I have a Myers jet pump with 2 lines coming out. The pump sits approx 20 feet high from the lake source with a 70 foot run to the lake. Pump kicks in at 20 and rises to 40-42 and will not shut off unless I manually do it and the pressure will hold constant at 40 until the water demand brings it down to 20 again. I cleaned out the pressure tube and put new switch and gauge. Pump is new to correct same symptoms with older pump. Do you think the run is too long or is it like the other problems and cures I have read about. Thanks John

How to adjust water pump pressure, pump cut-on pressure and pump cut-off pressure - private pump and well system do-it-yourself repairs

Check this site out. It will tell you about the smaller nut on your switch. It can be used to adjust the cut off pressure down. It sounds like your cut off pressure might be set a little higher than 42 and your pump can't get that high, which is not surprising since you are pumping from an elevation of about 20 feet. Jet pumps can't go much more than 25 feet, so you are getting close.