hydraulics Flashcards
Pascal’s Law states that:
that pressure applied to any part of a confined liquid is transmitted with undiminished intensity to every other part
Some of the properties and characteristics that must be considered when selecting a satisfactory liquid for a particular system are:
Viscosity
Chemical stability
flash point
The three principal categories of hydraulic fluids are:
Minerals
Polyalphaolefins
Phosphate esters
What is the Mil spec number for Mineral oil-based hydraulic fluid?
Petroleum MIL-H-505
What colour is it dyed?
Red
What type of seals are used with petroleum-based fluids?
Synthetic rubber seals
Should an aircraft hydraulic system be serviced with the wrong type fluid?
Immediately drain and flush the system and maintain the seals according to the manufacturer’s specifications.
What are the two general contaminants?
Abrasives
Nonabrasive
When should a check of the system be made?
Whenever it is suspected that a hydraulic system has become contaminated or the system has been operated at temperatures in excess of the specified maximum
Fill out sample identification label supplied in sample kit, making sure to include customer name,
aircraft type, aircraft tail number, hydraulic system sampled, and date sampled. Indicate on the sample label under remarks if this is a routine sample or if it is being taken due to a suspected problem.
What provides adequate control of the contamination during hydraulic system operations?
Filters
Where are filters placed in the system to control particulate contamination?
in the pressure line
What hydraulic fluid can dissolve away some of the fatty materials of the skin?
Phosphate esters
What PPE should be worn when handling any type of hydraulic fluid?
Proper gloves and eye protection
A basic system consists of a:
Pump
Reservoir
Directional valve
Check valve
Pressure relieve valve
Selector valve
Actuator
Filter
Describe an open centre Hydraulic system:
An open centre system is one having fluid flow, but no pressure in the system when the actuating mechanisms are idle.
Describe a closed-centre system.
In the closed-centre system, the fluid is under pressure whenever the power pump is operating.
An advantage of the open-centre system over the closed-centre system is:
Continuous pressurisation of the system is eliminated.
An advantage of the closed-centre system over the open-centre system is:
. Pressure is available the moment the selector valve is positioned.
What are Power boost systems?
Power boost systems help the pilot in overcoming high control forces, but the pilot still actuates the flight controls with push rod or cable
What are power supply systems and fly-by wire flight controls?
They are the electric system for modern in which the pilot sends input to the flight control servos.
Advantages of Small power packs
there is no need for a centralized hydraulic power supply system and long stretches of hydraulic lines, which reduces weight.
What is the purposes of a reservoir:
The reservoir not only supplies the operating needs of the system, but it also replenishes fluid lost through leakage.
What types of gauges are used to attain reservoir level/quantities?
Visual gauge indicate the quantity
What does the filler strainer (finger strainer) do?
to prevent the entry of foreign matter during servicing
What is the advantage of using s quick disconnect service port?
This method reduces the chances of contamination of the reservoir.
How do you get the correct results when the hydraulic fluid quantities are checked or the reservoirs are to be filled?
The airplane should be in the correct configuration
Describe a filter.
A filter is a screening or straining device used to clean the hydraulic fluid, preventing foreign particles and contaminating substances from remaining in the system.
What happens if the filter becomes blocked?
Contamination in your hydraulic system
What types of filter element can you get?
Macron, porous metal or magnetic type
What is the micron element designed to prevent the passage of solids greater than?
10 microns
When replacing filter elements, what should you be sure of?
ensure that the sealing element in the filter assembly is intact.
What is the purpose of the bypass relief valve in a filter?
The bypass relief valve opens if the filter clogs, permitting continued hydraulic flow and operation of aircraft systems.
How can you monitor the condition of installed filter elements?
by measuring the drop in hydraulic pressure across the element under rated flow conditions.
What does the red indicator popping out signify?
That the element has been cleaned
Power-driven pumps are the primary source of energy and may be either:
engine driven, electric motor driven, or air driven.
