The well pump water pressure switch controls the rate at which the pump will turn on and off. It makes use of two pressure systems to control the water flow, and adjusting the water pressure involves adjusting these systems. Normally, this switch is pre-set to the correct pressure, but you can modify it without any special tools or material, using just plumbers' pliers.
Step 1 - Remove Switch Cover
First, unplug the pump for safety purposes. Then, using your pliers, unfasten the nut that holds the protective cover in place. Doing so will reveal the inside of the pressure switch.
There are actually two types of well pump pressure switches and they will require slightly different adjustment methods depending on which type you have. Inside, there will either be one or two springs held down by adjustment nuts, denoting one or two-post types. These are the controls you will be working with.
Step 2 - Adjusting the Pressure
In a one-post pressure switch, the single nut will be used to change the cut-on and cut-off pressure for the pump. Turn the nut clockwise to increase the pressure for both the cut-on and cut-off, 2 1/2 PSI for each rotation. Alternatively, rotating the nut counter-clockwise will decrease the pressure.
For two-post switches, the nut on top of the large spring will adjust the timing on the cut-on and cut-off pressures. The rule for the one-post switch holds true for this type as well, clockwise rotation for increased pressure and counter-clockwise for decreased. However, the small nut on this kind can control the gap between the pressures. Turning it clockwise will raise the cut-off and tighten the nut. Do not set the cut-off pressure below the cut-on, as this will make the pump go into a never-ending cycle and can damage it. The cut-on pressure should never be below 20 PSI and the cut-off pressure should never be above 60 PSI. A 20 PSI differential between the two is best for your pump's performance overall.
Step 3 - Finishing Up
You might have to do a bit of tweaking before you get the right pressure. It is highly advisable to place the cover back on and tighten it in place every time you finish an adjustment, in order to avoid electrocution. Once happy with your modification, put the lid back on and plug the pump back in.
It may take a few different adjustments to get the pressure switch set to where you want it, so don't be afraid to go back in and change the pressure again if you need. Just keep your minimum and maximum PSI in mind.