PNEUMATIC AND HYDRAULICS (KEY)

AIRFRAME RATING

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

• The pressure regulator is set too high.

• No air pressure in the accumulator.

• The system relief valve setting is too high.

• No air pressure in the accumulator.

Which of the following is adversely affected by atmospheric humidity if left unprotected?

• MIL-H-5606 hydraulic fluid.

• Skydrol hydraulic fluid.

• None of the above.

• Skydrol hydraulic fluid.

A loud hammering noise in a hydraulic system having an accumulator usually indicates

• Air in the fluid.

• Too much preload in the accumulator.

• Too low or no preload in the accumulator.

• Too low or no preload in the accumulator.

Characteristics of MIL-H-5606 hydraulic fluid are

• Light purple color, phosphate ester base, fire resistant, uses butyl rubber seals.

• Blue color, will burn, uses natural rubber seals.

• Red color, petroleum base, will burn, uses synthetic rubber seals.

• Red color, petroleum base, will burn, uses synthetic rubber seals.

Hydraulic fluid filtering elements constructed of porous paper are normally

• Discarded at regular intervals and replaced with new filtering elements.

• Cleaned and reused.

• Not approved for use in certificated aircraft.

• Discarded at regular intervals and replaced with new filtering elements.

If two actuating cylinders which have the same cross-sectional area but different lengths of stroke connected to the same source of hydraulic pressure they will exert

• Different amounts of force but will move at the same rate of speed.

• Equal amounts of force and will move at the same rate of speed.

• Equal amounts of force but will move at different rates of speed.

• Equal amounts of force and will move at the same rate of speed.

Characteristics of MIL-H-8446 (Skydrol 500 A & B) hydraulic fluids are

• Light purple color, phosphate ester base, fire resistant, uses butyl rubber seals.

• Light green color, phosphate ester base, fire resistant, uses butyl rubber seals.

• Blue color, phosphate ester base, fire resistant, uses butyl rubber seals.

• Light purple color, phosphate ester base, fire resistant, uses butyl rubber seals.

Although dents in the heel of a bend are not permissible, they are acceptable in the remainder of a hydraulic tube providing they are less than what percent of the tube diameter?

• 10

• 20

• 5

• 20

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.

• With the power control valve in the OPEN position.

• While one or more actuating units are in operation.

• 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 forcing the oil/air mixture through a centrifugal separating chamber that prevents the air from leaving the accumulator.

• By including a valve that automatically closes when the fluid level lowers to a preset amount.

• By physically separating the air chamber from the oil chamber with a flexible or movable separator.

• By physically separating the air chamber from the oil chamber with a flexible or movable separator.

In a gear-type hydraulic pump, a mechanical safety device incorporated to protect the pump from overload is the

• Check valve

• Bypass valve

• Shear pin

• Shear pin

A unit which transforms hydraulic pressure into linear motion is called

• An actuating cylinder

• A hydraulic pump

• An accumulator

• An actuating cylinder

Components containing phosphate ester-base hydraulic fluid may be cleaned with

• Stoddard solvent

• Naphtha

• Carbon tetrachloride

• Stoddard solvent

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.

• At least one selector valve has been actuated to allow fluid to flow into the fluid side of the accumulator.

• The air pressure has become equal to the fluid pressure.

• The fluid side of the accumulator has been charged.

Quick-disconnect couplings in hydraulic systems provide a means of

• Easily replacing hydraulic lines in areas where leaks are common.

• Quickly connecting and disconnecting hydraulic lines without loss of fluid or entrance of air into the system.

• Quickly connecting and disconnecting hydraulic lines and eliminating the possibility of contaminants entering the system.

• Quickly connecting and disconnecting hydraulic lines without loss of fluid or entrance of air into the system.

A hydraulic pump is a constant-displacement type if it

• Delivers a uniform rate of fluid flow.

• Produces an unregulated constant pressure.

• Produces a continuous positive pressure.

• Delivers a uniform rate of fluid flow.

The installation of a new metal hydraulic line should be made with

• Enough bends to allow the tube to expand and contract with temperature changes and to absorb vibration.

