Look at the pipes, valves and fittings on your spray booms. Make sure you have no bottlenecks on the way to the end of the booms. Remember, if you have a 1/2" pipe boom and the spray must go through a 3/8" valve to reach it, you have a bottleneck.

This can cause lower pressures out at the end of the boom and then your nozzles will not be putting out the same patterns and volumes as those close in.

Be logical and think in terms of an efficient irrigation system: always from larger to smaller until the end. Spend some time on it, look carefully, you may find an elbow, tee, fitting, close coupling, hose nipple, hose, filter, valve, anything that could cause that bottleneck. And it could be anywhere between the pump and the last nozzle.