Common Pumping Mistakes
by Jim Elsey

When you think of your pump knowledge, does the word “ninja” come to mind? Take this quiz and write down your answers. Then find out if you are a true Pump Ninja by referencing the answer key here.

1. A centrifugal pump converts mechanical energy to pressure energy (head). It works…
a) by pure phenomenal magic as the impeller sucks the fluid into the pump and then rapidly expels it in the discharge pipe.
b) because the impeller imparts a velocity to the fluid, and the casing subsequently collects and converts the velocity to pressure head.
c) because the impeller sucks the fluid from the suction side of the system and creates a pressure by utilizing Charles’s and Bernoulli’s Law of Ideal Gases and Fluids in a pressure temperature relationship (fixed volume and constant temperature).

2. If you double the operating speed of a centrifugal pump…
a) the flow rate will double (simple speed ratio).
b) the head generated will increase by a factor of 4 (speed ratio squared).
c) the BHP will increase by a factor of 8 (speed ratio cubed).
d) all of the above: a, b and c.
e) flow, head and BHP will all simply double.

3. Refer to the same pump that you doubled the speed on in the previous question: There would be no need to change the pipe sizes because the higher fluid velocity would compensate for the added friction losses.
a) True
b) False

4. NPSH is an acronym for…
a) net pump suction hysteresis
b) not pumping so hot
c) net positive suction head
d) negative pump static head

5. NPSH3 is an acronym used by pump engineers to designate…
a) that the pump will require 3 times more NPSH than others of the same size.
b) that after three years of operation, the pump will require this amount of suction energy—unless it has a dual suction impeller.
c) the point during an NPSHR test where the developed head will drop by 3 percent with the flow rate held constant.

6. You have a pump with a “flooded suction,” so there is no valid reason to calculate the NPSHA, and to do so would be a waste of time and effort.
a) True
b) False

7. Your new self-priming pump is installed at a location that is basically at sea level. Ignoring friction losses and assuming the water you wish to pump is at or below 70 F (21.1 C), how high is your theoretical maximum suction lift?
a) 2.31 feet
b) 14.7 feet
c) 33.95 feet
d) No limits

8. You are installing a new American National Standards Institute (ANSI) B73.1M pump package that is motor-driven. The motor is 20 horsepower (hp), 460 volt, 3 phase and 60 Hertz. It operates at 3,550 rpm with a service factor of 1.15. It is Insulation Class G, totally enclosed fan-cooled (TEFC) enclosure and rated for chemical duty. You are upset that the manufacturer has not installed the coupling but has instead shipped it in a separate box attached to the baseplate. You …
a) contact the manufacturer to give a piece of your mind and refuse to pay some portion of the bill.
b) quietly install the coupling—and make a promise to never purchase from this vendor again—because of consumer protection afforded by and in accordance with National Electrical Manufacturers Association (NEMA) specifications CFR 19.20-2.BS.
c) realize that the coupling was left off because you have yet to perform a phase rotation check, set the mechanical seal and perform the alignment.

9. Is it 100 percent acceptable to have some water mixed with the oil in the pump bearing housing?
a) As long as it does not exceed 5 percent and the oil viscosity index is above 110
b) As long as the housing operating temperature is above 190 F
c) As long as the water stays below 500 parts per million (5 percent)
d) As long as the oil is a high-grade synthetic with the correct International Organization for Standardization (ISO) designation
e) None of the above

10. A stainless steel (ASM rated 316-SS) pump with 150-pound ANSI flanges is perfectly acceptable to use in which application?
a) With 285 pounds per square inch gauge (psig) suction pressure because the developed differential pressure across the pump will be less than 130 psig
b) With 285 psig suction pressure because you will use raised face flanges and an HP cadmium confined gasket in accordance with ANSI B 31.4 specifications
c) With 285 psig suction pressure because the temperature of the fluid is below 70 F (21.1 C)
d) None of the above. These applications are not acceptable.

11. You can operate any variable speed industrial centrifugal pump at extremely slow speeds (less than 200 rpm) for as long as you want without any ill effects to the pump, especially if it is multistage with close clearance wear rings.
a) True
b) False

12. A typical centrifugal pump operating backward (rotation in opposite direction) will…
a) pull fluid from the discharge and pump it out the suction.
b) not pump at all and will vibrate and cavitate profusely.
c) will not make any difference at all.
d) will generate about 50 percent of its normal flow and, depending on the specific speed of the impeller, produce 45 to 65 percent of the normal head.

