Hydraulic Structures: Fourth Edition

(Amelia) #1

the new discharge is 56.23 m. This head must be supplied by the pump and
hence its output, gQH, is 9.810.31956.23176 kW.
Therefore the power inputpower output/overall efficiency
176/0.90.7280 kW.


TYPE OF PUMP


The specific speed, NsNQ1/2/H3/41450(319)1/2/(56.23)3/41261. A radial-
flow type (medium-speed) pump is recommended (Table 13.2).


LOCATION OF THE PUMP


The pump is located so that the suction pressure at the inlet is zero. The
increased friction gradient to obtain 319 l s^1 156.23/10000.156 23.
The available gravity head of 100 m is lost over a length L, beyond which
the pump supplies the required additional head. Therefore, L
100/0.156 23640 m. Hence the pump must be located at a distance of
640 m or less from the impounding reservoir inlet.


Worked Example 13.2


Two identical pumps are installed in a pumping station. One of them is
mainly used as a standby, but due to increased future flow requirements it
is proposed to bring this also into continuous operation. The following are
the pump–pipeline characteristics:


Pump characteristics:
discharge (l s^1 ) 00204060
head (m) 50 45 33 19
efficiency (%) – 65 69 40
System characteristics:
head losses (m) – 01.0 04.0 10.0


The static head is 20 m.



  1. Determine the present maximum flow.

  2. Investigate the relative suitability of arranging the two pumps in
    series and in parallel to provide the increased flow. Justify your
    choice of arrangement.


Solution


The plots of the pump–pipeline characteristic curves with one pump oper-
ating, and two pumps operating in series and in parallel, are shown in
Fig. 13.14.


WORKED EXAMPLES 569

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