What are Hand pumps generally installed for?
for testing purposes, as well as for use in emergencies
Modern aircraft use a combination of:
Modern aircraft use a combination of engine-driven power pumps, electrical-driven power pumps, air-driven power pumps, power transfer units (PTU), and pumps driven by a RAT (Ram Air Turbine).
What component is required when a constant displacement pump is used in a hydraulic system in which the pressure must be kept at a constant value?
pressure regulator
What type of pump is a gear-type power pump?
Constant-displacement
What is the purpose of Pump drive couplings?
Designed to serve as safety devices
What 2 types of pumps can Piston pumps be?
Constant displacement
Variable displacement
How does the shear section of the drive coupling work?
preventing damage to the pump or driving unit
Describe a variable-displacement pump:
A variable-displacement pump has a fluid output that is varied to meet the pressure demands of the system. The pump output is changed automatically by a pump compensator within the pump.
What type of pump is a vane-type power pump?
Consistent-displacement pump
What is the function of the flow control valves?
Control the speed and/or direction of fluid flow in the hydraulic system.
What is the purpose of a selector valve?
A selector valve is used to control the direction of movement of a hydraulic actuating cylinder or similar device.
What are the two main types of selector valves?
open-centre
closed-centre
How are most selector valves controlled?
mechanically, manually, electrically, hydraulically, or pneumatically
Describe a check valve:
Is a type of flow control valve in aircraft hydraulic systems allows fluid to flow unimpeded in one direction, but prevents or restricts fluid flow in the opposite direction.
What is an integral check valve?
When part of a component, the check valve is said to be an integral check valve.
What does an arrow on the outside of the housing indicated?
It indicates the direction in which the fluid flow is permitted
What does orifice check valves allow?
Full fluid flow in one direction and restricted flow in the other direction
What do quick disconnect valves installed in hydraulic lines prevent?
Loss of fluid when units are removed
List the types/purpose of automatic pressure control valves:
Some of them are an escape for pressure that exceeds a set pressure; some only reduce the pressure to a lower pressure system or subsystem; and some keep the pressure in a system within a required range.
Why is a pressure relief valve necessary?
It is used to limit the amount of pressure being exerted on a confined liquid. This is necessary because to prevent failure of components or rupture of hydraulic lines under excessive pressures. The pressure relief valve is, in effect, a system safety valve.
The two purposes of a pressure regulator:
One purpose of the pressure regulator is to manage the output of the pump to maintain system operating pressure within a predetermined range
The other purpose is to permit the pump to turn without resistance
Why are pressure reducing valves used in a hydraulic system?
to lower the normal system operating pressure by a specified amount.
What is the main purpose of the shuttle valve?
is to isolate the normal system from an alternate or emergency system
What are shutoff valves used for?
Shutoff valves are used to shut off the flow of fluid to a particular system or component.
List the two general types of accumulators:
Cylindrical systems
Spherical systems
What type of valve is installed on the nitrogen side of the accumulator?
Schrader Valve
What separates the nitrogen and hydraulic fluid in an accumulator?
A synthetic rubber diaphragm, or bladder, is installed to create two chambers
What is the purpose of the heat exchanger in a hydraulic system?
to cool the hydraulic fluid from the hydraulic pumps.
What are of two major types of Actuating cylinders?
Single action
Double action
Seals are divided into three main classes:
Packings
Gaskets
Wipers
Describe Packings.
used internally on a sliding or moving assembly
Describe Gaskets
used between non-moving fittings and bosses
Describe Military Standard (MS) Hydraulic O-rings .
Military Standard (MS) specifications that offered improved low-temperature performance without sacrificing high temperature performance
Describe Air Force-Navy (AN) Hydraulic O-rings.
For use in fluid at operating temperatures ranging from –65 °F to +160 °F. When new designs raised operating temperatures to a possible +275 °F, more compounds were developed and perfected.
How are O-rings packaged?
O-rings are available in individual hermetically sealed envelopes labelled with all pertinent data.
