Hydraulic and Pneumatic Systems Flashcards
Which of the following is the most commonly used seal to prevent internal and external leakage in both directions of a hydraulic unit?
O-ring
Which of the following allows fluid to flow unimpeded in one direction but prevents fluid flow in the other direction?
Check valve
Select the valve used in a hydraulic system that directs pressurized fluid to one end of an actuating cylinder and simultaneously directs return fluid to the reservoir from the other end
Selector
What function does the absolute pressure regulator perform in the pneumatic power system?
Regulates the compressor inlet air to provide a stabilized source of air for the compressor
No.1 Relief valves are not used in pneumatic systems as damage preventing units
No.2 Check valves are used in both pneumatic and hydraulic systems.
Both No.1 and No.2 are true
One of the distinguishing characteristics of an open-centre selector valve used in hydraulic system is that
fluid flows through the valve in the off position
What type of packings should be used in hydraulic components to be installed in a system containing Skydrol?
Packings made from ester base material
Relief valves are used in pneumatics systems
as damage preventing units
An aircraft pneumatic system, which incorporates an engine-driven multistage reciprocating compressor also requires
a moisture seperator
The removal of air from an aircraft hydraulic system is generally accomplished
by operating the various hydraulic system through several cycles
Pneumatic systems utilize
relief valves
The components in the hydraulic systems that is used to direct flow of fluid is the
selector valve
What type of selector valve is one of the most commonly used in hydraulic systems to provide for simultaneous flow of fluid into and out of a connected actuating unit?
Four-port, closed centre valve
What is the purpose of using back up rings with O-rings in hydraulic systems above 1500 PSI?
Prevent high pressure from extruding the seal between the moving and stationary part
The purpose of the pressure regulator in a hydraulic system is to
maintain system operating pressure within a predetermined range and to unload the pump
A flexible sealing element subject to motion is a
packing
Which characteristics apply to aircraft hydraulic systems?
Minimum maintenance requirements, lightweight and simple to inspect
If a rigid tube is too short for the flare to reach its seat before tightening, pulling it into place by tightening
may distort the flare
The installation of a new metal hydraulic line should be made with
enough bends to allow the tube to expand and contract with temp changes and to absorb vibrations
Extrusion of an O-ring seal is prevented in a high pressure system by the use of a
back-up ring on the side of the O-ring away from the pressure
What is one advantage of piston type hydraulic motors over electric motors?
There is no fire hazard if the motor is stalled
Generally, the first step in removing an accumulator from an aircraft
is to remove system pressure
If an hydraulic brake system uses neoprene rubber packing materials, the correct hydraulic fluid to service is
mineral-base oil
The internal resistance of a fluid which tends to prevent it from flowing is called
viscosity
What is the viscosity of a hydraulic fluid?
The internal resistance of a fluid which tends to prevent it from flowing
Which is a characteristic of petroleum base hydraulic fluid?
Flammable under normal conditons
When servicing aircraft hydraulic systems, use the type fluid specified in the
aircraft manufacture maintenance manual or instruction plate affixed to the unit
No.1 When servicing aircraft hydraulic systems, use the type fluid specified in the aircraft manufacturers maintenance manual or on the instruction plate affixed to the unit
No.2 Hydraulic fluids for aircraft are dyed a specific color for each type of fluid
Both No.1 and No.2 are true
Petroleum base hydraulic fluid is which color?
Red
Which of the following is adversely affected by atmospheric humidity if left unprotected?
Skydrol hydraulic fluid
Which is a characteristic of synthetic-base hydraulic fluid?
High flash point
Which statement about fluid is true?
All fluids readily transmit pressure
Three types of hydraulic fluid currently being used in civil aircraft are
mineral base, vegetable base and phosphate ester base
Which of the following lists only desirable properties of a good hydraulic fluid?
Low viscosity, high flash point and high fire point
Characteristic of MIL-H-8446 (Skydrol A & B) hydraulic fluid are
light purple color, phosphate ester base, fire resistant, butyl rubber seals
Where can information be obtained about the compatibility of fire-resistant hydraulic fluid with aircraft materials?
Fluid manufactures technical bulletins
Characteristic of MIL-H-5606 are
red color, petroleum base, will burn, synthetic rubber seals
Characteristic of MIL-H-7644 are
blue color, vegetable base, will burn, natural rubber seals
If an aircraft hydraulic system requires mineral base hydraulic fluid, but phosphate ester base hydraulic fluid is used, what will the effect be on the system?
System will be contaminated, fluids will not blend and seals will fail
What is used to flush a system normally serviced with MIL-H-5606 hydraulic fluid
Naptha or varsol
Components containing phosphate ester base hydraulic fluid may be cleaned with
stoddard solvent
How can the proper hydraulic fluid to be used in an aircraft be determined?
