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

Basically, you'll wind up pulling the existing pump, and replacing it with the same. If it's no longer being made, you'll use a replacement with the same horsepower and number of stages. Usually, the well installation information will be documented somewhere.

No matter where the pump is located in a well shaft, its performance is based on the actual water level in the well. If you don't know the actual delivery capacity of the well shaft, using other than an original-performance pump risks running the well dry.

If you had time to spend, and were getting paid by the hour, you could get a big air compressor and run the system on air, and inventory the heads, including the nozzles. Then you could get the manufacturers' information on the various heads and nozzles, and do a calculation on what gpm is being used, at a head pressure you select. Then you could calculate the pressure being lost in the pipe and valves between the heads and pump. All that you need from there is the drawdown water level of the well, and you can select a pump.

Is there some particular reason to believe the original pump selection was incorrect? Is there no company that did maintenance on the well or pump, that would have the pertinent information?

Some states have a requirement that for each well drilled, the performance details of the well shaft be filed with the state, including the gallons per minute of replenishment capacity of the well shaft, which is the maximum number of gallons per minute you can draw without lowering the water level in the well. However, don't bet the ranch that the numbers on file are correct.

On pumps and wells, you don't get a 'cushion' per se. You want to draw enough water to keep the pump running continuously. With modern lawn heads, you can change out nozzles to adjust consumption up or down. If the system is an older one, nozzle swapping may not be possible.

It's okay if the water level in the well drops when the pump is running, if it gets to a certain point and goes no lower. When it continues to keep dropping, then there is a real point to the idea of a smaller pump, less capable of running the well dry. But you have to determine whether you can live with less water, based on what adjustments you make with the heads. Also, you need enough water to feed the acreage in a reasonable time period. The drip irrigation won't care about pump capacity, since you can design to fit.