When selecting an O-ring for installation, what is the most reliable way to identify O-ring?
the basic part number on the sealed envelope provides the most reliable compound identification.
Describe backup rings made of Teflon™.
They don’t deteriorate with age
Are unaffected by any system vapor or fluid
Can tolerate temperature extremes in excess of those encountered in high pressure hydraulic systems
What does their dash numbers indicate?
The size and dimensions which they are suited.
How do you identify backup rings?
Package labels
The inspection of backup rings should include:
a check to ensure that surfaces are free from irregularities
that the edges are clean cut and sharp
scarf cuts are parallel
What must you check on a Teflon™ spiral backup ring?
That the coils do not separate more than ¼ inch when unrestrained.
Some of the more common gasket materials are:
asbestos, copper, cork, and rubber
For systems that use MIL-H-5606, what are the 2 materials the seals are made of?
Neoprene
Buna-N
What should you be careful of while using the seal removal and the installation tools?
Avoid contact with cylinder walls, piston heads, and related precision components is not desirable
Each replacement O-ring should be removed from its sealed package and inspected for defects, such as:
for defects, such as blemishes, abrasions, cuts, or punctures
How do you inspect the inner diameter surface of an O-ring?
By rolling the ring on an inspection cone or down
What should the inner diameter surface be checked for on an O-ring?
small cracks, particles of foreign material, or other irregularities that cause leakage or shorten the life of the O-ring
What should you do after inspection and prior to installation?
Immerse the ring in hydraulic fluid
What should be avoided during the installation of an O-ring?
Twisting and rolling of ring to maneuverer it in to place.
After the O-ring is placed in the cavity provided, what should you do?
Gently roll the O-ring with fingers to move any twists that might have occurred during installation
What are wipers used for?
Wipers are used to clean and lubricate the exposed portions of piston shafts.
Pneumatic systems are sometimes used for:
- Brakes
- Opening and closing doors
- Driving hydraulic pumps, alternators, starters, water injection pumps, etc.
- Operating emergency devices
What type of pumps do low pressure systems obtain a supply of low-pressure air from?
Vane-type pump
Low-pressure systems are used for:
Wing de-icing boot systems
List the components that consist in a fuel system:
storage tanks
pumps
filters valves
fuel lines
metering devices
monitoring devices
Where must an engine fuel system firewall shutoff valve not be fitted?
Engine side of the firewall
On an aircraft, Lines and any components from each tank outlet to each engine must be:
Independant of each other
Each fuel quantity indicator must be adjusted to account for
Unusable fuel supply
Where must a fuel tank never be located on an aircraft system?
On the engine side of the firewall
Why must bladder tank pads be placed between each tank and its supports?
To prevent chafing between the tanks and its support
What must all Reciprocating engine fuel systems have?
sediment bowl or chamber that is accessible for drainage.
Fuel filling points must have a provision for?
electrically bonding the airplane to ground fueling equipment
Do pressure-fuelling points require a provision for electrically bonding?
No
To allow proper fuel flow, each fuel tank must be?
Vented from the top part of the expansion space
Where must the fuel tank strainer be?
Fuel tank outlet
Booster bump
What two things must a pressure fuelling system have to prevent fuel in each tank from exceeding the maximum quantity approved for that tank?
A means for automatic shutoff
To prevent fuel damage of the system
Where is the shutoff valve never positioned?
No shutoff valve may be on the engine side of any firewall. There must be means to guard against inadvertent operation of each shutoff valve and means to reopen each valve rapidly after it has been closed.
The tank selector positions must be located in such a manner that it is?
The tank selector positions must be located in such a manner that it is impossible for the selector to pass through the OFF position when changing from one tank to another.
There must be a fuel strainer, or filter, between the?
Fuel tank outlet or:
The inlet
The fuel metering device
an engine-driven positive displacement pump
whichever is nearer the fuel tank outlet
This fuel strainer, or filter, must be?
must be accessible for draining and cleaning and must incorporate a screen or element that is easily removable.
