Questions u3



Questions u3

Transcript of Questions u3

Page 1: Questions u3
Page 2: Questions u3

If NPSHA is too small then it can be increased by? A) Running the pump faster B) Reducing the length of the suction side C) Throttling the suction valve D) Using a priming pump

Page 3: Questions u3

Positive displacement pumps must not have their delivery

restricted because?

A) A constant volume is displaced

B) Internal losses lead to inefficient operation

C) Cavitation may occur

D) Pump delivery will be reduced

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The efficiency of a pump is not dependent on?

A) NPSHA B) Dynamic Head C) Pump Capacity D) Pump Losses

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A pump is to be used to pump fresh water at 25 degree C.

The vapour pressure of water at 25 degree C is 3kN/m2

If the atmospheric pressure is 105 kN/m2,the maximum

suction lift is 6.7m, and the pipeline losses on the suction

side are equivalent to a head of 3.2m.what will the pump

NPSH available be?

A) 1.1m

B) 0.7m

C) 0.5m

D) 0.3m

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If the NPSHA is less than the NPSHR then?

A) The pump will not draw the liquid

B) The pump will overheat

C) The pump will suffer damage

D) The pump needs to run faster

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Cavitation of the fluid in a centrifugal pump is caused by? A) Too high a speed of impeller rotation creating adverse heat . B) The vapour pressure in the suction pipe falls below the

vapour pressure of the liquid at a given temperature. C) The viscosity of the fluid is too high, the extra power

absorbed being converted into heat. D) Do not kown.

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Centrifugal pumps need priming because?

A) An excellent suction lift causes the surface of the liquid to


B) They must be started with the discharge valve open to

reduce the starting load, but this causes the pump to run


C) It is the movement of the liquid from the eye of the impeller

to the discharge that causes a low-pressure region at the

suction, if the pump is started full of air this movement of

liquid does not occur therefore no suction pressure is created. D) Don't know

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The energy transformation within a centrifugal pump is as follows?

A) Pressure is converted into kinetic energy by the impeller; this

kinetic energy is converted to an increase in velocity by the volute casing.

B) The impeller creates centrifugal force, which increases the liquid velocity, an increase in velocity means an increase in kinetic energy, the increased kinetic energy is converted into pressure by reducing the velocity in the volute casing.

C) Decreasing the velocity in the impeller decreases the kinetic energy, decreasing the kinetic energy whilst increasing the velocity of the fluid in the volute casing increases it's pressure.

D) Don't know

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Calculate the pump efficiency from following operating


Pump flow Q 0.40 cum/s

Motor power 325 kw

Suction head hs 1 meter

Discharge head hd 55 meters

Motor efficiency 88 %

Density of liquid 996 kg/cum

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A pressure gauge at the bottom of a storage tank

reads 30 psi. What is the water level in the tank?

Question 15 Question10

Page 12: Questions u3

A pump is installed at 5320 feet above sea level. The

overflow of the reservoir is at 5460 feet above sea

level. What is the discharge pressure on the pump in


Question 16 Question11

Page 13: Questions u3

A discharge pressure gauge on a pump reads 72 psi

when the pump is running. The pressure gauge at the

top of a hill 40 feet above the pump reads 45 psi.

What is the friction loss in the pipe in feet of head?

Question 16 Question12

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A double-suction centrifugal pump delivers 2000

litres of water per second against a head of 25 m

while running at 725 rmp. What type of impeller

should be used for this pump?

A six-stage centrifugal pumps delivers 0.1 m3/s

against a total head of 480 m. What is its specific

speed if it routes at 1450 rpm ? What type of impeller

would you recommended for the pump?

Question 16 Question13

Page 15: Questions u3

Explain the pump performance curve.

Question 16 Question14