Question 16.18: Water is to be pumped out of a deep well under total head 20......

Given: N = 1000 rpm, Q = 0.15 m³/s, N_{s} = 20 and Total head = 208 m
According to Eq. (16.20) of specific speed, we have

N_{s}={\frac{N{\sqrt{Q}}}{H^{3/4}}}     (16.20)

or              H_{m}={\frac{1000{\sqrt{0.15}}}{20^{3/4}}}

Thus,                 H_{m}=52~\mathrm{m}

Now,    {\mathrm{Number~of~pumps~required}}={\frac{Total \ head}{H_{m}}}

or              \mathrm{No}.\,\mathrm{of}\,\,\mathrm{pumps}={\frac{208}{52}}=4