The fuel strainer should have a?
sediment trap and drain, except that it need not have a drain if the strainer or filter is easily removable for drain purposes.
Each aircraft engine is designed to burn a certain fuel, Is mixing fuels permitted in any aircraft?
No, only use the fuel specified by the manufacturer. Mixing fuels is not permitted
What are the two basic types of fuel discussed in this section?
Reciprocating engine fuel
Turbine engine fuel
What is Volatility?
Volatility is a term used to describe how readily a substance changes from liquid into a vapor.
What is Vapour lock?
Vapor lock is a condition in which AVGAS vaporizes in the fuel line or other components between the fuel tank and the carburettor.
What can Vapour lock be caused by?
by excessively hot fuel
low pressure
or excessive turbulence of the fuel traveling through the fuel system.
What are Octane ratings and performance numbers given to fuels for?
To describe their resistance oof detonation
To increase anti-detonation characteristics of fuel, what substances is the most common that can be added?
Iso-octane
Heptane
What is the only desired AVGAS for all aircraft with reciprocating engines?
A single 100 octane low-lead fuel
What colour is 100LL AVGAS dyed to help identification?
It has a dyed blue colour
What areas would you find Decals marking the correct fuel for the aircraft?
Delivery trucks and hoses are marked as are aircraft tank fuel caps and fill areas.
How do they make it hard to fill avgas tanks with jet fuel?
sized too large to fit into an AVGAS tank fill opening
Where should debris settle in the aircraft fuel tank?
drain sumps to be removed before flight.
What two components can successfully capture the remaining sediment in the aircraft fuel system?
Filters & strainers
What is the purity of aviation gasoline most often compromised by?
water
Where else can Water settle given enough time?
The Drain sumps
Aircraft with turbine engines use a type of fuel Commonly known as?
Jet fuel
Can water enter the fuel even when the aircraft is parked on the ramp with the fuel caps in place? And Why?
Yes, because air in the tank vapor space above the liquid fuel contains water vapor.
What are the additives/inhibitors commonly added to fuel, used to control?
Corrosion
Oxidation
Ice
Microbial growth
Bacterial growth
What are the three basic turbine engine fuel types available worldwide?
Jet A fuel
Jet A-1 fuel
Jet B fuel
Turbine Engine Fuel retains water in two principal ways.
Some water is dissolved into fuel
Other water is also entrained in the fuel
What is the space above the liquid fuel vented to?
The space above the liquid fuel is vented to maintain atmospheric pressure on the fuel as the tank empties.
How do you ensure equal pressure when both tanks feed the engine?
The two tanks are also vented to each other to ensure equal pressure when both tanks feed the engine.
The selector valve provides four options:
fuel shutoff to the engine
fuel feed from the right wing tank only
fuel feed from the left fuel tank only
fuel feed to the engine from both tanks simultaneously.
Why does the main system strainer often have a drain function?
To remove sediment and water
Why can’t Low- and mid-wing single reciprocating engine aircraft utilize gravity-feed fuel systems?
Because the fuel tanks are not located above the engine.
Where are the boost pumps located?
At the outlet of each tank
Why are they located here?
This pressurizes the entire fuel system from the tank to the injectors eliminating the possibility of vapor lock
What is the purpose of the vapour separator?
Helps eliminate air from fuel
Typically, a helicopter has only one or two fuel tanks located:
Near the centre of gravity the aircraft which is near the main rotor mast. The tank, or tanks, are usually located in or near the aft fuselage.
What are the three basic types of aircraft fuel tanks?
Rigid removable tanks
Bladder tanks
Integral fuel tanks
How are they typically made to be vented?
Vent Cap
Vent Line
Aircraft fuel tanks have a low area called a sump, what is it designed for?
place for contaminants and water to settle
What is a sump equipped with to remove the impurities during pre-flight walk-around inspection?
A drain valve
