Pump Theory

Question 1

What is cavitation?

Answer 1

The formation and subsequent collapse of vapor bubbles.

Question 2

What are indications of gas binding?

Answer 2

Increased noise level.
Wildly fluctuating pump discharge pressure.
.

Question 3

A centrifugal pump is taking suction from the bottom of an open storage tank containing water at 70deg. Determine the net positive head available to the pump:
NPSH=(P atm + P tank+(P head or - P lift))- P sat.
-Atmospheric pressure supplies 33.0 feet of suction head.
-Tank water height = 5 feet.
-Suction lift (from bottom of tank) = 15 feet.
-P sat70deg = 0.36334psia, or 0.84ft.

Answer 3

NPSH = (P atm + P tank - P lift) - P sat.
=(33.9 + 5 - 15) - .84.
= 23.9 - .84.
= 23.06 (or 23ft).

Question 4

The available net positive suction head for a pump may be expressed as?
A. Discharge pressure minus saturation pressure of the fluid being pumped.
B. Discharge pressure minus suction pressure.
C. Suction pressure minus saturation pressure of the fluid being pumped.
D. Suction pressure plus discharge pressure.

Answer 4

C. Suction pressure minus saturation pressure of the fluid being pumped.

Question 5

A centrifugal fire water pump is operating to pressurize a fire main. The pump takes suction from a water reservoir. A fire hose connected fire main is being used to suppress an elevated fire.
Given:
- the eye of the pump impeller is located 5 feed above the reservoir water level.
- the pump has a design shutoff head of 120 feet.
- the required net positive suction head for the pump is 15 feet.
-the reservoir water temp is 60 Deg F.

At which one of the following elevations above the eye of the pump impeller will the fire hose spray nozzle first be unable to provide flow? (Disregard all sources of head loss).

A. 111 feet.
B. 116 feet.
C. 121 feet.
D. 126 feet.

Answer 5

B 116 feet.

Question 6

Which one of the following contains indications of cavitation for an operating centrifugal pump?
A. Low flow rate with low discharge pressure.
B. Low flow rate with high discharge pressure.
C high motor amps with low discharge pressure.
D. High motor amps with high discharge pressure.

Answer 6

A. Low flow rate with low discharge pressure.

Question 7

What is dead heading?

Answer 7

Occurs when pump operated with no flow. Close discharge valve or sealed check valve ( insufficient recirculation flow).

Question 8

What is runout?

Answer 8

Pump i experiencing maximum flow that may exceed the design of the prime mover. System breech or failed throttle valve.

Question 9

Shutting the discharge valve on an operating centrifugal pump will cause the motor amps to \_\_\_\_\_\_\_\_\_\_\_ and the pump discharge pressure to\_\_\_\_\_\_\_\_\_\_\_\_\_.
A. decrease; increase.
B. Decrease; decrease.
C. Increase; increase.
D. Increase; decrease.

Answer 9

A. Decrease; increase.

Question 10

A constant-speed centrifugal pump motor draws the most current when the pump is….

A. At maximum rated flow conditions.
B. Operating at runout flow.
C. Accelerating to normal speed during start.
D. At shutoff head with no recirculation flow.

Answer 10

C. Accelerating to normal speed during start.

Question 11

A positive displacement pump should be started with its suction valve\_\_\_\_\_\_\_\_\_\_\_\_\_and its discharge valve\_\_\_\_\_\_\_\_\_\_\_.
A. Fully open; throttled.
B. Throttled; throttled.
C. Fully open; fully open.
D Throttled; fully open.

Answer 11

C fully open; fully open.

Question 12

Which one of the following discribes the proper location for a relief valve that will be used to prevent exceeding the design pressure of a positive displacement pump and associated piping?

A. On the pump suction piping upstream of the suction isolation valve.
B. On the pump suction piping downstream of the suction isolation valve.
C. On the pump discharge piping upstream of the discharge isolation valve.
D. On the pump discharge piping downstream of the discharge isolation valve.

Answer 12

C. On the pump discharge piping upstream of the discharge isolation valve.

Question 13

An ideal positive-displacement pump is pumping to a abatement operating at 100psig. Assume pump speed is constant. There is zero pump slip, and pump back pressure remains within normal pump operating limits.

If system pressure increases to 200 psig, the pump head will__________and pump flow rate will___________.

A. Increase; remain the same.
B. Increase; decrease.
C. Remain the same; remain the same.
D. Remain the same; decrease.

Answer 13

A. Increase; remain the same.