A 500-m long pipeline carries oil (sp. gr. = 0. 85) from a storage tank to the bold of an oil tanker. The 0.5-m-diameter steel pipe has expansion joints and a wall thickness of 2.5 cm. The normal discharge rate is 1.45 m3/sec, but it can be controlled by a valve at the end of the pipeline. The surface of the oil in the storage tank is 19.5 m above the outlet of the pipe. Determine the maximum valve closure time that would put it into the category of a rapid closure.