BME Hydraulic Machines 5

Question 1

Priming a centrifugal pump is required because:

Accepted Answer

The pump cannot develop sufficient pressure to expel air and start flow unaided

Answer

Centrifugal pumps cannot self-prime because air is much less dense than liquid; the pressure developed by spinning air is insufficient to overcome the static head and initiate liquid flow.

Question 2

The runaway speed of a hydraulic turbine is the speed at:

Accepted Answer

Which the turbine operates if the load is suddenly disconnected with full flow maintained

Answer

Runaway speed is the maximum overspeed reached when the external load is lost but flow continues; turbine design must ensure structural integrity at this speed.

Question 3

In series pump operation, compared to a single pump:

Accepted Answer

The total head is increased while flow rate remains approximately the same

Answer

Pumps in series add their heads at the same flow rate, making this configuration suitable for high-head, moderate-flow applications.

Question 4

The pressure coefficient (ψ) in pump similarity analysis is defined as:

Accepted Answer

ψ = gH / (N²D²)

Answer

The head (pressure) coefficient ψ = gH/(N²D²) is a dimensionless group relating the developed head to the square of tip speed, used in pump similarity and scaling.

Question 5

A centrifugal pump operating far to the right of its Best Efficiency Point (BEP) will likely experience:

Accepted Answer

Recirculation at the impeller inlet and cavitation

Answer

At flows much higher than BEP, NPSHA may become insufficient relative to the elevated NPSHR, causing cavitation; inlet recirculation also develops at very high flows.

BME - Bachelor of Mechanical Engineering Practice Test

BME - Bachelor of Mechanical Engineering Practice Test

BME Hydraulic Machines 5