2 Flashcards
The main advantage of a ball and roller bearing is:
They have low starting friction
Deep groove ball bearings are designed for:
Radial loads and moderate thrust loads
Angular contact ball bearings are designed for:
Moderate combined thrust and radial loads
Tor F
Deep groove ball bearings can carry heavier radial loads than radial bearings with filling slots because the deep groove bearings have more balls.
False
T or F
The only difference between a heavy duty bearing and a light duty bearing is the size of the balls.
False
When handling bearings which of the following should not be done?
Wash out completely, all grease in which a bearing comes packed
T or F
Pressure should always be applied to the outer race when removing a ball bearing from a shaft.
False
What would happen if you attempted to pull a bearing on the shallow shoulder of an angular contact bearing?
It would disassemble the bearing
When a bearing must be pulled by the outer race because of a gear or shaft shoulder, what is the most important thing to remember?
Maintain a constant steady pull
Why shouldn’t galvanized pipe be used as a drift to remove bearings
Because the zinc can chip off into the bearing
T or F
Sometimes the inner bearing cap can be used to pull a bearing
True
A three way puller is particularly useful in pulling:
Gears through the spokes
T or F
It is a good idea to smooth off a shaft with emery cloth before mounting a ball bearing
False
A shaft shoulder for a bearing should be about ? the height of the inner race
1/2
What should be the maximum temp used to treat a bearing on a shaft?
225 deg F
What will happen if a ball bearing is fit loosely on a shaft?
Inner ring will slip and rotate on shaft
T or F
A ball or roller bearing should be fit onto the shaft as tightly as possible to prevent rotation of the inner race.
False
T or F
Face to face mounting of duplex bearings allows a moderate amount of alignment
True
T or F
Tandem mounting of duplex bearings is used for heavy radial loads
False
T or F
If one bearing in a duplex set is bad it is permissible to replace the bad bearing as long as it is replaced by one made by the same manufacturer
False
T or F
The wiping lip of a seal should usually be turned toward the inside of the housing
True
Oil lubrications will permit about ? the bearing speed of grease lubrication
Twice
T or F
The main advantage of oil lubrication over grease lubrication is it’s ability to circulate and cool the bearing
True
About how full should a bearing housing be filled with grease
1/3
What is the main detrimental affect of over lubrication in a grease lubricated bearing?
Heat
What is the best method of removing grease from an over lubricated bearing while it is in service?
Remove the drain plug and leave out for 15-20 min.
Ball or roller bearings which have failed because they have been pinched in the housing can be recognized by:
A definitely defined load track on opposite sides of the outer race diagonally across
T or F
A cracked inner race may mean that the shaft is oversized
True
Which one of the following should not be done in working with anti friction bearings
Use cotton waste to wipe bearings
The oil reservoir of an anti friction bearing is usually filled?
To cover the bottom half of the bottom ball
The libricating oil film in a sleeve bearing is about ? thick.
.001” to .003”
T or F
If you are looking at the end of a shaft turning counterclockwise the shaft will tends to assume a position to the left of the centerline in a journal bearing when the oil film is fully established
False
In 1839 Mr.babbit devises a material for sleeve bearing which consisted of
Tin, copper, and antimony
The two types of thrust bearings in general use on large hydroelectric units are:
The spring type and tilting shoe type
T or F
The GE type generator thrust bearing obtains its equalizing action from springs under the stationary segments.
True
T or F
The protective material on the bearing surfaces of the GE type generator thrust bearing should not be removed
False
T or F
The basic elements of a Kingsbury thrust bearing are rotating thrust collar, stationary tilting shoes, base ring, housings, lubricating system, cooling system and equalizing springs.
False
T or F
A Kingsbury thrust bearing is said to be “equalizing” if the load on the shoes is adjusted automatically
True
T or F
The principle behind the load carrying capacity of the Kingsbury type bearing is the formation of a wedge shaped oil film
True
T or F
The main advantage of calcium base grease is its water resistance
True
T or F
A trimetql bearing consists of a thin overlay of Babbitt in a leased bronze lining on a steal back
True
T or F
Turbine oil stability is its ability to resist foaming
False
T or F
Viscosity index is a measure of an oils rate of change of viscosity with temperature
True
The purpose of an oil lubricated oil bearing is to
Carry oil to the bearing from the reservoir
A machine is a device used for converting force to useful work. It can be used to:
All three (change size of force, direction of force, and speed or rate a force is acting)
Of the below statements concerning machine efficiency, which one is not a true statement?