• A straight tube to permit proper alignment of the fitting and thereby reduce fluid loss through leakage.

• A straight tube to withstand the shocks and vibration to which it will be subjected.

• Enough bends to allow the tube to expand and contract with temperature changes and to absorb vibration.

Unloading valves are used with many engine-driven hydraulic pumps to

• Dampen out pressure surges.

• Relieve system pressure.

• Relieve the pump pressure.

• Relieve the pump pressure.

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

• Leaking selector valve

• Low accumulator fluid preload

• Leaking accumulator air valve

If a hydraulic brake system uses neoprene rubber packing materials, the correct hydraulic fluid to service the system is

• Synthetic base oil

• Phosphate ester base oil

• Mineral base oil

• Mineral base oil

Generally, the first step in removing an accumulator from an aircraft is to

• Drain the reservoir

• Discharge the preload

• Relieve system pressure

• Relieve system pressure

Which of the following lists only desirable properties of a good hydraulic fluid that has chemical stability?

• High viscosity, low flash point, high fire point.

• Low viscosity, high flash point, high fire point

• High flash point, low viscosity, low fire point.

• Low viscosity, high flash point, high fire point

The component in the hydraulic system that is used to direct the flow of fluid is the

• Orifice check valve

• Check valve

• Selector valve

• Selector valve

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 bleed relief valve

• Air pressure regulator

• Air pressure regulator

The removal of air from an aircraft hydraulic system is generally accomplished

• By operating the various hydraulic components through several cycles.

• By allowing the system to remain inoperative for several hours.

• Through automatic bleed valves on individual components during system operation.

• By operating the various hydraulic components through several cycles.

Which valve installed in a hydraulic system will have the highest pressure setting?

• Pressure regulator valve

• Main relief valve

• Thermal relief valve

• Thermal relief valve

If an 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

• Mechanical interference to the movement of the cowl flap.

• A partial restriction in the inport of the selector valve.

• Restriction in the pump outlet.

• Restriction in the pump outlet.

Where can information be obtained about the compatibility of fire-resistant hydraulic fluid with aircraft materials?

• Aircraft manufacturer's specifications.

• Fluid manufacturer's technical bulletins.

• Fluid manufacturer's technical bulletins.

How can the proper hydraulic fluid to be used in an airplane be determined?

• By consulting the aircraft manufacturer's service manual.

• By referring to the Pilot Operating Handbook.

• By consulting the aircraft's Type Certificate Data Sheet.

• By consulting the aircraft manufacturer's service manual.

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.

• Regulates the pneumatic system pressure to protect the moisture separator from internal explosion.

• Regulates the compressor outlet air pressure to stabilize the system pressure.

• Regulates the compressor inlet air to provide a stabilized source of air for the compressor.

Before removing the filler cap of a pressurized hydraulic reservoir, in order to service the system, you must

• Relieve the hydraulic system pressure.

• Relieve the air pressure.

• Pressurize all hydraulic components in the system.

• Relieve the air pressure.

Seals used with a mineral base hydraulic fluid are identified by which color code?

• Green dash

• Yellow dot or stripe

• Blue dot or stripe

• Blue dot or stripe

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 incorrectly installed

• Hand pump inport check valve

• Hand pump outport check valve

• Inport/outport orifice check valve

• Hand pump outport check valve

Chattering of the hydraulic pump during operation is an indication

• Of low accumulator preload.

• That the main system relief valve is sticking open.

• That air is entering the pump.

• That air is entering the pump.

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.

• 2, 3

• 1, 2, 3

• 1, 2, 3, 4

• 1, 2, 3

Pressure is a term used to indicate the force per unit area. Pressure is usually expressed in

• Pounds per inch.

• Pounds per square inch.

• Pounds per cubic inch.

• Pounds per square inch.

To protect seals from damage when installed over a threaded section, the threaded section should be

• Covered with tape.

• Covered with a suitable sleeve.

• Coated with a heavy grease.

• Covered with a suitable sleeve.

What type of packings should be used in hydraulic components to be installed in a system containing Skydrol?

• AN packings made of neoprene.

• Packing materials made for ester base fluids.

