- 2079 Bhadra · 8 marks
Balancing tank: village 80000 L/day, spring 0.8 lps
Short answer
Daily demand 80 m3, spring yield 69.12 m3/day (deficit). Assuming inflow = demand/24 = 3.33 m3/h, peak rates exceed inflow. Balancing capacity by mass curve = 29.33 m3 (adopt 30 m3).
A village has a design year demand of 80000 liter per day. This demand is to meet by continuous system of supply from a spring source with safe yield 0.8 lps. The consumption pattern is as follows:
| Time: hour | Consumption % |
|---|---|
| 5.00 - 7.00 | 20 |
| 7.00 - 12.00 | 30 |
| 12.00 - 17.00 | 20 |
| 17.00 - 19.00 | 25 |
| 19.00 - 5.00 | 5 |
Is a balancing storage tank necessary? Calculate its capacity if necessary.
Given data
- Daily demand = 80,000 L = 80 m³/day
- Spring safe yield = 0.8 lps = 0.8 × 86,400 = 69,120 L/day = 69.12 m³/day (2.88 m³/h)
- Demand: 5–7 h 20%, 7–12 h 30%, 12–17 h 20%, 17–19 h 25%, 19–5 h 5%
Check of source and need of storage
The yield (69.12 m³/day) is less than the demand (80 m³/day), a shortage of 10.88 m³/day (13.6%). A storage tank cannot remove this shortage; another source or a reduced demand is needed. To balance the hourly variation, the inflow is taken equal to the demand (80/24 = 3.33 m³/h). The demand rate is 8 m³/h in 5–7 h, 4.8 m³/h in 7–12 h and 10 m³/h in 17–19 h, all more than the inflow, so a balancing tank is necessary.
Mass-curve table (analytical method)
Inflow: 3.33 m³/h (daily demand spread over 24 h). 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 | 16.00 | 6.67 | -9.33 | -9.33 |
| 07:00–12:00 | 24.00 | 16.67 | -7.33 | -16.67 |
| 12:00–17:00 | 16.00 | 16.67 | +0.67 | -16.00 |
| 17:00–19:00 | 20.00 | 6.67 | -13.33 | -29.33 |
| 19:00–05:00 | 4.00 | 33.33 | +29.33 | 0.00 |
Total demand = 80.00 m³; total inflow = 80.00 m³.
Capacity
- Maximum cumulative surplus = 0.00 m³
- Maximum cumulative deficit = 29.33 m³
- Balancing capacity = max. surplus + max. deficit = 0.00 + 29.33 = 29.33 m³
Answer: A balancing tank is necessary; capacity ≈ 29.3 m³ (adopt 30 m³), provided the source shortage of 10.9 m³/day is made up.
✓ Answer checked by Claude Opus 5.5 (high effort)
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