A 1000 ft long steel pipe carries water from a reservoir with a water elevation at 826 ft. The pipe has a diameter of 12 in. with a wall thickness of .5 in. A gate valve at the downstream end is slowly closed during a half-mintue period. Determine the maximum water hammer pressure if the initial pressure at the valve was measured to be 742 ft above the datum. The elevation of the valve is 545 ft.