I have a shallow well,there is 30 ft. of horizontal run before well goes down 20 ft. I have not used the well for 4 yrs. I would like to use it for auto sprinkler and hose spickets.The pump is 1.5 hp Century jet pump with a 20 gallon diaphragm tank.The well I could not get the pump primed and working so I finally pressurized it with a hose from city water line, bled air out and removed hose ,pressure held at 40 lbs ,I turned on pump,pressure dropped to 30 and pump would not fill tank or keep any pressure with hose bib open and shut.I have tried several ways to prime pump ,let water run through system with bib open pump on and city water running through,still turn pump off pressure builds ,remove city water turn pump on pressure drops off never builds .Bad foot valve??