Long sentence.

Try adding up your gallons per minute per zone and getting a pump to deliver that at the appropriate pressure + elevation and distance from the pump.

If too much pressure is the problem, running multiple zones isn't likely to fix the problem. The pressure should remain about the same and only the flow will increase.

Think of it this way, plumbing and electricity are similar: Pipes are the wires, water flow is the current, and pressure is the voltage.

If the power company is supplying too much voltage to your house, turning on more lights isn't going to fix the problem. The source voltage will remain the same, you're just increasing your amperage.

Of course that's not 100% correct, because there is some voltage loss in wires when current flows through them... think of the situation where bathroom lights dim just a little bit when you run a hair dryer (the hair dryer pulling 15 amps will cause the wiring to the bathroom to have about a 2 volt drop from the resistance of the wire. You will get a similar thing happening in the plumbing... the pipe that supplies both valves would have increased water flow, resulting in more friction (pressure) losses as the water flows through the pipe.

So if replacing the pumb isn't an option, then it sounds like to me you just need a pressure regulator. For any irrigation project, if the source pressure is about 80psi or higher, you should be using a pressure regulator.