1
Q
List the four functions of hydraulic fluid
A
- power transmission
- lubrication
- sealing
- cooling
2
Q
The bulk modulus of an oil is independent of the temperature
A
- false
3
Q
The compressibility of petroleum based oils is approximately 0.5% per 1000psi
A
- true
4
Q
High viscosity oil may cause excess internal leakage in components
A
- false
5
Q
A thick fluid that pours and flows slowly is said to have a low viscosity
A
- false
6
Q
The viscosity of hydraulic fluid decreases as the temperature rises
A
- true
7
Q
The viscosity of oil is independent of any pressure changes
A
- true
8
Q
The viscosity of grease will change as the shear rate changes
A
- true
9
Q
List four possible outcomes of having the viscosity of hydraulic fluid too high
A
- power will be lost overcoming friction
- the system will operate at a high temperature due to internal friction
- there will be increased pressure drops throughout the system
- systems may operate more slowly, if resistance to flow in the pressure line causes the relief valve to open
- pumps may cavitate due to low suction pressures
10
Q
List four possible outcomes of having the viscosity of hydraulic fluid too low
A
- cylinder may creep due to valve leakage
- the pump output may be reduced due to internal leakage
- actuators may slow down due to seal leakage
- the temperature may increase when pressurized fluid leaks back to a low pressure area with no work being done
- there may be increased wear and friction due to metal to metal contact of sliding parts
11
Q
List the two methods used to measure viscosity
A
- absolute (dynamic)
- kinematic (relative)
12
Q
What is the SI unit of absolute viscosity?
A
- pascal second
13
Q
What is the SI unit of kinematic viscosity?
A
- mm2/second
14
Q
An oil is designated as ISO VG 68. What would be the approximate viscosity in Centistokes at 400C?
A
- 68
15
Q
The viscosity index (VI) of an oil will change as the temperature changes
A
- false
16
Q
Equipment that is subject to low temperature starts will require fluid that has a high viscosity index
A
- true
17
Q
The result of plotting a viscosity versus temperature graph is a straight line
A
- false
18
Q
The maximum start up viscosity for the system is usually set by the ???
A
- pump
19
Q
The temperature at which wax crystals begin to form and change the appearance of the oil is known as the ???
A
- cloud point
20
Q
An oil that is at its flash point temperature will spontaneously ignite
A
- false
21
Q
The fire point temperature of an oil is higher than the flash point
A
- true
22
Q
List four factors that will increase the oxidation rate of an oil
A
- high temperatures
- high pressures
- agitation
- catalysts
- contaminants
23
Q
An oil with a high degree of demulsibility will ???
A
- require a short time to separate from water
24
Q
A hydraulic system designed to operate on petroleum based fluid can not be converted to operate on fire resistant fluid
A
- false
25
All fire resistant fluids must not be allowed to come into contact with water
- false
26
All biodegradable oils are synthetically manufactures
- false
27
Which of the following contaminants is the major cause of wear and sticking problems
- solid contaminants
28
Solid contaminant particles that are too large to enter the clearance space between moving parts will
- eventually cause problems
29
List four sources of contamination
- maintenance
- built in
- ingressed
- internally generated
30
New hydraulic fluid is alway completely free of contamination
- false
31
After assembling a new system what procedure should be followed to reduce the amount of built in contamination
- flush with a low viscosity hydraulic fluid
32
List four likely entry points for ingressed contamination
- piston rod seals
- pump shaft seals
- motor shaft seals
- reservoir vents
- pipe and tubing connections to the reservoir
33
To prevent the contaminants present in air from contaminating the hydraulic fluid a rubber or plastic membrane may be used in the reservoir
- true
34
Contamination particles that are the result of component wear are not usually a problem because they are generally very soft
- false
35
The rate of erosive wear will be increased if the fluid contains solid contaminants
- true
36
Below a certain size, solid particles are usually referred to as silt. What is this size?