Transformers are less efficient than reciprocating pumps
A shaft or journal re loving in an oil lubricated bearing is usually identified with?
Fluid friction
A bearing that supports or restricts the longitudinal motion of a rotating shaft is called a:
Thrust bearing
All of the below factors have an effect on the formation of the desired oil wedge. Which one must operators give the most careful attention to prevent bearing damage?
Shaft or journal speed
Lubricating oil is normally fed into a horizontal journal bearing from the?
Top
Journal and thrust bearings are more susceptible to damage during?
Both start up and shut down operations
While bearing clearances will vary because of different design and loading characteristics, it is generally est. that for each in. Of shaft diameter the clearance should be about?
.001”
T or F
The GE type generator thrust bearing obtains its equlalizing action from springs under the stationary segments.
True
Tor F
the protective material on the bearing surfaces of a GE type generator thrust bearing should not be removed.
False
Tor F
the basic elements of a Kinsbury thrust bearing are a rotating thrust collar, stationary tilting shoes, base ring, housings, lubricating system, cooling system and equalizing springs.
False
T or F
A Kingsbury thrust bearing is said to be “equalizing” if the load on the shoes is adjusted automatically
True
T or F
The principle behind the load carrying capacity of the Kingsbury type bearing is the formation of the wedge shaped oil film
True
T or F
The main advantage to calcium base grease is its water resistance
True
T or F
A trimetal bearing consists of a thin overlay of Babbitt on a leaded bronze lining on a steal back
True
T or F
Turbine oil stability is its ability to resist foaming
False
T or F
Viscosity index is a measure of an oils rate of change of viscosity with temperature.
True
The purpose of an oil ring in an oil lubricated oil bearing is to:
Carry oil to the bearing from the reservoir
A machine is a device used for converting force to useful work. It can be used to:
All three
change size of force, and speed or rate a force is acting
of the below statements concerning machine efficiency, which one is not a true statement?
Transformers are less efficient than reciprocating pumps.
A shaft or journal revolving in an oil lubricated bearing is usually identified with:
FLuid friction
a bearing that supports or restricts the longitudinal motion of a rotating shaft is called a:
Thrust bearing
all of the below factors have an effect on the formation of the desired oil wedge. Which one must the operators give the most careful attention to prevent bearing damage?
Shaft or journal speed
Lubricting oil is normally fed into a horizontal journal bearing from the:
top
journal and thrust bearings are more susceptible to damage during:
Both start up and shut down operations
while bearing clearances will vary somewhat because of different design and loading characteristics, it is generally est that for each inch of shaft diameter the clearance should be about:
.001”
all of the below statements relating to bearing load are true except:
Heavily loaded bearings generally require an oil low in viscosity.
all of the below statements concerning oil grooves in bearings are true except:
The oil bgroove is generally located in the high pressure area of the bearing.
An increase in bearing temp may indicate:
A combination of all three
change in surrounding air temp, insufficient oil, dirty oil
anti friction or roller bearings are made to carry:
any or all of the above
radial, thrust, or angular
ball bearing life may be shortened by:
all of the above
if the oil reservoir in a ring oiled bearing is carried too high the ring:
turns more slowly due to the increased friction in turning through the oil
the desired oil wedge is formed in a Kingsbury thrust bearing by:
tilting pivoted shoe
the below statements concerning a Kingsbury spherical thrust bearing are all true except:
The Kingsbury spherical thrust bearing combines the functions of a lower generator guide bearing and a thrust bearing.
Which of the following statements concerning vertical turbine guide bearings is true?
The lignum-vitae strips are inserted in the bearing shell.
Which of the below features is not normally found on a horizontal turbine thrust bearing installation?
Provisions for pressurized lubrication.
