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Millwright 3rd Block Harmonized 2022 > Dynamic pumps > Flashcards

Dynamic pumps Flashcards

1
Q

What is specific gravity?

A

It is the ratio of the density compared to cool water. SG of water is 1. Less than 1 is lighter than water and more than 1 is heavier than water.

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2
Q

What is the conversion of psi to kpa?

A

1 psi = 6.9 kpa

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3
Q

What is the formula to determine pressure?

A

Pressure=force / area

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4
Q

What is atmospheric pressure?

A

14.7 psia

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5
Q

How much pressure is lost with elevation gain?

A

Approx 1/2 psi per 1000 feet gain

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6
Q

What is head pressure?

A

It is the height, in feet, of a column of water that is one foot square at the base

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7
Q

What does water weigh?

A

62.4 lbs/cubic foot

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8
Q

How much pressure is on One cubic foot of headwater?

A

.433 psi

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9
Q

What is differential pressure?

A

It is the difference between the discharge pressure and the suction pressure

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10
Q

What is vapour pressure?

A

It is the pressure at which a liquid flashes into a vapour at a given temperature

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11
Q

When the Pressure increases what happens to the boiling point?

A

The boiling point also increases

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12
Q

What are some causes of turbulent flow

A

Bends, abrupt changes in cross-section, fittings in the pipe, velocity that is too high

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13
Q

In Bernoulli’s principle, what are the two types of energy that make up total head?

A

Head pressure, velocity head

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14
Q

What is the difference between static head, and dynamic(or total) head

A

Static is the distance, and dynamic is the distance plus all the energy needed to move the fluid

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15
Q

What is net positive suction head?

A

It is a measure of head at the pump suction. It is commonly referred to as npsha or net positive suction head available

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16
Q

How is net positive section head required determined?

A

It is done by the pump manufacturers testing

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17
Q

The npsha should be at least how much more than npshr?

A

10% higher

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18
Q

What is another name for radial pumps?

A

Centrifugal pump

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19
Q

What creates the kinetic(speed,velocity) energy?

A

The impeller

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20
Q

Describe an axial pump

A

There is no change in the direction of flow. It is also known as a propellor pump. They produce low discharge head, but large volume of flow.

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21
Q

Describe a radial (centrifugal) pump.

A

Discharge is perpendicular to the intake, has reasonably high discharge head.

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22
Q

What is the only pump that has straight blades?

A

High speed peripheral pumps. They can reach 25,000 rpm and head capabilities of 12,000 feet

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23
Q

Where would you find a stripper?

A

They are in a regenerative turbine pump, Inbetween the suction and discharge ports

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24
Q

What is the most common centrifugal pump?

A

Single stage, end suction pump.

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25
Q

What is the benefit of the vertical single stage end suction pump?

A

It saves space because pump can be incorporated in the piping

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26
Q

What is benefit of a single stage double suction pump?

A

It has a single suction inlet that then splits to allow flow to both sides. The opposing forces on either side cancel each other out, so it limits axial thrust.

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27
Q

What pump handles the most amount of pressure?

A

Multi stage barrel pumps. Handles pressures up to 6500 psi and 20,000 gpm. It has a double casing

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28
Q

What are the three types of impellers?

A

Open, semi open, closed

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29
Q

What are the shaped lines running from the center outward on the back side of the impeller?

A

Pump out vanes

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30
Q

What is a drawback of the open impeller?

A

The vanes are weak and bend easily.

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31
Q

Where are the fixed bearings normally located?

A

Typically on the coupling end

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32
Q

What is the big benefit of a double suction impeller?

A

Because of the two suction intakes, it is hydraulically balanced, and has minimal axial thrust. Because it requires two stuffing boxes, it is not recommended for abrasive service.

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33
Q

What is considered the most efficient impeller design?

A

The Francis impeller. It has double curved vanes.

34
Q

Describe an axial flow impeller.

A

Also known as a propeller. It moves the liquid parallel with the shaft. These move large quantities of liquid at low head

35
Q

What are the four types of pump casings?

A

Volute, double volute, concentric, diffuser

36
Q

In a volute casing how much can you vary the capacity?

A

The impeller can be trimmed by 20%

37
Q

Describe a diffuser casing

A

It has a series of stationary curved beans with each space between the two vanes gradually expanding to slow the liquid down. This converts velocity head into pressure head and there is no radial thrust. The impeller can only be trimmed 5 to 10%

38
Q

When should wear rings be replaced?

A

When they reach three times the initial clearance

39
Q

Where would you find renewable sleeves on the shaft?

A

On medium and large pumps

40
Q

What is the most common driver for centrifugal pumps

A

Electric motors

41
Q

What is the difference between a dual drive or tandem drive pumps

A

Dual drives that have one of two drivers operating at one time, and tandem drives have two drives operating simultaneously

42
Q

What position should gate valves be in?

