My well pump won't rise over 18psi. If I prime the pump and shut the valve between the pump and expansion tank and hold down the pressure switch I get up to 80psi then open the valve it drops down to 15 again. I have water with a lot of air and the pump won't shut off. I was wondering if there is something that will bleed the air out before the pump or if there is any other way to get the pump to shut of