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4th Year Millwright > Dynamic Pumps > Flashcards

Dynamic Pumps Flashcards

1
Q

What are dynamic pumps also known as?

A

continuous flow, kinetic, centrifugal, or non-positive displacement

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2
Q

What is the term used in regards to the ratio of the density of a substance to that of water?

A

specific gravity

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3
Q

What is the conversion from psi to kPa?

A

1 psi = 6.9 kPa

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4
Q

What is the formula used to determine pressure?

A

pressure = force/area

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5
Q

What is atmospheric pressure at sea level in psi?

A

14.7 psia (0 psig)

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6
Q

How much atmospheric pressure is lost for every 1000 ft of elevation gained?

A

about .5 psi

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7
Q

What is the head pressure of one foot head of water in psi?

A

0.433 psi

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8
Q

How much does a cubic foot of water weigh?

A

62.4 lbs

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9
Q

What is the difference between the discharge pressure and the suction pressure of a pump called?

A

differential pressure

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10
Q

What is the name for the pressure at which a liquid flashes into a vapour (boils) at a given temperature?

A

vapour pressure or boiling point

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11
Q

What two components is the total head (total energy) in a system made up of?

A

head pressure (from the pressure acting upon the liquid) and velocity head (from the speed of the liquid)

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12
Q

What is the condition called where the supply reservoir is located below the pump?

A

suction lift

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13
Q

What is the vertical distance from the centre of the suction eye of the pump to the surface of the supply called?

A

static suction head

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14
Q

How can Net Positive Suction Head available (NPSHA) be expressed?

A

NPSHA = suction pressure (gauge) + atmospheric pressure - vapour pressure

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15
Q

What is needed for a pump to overcome friction losses and increase the velocity of a fluid as per the pump manufacturer?

A

Net Positive Suction Head Required (NPSHR)

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16
Q

How much greater should the NPSHA be than the NPSHR to prevent cavitation?

A

at least 10%

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17
Q

What are the 4 categories of dynamic pumps?

A

radial-flow centrifugal, axial-flow centrifugal, mixed flow, peripheral

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18
Q

Which type of dynamic pump is most common in industry?

A

radial-flow centrifugal

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19
Q

What is another name for an axial-flow pump? What are the pressure/flow properties of this type of pump?

A

propeller pump, relatively low discharge head, large flow

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20
Q

What are the two types of peripheral pumps?

A

high-speed, regenerative turbine

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21
Q

Which type of pump has a bulbous, concentric casing with a close axial clearance between it and the impeller? This pump is also “self-priming”

A

regenerative turbine pump

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22
Q

What are the 3 impeller designs available in a horizontal single-stage end suction pump?

A

open, semi-open, enclosed

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23
Q

What type of pump mounting is recommended for high temperature liquids?

A

centreline or pedestal mounted

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24
Q

What type of shaft is used on a vertical column pit pump in abrasive service and why?

A

A cantilever shaft is used, which keeps the bearings out of the abrasive liquid.

25
Q

What is a main advantage of using a wet pit?

A

The pump can be installed at a lower level increasing the NPHSA.

26
Q

What is the advantage to a vertical single-stage end suction pump compared to a horizontal one?

A

It can be incorporated with the piping and in turn saves floor space.

27
Q

What is a key characteristic in a single-stage double suction pump in regards to axial loads?

A

The double suction design results in opposing forces which balance out axial loads.

28
Q

What happens to the pressure of a liquid in a multi-stage pump as it passes through the pump?

A

The pressure of the liquid increases progressively as it moves from one end of the pump to the other.

29
Q

What prevents back pressure leakage in a multi-stage pump?

A

a diaphragm or stage piece

30
Q

Which pump handles the highest pressures in the dynamic pump family (up to 6500 psi)?

A

multi-stage barrel pumps

31
Q

What can occur if liquid vaporizes in a closed system?

A

cavitation

32
Q

What pump characteristic does flow vary directly with?

A

impeller diameter

33
Q

Where is the stripper in a regenerative turbine pump located?

A

between the suction and the discharge

34
Q

What pump characteristic does the head produced vary with?

A

the square of the impeller diameter

35
Q

What is the name for a shock wave from a sudden change in velocity in a pipe? What can cause this condition?

A

water hammer, can be caused by opening/closing valves, or starting/stopping a pump

36
Q

What are some methods of counter-acting axial forces in a centrifugal pump?

A

balancing disc/drum or combination, pump out vanes, balance holes, thrust bearings

37
Q

What impeller style would be best suited to handle fibrous slurries and abrasives?

A

semi-open

38
Q

What are some possible causes of cavitation in a centrifugal pump?

A

a block or restriction in the suction, too much suction lift, high temperatures, high liquid viscosity

39
Q

What is the purpose of a diffuser in a pump?

A

convert velocity to pressure, reduce radial bearing loads, direct flow (some multi-stage pumps)

40
Q

What is the purpose of the volute casing?

A

to convert velocity energy into pressure energy of head

41
Q

What are the 2 main types of pump shaft sealing devices?

A

mechanical seals, compression packing

42
Q

How would an increase in wear ring clearance affect pump efficiency? At what point should wear rings be replaced?

A

it would reduce pump efficiency, wear rings should be replaced when clearance reaches 3 times original amount

43
Q

What is the energy in a system due to the liquid’s velocity known as?

A

velocity head

44
Q

What is used to direct more flow to the pump impeller and help reduce the NPSHR?

A

inducer

45
Q

Name 4 single stage end suction pump casing types

A

concentric, double volute, volute, diffuser

46
Q

What is a “thrust pot”?

A

a bearing housing that helps support weight and thrust

47
Q

What will happen when pressure exceeds the rated capacity of a centrifugal pump?

A

the impeller will slip in the liquid

48
Q

How do you check for classic cavitation in a centrifugal pump?

A

throttle the discharge line

49
Q

Where is the velocity of fluid flow greatest within the centrifugal pump?

A

near the tips of the impellers

50
Q

Why is the double eye impeller not recommended for abrasive service?

A

because it requires 2 stuffing boxes

51
Q

What is the most efficient impeller style?

A

the Francis vane impeller

52
Q

How much is it possible to reduce the impeller of a volute pump before it affects pump efficiency? What about the impeller of a diffuser pump?

A

20% in a volute pump, 5-10% in a diffuser pump (depending on design)

53
Q

What can happen to a pump if an object is stuck in the foot valve?

A

the pump won’t prime

54
Q

What’s the minimum amount of straight pipe that should be between the elbow and the pump suction to prevent swirl or uneven flow?

A

10 diameters of straight pipe

55
Q

What is considered the max shaft runout or radial movement (respectively) allowable in a dynamic pump?

A

0.003” (for either one)

56
Q

Where are balance holes drilled through?

A

the rear shroud on the inside of the wear ring

57
Q

Another name for a high speed impeller is:

A

paddlewheel impeller

58
Q

How many suction inlet nozzles are there in a double suction single-stage pump?

A

one

59
Q

What condition can occur when a check valve closes too quickly?

A

hydraulic slap

4th Year Millwright (11 decks)

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