By consulting the aircraft manufacturers service manual
Phosphate ester base hydraulic fluid is very susceptible to contamination from
water in the atmosphere
Materials which are Skydrol compatible or resistant include
common aircraft metals, polyurethane and epoxy paints
The hydraulic component that automatically directs fluid from either the normal source or an emergency source to an actuating cylinder is called a
shuttle valve
What is commonly used to connect an emergency source of power, and at the same time disconnect the normal hydraulic source from critical parts of a landing gear or wheel braking system for operation (when the normal source fails)
Shuttle valve
The primary purpose of a hydraulic actuating unit to transform
fluid pressure into useful work
The primary function of the flap overload valve is to
prevent the flaps form being lowered at airspeed which would impose excessive structural loads
A unit which transforms hydraulic pressure into linear motion is called
an actuatuating cylinder
If it is necessary to adjust several pressure regulating valves in a hydraulic system, what particular sequence, if any, should be followed?
Units with the highest pressure settings are adjusted first
If an aircraft’s constant-pressure hydraulic system cycles more frequently than usual and no fluid leakage can be detected, the most probable cause
low accumulator air preload
Unloading valves are used with many engine-driven hydraulic pumps to
relieve the pump pressure
What safety device is usually located between the the driving unit and pump drive shaft?
Pump drive coupling shear section
Which valve installed in a hydraulic system will have the highest pressure setting?
Thermal relief valve
Excluding lines, which components are required to make up a simple hydraulic system?
Pump, reservoir, selector valve and actuator
Most variable displacement aircraft hydraulic pumps in use
contain a built in means of system pressure regulation
In a gear type hydraulic pump, a mechanical safety device incorporated to protect the pump from overload is the
shear pin
After installation of a rebuilt hydraulic hand pump, it is found that the handle cannot be moved in the pumping direction (pressure stroke). The most likely cause is an incorrectaly installed
hand pump outport check valve
Pressure is a term used to indicate the force per unit aurea. Pressure is usually expressed in
pounds per square inch
If two actuating cylinders which have the same cross-sectional area but different lengths of stroke are connected to same source of hydraulic pressure, they will exert
equal amounts of force and will move at the same rate if speed
Using a hand pump, pressure of 100 PSI has been built up in a hydraulic system. The hand pump piston is 1 inch in diameter. A 1/2 inch connects the hand pump to an actuating cylinder 2 inches in diameter. What is the pressure in the line between the hand pump and the actuator?
100 PSI
Heat exchanger cooling units are required in some aircraft hydraulic systems because of
high pressures and high rates of fluid flow
Which is true regarding the ground check of a flap operating mechanism which has been installed?
If the time required to operate the mechanism decreases with successive operations, it indicates the air is being worked out the system
A hydraulic system operational check during ground runup of an aircraft indicates that the wing flaps cannot be lowered using the emergency hand pump. Which is the likely cause?
The fluid level in the reservoir is low
Many hydraulic systems contain a small quantity of fluid which is not available to the main system pump. This fluid is retained to
supply fluid to a auxiliary pump
The unit in a hydraulic system that requires a certain action to be completed before another action can begin is called a
sequence valve
The purpose of a hydraulic pressure regulator is to
relieve the pump of its load when no actuating units are being operated
Severe kickback of the emergency hydraulic hand pump during the normal intake stroke will indicate which of the following?
The hand pump outport (outlet) check valve is sticking open
What type of valve in an aircraft hydraulic system permits fluid to flow freely in one direction, but restricts the rate at which allowed to flow in the other direction?
Orifice check valve
The main system pressure relief valve in a simple hydraulic system equipped with a power control valve should be adjusted
with the power control valve held in the CLOSED position
Which of the following safeguards ensures proper system operation and mitigates damage to non-metallic components of the hydraulic system?
When adding fluid to a system, use the type specified in the aircraft manufacturers maintenance manual or the instruction plate affixed to the reservoir or unit being serviced
A hydraulic accumulator is charged with an preload of 1,000 PSI. When a hydraulic system pressure of 3000 PSI has developed, the pressure on the air side of the accumulator will be
3000 PSI
How is the air in a hydraulic accumulator prevented from entering the fluid system?
By physically separating the air chamber from the oil chamber with a flexible or moveable separator
After a hydraulic accumulator has been installed and air chamber charged, the main system hydraulic pressure gauge will not show a hydraulic pressure reading until
the fluid side of the accumulator has been charged
Which must be done before adjusting the relief valve of a main hydraulic system incorporating a pressure regulator
eliminate the action of the unloading valve
Which seals are used with petroleum-base hydraulic fluids?
