Part One Hydraulics Flashcards
(119 cards)
1
Q
Fluid power
A
Is the technology that deals with the generation, control, and transmission of power using pressurised fluids
2
Q
How is fluid power used
A
Throughout industry to push, pull regulate and drive machines
3
Q
Fluid power is used on
A
Steer and brake vehicles
Drive machine tools
Control aircraft ect
4
Q
Fluid can be (what state)
A
Liquid (hydraulic)
Gas (pneumatic)
Fluid power describes both
5
Q
First hydraulic system
A
Water
6
Q
Disadvantage to water
A
It freezes rapidly
Poor lubricant
Rusts metals
7
Q
What is better than water
A
Hydraulic oils
8
Q
What is added to reduce oxidation
A
Oxidation inhibiter
9
Q
What does pneumatic systems use
A
Air
10
Q
2 different types of fluid systems
A
Fluid transport - delivers liquid or gas
Fluid power - pressurised liquid or gas
11
Q
3 basic methods of transmitting power
A
Electrical
Mechanical
Fluid power
12
Q
Most efficient
A
Is all three of the methods
13
Q
Fluid systems main advantages
A
Ease and accuracy
Multiplication of force
Constant force
Safety
Economy
14
Q
Hydraulic power
A
Influences its selection to power systems instead on electrics and pneumatic
15
Q
Advantages of hydraulic power
A
Tramits high forces
Rapid and precise
Good power to weight ratio
Not affected by electro-magnetic interference
16
Q
What is hydraulic power used in
A
Flying controls
Flaps
Retractable undercarriage
Wheel brakes
17
Q
What is in Hydraulic oil
A
Complex compounds that have been carefully prepared
18
Q
Hydraulic oil primary functions
A
Transmits power
Lubricate moving parts
Transfer heat
19
Q
Hydraulic oil properties
A
Good viscosity
Low density
Foam resistance
Non toxic
Chemical and environmental stability
Fire resistance
Readily available
20
Q
Chemical stability
A
The ability of a liquid to resist oxidation and deterioration for long periods
21
Q
What is flash point
A
To do with temperatures
Higher the flash point the more safer it is
22
Q
What level of flash point is needed for hydraulic fluid
A
High flash point
23
Q
Oil identification
A
Different colour DYES
NATO code
Joint service designation
24
Q
Hydraulic principles
(About air and liquid)
A
Air can be compressed
Liquid can not be compressed
25
Pascal's law
When pressure is applied to a confined liquid, the liquid exerts an equal pressure at right angles to the container that enclosed it
26
Force pressure and ares formula
Force = pressure × area
27
Volume area and distance formula
Volume = area × distance
28
Mechanical advantage
Shape of container has no effect on pressure
29
Jacks/actuators
Translate hydraulic fluid into linear mechanical movement
30
Jack's-ISO hydraulic symbols (2)
Cylinder, double acting, differential
Cylinder, double acting, non differential
31
Reservoir
Storage for hydraulic fluid
32
Reservior Secondary functions
Cools fluid
Allows any absorbed air to separate out
33
Reservoir baffles
Prevent fluid surging during aircraft
Promotes absorbed air to separate out
34
Unpressuried Reservoir
Has a vent line so it doesn't pop
This type is mounted at the highest point in the hydraulic system
35
What are unpressurised Reservoirs not designed for
Not designed for violent, high G manoeuvres
36
Pressurised reservoir
Rarely used in helicopters as they do not fly at high altitudes
Provided boost pressure at the pump
Relief valve fitted due to heating or malfunction
37
Basic power transmission (brakes)
Used on light aircraft
Limited system
38
Hydraulic pump
Pumps circulate the fluid
Pressure created by restriction to flow
39
Rotary swashplate pump
Can have up to 10 pistons
More angle the more fluid
40
Constant displacement pump
Is fixed displacement output
Constant displacement pumps absorb constant driving power whatever the output demand
41
Self regulating pump
More expensive
Allows simplification
Usually used for primary and secondary systems
42
Hydraulic motor
Mechanical actuator that converts hydraulic pressure and flow into torque and rotation
43
Hand pump
Mostly used for emergency. Mainly used for opening and closing doors and canopies and for lowing and raising ramps
44
Different types or hydraulic control valves
Selector valves
Sequence valves
Priority valves
45
Selector valves
Determines the direction of flow of fluid
Both linear and rotary are used
46
Sequence valves
Allow a flow in one direction only
Me be opened manually to allow fluid to flow in either direction
Eg used on retractable undercarriage
47
