What device in a hydraulic systems with a constant delivery pump allows circulation of the fluid when no demands are on the system?
A fully charged hydraulic accumulator provides....
A source for additional hydraulic power when heavy demands are placed on the system.
A hydraulic systems referred to as a power pack system will....
Have all hydraulic power components located in one unit.
A hydraulic hose identified as MIL-H-8794 will have a yellow stripe running the length of the hose. This stripe..
is used to ensure that the hose is installed without excessive twisting..
An O-ring intended for use in a hydraulic system using MIL-H-5606 (mineral base) fluid will be marked with..
a blue stripe or dot
What condition would most likely cause excessive fluctuation of the pressure gauge when the hydraulic pump is operating?
Inadequate supply of fluid.
A filter incorporating specially treated cellulose paper is identified as a....
The purpose of an orifice check valve is to...
Restrict flow in one direction and allow free in the other.
To prevent external and internal leakage in aircraft hydraulic units, the most commonly used is the...
Which allows free fluid flow in one direction and no fluid flow in the other direction?
Select the valve used in a hydraulic systems that directs pressurize fluid to one end of an actuating cylinder and simultaneously directs return fluid to the reservoir from the other end.
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.
1) Relief valves are used in pneumatic systems damage-preventing units.
2) Check valves are used in both hydraulic and pneumatic systems.
both #1  are True
One of the distinguishing characteristics of an open-center selector valve used in a hydraulic system is that..
Fluid flows through the valve in the OFF position.
If a hydraulic brake system uses neoprene rubber packing materials, the correct hydraulic fluid to service the system is...
Mineral base oil.
The internal resistance of a fluid which tends to prevent it from flowing is called..
What is the viscosity of 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 conditions.
1)When servicing aircraft hydraulic systems, use the type fluid specified in the aircraft manufacture's maintenance manual or on the instruction plate affixed to the reservoir or unit.
2)Hydraulic fluids for aircraft are dyed a specific color for each type of fluid.
Both #1 & #2 are True.
Petroleum base hydraulic fluid is which color?
Which of the following is adversely affected by atmospheric humidity if left unprotected?
1.MIL-H-5606 hydraulic fluid.
2.Skydrol hydraulic fluid
3.None of the above.
2. Skydrol hydraulic fluid.
Which is characteristics of synthetic base hydraulic fluid?
High Flash Point.
Which statement about fluids is correct?
All fluids readily transmit pressure.
Two types of hydraulic fluids currently being used in civil aircraft are...
mineral base, and phosphate ester base.
Which of the following lists only desirable properties of a good hydraulic fluid that has chemical stability?
Low viscosity, high flash point,high fire point.
Characteristics of MIL-H-8446 (skydrol 500 A & B) hydraulic fluid are..
light purple color,phosphate ester base, fire resistance, butyl rubber seals.
Where can information be obtained about the compatibility of fire-resistant hydraulic fluid with aircraft materials?
Fluid manufacture's technical bulletins.
Characteristics of MIL-H-5606 hydraulic fluid are..
Red color, petroleum base, will burn, synthetic rubber seals.
If an aircraft hydraulic system requires mineral base hydraulic fluid but phosphate ester base hydraulic fluid is used, what will be the effect on the system?
System will be contaminated, fluids will not blend, and the seals will fail.
Characteristics of MIL-H-7644 hydraulic fluid are...
blue color, vegetable base will burn, natural rubber seals.
What is used to flush a system normally services with MIL-H-5606 hydraulic fluid?
Naphtha or varsol.
Components containing phosphate ester base hydraulic fluid maybe cleaned with..
How can the proper hydraulic fluid to be used in an airplane be determined?
Consult the aircraft manufacture's service manual.
Phosphate ester base hydraulic fluid is very susceptible to contamination from..
water in the atmosphere.
1)materials which are Skydrol compatible or resistant include most common aircraft metals and polyurethane and epoxy paints.
2)Skydrol hydraulic fluid is compatible with nylon and natural fibers.
Both #1 & #2 are True
The hydraulic component that automatically directs fluid form either the normal source or an emergency source to an actuating cylinder is called a..
The primary purpose of a hydraulic actuating unit is to transform...
fluid pressure into useful work.