Buna-N
Seals used with a mineral base hydraulic fluid are identified with by which color code?
Blue dot or strip
Which seals are used with vegetable base hydraulic fluid?
Natural rubber
The air is expended and no longer needed when an actuating unit is operating in a pneumatic system is
exhausted or dumped, usually overboard
Some hydraulic systems incorporate a device which is designed to remain open to allow a normal fluid flow in the kline but closed if the fluid flow increases above an established rate. This device is generally referred to as
hydraulic fuse
When hydraulic system pressure control and relief unit to function properly, how are most systems protected against overpressure?
A shear section on the main hydraulic pump drive shaft
A worn hydraulic pump shaft seal can normally be detected by
hydraulic fluid flowing from the pump drain line
If an engine-driven hydraulic of the correct capacity fails to maintain normal system pressure during the operation of a cowl flap actuating unit, the probable cause is
restriction in the pump outlet
Before removing the filler cap of a pressurized hydraulic reservoir, in order to service the system, you must
relieve the air pressure
What happens to the output of a constant displacement hydraulic pump when the hydraulic system pressure regulator diverts the fluid from the system to the reservoir?
The output pressure reduces but the volume remains the same
Hydraulic system accumulator serves which of the following functions?
Dampens pressure surges
Hydraulic system accumulators serve which of the following functions?
- Dampen pressure surges
- Supplement the system pressure when demand is beyond the pumps capacity
- Store power for limited operation of components if the pump is not operating
Chattering of the hydraulic pump during operation is an indication
that air in entering the pump
Quick disconnect couplings in hydraulic systems provide a means of
quickly connecting and disconnecting hydraulic lines without loss of fluid or entrance of air into the system
Which seal/material is used with phosphate ester base hydraulic fluids?
Butyl rubber
A hydraulic pump is a constant-displacement type if it
delivers a uniform rate of fluid flow
A hydraulic motor converts fluid pressure to
rotary motion
A crossflow valve which is designed to bypass fluid from one side of an actuating cylinder to the other side, under certain conditions, may be found in some aircraft installed in the
landing gear system
Hydraulic fluid filtering elements constructing of porous paper are normally
discarded at regular intervals and replaced with new filtering elements
A pilot reports that when the hydraulic pump is running, the pressure is normal. However, when the pump is stopped, no hydraulic pressure is available. This is a indication of
leaking accumulation air valve
If fluid is added to a constant pressure hydraulic system while the system is pressurized, what will result?
The fluid level will increase when the system pressure is reduced
In a hydraulic system that has a reservoir pressurized with turbine-engine compressor bleed air, which unit reduces the air pressure between the engine and reservoir?
Air pressure regulator
What is the main purpose of a pressurized reservoir in a hydraulic system?
Prevent hydraulic pump cavitation
One main advantage of Skydrol is its
wide operating temp
Hydraulic fluid reservoirs are sometimes designed with a standpipe in one of the outlet ports to assure emergency supply of fluid. The outlet port with the standpipe in it furnishes fluid to the
normal system power pump
An emergency supply of fluid is often retained in the main hydraulic system reservoir by the use of a standpipe. The supply line is connected to the
inlet of the main hydraulic system
To check the air charge in a hydraulic accumulator,
reduce all hydraulic pressure, then observe the reading on the accumulator air gauge
How would the air pressure charge in the accumulator be determined if the engine is inoperative, but the system still has hydraulic pressure?
Operate a hydraulic unit slowly and note the pressure at which a rapid pressure drop begins as it goes toward zero
How many of these seals are used with petroleum base base hydraulic fluids?
Neoprene, Buna-N (could say synthetic)
Hydraulic system thermal relief valves are set to open at a
higher pressure than the system relief valve
Chatter in a hydraulic system is caused by
air in the system
If hydraulic fluid is released when the air valve core of the accumulator is depressed, it is evidence of
a ruptured diaphragm or leaking seals
Although dents in the heel of a bend are not permissible, they are acceptable in the remainder of the hydraulic tube providing they are less than what percentage of the tube diameter?
20%
If the hydraulic system pressure is normal while the engine-driven pump is running, but there is no pressure after the engine has been shut off, it indicated
no air pressure in the accumulator
The purpose of restrictors in hydraulic systems is to
control the rate of movement of hydraulically operated mechanisms
A common cause of slow actuation of hydraulic components is
internal leakages in the actuating unit
A loud hammering noise in a hydraulic system having a accumulator usually indicates
too low or no preload in the accumulator
Teflon hose that has developed a permanent set from being exposed to high pressure or temperature should
not be straightened or bent further
