I have the Square D 40/60 pressure switch on my pressure tank coming from a well. I have set my air in the tank at 38lbs with the system purged. My pump cuts out around 65-70 lbs but will not come back on until it reaches a low 10 lbs. I have cranked the main nut in, the one that has the bigger spring a good many turns and it still only cuts in at 10lbs. Do I need to keep cranking to raise the bottom end or do I have other issues. The well is 400 foot deep with loads of water.