Of practical interest is the general flatness of the efficiency map,
particularly around the BEP. This is also shown in Fig. 5, presented
for three cases of constant specific energy corresponding to tank
minimum supply level, BEP condition and tank maximum supply
level. The variation in head represents a range of static head between
approximately 0.85HBEP and 1.2HBEP. The efficiency in each
case remains considerably high even with significant decreases in
flow. Indeed, in all cases a 30% flow reduction is required to see a
10% reduction in overall efficiency, and a further 20% decrease in