Priority valve (pressure maintaining valve)
They are opened by hydraulic pressure
48
Pressure relief valve
Are fitted at critical points to stop damage
49
How does a pressure relief valve operate
Balancing system pressure against a reference spring
Valve opens if system pressure rises above spring
Fluid passes to return reducing pressure
Valve resets once system preference level
50
Filtration
Clearance are minute
Particles in fluid would cause damage
High levels of filtration
Several filters may be fitted
51
3 locations of filter
Suction
Pressure
Return
52
2 types of filter
Paper
Steel
53
What are most filters equipped with
By pass valve
54
Filter blockage indicator
Has a button that comes up which tells you when the pressure is high
Goes off earlier than the by pass
55
Accumulator
Purpose is to absorb shocks and system pressure
Limits of the piston movement
56
Non return valve
Allows fluid to go one way but not the other
57
Temperature switch
Bi-metallic switch (like a kettle)
Two straps of metal one expands more than the other and makes it switch
58
Rigid fluid lines
Used in stationary applications where long, relatively straight runs are possible
59
What materials are used for fluid lines
Alluminium alloy
Corrosion resistant steel
60
In rigid fluid lines what material is used in low pressure
Aluminium
61
In rigid fluid lines what is used in high pressure
Corrosion resistant steel
62
Flexible hoses
Connect stationary parts to moving parts
63
Hose construction consists off
Inner liner covered with layers
Outer cover to protect from physical damage
64
Inner liner
Carries the fluid and must have a minimum porosity and chemical compatible with the material being carried
Must be smooth
65
Inner liner compounds
Butl - operate at different temperature
Teflon - breaks down if used with petroleum
- rubber compound
66
Reinforcement layers
Placed over inner layer
Cotton
Rayon
Polyester fabric
Carbon steel wire
Stainless wire braid
67
Outer layer
Usually made of rubber
Protects the hose from damage
Designed a fire sleeve
68
Lay line
A cover stripe
Shows if it is twisted when it is installed
69
Sealing devices
Prevent excessive internal and external leakage and to keep out contamination
70
Types of seals
Positive - do not allow any leakage either external or internal
Non-positive - permits small amount of internal leakage
71
Mating parts
Used between mating parts
Compressed between two connected parts
Nok wearing joint
72
O ring
Most widely used seal for hydraulic systems
Effective sealing across a wide range of pressures, temperatures, and movements
73
Back up ring
At high pressures O ring may extrude into the clearance
This can be prevented by a back up ring
If pressure is applied in both directions a backup ring is installed on both sides
74
Vring
Compression type seal
Used in reciprocation motion
75
Wiper rings
Wipes of any dust or dirt restricting movement of the ram
76
Piston rings
Offer less opposition to motion than do synthetic rubber seals
77
Bomded rings
square section metal washer
Clamped between two flat surfaces of rubber. Creates seal
Metal washer prevents overcompression and limits deformation
78
Pipe to pipe couplings
Coupling of lengths of metal tubing
79
Internal pipe coned adapter
Has an adapter nipple
80
Pipe to externally coned adapter
Doesn't have a nipple adapter
81
Standard adapters
Double ended fitting with a central hexagonal collar
This enables it to be held securely in the jaws of a spanner whilst pipe connections are made at either end
82
Standard adapters
Threaded externally and are coned internally or externally at each end
Range of adaptors for various types of pipes
83
Standard banjo
Fitted into a single or double ended pipe connection
Sealed top and bottom by bonded seals or soft metal joint rings
Made of light alloy
84
Self sealing couplings
These are installed in hydraulic lines to prevent loss of fluid when units are removed
85
Standard pipe unions
Series of elbows, t-peices and four war pipes
86
Hydraulic pipe identification
Marked at certain intervals and where they pass through a structure 600mm
All pipeing can be traced throughout its length
Marked with:
Filter lines
Pressure transmitter lines
Drain lines
87
Hydraulic pipe identication (what colour and shape)
Blue yellow and white with black dots
88
Warning symbols
Skull and cross bones
89
Powered flying control unit
Servo actuator, servo jack
Can be powered assisted or power operated