- 5 micrometers
37
The ISO contamination code of 19/14 is cleaner than 17/11
- false
38
The maximum operating pressure and the system components has a direct bearing on the required cleanliness level for a hydraulic system
- true
39
The pump is always the component that sets the cleanliness requirements for a hydraulic system
- false
40
A mesh strainer with a US Sieve number of 270 (53 micrometer opening) would have an absolute rating of
- 53 micrometers
41
A mesh strainer with a US Sieve number of 270 (53 micrometer opening) would have an nominal rating of
- less than 53 micrometers
42
The ISO standard for rating hydraulic filters is
- Beta ratio
43
During a filter test for beta ratio using particles 5 micrometers and larger, a filter had 10000 particles the upstream side and 80 particles on the downstream side of the filter. The filter would be rated at
- b5 = 125
44
For a filter rated at b5=150, the removal efficiency would be
- 99.33%
45
Name two sources of contaminant ingression that can be controlled by filters
- air entering the reservoir as the fluid level drops
| - fluid being added to the system
46
The relief valve must always be between the pump and a bypass type filter
- false
47
The relief valve must always be between the pump and a non bypass filter
- true
48
Return line filters may have to deal with flow rates greater than the maximum pump output
- true
49
Component isolation filter should have the highest removal efficiency of all the system filters
- false
50
A typical surface type filter would be a mesh strainer
- true
51
When low micron filtration is required, a strainer is usually used
- false
52
Most depth type filters can be reused by washing
- false
53
The pressure drop through a filter and housing is independent of the flow rate
- false
54
Which type of line is most likely to return fluid to the reservoir with no filtration?
- drain
55
What is the best way to add fluid to the system?
- use a pump and filtration system piped directly into the circuit or reservoir
56
Why should a system of regularly taking oil samples for laboratory analysis be set up?
- to check for filter effectiveness, component wear and general fluid quality
57
Compared to the pump displacement per minute, what is the recommended size for reservoirs?
- 2 to 3 times
58
Return lines to the reservoir should terminate below the fluid level
- true
59
List 5 common features found on reservoirs
- oil level indicator
- filler/breather
- internal access doors
- baffles
- drain plug
- temperature gauge
60
A vertical sight glass is preferable to a dipstick for monitoring the reservoir fluid level because
- there is no possibility of introducing contaminants
61
List the three basic accumulator types
- weight loaded
- spring loaded
- gas loaded
62
Of the three basic types of accumulators, which one will produce a constant pressure when discharging fluid?
- weight loaded
63
The spring loaded accumulator can only be mounted in a vertical position
- false
64
One factor that affects the pre-charge pressure on a gas loaded accumulator is the displacement of the hydraulic pump
- false
65
What is the usual type of gas used for pre-charging gas loaded accumulators?
- nitrogen
66
Which type of gas must not be used for pre-charging gas loaded accumulators?
- oxygen
67
List three types of gas loaded accumulators
- piston
- bladder
- diaphragm
68
List two of the disadvantages the piston type accumulator has when compared to the other gas loaded types
- slow response time
| - possibility of seal leakage
69
If the piston area ratio of an intensifier is 8 to 1, what is the output pressure if 4000KPa is applied to the input (large piston end)
- 32000 KPA
70
If the piston area ratio of an intensifier is 6 to 1, what is the output pressure if 500 psi is applied to the input?
- 3000 psi
71
An intensifier with an area ration of 6 to 1 require 1-1/2 gallons of hydraulic fluid at the inlet when moving through its full stroke. What amount of fluid will be discharged from the outlet?
- 1/4 gallon
72
The major advantage of the Bourdon tube type pressure gage is that it has no moving parts
- false
73
A bourdon tube type of pressure gage is calibrated from 0 to 2000 psi, which of the following readings would be most accurate?
- 1000 psi
74
List two devices that should be installed with the pressure gage to increase pressure gage life
- pressure snubber
| - venting isolation valve
75
List two types of pressure switches
- bourdon tube type
| - piston type
76
Which type of pressure switch does not have any possibility of dynamic seal leakage?
- bourdon tube type
77
The operating temperature of petroleum based oils should normally not be higher than
- 55°C
78
Heat exchangers used with hydraulic systems are always used to remove heat from the system
- false
79
The shell and tube cooler uses liquid as a medium to transport heat away from the system
- true
80
Immersion type heat exchangers can only be used as heaters to add heat to the hydraulic system
- false
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