• AN packings made of natural rubber.

• Packing materials made for ester base fluids.

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 shuttle valve interconnecting the main and emergency systems.

• One or more hydraulic fuses installed in the pressure and return lines.

• A shear section on the main hydraulic pump drive shaft.

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 pressure accumulator is not supplying pressure to the system.

• The flap selector valve has a severe internal leak

• The fluid level in the reservoir is low.

• The fluid level in the reservoir is low.

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.

• Inlet of the emergency pump.

• Outlet of the main system pump.

• Inlet of the main hydraulic system.

A hydraulic motor converts fluid pressure to

• Angular motion

• Linear motion

• Rotary motion

• Rotary motion

To check the air charge in a hydraulic accumulator,

• Reduce all hydraulic pressure, then observe the reading on the accumulator air gauge.

• Observe the first reading on the hydraulic system gauge while operating a component in the system.

• Read it directly from the auxiliary pressure gauge.

• Reduce all hydraulic pressure, then observe the reading on the accumulator air gauge.

Which characteristics apply to aircraft hydraulic systems?

1. Minimum maintenance requirements.

2. Lightweight.

3. About 80 percent operating efficiency (20 percent loss due to fluid friction).

4. Simple to inspect.

• 1, 2, 3, 4

• 1, 2, 4

• 1, 3, 4

• 1, 2, 4

What safety device is usually located between the driving unit and hydraulic pump drive shaft?

• Pump motor safety switch

• Pump drive coupling shear section

• Thermal relief valve

• Pump drive coupling shear section

Most variable displacement aircraft hydraulic pumps in use

• Contain a built-in means of system pressure regulation.

• Must be driven at a nearly constant speed in order to be practical for use.

• Are not practical for use with a closed-center hydraulic system.

• Contain a built-in means of system pressure regulation.

One of the distinguishing characteristics of an open-center selector valve used in a hydraulic system is that

• A limited amount of fluid flows in one direction and no fluid flows in the opposite direction.

• Fluid flows through the valve in the OFF position.

• Fluid flows in three directions in the ON position.

• Fluid flows through the valve in the OFF position.

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.

• Units most distant from the hydraulic pump should be adjusted first.

• Units are independent of each other, and therefore, no particular sequence is necessary.

• Units with the highest pressure settings are adjusted first.

The purpose of a hydraulic pressure regulator is to

• Boost the pressure in portions of the system.

• Relieve the pump of its load when no actuating units are being operated.

• Prevent the system pressure from rising above a predetermined amount due to thermal expansion.

• Relieve the pump of its load when no actuating units are being operated.

If hydraulic fluid is released when the air valve core of the accumulator is depressed, it is evidence of

• Excessive accumulator air pressure.

• A ruptured diaphragm or leaking seals.

• A leaking check valve.

• A ruptured diaphragm or leaking seals.

The primary function of the flap overload valve is to

• Prevent the flaps from being lowered at airspeeds which would impose excessive structural loads.

• Cause the flap segments located on opposite sides of the aircraft centerline to extend and retract together.

• Boost normal system pressure to the flaps in order to overcome the air loads acting on the relatively large flap are.

• Prevent the flaps from being lowered at airspeeds which would impose excessive structural loads.

Two types of hydraulic fluids currently being used in civil aircraft are

• Petroleum base and mixed mineral base

• Mixed mineral base and phosphate ester base

• Mineral base and phosphate ester base

• Mineral base and phosphate ester base

The unit in a hydraulic system that requires a certain action to be completed before another action can begin is called a

• Check valve

• Snubber valve

• Sequence valve

• Sequence valve

What is one advantage of piston-type hydraulic motors over electric motors?

• They are considerably quieter in operation.

• They work satisfactorily over a wider temperature range.

• There is no fire hazard if the motor is stalled.

• There is no fire hazard if the motor is stalled.

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

• Three-port, four-way valve

• Two-port, open-center valve

• Four-port, closed-center valve

The internal resistance of a fluid which tends to prevent it from flowing is called

• Stability

• Viscosity

• Volatility

• Viscosity

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?

• No effect.