The primary function of the flap overload valve is to ...
prevent the flaps from being lowered at air speeds which would impose excessive structural loads.
A unit which transforms hydraulic pressure into linear motion is called....
An actuating 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 is
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 driving unit and hydraulic 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 over load is the
After installation of a rebuilt hydraulic hard pump, it is found that the handle cannot be moved in the pumping direction (pressure stroke). the most likely cause is an incorrectly installed
Hand pump out-port check valve.
Pressure is a term used to indicate the force per-unit area. 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 the same source of hydraulic pressure, they will exert
equal amounts of force and will move at the same rate of speed.
Heat exchanger cooling units are required in some aircraft hydraulic systems because of
high pressure and high rates of fluid flow.
Which is true regrading the ground check of a flap operating mechanism which has just been installed?
If the time required to operate the mechanism decreases with successive operations, it indicates the air is being worked out of the system.
A hydraulic system operational check during ground run-up of an aircraft indicates that the wing flaps cannot be lowered using the main hydraulic system, but can be lowered by using the emergency hand pump. Which is the most likely cause?
The fluid level in the reservoir is low.
Many hydraulic reservoirs contain a small quantity of fluid which is not available to the main system pump. this fluid is retained to
supply fluid to the auxiliary pump.
The unit which causes one hydraulic operation to follow another in a definite order is called a
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 handle during the normal intake stroke will indicate which of the following?
The hand pump outlet check valve is sticking open.
What type of valve in an aircraft hydraulic system permits fluid freely in one direction, but restricts the rate at which fluid is 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.
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 movable 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?
Seals used with a mineral base hydraulic fluid are identified by which color code?
Blue dot or stripe.
The air that is expended and no longer needed when an actuating unit is operated 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 line, but closed if the fluid flow increases above an established rate. The device is generally referred to as a
When hydraulic system pressure control and relief units fail 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 en engine-driven hydraulic pump 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 the system to the reservoir?
The output pressure reduces, but the volume remains the same.
Hydraulic system accumulators serve which of the following functions?
1)Dampen pressure surges.
2)Supplement the system pump when demand is beyond the pump's capacity.
3)Store power for limited operation of components if the pump is not operating.
4)Ensure a continuous supply of fluid to the pump.
Chattering of the hydraulic pump during operation is an indication
that air is 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 fluid?
A hydraulic pump is a constant-displacement type if it
delivers a uniform rate of fluid flow.
A hydraulic motor converts fluid pressure to
A cross-flow 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 constructed 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 an indication of a
leaking accumulator air valve.
If fluid is added to a reservoir in a constant pressure hydraulic system while the system is pressurized, what will result?
The fluid level will increase when 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 of the main advantages of skydrol is its
wide operating temperature.
Hydraulic fluid reservoirs are sometimes designed with a standpipe in one of the outlet ports in order 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 hydraulic fluid?
Hydraulic system thermal relief valves are set to open at a
higher pressure than the system relief valve.
Chatter in the 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.
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 indicates
no air pressure in the accumulator.
The purpose of restrictions in hydraulic system is to
control the rate of movement of hydraulically operated mechanisms.
A common cause of slow actuating of hydraulic components is
internal leakage in the actuating unit.
A loud hammering noise in a hydraulic system having an accumulator usually indicates
too low or no preload in the accumulator.
What type of packings should be used in hydraulic components to be installed in a system containing Skydrol?
Packing materials made for ester base fluids.
Relief valves are used in pneumatic systems
as damage-preventing units.
An aircraft pneumatic system, which incorporates an engine-driven multistage reciprocating compressor, also requires
a moisture separator.
The removal of air from an aircraft hydraulic system is generally accomplished
by operating the various hydraulic components through several cycles.
Pneumatic system utilize
The component in the hydraulic system that is used to direct the flow of fluid is the
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-center valve.
What is the purpose of using backup rings with O-rings in hydraulic systems above 1,500 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
Which characteristics apply to aircraft hydraulic system?
1.Minimum maintenance requirements.
3.About 80% operating efficiency (20% loss due to fluid friction)
4.simple to inspect.
Extrusion of an O-ring seal is prevented in a high pressure system by the use of a
backup 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 in removing an accumulator from an aircraft is to