Corroded Impeller
One of the main cause of poor distance, especially in an
aging system is a corroded impeller. After a pump has
been in service for many years, its constant immersion in
water begins to corrode its surface.
This corrosion often causes the fins on the impeller to
get smaller or completely disappear all together.
Without the fins operating at full capacity, the pump
can't build pressure as it should. This causes a loss in
pressure and poor distance from your sprinklers.
If you suspect that your pump is performing poorly, I
would recommend taking your pump to an expert.
Many hardware stores offer pump repair, or if yours
doesn't the dealer you bought the pump from is also a
good place to take it to. They'll perform a full
inspection and recommend what parts you're going to
need.