90
Servo jack operation
Pilot moves controls
Servo valve allows high pressure fluid to enter the jack and act upon the chamber
The piston remains stationary the whole body moves under the fluid pressure, and operates the control surface
(Think of diagram where fluid goes through and body moves to move that little thing)
91
Powered flying controls
Requirement
highly loaded aircraft must utilise fully powered systems in which the pilot provides the basic command signal and the system implements that command
92
Difference between the power assisted and power operated control system
In the ASSISTED you may have abit of control if the hydraulics fail
In the OPERATED you won't have any input if the hydraulics fail
93
Performance of powered flying control systems:
Satisfactory handling characteristics throughout the aircrafts flight envelope
Good power to weight ratio
Appropriate power and range of movement to prevent jack stall
94
Jack stall
With aggressive manoeuvring it is possible for the forces in the rotor system to exceed the maximum force produced by the servo actuators
Force required to move the flight controls becomes very high and could give and pilot an unaware impression that controls are jammed
95
Feed back loop
What happens when the pilot does a control to then what that control does to then what the pilot then does about what happens. It's like a circle pilot controls reaction to controls
96
Feedback feel
A pilot requires to recieve degree of feedback of flight forces. (This explains)
Forces are essential to provide the pilot with tactile cues of the performance of the aircraft during flight
97
What's accuracy
Pilots must respond accurately
Amplitude of control input
Rate of control input
If not:
Divergent oscillations caused by pilot overcompensating
98
Irreversibility
Designed to offload the aerodynamic forces from pilots controls
99
Safety and reliability
For reliability controls are duplicated
Reversion to manual controls in event of failure may be permissible
100
Manual reversion
Manual control in event of hydraulic failure
101
Artificial feel
Forces should increase as stixk displacement is increased
Forces should be proportional to airspeed
To prevent overstressed in the longitudinal plane feel Forces proportional to g Forces should be applied
102
Spring feel
It's simulates the increase in force caused by an increase in speed
Incorporates pitot-static, speed-sensing device
103
Basic auto pilot
Holds the aircraft on a flight path selected by the pilot
104
Auto pilots can be described as
Single axis
Two axis
Three axis
105
How auto pilot works
Amplified from gyros and sensors
Summated with the datum alttitdude
Fed back to the processor
Correcting signals sent to the servos
Drives control services
106
Automatic flight control system
Compare the actual response with that demanded by the pilot
Process any error between actual and required performance in order to generate a Correcting control command
Communicate the Correcting control command to the relevant aircraft control commands
Monitor compliance with the original command by feeding back the actual effect of the control input to comparator unit
107
System integrity AFCS must be
Be reliable
Be accurate
Provide a stable output
Offer a fail-safe solution
108
External control input
Different profiles (different movements) the pilot has set up
Planned routes that an aircraft can use (ground beacons)
109
Abnormal flight characteristics
Aircraft with simple flying controls may experience failure
Unexplained Control movements due to the generation of spurious control signals
110
Safety and limitations what must a aircraft have
Must have a back up system for most things in the aircraft
111
Emergency power
Emergency power unit
Ram air turbine
112
What happens under emergency power in wheel brakes and undercarriages
The stored energy of accumulators or 'blow down' nitrogen cylinders in the system is used
113
How do you get rid of heat
Reserviors container the separation of gasses
Large surface area for cooling
114
Hygroscopic
Attracts water
115
What do filter need doing to them
Renewing filter elements
116
If taking parts of to do with pressure what must you do
Remove air from the system
Make sure pressure is at 0
117
Functional test
Make sure everything works well
118
What must be done to fluids for testing
Fluid sampling
119
How to replenish hydraulics
Risbridger pump
Juniper rig - for more hydraulic fluid