High pressure oil is injected into the bottom of a horizontal shaft turbine journal bearing help:
all of the above
lifting the weight of the rotating element off of the bearing Babbitt, during periods of starting and stopping, provides oil film between the surfaces at extremely low speeds.
Which of the following features is not normally found on a Gibbs horizontal turbine shaft thrust and journal bearing?
pivoted blocks and shoes
The revolving runner of a hydraulic turbine is said to have
rotating plane motion
the balls of the flyball governor, when the speed of rotation is increasing or decreasing, is said to have:
spherical motion
critical speed is defined as:
a speed that creates a centrifugal force greater than the elastic resolving force of the shaft.
all of the below statements concerning critical speed are true except:
each shaft will have only one critical speed
A mechanism that produces the snapping action when circuit breakers are opened or closed uses the principle of the:
toggle
which one of the below statements concerning belts and pulleys are not true?
the idler is to reverse direction of rotation of a belt drive
select one of the below statements concerning gears that is false.
Herringbone gears cause end thrust on the shafts.
most flexible couplings:
require some form of lubrication to reduce friction
hydraulic couplings are generally used with:
variable speed units
magnetic drives can be used as a:
all three:
clutch, slip coupling, reversible drive
the property which causes fluid lubricants to stick to solid bearings, or he force that attracts fluids to solids is:
adhesion
a rapid rise in total bearing friction is caused by:
All of the above
loss of fluid film, reduction in cohesion and an increase in adhesion qualities of the lubricant, excessive heat.
the ideal lubricant is one that will:
All of the above:
carry bearing load at max operating temp, maintain max adhesion at normal operating speeds, maintain proper degree of fluid friction.
which one of the below statements concerning the effect of lubrication on antifriction is not true?
the friction is generally lower when lubricated than when dry.
bearing lubricants:
all three:
reduce friction, carry away bearing heat, reduce wear and erosion of bearing surfaces.
the viscosity of an oil is generally measured by a:
viscosometer
which one of the below engine oils would have highest viscosity rating?
SAE 50
the rate of change in the viscosity of an oil for a given temp change refers to its:
viscosity index
a grease with a consistency number of 6 is:
harder than a number 2
the type of flood oil system used when the lubricated surfaces are to be always submerged in oil is:
bath
which of the below items that affect the ability of an oil to perform properly cannot be removed by a centrifuging process:
acid
grease is used in preference to oil to lubricate certain types of plain bearings because:
all three:
minimizes leakage, reduces throw, provides an effective seal.
the ideal quantity of grease for an antifriction bearing on a shaft 2 1/2 in in diameter would be:
1/3 to 1/2 full
centralized lubrication most nearly means:
the positive delivery of a predetermined amount of lubricant from one central point to a scattered # of lubrication points.
The pump that has 3 moving parts, a power rotor and two idler rotors is:
screw pump
in gear pumps the liquid is carried:
between the teeth and pump casing
the pump with no moving parts is the :
jet pump
the energy which a body or system of bodies has by virtue stresses, or the energy of position is:
potential energy
the cross section of the passage into which the water is discharged by the impeller of a volute pump gradually___ in area as the discharge opening of the pump Is approached.
increases
multistage centrifugal pumps are used where the discharge head is:
high
an impeller that has a side wall or shroud on each side of the vanes is classified as:
closed
the clearance between the rotating and stationary rings of a centrifugal pump is normally____ of an inch.
.012+.020
all centrifugal pumps are equipped with stuffing boxes or mechanical seals to prevent leakage through the clearance between the:
pump shaft and casing.
in stuffing boxes where the packing is placed on both sides of the lantern ring, the water is called:
seal water
one of the most common causes of centrifugal pump trouble is:
leaking stuffing boxes
the static force exerted by a column of water one foot high on an area of one square inch is:
.434 psi
the relation between capacity, rotative speed and head developed by an impeller is called:
specific speed
the ____ indicates the ratio, expressed in %, of useful output to the input, at different capacities and heads
efficiency curve
the frictional heat released in pumps is normally carried away by:
the liquid leaving the pump discharge
T or F
The term “specific speed” relates more to casing design and less to impeller design.
