Water Storage, Tanks and Pumps: Capacity, Suction and Controls
What this domain tests
Storage and pumping questions cover tank types, capacity calculation, pump selection, suction arrangements and controls. Expect questions on overhead and underground tanks, foot valves, non-return valves and dry-run protection.
Core rules and concepts
- Overhead tanks (OHT) supply fixtures by gravity; underground tanks (UGT) store water before pumping.
- Common tank materials: polyethylene, RCC, GI and stainless steel. Tanks need a tight lid, mosquito-proof vent, overflow and cleaning access.
- Domestic demand is often taken as 135 litres per person per day; add fire, garden and commercial demand where required.
- Pump types include centrifugal, submersible, jet and booster pumps. A submersible pump sits in the water; a centrifugal pump needs priming.
- Fit a foot valve on the suction line, a non-return valve on the delivery, and a pressure switch or level controller.
- Protect against dry running, which overheats the pump.
Worked example
A building has 20 residents at 135 litres per person per day. Demand = 20 × 135 = 2700 litres. For one day of storage, choose a 3000-litre tank. If the pump delivers 30 L/min, filling time = 3000 ÷ 30 = 100 minutes. The reasoning: capacity must cover demand, and pump flow sets the refill time. Check that the suction lift is within the pump curve.
Traps that cost marks
- Sizing a tank below daily demand.
- Omitting an overflow or mosquito-proof vent.
- Running a centrifugal pump without priming.
- Forgetting the foot valve or non-return valve.
- Ignoring dry-run protection and burning out the pump.