• System will be contaminated, fluids will not blend, but there will be no seal problem.

• System will be contaminated, fluids will not blend, and the seals will fail.

• System will be contaminated, fluids will not blend, and the seals will fail.

(1) When servicing aircraft hydraulic systems, use the type fluid specified in the aircraft manufacturer's maintenance manual or on the instructions plate affixed to the reservoir or unit.

(2) Hydraulic fluids for aircraft are dyed a specific color for each type of fluid. Regarding the above statements,

• Only No. 1 is true.

• Only No. 2 is true.

• Both No. 1 and No. 2 are true.

• Both No. 1 and No. 2 are true.

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.

• Charged or pressurized for use during the next operating cycle.

• Returned to the compressor.

• Exhausted or dumped, usually overboard.

Excluding lines, which components are required to make up a simple hydraulic system?

• Pump, reservoir, relief valve, and shuttle valve.

• Pump, reservoir, selector valve, and actuator.

• Actuator, pressure reservoir, accumulator, and selector valve.

• Pump, reservoir, selector valve, and actuator.

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 (usually when the normal source system fails)?

• Sequence valve

• Shuttle valve

• Selector valve

• Shuttle 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.

• Air will be drawn into the system, when the filler neck cap is removed.

• Fluid will spray violently out of the reservoir when the filler neck cap is removed.

• The fluid level will increase when system pressure is reduced.

How many of these seals are used with petroleum base hydraulic fluids?

• Neoprene, Buna-N.

• Natural rubber, ethylene-propylene.

• Natural rubber, Butyl rubber.

• Neoprene, Buna-N.

The primary purpose of a hydraulic actuating unit is to transform

• Fluid pressure into useful work.

• Energy from one form to another.

• Fluid motion into mechanical pressure and back again.

• Fluid pressure into useful work.

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. This device is generally referred to as a

• Metering check valve

• Flow regulator

• Hydraulic fuse

• Hydraulic fuse

Teflon hose that has developed a permanent set from being exposed to high pressure or temperature should

• Not be straightened or bent further.

• Not be reinstalled once removed.

• Be immediately replaced.

• Not be straightened or bent further.

A hydraulic accumulator is charged with an air preload of 1,000 PSI. When a hydraulic system pressure of 3,000 PSI is developed, the pressure on the air side of the accumulator will be

• 1,000 PSI

• 3,000 PSI

• 4,000 PSI

• 3,000 PSI

Petroleum base hydraulic fluid is which color?

• Purple

• Blue

• Red

• Red

(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. Regarding the above statements,

• Neither No. 1 nor No. 2 is true.

• Only No. 1 is true.

• Both No. 1 and No. 2 are true.

• Both No. 1 and No. 2 are true.

Which is true regarding 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.

• If the time required to operate the mechanism increases with successive operations, it indicates the air is being worked out of the system.

• All hydraulic lines and components should be checked for leaks by applying soapy water to all connections.

• If the time required to operate the mechanism decreases with successive operations, it indicates the air is being worked out of the system.

A flexible sealing element subject to motion is a

• Packing

• Compound

• Gasket

• Packing

Which seals are used with petroleum base hydraulic fluids?

• Polyester

• Buna-N

• Butyl rubber

• Buna-N

Which is a characteristic of synthetic base hydraulic fluid?

• Low moisture retention

• High flash point

• Low flash point

• High flash point

Hydraulic system thermal relief valves are set to open at a

• Lower pressure than the system pressure regulator.

• Lower pressure than the system relief valve.

• Higher pressure than the system relief valve.

• Higher pressure than the system relief valve.

Which statement about fluids is correct?

• All fluids are considered to be highly compressible.

• All fluids readily transmit pressure.

• Any fluid will completely fill its container.

• All fluids readily transmit 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 remains the same, but the volume reduces.

• The output pressure reduces, but the volume remains the same.

• The output pressure and volume remain the same.

• The output pressure reduces, but the volume remains the same.

Which of the following allows fluid to flow unimpeded in one direction but prevents fluid flow in the other direction?

• Check valve.

• Relief valve

• Sequence valve

• 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.