false
a 90 degree pipe bend has as much friction as ___feet of straight pipe
16ft
reciprocating pumps are:
positive displacement
the addition of energy to a liquid to move it from one point to another is called:
pumping
the faces of mechanical seals are held together by:
springs
which of the following would not be used with a pelton wheel?
wicket gates
pelton wheels:
may use two or more jets per wheel to obtain increased power
power available at the nozzle varies:
directly with the head and quantity of water.
water hammer:
can damage a penstock if not kept within reasonable limits
the purpose of an auxillary needle is to:
provide a means for reducing flow to an impulse wheel rapidly while reducing the flow more slowly through the penstock.
to deliver the same amount of power, a smaller diameter runner is required for a reaction turbine than for an impulse wheel because:
the entire circumference of the runner of the reaction turbine is being acted on by the water stream.
which of the following would not be found on a reaction turbine?
stripper
for most reaction turbines, greatest efficiency is obtained when the wicket gates are:
80-90% open
a draft tube:
increases the effective head of the turbine.
readings from a pressure gauge on the crown plate of a reaction turbine give a good indication of the :
seal ring effectiveness
a Kaplan turbine:
propeller blades adjust automatically to maintain best efficiency for gate position and variations in head.
Net head most nearly means:
gross or static head less the frictional losses in ft
which of the below factors would not generally contribute to cavitation damage?
little or no variation in effective head
how much head would not be required to develop 10,000hp from a turbine operating at 80% efficiency from a stream with a flow of 100cu/ft/sec
1100ft
what is the best speed of rotation in rpm for a pelton wheel 54in in diameter, on which the net head is 625ft?
360
commutator segments are insulated from each other by:
sheet mica
most DC generator brushes that carry the current from the commutator to the external circuit are made of:
carbon and graphite
the degree that the neutral plane of a DC generator will shift under load is:
proportional to the load
DC generators are generally classified according to the manner in which:
the field windings are connected to the armature circuit
the effects of armature reaction in a DC generator are reduced by the use of:
commutating or interpoles
a shunt wound DC generator will build up to full terminal voltage with no external load connected to it due to:
self excitation
the part of a DC generator into which the working voltage is induced is the:
armature
the field coil windings of a self excited DC generator are:
any of the above:
series, shunt,compound
the rated voltage value of a DC generator will be reached faster if the generator is:
self excited
A shunt most nearly means a:
parallel circuit
which of the following is true regarding the speed regulation of a shunt motor?
it has a constant speed characteristic under carrying loads
a DC series motor is more adaptable where a:
wide variation of torque is req’d and wide variation in speed are allowable
when the load is applied to a DC shunt motor, hich one of the following will happen?
speed decreases- counter EMF goes down
the counter EMF of a DC motor is zero when the:
armature is not turning
the horsepower developed by a motor depends mainly upon which of the following 2 factors?
speed and torque
a motor which has an output of 820 watts and an input of 960 watts has an efficiency of approx.:
85%
if the no load speed of a shunt motor is 1800 rpm and the full load speed is 1475rpm, the speed regulation is:
22%
the generated voltage (counter emf) if a motor:
opposes the impressed voltage
too much resistance inserted in the field circuit of a shunt or compound motor will:
allow the motor to overspeed and destroy itself
the main purpose of the commutator on a DC motor is to:
automatically reverse the armature polarity each time the brushes move from one segment to another.
the variable resistance placed in the rotor circuit of the wound rotor AC motor is for the purpose of:
starting torque control
the more common method of starting a synchronous motor is:
with a squirrel cage type of winding on the outer edge of the field poles.
the synchronous speed of an induction motor is the:
speed of the revolving field
what factor determines the rotor speed of an induction motor?
any or all of the above
frequency, slip, # of poles
A synchronous motor differs from an induction motor in that it:
all of the above
not self starting, requires an AC and DC power supply, may be used for power factor correction.
the direction of rotation of an induction is:
same as direction of revolving field
the principle parts of an induction motor are the:
stator and rotor
the type of connection used with a 3 phase squirrel cage motor where 58% of the line voltage is impressed on the field coils for starting, and 100% full load operation is called.
wye-delta
