What will be the discharge of a single-acting pump if it has one cylinder of area 0.5 m² and stroke of length 20 cm and if the pump has 180 rpm of speed?
- A0.2 m³/s
- B0.3 m³/sCorrect
- C0.1 m³/s
- D0.25 m³/s
Solution
Concept
A single-acting reciprocating pump delivers one swept volume (A × L) per revolution.
Formula
Qth = A × L × N / 60
Step-by-step solution
1. Given: A = 0.5 m², L = 20 cm = 0.2 m, N = 180 rpm. 2. Volume per stroke = A × L = 0.5 × 0.2 = 0.1 m³. 3. Single-acting pump: one delivery per revolution. 4. Q = A × L × N / 60 = 0.1 × 180 / 60. 5. Q = 0.3 m³/s.
Explanation
In a single-acting pump, water is delivered only once in each revolution. So discharge = swept volume × revolutions per second. 0.1 m³ × 3 rev/s = 0.3 m³/s.
Why the other options are wrong
A (0.2) and D (0.25) do not match the calculation. C (0.1) is the volume per stroke only, not the discharge per second.
Shortcut
180 rpm = 3 rev/s, so Q = 0.5 × 0.2 × 3 = 0.3 m³/s.
Common mistake
Forgetting to convert the stroke from cm to m, or forgetting to divide rpm by 60.
Correct answer: B) 0.3 m³/s