My 40/60 3/4hp shallow well jet pump will run continuously and will not build up pressure in the bladder. The bladder will hold pressure though. I have filled it with air and when I turn on the water it loses its pressure and when the pump kicks on it just keeps running without building the pressure back up. The pump will not shut off unless I fill up the bladder with air again. I have no visible leaks and I have tried to lower the pressure on the switch to no avail. Do I need a new pump?