How do the last four pump characteristic curves apply to thi

How do the last four pump characteristic curves apply to this problem if the system distributes 420L/s and the maximum the flow ranges the graphs is 250L/s?

A pumping system is designed to pump water from a 6-m-deep supply reservoir to a water tower 40 m above the ground. The system consists of a pump (or a combination of pumps), a 20-m long pipeline with one elbow on the suction side of the pump, a 60-m long pipeline, a gate valve, a check valve, and two elbows on the delivery side of the pump. The system is designed to pump 420 Lsec of water 350 days a year. Select a pump (or pumps) based on the characteristics provided in Figures 1 and 2 and a pipe size for optimum economy. Assume CHw 100 for all pipe sizes listed in the following table, and all elbows are 900 (RD -2.0). Power cost is $0.04/kW-hr Motor efficiency is 85 percent for all sizes listed. Pumps Cost Motor (hp) Cost 60 200 700 95 250 800 900 300 1,020 250 340 Appurtenances Size/Cost 20 cm 25 cm 30 cm Pipe (10 m) go 120 Gate valve Check valve 105 130 Figure 1 Pump model selection chart

Solution

If the maximum discharge rate of the pumps is less than the desired discharge rate, then we have the option of using two or more pups to meet the desired discharge rate. But be sure to connect the pumps in parallel so that the discharges of the pumps add to the required discharge while the head will be the same as that of a single pump. The apparent head is 46 m. But actual head required will be more than this after including the friction head of pipes, fittings and valves. So if the final head required is also more than the head that cab be produced by a single pump or pumps in parallel, then you need to add the pump or pumps(already in parallel to inrease the discharge) in series to increase the head to the desired level.