- 2072 Kartik · 8 marks
Is balancing tank necessary: 20000 L/day spring
Short answer
Daily demand 20 m3, spring yield 21.6 m3/day. Peak demand exceeds inflow, so tank needed. Capacity by mass curve method is 9.0 m3 (adopt 10 m3).
A village has design year demand of water 20000 liters per day. The demand is met by a continuous system of supply from a spring source with measured yield of 0.25 lps. The consumption pattern is as follows:
| Time (Hours) | 5-7 | 7-12 | 12-17 | 17-19 | 19-5 |
|---|---|---|---|---|---|
| Consumption (%) | 25 | 35 | 20 | 20 | 0 |
Is balancing storage tank necessary? Calculate its capacity if necessary. Justify your answer.
Given data
- Daily demand = 20,000 L = 20 m³/day
- Spring yield = 0.25 lps = 21,600 L/day = 21.6 m³/day = 0.9 m³/h
- Demand: 5–7 h 25%, 7–12 h 35%, 12–17 h 20%, 17–19 h 20%, 19–5 h 0%
Check of source and need of storage
The yield (21.6 m³/day) exceeds the demand (20 m³/day), so the source is adequate. The demand rate in 5–7 h is 2.5 m³/h and in 7–12 h it is 1.4 m³/h, which are greater than the inflow rate 0.9 m³/h. The balancing tank is therefore necessary.
Mass-curve table (analytical method)
Inflow: 0.9 m³/h (spring yield). Time is counted from the start of the first demand period; a positive cumulative value means surplus in the tank.
| Time | Demand (m³) | Inflow (m³) | Inflow − demand | Cumulative |
|---|---|---|---|---|
| 05:00–07:00 | 5.00 | 1.80 | -3.20 | -3.20 |
| 07:00–12:00 | 7.00 | 4.50 | -2.50 | -5.70 |
| 12:00–17:00 | 4.00 | 4.50 | +0.50 | -5.20 |
| 17:00–19:00 | 4.00 | 1.80 | -2.20 | -7.40 |
| 19:00–05:00 | 0.00 | 9.00 | +9.00 | +1.60 |
Total demand = 20.00 m³; total inflow = 21.60 m³.
Capacity
- Maximum cumulative surplus = 1.60 m³
- Maximum cumulative deficit = 7.40 m³
- Balancing capacity = max. surplus + max. deficit = 1.60 + 7.40 = 9.00 m³
- Because the inflow in a day (21.60 m³) is more than the demand, the extra water simply overflows once the tank is full. The minimum storage that still meets every demand is the largest draw-down, 7.40 m³. The textbook value 9.00 m³ is on the safe side.
Answer: Balancing tank is necessary because peak demand exceeds the continuous inflow; capacity ≈ 9 m³ (adopt 10 m³).
✓ Answer checked by Claude Opus 5.5 (high effort)
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