Test Review Flashcards
Main functions of a bearing are to…
- Reduce wear
- Absorb and dissipate heat
- Guide and aid moving parts
Three types of loads are…
- Thrust or axial
- Radial
- Combination
The main bearings in a turbine generator are what type?
Plain bearings
In a rolling element bearing, what is the cage used for?
Keeps elements precisely aligned and in position
When multiplying the shaft diameter times the rpm, the result represents the…
speed limitations of the bearings
What is the function of the bearing housing?
Protection and alignment
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
What is one method that guarantees no movement between the bearing and shaft?
Press fit
A bearing should not be heated above 250* because…
the bearing will lose the temper (hardness)
What are two methods to heat a bearing?
Induction heater and electric oven
Why is lubrication necessary?
Heat transfer and reduces friction
What determines condition of a bearing?
Temperature, proper lubrication, changes in noise and vibration, and condition of bearing seals
True or false:
In a stuffing box, the cooling liquid is injected into the lantern ring to cool and lubricate packing and seals.
True
Pumps connected to their driver with a coupling is said to be ______.
Direct-coupled
True or false:
Radial bearings support axial loads.
False
Thrust bearings support axial loads. Journal bearings support radial loads.
When small pieces of metal flake off a bearing, it is a clear sign of ______.
Spalling
Blade angle adjustment on a Kaplan turbine is controlled by ______.
A servomotor
A common mechanical reason for excess vibration is ______.
A clogged or broken impeller
A pumps delivery rate can be changed by varying a pumps displacement or ______.
The speed of the drive shaft rotation
The propeller turbine develops its power almost entirely from ______.
The weight of the water
What are the mechanical devices that convert water power potential into usable power?
Hydraulic turbines
True or false:
To control runaway speeds in case of load rejection on an impulse wheel, deflector plates and tilting nozzles are used.
True
Cavitation occurs in any point in a hydraulic system where…
A reduction of pressure causes water vapor to form
The size of the jet of water on the discharge line of an impulse wheel is usually controlled by ______.
Needle valves
On an umbrella turbine unit, where are the thrust collar and runners located?
Under the rotor
The principle factor in the selection of a turbine is the ______.
Operating head
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
True or false:
A centrifugal pump can not operate against a deadhead or closed valve.
False
A ______ turbine has the greatest capacity among turbines.
Francis
How do you determine the proper lubrication schedule for equipment?
Equipment application and speed
What is a common cause of premature bearing failure?
Improper installation
What can happen to a plain bearing when there is frictional heat?
It can melt
On a GE thrust bearing the greatest pressure area is on the…
Middle
What is the advantage of a Kingsbury pivoted shoe over a plain or pillowback thrust bearing?
Kingsbury shoes are completely submerged in oil
What are the six ways to classify a centrifugal pump?
Volute design, suction position, impeller design, shaft position, single-stage, or multi-stage
One classification of the centrifugal pump characterized by shape is the …
Francis vane
Which wear rings have clearance in an axial and radial direction?
L rings
In addition to supporting the shaft, what else do pump bearings do?
Center the impeller
To remove trapped air in a pump, what must be opened?
The suction valve and casing vent
Air entering the suction side or packing may cause a pump to…
Lose prime
What are the steps in securing turning off a pump?
- Close discharge valve
- Stop the motor
- Close suction valve
What is a symptom of misalignment?
Vibration
In which type of hydraulic pump does delivery dramatically decrease as fluid pressure increases?
Centrifugal pump
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
In external gear pumps, pumping chambers are formed between…
The gear teeth and pump housing
In vane pumps, reverse flow thru the pump can be achieved by…
Moving the cam ring to an under-the-center position
At a head of 1400 ft, what type of wheel would normally be used?
Impulse
What is the purpose of speed rings on a Francis turbine?
To increase velocity of water entering the turbine.
Which is not a classification of impeller type runners?
- auto adjustable
- fixed blade
- impulse
- manually adjustable
Impulse
With reaction turbines, water enters ______% of the wheel.
100
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
The spiral or scroll of a turbine case is always arranged so the direction of flow of water is…
In the direction of rotation
Define:
Hydrostatic
Load supported by high pressure fluid
Define:
Journal
The part of a rotating shaft, axle, roll, or spindle that turns in a bearing.
Define:
Spalling
The chipping or flaking of metal from the surface of a bearing
Define:
Fretting
Damage caused by rubbing, chaffing or wearing away
Define:
Radial
In the direction extending from the center point of the shaft
Define:
Volute
Designed so that the speed of a liquid is converted into pressure without shock
Define:
Hydrodynamic
Load supported by a lubricant film
What are indentations formed in the surface of a bearing called?
Pitting
What allows cooling fluid into the stuffing box?
Lantern ring
Define:
Axial
In the direction of or along the axis
What compares the speed of all types of turbines for a given head and capacity?
Specific speed
What are the vertical ribs that separate and support the speed ring called?
Stay vanes
What is a load supported by balls or rollers?
Rolling contact
Define:
Thrust runner
Provides circular flow and drags a film of oil with it
What is the amount of space between the component parts of a bearing assembly?
Clearance
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.
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
What are the five principle effects of cavitation?
- Discharge of water is lowered
- Reduces output power
- Reduces efficiency of unit
- Unusually noisy operation
- Increased vibration
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.
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.
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
