First, let me say that I am a novice at pumps, wells, etc.

I had a 1 HP irrigation shallow well jet pump with no pressure gauge, a pressure switch with "fried" contacts, no hose bib, and no ball valve on the discharge line. It did have a deflated 1 gallon bladder tank.

I went to buy a new pressure switch at the local supply house and he asked me if I needed a 20/40 or a 40/60 (only 2 choices at this particular supply house). How did I know which one I needed since I had no pressure gauge? Not knowing for sure what to do, I chose the 20/40 since I did not know if the well / pump could produce the 40/60.

(I have since installed a new 20/40 pressure switch, a liquid-filled pressure gauge, hose bib, ball valve, and set the tank pressure 2 pounds below the the cut-in pressure.)

Since I am a novice, I did not "mess with" the adjustment nut on the pressure switch since it was pumping up to 40 PSI and cutting out and dropping down to 24 PSI and cutting in with no cycling issues and the irrigation zones all ran just fine.

Just trying to learn! Thanks for any advise about the pressure switch selection process.