I Have A Water Pump That Is Feeding About 40 Seedling Trees,i Turn The Pump On And It Works For A Few Seconds Then Quits,the Line Is Only About 18 Feet Long And 40 Drip Lines Going To The Trees,the Pump Is New And Just Wont Pump The Water?

Does the motor on the pump stop running?
If so, you may have a problem with the contacts disengaging on the pump itself. Sometimes new parts can be faulty.
Is the pump motor still running but the water isn't going through the pipes?
If so, then the pump may not be powerful enough to push the water that distance.

If this is a well pump it could be doing what is known as short cycling. The pump pressure switch is closing before it is suppose to.or in other words the switch is not sensing the water pressure drop causing it to turn on and stay on until the water valve/spicket/hose is closed off. My water well was doing this so i spent about a half day looking up home inspection information on how to fix it. Basically you just replace the switch.they range from 19-30 dollars(at lowes). At least for my pump.