I have been losing water pressure from my well. When water is turned on the pump starts at appropriate time and will pump up to shutoff , but occasionally when pump starts it will not pump up pressure and will drop down to 5-10 lbs. When let run (with water off) it will eventually pump up to pressure ( about 10-15 minutes).I purchased this property in 2005 from a deceased family member.This is a 12ft well with water at 9 foot. It was put in around 1975 ( hand drove) with 2" galv piping ( 1pipe) and a 1/2 hp pump. I am having problems with lose of pressure when run for a length of time ( varies from 5 min and more). This is an intermittent problem and does not happen at any particular point. To date I have replaced the pump and pressure switch,drained the bladder ( 3 times) and checked pressure (28lbs) and have verified 30/50 switch setting. I have gone over the pipes and replaced all that even looked like the culprit. Note that this unit will work perfectly for a time and than out of nowhere will have this problem. I also have noticed it seems to have air in system at times. I live alone with an occasional overnight from my girlfriend and holidays my children and grandchildren visit . I would love to figure this out before cold weather and/or holiday visitors. Any advice or suggestions would be greatly appreciated.