Basic Hydraulics Flashcards
(90 cards)
1
Q
science relating to the behavior of liquids under various conditions and in aircraft
A
hydraulics
2
Q
provides a means of operating large and remote components that it would not be possible to operate satisfactorily by other means
A
hydraulic system
3
Q
provide a means of power transmission through the medium of hydraulics through an incompressible fluid via pipelines and actuators
A
aircraft systems
4
Q
provide the power for the operation of components
A
hydraulic systems
5
Q
stated that if a force is applied to a liquid in a confined space, then this force will be felt equally in all directions
A
Blaise Pascal
6
Q
17th century mathematician concerned with Pascal’s Law
A
Blaise Pascal
7
Q
Principle where all hydraulic systems operate
A
Pascal’s Law
8
Q
force employed when a hydraulic system is operated
A
pressure
9
Q
created only when an attempt is made to compress fluids
A
hydraulic pressure
10
Q
Without some form of _____, there can be no pressure
A
restriction
11
Q
required to deliver a flow of fluid into the system
A
pump
12
Q
In hydraulic systems, this restriction is provided by movable pistons which travel backwards and forwards in cylinders.
A
hydraulic jacks or actuators
13
Q
invented a hydraulic press called the Bramah Press
A
Joseph Bramah
14
Q
The _____ the area under load, the greater the pressure generated. The _____ the area under pressure, the greater will be the load available.
A
smaller, larger
15
Q
Name at least 3 hydraulic fluid properties
A
- Incompressible
- Good Lubricating Properties
- Good Viscosity
- High Boiling Point/Low Freezing Point
- High Flash Point/Non-Flammable
- Chemically Inert/Non-Corrosive
- Resistant to Evaporation
- Free from Sludging and Foaming
- Reasonably Priced
- Readily Available
16
Q
DEF STAN 91-48 is also known as
A
H515 NATO, OM15, MIL-H-5606F
17
Q
Clean mineral hydraulic fluid
A
DEF STAN 91-48
18
Q
hydraulic fluid colored red
A
DEF STAN 91-48
19
Q
Used with synthetic neoprene rubber seals
A
DEF STAN 91-48
20
Q
Recommended for all hydraulic systems under high pressures and low or very low temperatures
A
DEF STAN 91-48
21
Q
temperature for DEF STAN 91-48
A
-54 deg cel to 90 deg cel
22
Q
Phosphate ester based synthetic hydraulic fluid
A
Skydrol
23
Q
hydraulic fluid purple in color
A
Skydrol
24
Q
Used with Synthetic Butyl Rubber Seals
A
Skydrol
25
Prolonged exposure will damage skin and eyes
Skydrol
26
Very high flashpoint
Skydrol
27
flashpoint of Skydrol
170 deg cel
28
less prone to cavitation
Skydrol
29
Force is expended in overcoming static resistance (friction) which are:
- Friction in cylinders caused by moving parts
- Piston rods rubbing against bearings and seals
- Fluid rubbing against the pipe walls
30
Large bore pipes and frictionless pistons would allow ______ of the force to be utilized but would incur large weight and cost penalties.
nearly 100%
31
Friction between pistons and cylinders and piston rods and bearings cannot be completely eliminated, it can only be lessened by _______.
good design and workmanship
32
The friction between the walls of the pipes and the fluid depends upon:
- velocity of the fluid in the pipes
- Length, bore, and the internal finish of the pipes
- number of bends
- viscosity of the oil
33
prevents leakage of fluid in hydraulic systems
seals
34
prevent fluid leaks by being squeezed between two non-moving surfaces
static seals, gaskets, packing
35
these seals are effective in one direction only
U and V ring seals
36
these seals are often used where pressure is applied in either direction
O ring seal, square section seal
37
it is usually fitted with O-ring, where high pressures are used
stiff backing ring
38
retains the shape of the seal and prevents it from being squeezed between the two moving surfaces
stiff backing ring
39
these seals require lubrication to remain effective
dynamic seals
40
_____ of the bearing surface or a slight seepage from the seals is normally acceptable.
wetting
41
often installed on actuators to prevent any grit that may be deposited on the piston rod from contaminating the seals
wiper ring
42
Components of a Basic Hydraulic System
Reservoir, Pump, Filter, Relief Valve, Selector Valve, Actuator
43
delivers oil to the pump and receives oil from the actuators
reservoir of oil
44
either hand, engine, or electrically driven
pump
45
enables the operator to select the direction of the flow of fluid to the required service and providing a return path for the oil to the reservoir
selector valve or control valve
46
actuate the component
jack or set of jacks or actuators
47
keep the fluid clean
filter
48
as a safety device to relieve excess pressure
relief valve
49
Apart from light aircraft breaks, it has little practical use
Passive Hydraulic System
50
in such a system, the pump supplies the pressure
Active Hydraulic System
51
Two Types of Active Hydraulic System
Open Center System, Closed System
52
main advantage of this system is that it is simple, the main disadvantage is that only one service can be operated at a time
Open Center System
53
Fluid is passed directly to the reservoir when no services are being operated
offloaded condition
54
When the actuator reaches the end of its travel, selector is ________ in order to offload the pump and allow other services to be selected.
returned to neutral
55
The relief valve will relieve excess pressure if the selector is ______ to its neutral position.
not returned
56
Its great advantage is that multiple services can be operated at the same time. However, its use is only limited by the volume flow capacity of the pump.
