Discharge pressure and flow measurements were recorded at a city’s high-lift station under a variety of pumping conditions at different system demands and varying water levels in the elevated storage tank. Based on these measurements, the system head-discharge curves were defined as follows:
|
| System Heads at Different Water Levels in Elevated Storage | ||
System Discharge (I/s) | Low (m) | Mid Height (m) | Full (m) | |
Consumption | ||||
(Static pressure) | 0 | 30 | 35 | 40 |
Winter average | 140 | 37 | 42 | 47 |
Annual average | 180 | 40 | 45 | 50 |
Summer average | 225 | 45 | 50 | 55 |
Maximum day | 270 | 50 | 55 | 60 |
Maximum day and fire flow | 350 | 60 | 65 | 70 |
The pumping station has a total of six constant-speed pumps. Numbers l , 2, and 3 are identical with a best efficiency point (bep) at 100 l/s and 45 m; 60 percent bep is 60 l/s and 60 m; and 120 percent bep is 120 l/s and 30 m. Numbers 4, 5, and 6 are identical with a bep at 150 l/s and 60 m; 60 percent bep is 90 l/s and 80 m; and 120 percent bep is 180 l/s and 35 m. Draw the pump head-discharge curves for the following combinations of pumps operating in parallel: pump l alone; pumps l and 2; pumps l , 2, and 3; pump 4 alone; pumps 1 and 4; pumps 4 and 5; and pumps 4, 5, and 6. Draw the system head-discharge curves on the same graph.
What pumps would normally be operated during days when the consumption is at
(a) winter average,
(b) annual average,
(c) summer average, and
(d) the maximum day?
Assume that the volume of the storage tank is adequate to equalize the pumping rate on the maximum day with reserve storage for fire demand, is the pumping capacity of the station adequate?
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