Use the data given in Problem 12.18 and plot the dimensionless coefficients \(C_{H}, C_{\mathscr{P}}, \eta\) versus \(C_{Q}\) for this pump. Calculate a meaningful value of specific speed, discuss its usefulness, and compare the result with data of Fig. 12.18.

Fig. 12.18

Problem 12.18

The centrifugal pump shown in Fig. P12.18 is not selfpriming. That is, if the water is drained from the pump and pipe as shown in Fig. P12.18(a), the pump will not draw the water into the pump and start pumping when the pump is turned on. However, if the pump is primed [i.e., filled with water as in Fig. P12.18(b)], the pump does start pumping water when turned on. Explain this behavior.

Figure P12.18

0.2 Hub1 0.3- Vanes Hub Radial flow 0.4- -0 0.5- 0.6- 0.7 0.8 500 600- 700- 800- 900- 1000 shrouds -Impeller 1500- -Impeller shrouds 2000- Specific speed, Nsd 3000 Hub Hub Vanes Vanes Vanes Vanes Mixed flow Specific speed, N, 2.0- 3.0- 4000 shrouds -Impeller- Axial flow 4.0- 5000- 6000- 7000- 8000- 9000- 10000- -Impeller hub Axis of rotation 50 5.0- 6.0- 7.0- 8.0 15000- 20000