Closed System
57
With this type of system, operating pressure is maintained in that part of the system which leads to the selector valves, and some method is used to prevent over-loading the pump.
Closed System
58
fitted in systems that employ a fixed volume pump (constant delivery) to divert pump output to the reservoir when pressure has built up to normal operating pressure
automatic cut-out valve
59
Difference of a Closed System and an Open Center System
- two or more services can be operated at the same time
- not important to return the selector valve to neutral once operation is complete
60
Why is it not important to return the selector valve to neutral once operation is complete in a closed system?
A closed system is designed to deal with the consequent pressure increase.
61
Extra fluid is stored in the reservoir due to the following reasons:
- No system is leak free.
- Fluid expands and contracts as heated or cooled.
- Actuator need more fluid when they are extended than contracted.
- Cavitation
62
monitor the system in a reservoir
quantity transmitter unit
63
prevents debris in entering the reservoir
filling inlet (normally sealed with filler cap)
64
fitted in both suction and pressure lines that is at both sides of the pump
filters
65
protects the pump
suction filter
66
ensures the cleanliness of fluid during use
pressure filter
67
filter in the fluid return line to the reservoir to remove particles picked up during operation
return filter
68
allows unfiltered fluid to pass to the system when the element becomes clogged
relief or bypass valve
69
This type of filter element must be changed at regular intervals before clogging occurs
relief or bypass valve
70
draws oil from the reservoir and deliver a supply of fluid to the system
pumps
71
used to provide alternate supply as part of the redundancy provision for the safe operation of the aircraft
air pump, ram air turbine, power transfer unit (PTU)
72
may be the only source of power in a small, light aircraft hydraulic system; may also be used on larger aircraft in some cases
hand pumps
73
allows ground servicing to take place without the need for engine running; so that the lines and joints can be pressure tested; so that cargo doors can be operated without power
hand pumps
74
Classification of Pumps
- Constant Delivery (Fixed Volume) Pump
- Constant Pressure (Variable Volume) Pump
75
Supplies fluid at constant rate irrespective of demand and therefore needs an automatic cut out or relief valve to return the fluid to the reservoir
Constant Delivery (Fixed Volume) Pump
76
fitted to a system employing a constant delivery (fixed volume) pump, to control system pressure and to return fluid to the reservoir
Automatic Cut-Out Valve
77
This pump supplies fluid at a variable volume and controls its own pressure
Constant Pressure (Variable Volume) Pump
78
Constant Pressure (Variable Volume) Pump is typically fitted in modern aircraft whose systems operate at ________.
3,000 to 4,000 psi
79
This is fitted:
a) To store hydraulic fluid under pressure
b) To dampen pressure fluctuations
c) To allow for thermal expansion
d) To provide an emergency supply of fluid to the system in then event of pump failure
e) To prolong the period between cut out and cut in time of the ACOV and so reduce the wear on the pump
f) Provides the initial fluid when a selection is made, and the pump is cut out
hydraulic accumulator
80
Used to convert fluid flow into linear or rotary motion
hydraulic jacks or actuators
81
consist of an outer cylinder within which slides a piston and seal assembly
hydraulic jacks or actuators
82
passes through a seal and wiper ring assembly fitted into the end of the cylinder
piston rod (or ram)
83
Hydraulically operated in one direction only; normally used as a locking device; has more fluid in the cylinder when the rod is extended
Single Acting Actuator
84
actuator used in most aircraft systems
double acting unbalanced actuator
85
equal force can be applied to both sides of the piston on this actuator; often used in applications such as nose wheel steering; Either one or both sides of the piston rod may be connected to a mechanism
double acting balanced actuator
86
formed when fluid is trapped between the piston of the actuator and a non-return valve or a selector valve at its neutral position
hydraulic lock
87
used to maintain or limit fluid pressures in various parts of a hydraulic system
relief valves, pressure maintaining valves, pressure reducing valves
88
components used to control the flow of fluid to the various services operated by the hydraulic system
flow control components
89
Give at least three flow control components
- non-return valves
- restrictor valves (or choke)
- selectors
- electrically operated selectors
- shuttle valves
- sequence valves
- modulators
- flow control valves
- fuses
90
disadvantage of pneumatics
air is extremely compressible
