Pressure switches for water well pumps use a double-spring type switch. One spring is for the cut in pressure and the other is for the cut out pressure. Typical pressure settings for a low-pressure system will be a cut in (start pressure) of 20 PSI and a cut out (stop pressure) of 40 PSI. A higher-pressure system will use a cut in pressure of 30 PSI and a cut out of 50 PSI. When adjusting any pressure switch, you must have a pressure gauge installed on the water system.
Safety and Identification of a Square D Pressure Switch
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Pull the plastic cover from the pressure switch by removing the single nut on top of the cover. Be aware that there are live electrical parts within easy reach on the pressure switch. Use a wrench that fits the two small nuts on top of the two springs. Typically, one nut size is a 7/16 inch and the other is either a 3/8 inch or ½ inch wrench. The larger of the two springs, called "nut #1," is used for raising and lowering the cut in and cut off pressure. The smaller nut and spring, called "nut #2," is used for widening the gap of the cut off pressures. The smaller spring will raise or lower the gap or pressure difference of the pump turning off. That pressure difference will fall in the range from 1 PSI generally up to 50 PSI. The larger spring raises and lowers the overall pressure of that gap.
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Adjust the Big Spring Nut #1
Turn the nut on top of the large spring to raise the cut in and cut off pressures. Open a water faucet and watch the pressure gauge. Under a normally set pressure switch, the pump should come on at 30 PSI and shut off at 50 PSI. If the pump is starting and stopping at too low a pressure, turn the larger nut clockwise. Adjust just a little at a time and allow the pump to operate. The large nut adjustment is the easiest adjustment to make on the switch.
Set the Pressure Gap Nut #2
Turning the smaller nut and spring will adjust the upper end cut off pressure. Moving the nut in a clockwise direction will raise the upper limit of the pumps operation. Turning the nut in a counter clockwise direction will lower that overall cut off pressure. Exercise caution when adjusting this setting. If the nut is too loose, the pump will never shut off because the cut in and cut off pressures are to close together.
The Actual Instructions
The actual instructions printed on the underside of the cover are: "Turn Nut #1 clockwise to raise both the cut in and cut off pressures. Turn Nut #2 clockwise to raise cut out pressure only."