No oil to pump. Turned off shutoff valve and replaced Filter Cartridge. Started Moter and proceded to bleed pump. NO oil! Opened Filter and no oil. Removed in line shutoff valve and no oil.Have a 500 gal. tank and 135 gal of oil.Also my system is a two stage pump equiped with two lines between pump and tank, one in and one return for excess pressure. How do I get oil to the pump/burner moter.