hydraulic and pneumatic systems

Question 1

what is the first step when checking hydraulic reservoir fluid level

Answer 1

verify that the hydraulic systems are set to the configuration specified in the maintenance manual

Question 2

what is the most likely cause of hydraulic fluid flowing through a filter bypass valve

Answer 2

the filter has become clogged

Question 3

what are 2 basic differences between a hydraulic and a pneumatic system

Answer 3

the fluid in a pneumatic system is compressible and that used in a hydraulic system is incompressible. a pneumatic system has no return system

Question 4

what are 2 functions of a low pressure pneumatic system in a aircraft

Answer 4

to operate the gyros in flight instruments, and to inflate pneumatic deicer boots

Question 5

what type of pump is used in a low pressure pneumatic system

Answer 5

a vane-type pump

Question 6

why do high altitude aircraft that have pneumatic gyro instruments are pressure actuated instruments rather than vacuum actuated instruments

Answer 6

at high altitude there is not enough air mass to drive the gyros at their required speed

Question 7

what effect would a dirty inline air filter have on the operation of pneumatic gryo instruments

Answer 7

the instruments would not get enough air to spin up to their required speed

Question 8

of what material are the vanes in a dry type air pump made

Answer 8

carbon

Question 9

what kind of device is used to control the speed of movement of the piston in a pneumatic actuator

Answer 9

a variable orifice

Question 10

what is the purpose of the moisture separator in a high pressure pneumatic system

Answer 10

the separator collects moisture from the air and holds it on a baffle until the system is shut down. when the inlet pressure to the moisture separator drops below 450 PSI, a drain valve opens and all of the accumulated moisture is discharged overboard. a moisture separator removes about 98% of the moisture in the air

Question 11

what are 2 types of filters that are used in an aircraft pneumatic system

Answer 11

micronic (paper) type, and screen type

Question 12

is a chevron seal a one way or two way seal

Answer 12

a one way seal

Question 13

to which side of a chevron seal should the pressure be applied

Answer 13

to the open side

Question 14

is an O ring seal a one way or two way seal

Answer 14

a two way seal

Question 15

how can you be sure of getting an O ring made of the correct material for a specific hydraulic component

Answer 15

the O ring must have the correct part number and it must have been obtained from reputable source

Question 16

on which side of an O ring should the backup ring be replaced

Answer 16

on the side away from the source of pressure

Question 17

what should be done to the sharp edges of threads and actuator pistons when installing O rings

Answer 17

the sharp edges should be covered with paper

Question 18

what is the purpose of an orifice check valve in an aircraft hydraulic system

Answer 18

an orifice check valve allows full flow of fluid in one direction through the valve, but restricts the flow in the opposite direction

Question 19

what is the difference in function between a pressure regulator and a pressure relief valve

Answer 19

pressure regulators control overall system pressure. pressure relief valves act a back up to the pressure regulator to prevent overpressure damage to the system and components

Question 20

what does an unloading valve/ pressure regulator do in a hydraulic system

Answer 20

the unloading valve, or pressure regulator, controls system pressure by shifting the pump outlet fluid from the pressurized system back into the reservoir when the system pressure is high enough. the fluid circulates with very little load on the pump until the system pressure drops to the regulator kick in value. the pump then forces fluid into the system until the pressure builds back up the regulator kick out valve