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Flashcards in Test Review Deck (73)
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1

Main functions of a bearing are to...

-Reduce wear
-Absorb and dissipate heat
-Guide and aid moving parts

2

Three types of loads are...

-Thrust or axial
-Radial
-Combination

3

The main bearings in a turbine generator are what type?

Plain bearings

4

In a rolling element bearing, what is the cage used for?

Keeps elements precisely aligned and in position

5

When multiplying the shaft diameter times the rpm, the result represents the...

speed limitations of the bearings

6

What is the function of the bearing housing?

Protection and alignment

7

When handling new small bearings, the first step after removing from the package should be...

Clean with solvent, wipe dry, and lubricate with proper oil or grease

8

What is one method that guarantees no movement between the bearing and shaft?

Press fit

9

A bearing should not be heated above 250* because...

the bearing will lose the temper (hardness)

10

What are two methods to heat a bearing?

Induction heater and electric oven

11

Why is lubrication necessary?

Heat transfer and reduces friction

12

What determines condition of a bearing?

Temperature, proper lubrication, changes in noise and vibration, and condition of bearing seals

13

True or false:
In a stuffing box, the cooling liquid is injected into the lantern ring to cool and lubricate packing and seals.

True

14

Pumps connected to their driver with a coupling is said to be ______.

Direct-coupled

15

True or false:
Radial bearings support axial loads.

False
Thrust bearings support axial loads. Journal bearings support radial loads.

16

When small pieces of metal flake off a bearing, it is a clear sign of ______.

Spalling

17

Blade angle adjustment on a Kaplan turbine is controlled by ______.

A servomotor

18

A common mechanical reason for excess vibration is ______.

A clogged or broken impeller

19

A pumps delivery rate can be changed by varying a pumps displacement or ______.

The speed of the drive shaft rotation

20

The propeller turbine develops its power almost entirely from ______.

The weight of the water

21

What are the mechanical devices that convert water power potential into usable power?

Hydraulic turbines

22

True or false:
To control runaway speeds in case of load rejection on an impulse wheel, deflector plates and tilting nozzles are used.

True

23

Cavitation occurs in any point in a hydraulic system where...

A reduction of pressure causes water vapor to form

24

The size of the jet of water on the discharge line of an impulse wheel is usually controlled by ______.

Needle valves

25

On an umbrella turbine unit, where are the thrust collar and runners located?

Under the rotor

26

The principle factor in the selection of a turbine is the ______.

Operating head

27

True or false:
Fluid is drawn into a positive displacement pump as a slight vacuum forms at the pump outlet.

False
A slight vacuum forms at the pump inlet

28

True or false:
A centrifugal pump can not operate against a deadhead or closed valve.

False

29

A ______ turbine has the greatest capacity among turbines.

Francis

30

How do you determine the proper lubrication schedule for equipment?

Equipment application and speed

31

What is a common cause of premature bearing failure?

Improper installation

32

What can happen to a plain bearing when there is frictional heat?

It can melt

33

On a GE thrust bearing the greatest pressure area is on the...

Middle

34

What is the advantage of a Kingsbury pivoted shoe over a plain or pillowback thrust bearing?

Kingsbury shoes are completely submerged in oil

35

What are the six ways to classify a centrifugal pump?

Volute design, suction position, impeller design, shaft position, single-stage, or multi-stage

36

One classification of the centrifugal pump characterized by shape is the ...

Francis vane

37

Which wear rings have clearance in an axial and radial direction?

L rings

38

In addition to supporting the shaft, what else do pump bearings do?

Center the impeller

39

To remove trapped air in a pump, what must be opened?

The suction valve and casing vent

40

Air entering the suction side or packing may cause a pump to...

Lose prime

41

What are the steps in securing turning off a pump?

-Close discharge valve
-Stop the motor
-Close suction valve

42

What is a symptom of misalignment?

Vibration

43

In which type of hydraulic pump does delivery dramatically decrease as fluid pressure increases?

Centrifugal pump

44

In what type of pump do sealed chambers increase in size to draw fluid in the pump and decrease in size to force fluid out of the pump?

Positive displacement pump

45

In external gear pumps, pumping chambers are formed between...

The gear teeth and pump housing

46

In vane pumps, reverse flow thru the pump can be achieved by...

Moving the cam ring to an under-the-center position

47

At a head of 1400 ft, what type of wheel would normally be used?

Impulse

48

What is the purpose of speed rings on a Francis turbine?

To increase velocity of water entering the turbine.

49

Which is not a classification of impeller type runners?
-auto adjustable
-fixed blade
-impulse
-manually adjustable

Impulse

50

With reaction turbines, water enters ______% of the wheel.

100

51

One of the accessories installed on a turbine is a vacuum breaker. What is the purpose of the vacuum breaker?

To prevent excess negative pressure beneath the turbine cover

52

The spiral or scroll of a turbine case is always arranged so the direction of flow of water is...

In the direction of rotation

53

Define:
Hydrostatic

Load supported by high pressure fluid

54

Define:
Journal

The part of a rotating shaft, axle, roll, or spindle that turns in a bearing.

55

Define:
Spalling

The chipping or flaking of metal from the surface of a bearing

56

Define:
Fretting

Damage caused by rubbing, chaffing or wearing away

57

Define:
Radial

In the direction extending from the center point of the shaft

58

Define:
Volute

Designed so that the speed of a liquid is converted into pressure without shock

59

Define:
Hydrodynamic

Load supported by a lubricant film

60

What are indentations formed in the surface of a bearing called?

Pitting

61

What allows cooling fluid into the stuffing box?

Lantern ring

62

Define:
Axial

In the direction of or along the axis

63

What compares the speed of all types of turbines for a given head and capacity?

Specific speed

64

What are the vertical ribs that separate and support the speed ring called?

Stay vanes

65

What is a load supported by balls or rollers?

Rolling contact

66

Define:
Thrust runner

Provides circular flow and drags a film of oil with it

67

What is the amount of space between the component parts of a bearing assembly?

Clearance

68

Where are wear/seal rings located on pumps and turbines?

Each runner has rotating/impeller wear rings located on the top and bottom. The two stationary/casing wear rings are located on the head cover and in the pump case.

69

Explain the purpose of the wear/seal rings.

-Provide a replaceable wear surface and renewable clearance between the impeller and casing.
-The tight clearance between the suction side and discharge side of the impeller maintains a seal
-Flat rings are for axial or radial seals
-L rings are for both axial and radial seals
-Labyrinth seals dissipate pressure

70

What are the five principle effects of cavitation?

1. Discharge of water is lowered
2. Reduces output power
3. Reduces efficiency of unit
4. Unusually noisy operation
5. Increased vibration

71

What can be done to minimize the formation of cavitation?

Admission of air to turbines at light loads sometimes aids in controlling turbulence and cavitation.

72

How is damage caused by cavitation repaired?

Cavitation results in pitting and honeycombing exposed surfaces. Damage is repaired by arc welding and rebuilding the damaged area.

73

The portion of the water passage of a reaction turbine which conducts the water discharged from the turbine runner to the tailrace is the

Draft tube