13. Water will boil at what temperature (F)?
a) 212
b) 100
c) 33
d) 600
e) It depends on the pressure.

14. Cavitation is defined as…
a) the introduction of cavoid solids into the stream of the pumped fluid.
b) a condition that occurs when the specific gravity of the fluid is exceeded by the vapor pressure.
c) the formation of vapor bubbles in the fluid due to a drop below its vapor pressure and the subsequent collapse of those bubbles as the fluid moves to an area of higher pressure.
d) the noise some pumps generate when operating.

15. If you cannot hear the pump cavitating, then it is not cavitating.
a) True
b) False

16. Which fluid, when subjected to cavitation conditions, will normally create the most damage in a pump (assuming all other conditions are the same)?
a) gasoline (87 octane) at 75 F
b) ethylene glycol mixed with water at 50 percent (180 F)
c) ethanol at 75 F
d) naval jet fuel JP5 at 68 F
e) water at 68 F
f) water at 300 F

17. Specific speed (Ns) is generally defined as…
a) the maximum speed (in rpm) a pump can be operated safely.
b) the speed range in a rotor dynamics analysis between first and second critical speeds.
c) the speed at which the pump vibration is predicted to exceed 1 mil displacement in a horizontal plane.
d) a calculation method (tool) and subsequent result (with no units) to define the impeller geometry and performance characteristics.

18. Which best describes suction specific speed (Nss)?
a) A concept calculation (no units in the answer) initially postulated by a guy named Igor in his kitchen with several other pump engineers over breakfast on a Saturday morning in the 1930s
b) The maximum speed in rpm that the inlet vanes (impeller) can sustain without recirculation eddies on the high pressure side of the vane
c) The tangential (or Mercator) speed of the impeller inlet vanes (assume 21-degree angle) where there is “shockless” entry of the fluid into the channels

19. Submergence is defined as…
a) the maximum operating depth of a USN 637 Class Fast Attack Submarine.
b) the minimum depth that a submersible pump will operate satisfactorily.
c) the vertical distance from the pump inlet pipe to the top of the liquid being pumped.
d) the depth of the suction tank divided by the pump inlet size (units are feet).
e) the diameter of the suction line squared and then multiplied by 4.

20. Submergence is an important parameter to the pump because…
a) if the submergence is not sufficient, the pump will cavitate.
b) if the submergence is not sufficient, the pump will ingest air by vortexing.
c) if the submergence is not sufficient, the pump will likely air bind and stall.
d) None of the above.
e) Both b and c.

21. Pump shafts have hp and speed limitations. Which of these apply?
a) As speed goes up, the torque will go down, and vice versa.
b) There is a BHP per 100 rpm limit on shafts.
c) On ANSI B73.1 M pumps, the first critical speed for the shaft is much higher than the operating speed.
d) All of the above.

22. When starting up a centrifugal pump, the suction valve should always be…
a) partially open, then opened the rest of the way a few minutes afterward.
b) fully open.
c) fully closed.
d) It doesn’t matter because it is a centrifugal pump.

23. When starting up a centrifugal pump, the discharge valve should be…
a) open.
b) closed.
c) partially open a small amount.
d) It depends. All of the above can apply or not because it depends on the pump specific speed, the system design and operating procedures.

24. If you use an expensive coupling that can withstand misalignment (per the manufacturer), you don’t need to do a time-consuming alignment process (the driver to the pump).
a) True
b) False

25. Viscosity corrections for hydraulic performance are not required or necessary on a centrifugal pump if the fluid viscosity is below 500 centipoise.
a) True
b) False

Assume a single-stage horizontal end suction centrifugal pump is operating at 1,750 rpm and the fluid is water at 65 F.
Where the pump operates on its performance curve (flow and head) is determined by which, if any, of the following?
a) Where the pump curve intersects the system curve
b) Magic, the space-time continuum and phenomenal luck
c) NPSHR divided by the NPSHA result multiplied by the square root of the induction speed
d) Submergence if in a lift situation and NPSH3 if in a flooded suction condition
e) Where the customer specified in his or her purchase order

Grab your answers and go here to find out if you are a true Pump Ninja.