A

Valves should be only fully open or fully closed and never used for throttling

43
Q

How big should a inverted suction strainer be?

A

Ideally they are four times the surface area of the pipes ID

44
Q

What is another name for the inverted cone suction strainer

A

Witches hat

45
Q

What is the purpose of an expansion joint

A

They help eliminate pipe strain on the pump flanges due to thermal growth or misalignment

46
Q

What are some common problems that could result in low flow?

A

Blockage, pump needs to be primed, air leaks, motor turning the wrong rotation, insufficient NPSHA, worn parts, inadequate foot valve size

47
Q

How should an elbow be in relation to the straight piping on the suction side?

A

A minimum of 10X the pipe diameter of straight pipe between the elbow and the pump suction to avoid swirl or uneven flow

48
Q

What is a simple test to check for cavitation?

A

Throttle the discharge valve.

49
Q

What does increasing the impeller eye size do?

A

Increases the capacity, or GPM

50
Q

What does increasing the OD of the impeller do?

A

It increases the pressure, and to a smaller extent the capacity.

51
Q

What is water hammer? How can you help control it?

A

Opening, or closing a valve too quickly cause a shock wave to travel up and down a pipe. A long stem gate valve will take a long time to close and slow down how fast the flow is stopped

52
Q

What is hydraulic slap?

A

When a pump stops with the discharge valve left open. The pressure difference between the suction head discharge head quickly closes the check valve creating the slap

53
Q

How big should the foundation be relative to the pump?

A

It should be 2.5 times the mass of the pump

54
Q

What are some causes of excessive power consumption?

A 
Tight packing
Tight mechanical seals
High viscosity, or specific gravity
Bent shaft
Wrong rotation
Faulty motor windings
excessive flow
55
Q

How much should compression pickings leak, as a rule of thumb?

A

40 drops per minute

56
Q

If performance gradually decreases, what is likely the problem.

A

Component wear. An abrupt failure could be something broke, plugged, or a valve accidentally closed

57
Q

How can a suction or discharge line be isolated, before maintenance is performed?

A

By using blinds (pancake or spectacle). Never trust a valve

58
Q

Where should readings take place to determine wear?

A

Shaft radial runout
Shaft radial movement
Stuffing box squareness
Shaft axial movement

As a rule of thumb, none of these should be more than .003”

59
Q

What should never be used to loosen a stuck impeller?

A

Heat

60
Q

What does NPSH stand for?

A

Net positive suction head. It can either be
a for available or
r for required. NPSHa must be higher than NPSHr

61
Q

Describe NPSH

A

The amount of energy in the liquid, measured at the suction eye center line

62
Q

Describe total static head

A

The vertical distance from supply liquid level, to liquid discharge level

63
Q

What are inducers used for?

A

High speed pumps. It feeds flow into the eye of impeller

64
Q

Name two styles of peripheral pumps

A

High speed and regenerative

65
Q

Name for single stage end suction pump casing types

A

Volute
Double volute
Concentric - produces the highest radial load
Diffuser- no radial loading

66
Q

When should wear rings be replaced?

A

When the clearances reach three times the minimum clearance

67
Q

What is a thrust pot?

A

It is an extra bearing housing usually used in turbines to support the shaft

68
Q

Where is suction lift or section head measured from?

A

From the fluid surfaces to the centreline of the pump

69
Q

.Between balance disc, drums, combination disk and drum which is the simplest?

A

The balance drum

70
Q

Which balancing device uses an intermediate relief chamber?

A

The combination disk and drum

71
Q

How can the flow be changed on some reciprocating plunger pumps?

A

Either the stroke or the speed can be changed

72
Q

Name some benefits of a diaphragm pump?

A

They are self priming, they can be used to vary output through metering, there is no contamination because it’s self contained and they can be run dry

73
Q

Does the diaphragm pump require a relief valve?

A

Yes unless it indicated that it is only run at shop air pressure

74
Q

Can a plunger pump be double acting?

A

No

75
Q

How many pumping chambers does a triplex pump have?

A

3

76
Q

What kind of positive displacement pump has a rotor and elastomeric stator?

A

Progressive cavity

77
Q

If you have a double-acting duplex pump how many times will fluid be delivered per revolution?

A

4

78
Q

Two pumps can be referred to as peristaltic what are they?

A

The progressive cavity, and flexible tube

79
Q

If a pump has suction lift what is used to help prime the pump?

A

Foot valve

80
Q

When discharge pressure exceeds air pressure on the air powered diaphragm pump, what happens?

A

It stops

Millwright 3rd Block Harmonized 2022 (26 decks)

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