Spray heads in an agricultural spraying system are to be supplied with water through 500 ft of drawn aluminum tubing from an engine-driven pump. In its most efficient range the pump output is 1500 gallons per minute at a discharge pressure not greater than 65 psig. For satisfactory operation the sprinklers must operate at 30 psig or higher. Neglect minor losses and elevation changes. Determine the smallest standard pipe size that can be used.