My well pump frequently stops and starts. The PSI only shifts slightly before the pump goes on automaticaly during use. Could this be the air content in the expansion tank, a setting on the pump? Please help!

You posted this twice, but here it is again.

Could be a couple of things. I will give the most likely ones.

First check the pressure gauge and see if the cut-in and cut-out pressures still differ by about 20 psi. If they don't (and the pressure gauge is functioning correctly, a big IF), then I would suspect the pressure switch, but keep going.

If it appears that the cut-in/out pressures are correct, then I would suspect a waterlogged pressure tank. (This actually is the most likely, but you have to do that other check first.) That happens when the bladder in the pressure tank fails and the air that is supposed to be in there is absorbed by the water. As the air volume in the tank decreases, the volume of water required to change the pressure over the cut-in/out range becomes smaller, hence the rapid cycling. To test this, turn the pump off, make certain nothing in the house is using water (shut off the main valve) and drain the pressure tank until the WATER pressure reads zero (you DO have a tank drain don't you?). If the tank still has water in it (often you can rock it slightly to tell but BE CAREFUL) it most likely needs replaced. Then check the residual AIR pressure in the tank. It should read 2 psi less than the pump cut-in pressure with the tank empty. If the bladder is ruptured, it will read the same as the water pressure which is zero (right?).

When you replace the tank, you can reuse the manifold if it is a modern one compatible with the new tank, but REPLACE THE PRESSURE RELIEF VALVE with a new one. Also replace the pressure gauge if it is old, and the pressure switch if it is old too. And DON'T cheap out and use a galvanized nipple on the pressure switch, especially with a brass manifold. I've seen dangerous overpressure situations when that steel nipple corrodes closed.

I've already written too much, so I'll let you work on this. There are other things too, but they often are a bit more system specific and I can't see your system from my keyboard.

Have a happy new year.

EPM

I would add this. Your tank probably has an air valve (like one on a tire) towards the top. Press the valve a few seconds. If water comes out, then your diaphragm in the tank is ruptured and the tank needs to be replaced.

This site gives a lot of good information about your situation.

Bladder Type Water Storage & Pressure Tanks - Diagnosis & Repair (http://inspectapedia.com/water/Water_Tank_Bladders.htm#Bladders)