Pipe Flow and Pumps
JKSSB Junior Engineer (Civil) · Fluid Mechanics and Hydraulics · 22 practice questions with answers and explanations: 16 Easy, 4 Medium, 2 Hard.
Sample questions
Sample Easy question 1
For pipes in parallel, the:
- Head loss is the same in each pipe and the discharges add
- Discharge is the same and the head losses add
- Head loss and discharge both add
- Velocity is the same in each pipe
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Answer: A. The opposite holds for pipes in series.
Sample Easy question 2
Water hammer in a pipeline is caused by:
- Laminar flow
- A change in the pipe material
- A slow change in the head
- A sudden closure of a valve
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Answer: D. The sudden stop converts kinetic energy into a pressure surge.
Sample Easy question 3
A centrifugal pump delivers liquid by:
- Pushing it with a piston
- Converting the kinetic energy given by the impeller into pressure
- Using the weight of the liquid
- Compressing the liquid
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Answer: B. The casing converts the velocity head into pressure head.
Sample Medium question 4
Water flows at 3 m/s in a small pipe and then enters a larger pipe at 1 m/s through a sudden enlargement. The head loss is:
- 0.46 m
- 0.41 m
- 0.2 m
- 0.1 m
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Answer: C. hL = (v₁ − v₂)² ÷ 2g = (3 − 1)² ÷ 19.62 = 0.204 m.
Sample Medium question 5
A pump delivers 0.02 m³/s against a head of 30 m with an overall efficiency of 70%. The input power is about:
- 5.9 kW
- 0.84 kW
- 16.8 kW
- 8.4 kW
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Answer: D. P = ρgQH ÷ η = 1,000 × 9.81 × 0.02 × 30 ÷ 0.7 = 8,409 W.
Sample Medium question 6
The rise in pressure on a sudden and complete closure of a valve in a pipe where the pressure wave speed is 1,000 m/s and the water velocity is 2 m/s is:
- 0.02 MPa
- 2 MPa
- 20 MPa
- 0.2 MPa
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Answer: B. Δp = ρ c v = 1,000 × 1,000 × 2 = 2 × 10⁶ Pa.
Sample Hard question 7
The available NPSH for a pump with atmospheric head 10.33 m, vapour pressure head 0.24 m, suction lift 3.0 m and friction loss 0.5 m in the suction pipe is:
- 10.33 m
- 7.07 m
- 6.59 m
- 13.59 m
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Answer: C. NPSHa = H_atm − H_vap − h_s − h_f = 10.33 − 0.24 − 3.0 − 0.5 = 6.59 m.
Sample Hard question 8
For water (ρ = 1,000 kg/m³, μ = 0.001 Pa·s) flowing at 0.5 m/s in a 0.04 m pipe, the Reynolds number is:
- 2,000
- 20,000
- 500
- 200,000
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Answer: B. Re = ρvD ÷ μ = 1,000 × 0.5 × 0.04 ÷ 0.001 = 20,000, so the flow is turbulent.