Correct Answer - Option 2 : 21.25 lps
When pumps are connected in series:
Total head = Sum of heads of all the pumps connected in series.
Required Head for a given discharge =Static head + head Loss
Pump will operate only when available head ≥ total required head
S No
|
Discharge, Q in lps
|
Available head (Hm1 + Hm2 ) in m
|
Required head = 100 + in m
|
Remarks
|
1
|
15
|
111.4
|
102.25
|
Pump will work
|
2
|
18
|
112.2
|
103.24
|
Pump will work
|
3
|
20
|
110.8
|
104
|
Pump will work
|
4
|
22
|
100.8
|
104.82
|
Pump will not work
|
5
|
25
|
88
|
106.25
|
Pump will not work
|
The delivery discharge lies in between 20 to 22 lps. The exact solution can be obtained by plotting the graph between Q Vs available head and Q Vs required head, the point of intersection gives the exact delivery discharge and we may get Q = 21.25 lps.