A pump delivers water at 10°C between a reservoir and a water tank 20 m higher. The suction side consists of a strainer (ks= 2.5 ), three 90° bends (R/D = 2), and 10 m of ductile iron pipe, 25 cm in diameter. The discharge side includes a 160-m-long, ductile-iron pipe, 20 cm in diameter, and a gate valve. The friction factor for the pipeline is 0.02, the net positive suction head is 7 .5 m, and the design discharge is 170 li ters/sec. Determine the allowable elevation difference between the pump and the reservoir water surface to avoid cavitation.