Two reservoirs whose difference of level is 15 m are connected by a pipe ABC whose highest point B is 2 m below the level in the upper reservoir A. The portion AB has a diameter of 200 mm and the...

Two reservoirs whose difference of level is 15 m are connected by a pipe ABC whose highest point B is 2 m below the level in the upper reservoir A. The portion AB has a diameter of 200 mm and the portion BC a diameter of 150 mm, the friction coefficient being the same for both portions. The total length of the pipe is 3 km. Find the maximum allowable length of the portion AB if the pressure head at B is not to be more than 2m below atmospheric pressure. Neglect the secondary losses.