• Sequence

• Selector

• Shuttle

• Selector

(1) Relief valves are used in pneumatic systems as damage-preventing units.

(2) Check valves are used in both hydraulic and pneumatic systems.

Regarding the above statements,

• Neither No. 1 nor No. 2 is true.

• Both No. 1 and No. 2 are true.

• Only No. 1 is true.

• Both No. 1 and No. 2 are true.

An aircraft pneumatic system, which incorporates an engine-driven multistage reciprocating compressor, also requires

• A surge chamber.

• A moisture separator.

• An oil separator.

• A moisture separator.

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

• Engine cowl flap system

• Flap overload system

• Landing gear system

• Landing gear system

Which seal/material is used with phosphate ester base hydraulic fluids?

• Neoprene rubber

• Butyl rubber

• Silicone rubber

• Butyl rubber

Which of the following is the most commonly used seal to prevent internal and external leakage in both directions of a hydraulic unit?

• U-ring

• V-ring

• O-ring

• O-ring

Which is a characteristic of petroleum base hydraulic fluid?

• Non-flammable under all conditions.

• Flammable under normal conditions.

• Compatible to natural rubber seals and packings.

• Flammable under normal conditions.

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

• Bypass valve

• Crossflow valve

• Shuttle valve

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 cone.

• May distort the flare.

• Is acceptable.

• May distort the flare.

What is the main purpose of a pressurized reservoir in a hydraulic system?

• Prevent hydraulic fluid from foaming.

• Prevent tank collapse at altitude.

• Prevent hydraulic pump cavitation.

• Prevent hydraulic pump cavitation.

Phosphate ester base hydraulic fluid is very susceptible to contamination from

• Icing conditions

• Rapid changes in temperature

• Water in the atmosphere

• Water in the atmosphere

Pneumatic systems utilize

• Thermal valves

• Shutter valves

• Relief valves

• Relief valves

What type of valve in an aircraft hydraulic system permits fluid to flow freely in one direction, but restricts the rate at which fluid is allowed to flow in the other direction?

• Orifice restrictor

• Check valve

• Orifice check valve

• Orifice check valve

Relief valves are used in pneumatic systems

• As damage-preventing units

• For one direction flow control

• To reduce rate of airflow

• As damage-preventing units

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.

• Prime the main system.

• Supply fluid to the pressure accumulator.

• Supply fluid to the auxiliary pump.

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

• Emergency pump when the fluid supply to the normal system has been depleted.

• Emergency pump at any time it is required.

• Normal system power pump.

• Normal system power pump.

Extrusion of an O-ring seal is prevented in a high-pressure system by the use of a

• U-ring on the side of the O-ring away from the pressure.

• Backup ring on the side of the O-ring next to the pressure.

• Backup ring on the side of the O-ring away from the pressure.

• Backup ring on the side of the O-ring away from the pressure.

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

• A too high relief valve setting.

• Pump volume output too high.

• Low accumulator air preload.

• Low accumulator air preload.

What is the viscosity of hydraulic fluid?

• The increase in volume of a fluid due to temperature change.

• The internal resistance of a fluid which tends to prevent it from flowing.

• The fluid's ability to resist oxidation and deterioration for long periods.

• The internal resistance of a fluid which tends to prevent it from flowing.

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.

• The main system relief valve is set too high.

• The hand pump inlet check valve is sticking open.

• The hand pump outlet check valve is sticking open.

In a typical high-pressure pneumatic system, if the moisture separator does not vent accumulated water when the compressor shuts down, a likely cause is a

• Malfunctioning pressure transmitter

• Malfunctioning solenoid dump valve

• Saturated chemical dryer

• Malfunctioning solenoid dump valve

One of the main advantages of Skydrol is its

• Wide operating temperature

• Inability to mix with water

• High operating pressure

• Wide operating temperature

Characteristics of MIL-H-7644 hydraulic fluid are

• Red color, petroleum base, will burn, synthetic rubber seals.

• Blue color, vegetable base, will burn, natural rubber seals.

• Light purple color, phosphate ester base, fire resistant, butyl rubber seals.

• Blue color, vegetable base, will burn, natural rubber seals.