How to Adjust Square D Pressure Switches

In a typical well setup, a pump in the well transfers water to a pressurized holding tank, and a second pump maintains the tank pressure so that water flows from your faucets. The pressure pump is controlled by a switch, such as the Square D Pumptrol, and you can regulate the system pressure by adjusting this switch. This is a simple procedure that may be required when the pump behaves erratically or you don't have enough water pressure in the house.

Two Adjustment Modalities

Square D switches are factory-set with a 20 psi range between the pump cut-in pressure -- which is the pressure at which the pump starts working -- and the cut-out pressure, which is the pressure at which it stops. All Square D switches have a range screw that allows you to adjust these two pressure simultaneously, thus maintaining the 20-psi range. In addition, some Square D models have a differential screw that allows you to adjust only the cut-out pressure, thus altering the range. When both screws are present, the differential screw is the smaller one.

Screw Adjustment Procedure

Step 1 Turn Off the Power

Removing the cap to expose the adjustment nuts also exposes the pump's electrical terminals, and inadvertently touching these with your tools if they are live can give you a serious -- perhaps fatal -- shock. To prevent this, turn off the circuit breaker in the main panel that controls the pump before starting work.

Step 2 Remove the Cap, Test the Leads

Loosen the nut in the top of the cap with a wrench, then lift the cap off the switch. Test the pump's electrical terminals with a voltage tester by putting one lead of the tester on each terminal and verifying that the meter registers zero or the light remains off.

Step 3 Adjust the Pressure Range

Turn the nut on the large central post clockwise to increase the pressure range. Turn the nut through 3 1/2 rotations to increase the range by 10 psi. For example, if the current range is 20/40 psi, which means the pump cuts in at 20 psi and cuts out at 40 psi, turning the nut through 3 1/2 rotations increases the range to 30/50 psi. Turn the nut counterclockwise by the same amount to decrease the range.

Step 4 Adjust the Pressure Differential

Turn the nut on the smaller of the two posts -- if there is one -- clockwise to increase the range between the cut-in and cut-out pressures. One reason you may want to this is to raise the cut-out pressure to increase the time between pump cycles. On the other hand, you may want to reduce the amount of time the pump has to run during a cycle. To do this, turn the nut counterclockwise to decrease the range between cut-in and cut-out pressures.

Cut-In Pressure and Pressure Tank

Most modern pressure tanks have a rubber bladder that separates the water in the tank from an air chamber, and the pump cut-in pressure should be 2 psi higher than the air pressure in this chamber. After adjusting the pump switch, adjust the tank pressure by pumping air into the chamber with a compressor or letting some air out through the valve on the top or side of the tank. To measure the tank pressure, turn the pump off, run water to relieve pressure, then attach a gauge to the valve on the pressure tank.