Hyd., Pne., Fuels - Valves

Front 1

what must be done to accumulators before charging them with nitrogen?

Back 1

all hydraulic pressure should be bled from the system.

Front 2

what is the main purpose of an accumulator? what is a secondary purpose of it?

Back 2

Main: to prevent large pressure drops in the system

Secondary: provide a limited source of power for a short time

Front 3

name 3 types of accumulators

Back 3

1) piston type

2) bladder type

3) diaphragm type

Front 4

why must all hydraulic pressure be bled off before charging an accumulator with Nitrogen?

Back 4

because if the system has hydraulic pressure, and the Nitrogen is charged to its required pressure, then the pressure in system drops due to actuators being actuated, the pressure in the Nitrogen side of the accumulator will be too low.

Front 5

list the designations for the 3 types of Schrader valves

Back 5

1) AN812

2) AN6287-1

3) MS28889-1

Front 6

describe an AN812 valve

Back 6

low pressure (up to 1500 psi), one nut (3/4")

Front 7

describe an AN6287-1

Back 7

medium pressure (1500 - 3000 psi), valve core 2000 psi rating, two nuts (one 5/8", one 3/4")

Front 8

describe a MS28889-1

Back 8

high pressure (up to 5000 psi), 2 nuts (both 3/4")

Front 9

name the 4 types of linear actuators used in aviation

Back 9

1) single-acting

2) double-acting unbalanced

3) double-acting balanced

4) cushoning actuator

Front 10

what returns a single-acting actuator to its retracted position when hydraulic pressure is released?

Back 10

a return spring

Front 11

does an unbalanced actuator move at the same speed in both directions?

Back 11

No; it will move faster in the direction where there is less volume to fill the actuator. the lower volume inside the side of the piston with the piston rod allows it to fill more quickly, speeding up the actuation.

Front 12

what is used in unbalanced landing gear actuators to prevent the gear from extending too quickly?

Back 12

a small opening to allow fluid into the actuator piston. this increases the time necessary to fill the piston on the extension side, slowing the gear extension.

Front 13

does an unbalanced actuator produce the same force in both directions? why or why not?

Back 13

No; since there is a greater piston area being acted upon by the hydraulic fluid on one side, that side will produce a greater force when actuating.

Front 14

what is the benefit of a cushion-type actuator? how is this accomplished?

Back 14

it prevents shock or "slamming" at the end of actuator travel. this is accomplished using a metering pin or other similar device. (such as is used in oleo struts)

Front 15

how does a locking actuator function, and where are they commonly used?

Back 15

small balls drop into grooves inside the outer piston at a certain point during actuator travel. these balls "lock" the cylinder from retracting mechanically.

Front 16

a rotary actuator (rack-and-pinion type) converts __________ __________ into __________ ___________.

Back 16

linear motion, circular motion. (or vice-versa)

Front 17

what applications does a piston-type hydraulic motor have on many aircraft?

Back 17

used for backup electrical or hydraulic power for generators, gear retractions, AC, etc. (*the hydraulic motor is powered by the hydraulic pressure in the system, and it in turn provides backup electrical power for the generators, or backup hydraulics for a parallel hydraulic system)

Front 18

what is the major difference between a hydraulic motor and a hydraulic pump?

Back 18

motor: requires hydraulic pressure to create mechanical motion

pump: uses mechanical motion to create hydraulic pressure

Front 19

name 2 types of seals, and describe the difference between them.

Back 19

1) gaskets - for sealing stationary areas, with no relative motion

2) packings - for sealing areas that have relative motion (piston seals, rotating shafts, etc.)

Front 20

name 2 types of one-way seals

Back 20

1) v-ring (also called "chevron")

2) u-ring

Front 21

is an o-ring a one-way or two-way seal? what does this mean?

Back 21

2-way, means it blocks leakage in both directions

Front 22

describe the requirements for achieving a good o-ring seal

Back 22

the width of the o-ring groove should be slightly wider than the o-ring, and the o-ring should be a little thicker than the gap between the two surfaces being sealed

Front 23

what is the purpose of back-up rings, and when must they be installed?

Back 23

they prevent o-rings from "rolling" out of their positions. they must be installed when system pressure is 1500 psi or greater on the opposite side of the o-ring. (*opposite from where the back-up ring is installed)

Front 24

what precautions should be taken when installing o-rings?

Back 24

use brass (or other soft metal) tools to avoid scratching the actuator or seal surfaces. cover threads if installing o-rings over them

Front 25

what type of aircraft use open-type selector valves?

Back 25

general aviation aircraft, usually with power packs

Front 26

are open-type selector valves ("open center") used with constant or variable displacement pumps?

Back 26

constant displacement

Front 27

are plug-and-poppet type selector valves considered open or closed type selector valves?

Back 27

closed

Front 28

what is the purpose of an unloading valve?

Back 28

to relieve the pump of its load when system pressure reaches a certain level

Front 29

what is the purpose of a system pressure relief valve?

Back 29

backup system protection if unloading valve fails; it prevents system overpressure

Front 30

how does a direct operating solenoid valve work?

Back 30

the solenoid pushes/pulls directly on the valve spool

Front 31

how does a pilot operated solenoid selector valve work?

Back 31

a small "pilot" hydraulic pressure is used to move the valve spool over to open or close the main hydraulic flow. this "pilot" pressure is all that is controlled by the solenoid, so the solenoid can be smaller than that on a direct operating solenoid valve

Front 32

what are the 3 types of check valves?

Back 32

1) ball-type = uses a ball and spring

2) cone-type = uses a cone and spring

3) swing-gate type = common with pneumatics

Front 33

how does one operationally check a check valve on or off of an aircraft?

Back 33

remove the line before the check-valve coming from the onboard pump. pressurize system using a ground unit, and check for leaks

Front 34

what is the purpose of an orifice-type check valve? where are they commonly found?

Back 34

purpose is to slow hydraulic flow, usually to slow down landing gear extension. it allows free-flow in one direction, and restricted flow in the other.

Front 35

what is a sequencing valve?

Back 35

a valve that ensures that the extension and retraction of the gear happens in the proper sequence. this prevents the gear from hitting the doors, etc. they are usually activated by mechanical contact

Front 36

what is a priority valve?

Back 36

valve that prioritizes certain hydraulic systems over others. a set psi is required to open the valve, and if this psi is not met the valve will restrict flow from getting to less important systems until the psi rises.

Front 37

where are quick-disconnect valves commonly used in aircraft?

Back 37

ground servicing ports, such as for external hydraulic mule use. some pumps will have quick-disconnects

Front 38

describe the operation of the 2 types of hydraulic fuses

Back 38

1) pressure drop - will cut off flow when a certain pressure drop limit is reached

2) volume pass - will cut off flow when a certain volume of fluid passes through in a certain amount of time

Front 39

name 3 types of pressure control valves used in aviation

Back 39

1) relief valve

2) pressure regulator (also "unloading valve")

3) pressure reducer

Front 40

describe how the pressure reducer in the Jeppesen textbook works

Back 40

pressure from the system equalizes on either side of a piston.

a small ball-type relief valve opens only when the downstream (reduced) pressure drops too low.

this will allow pressure through until the reduced pressure reaches the desired level, and the ball valve closes again

Front 41

what happens in an "open center" type selector valve when system pressure builds too high?

Back 41

the valve will "pop out" of the actuate position to the open center position, relieving the pump load

Front 42

what type of selector valves are generally found in power packs?

Back 42

open center type

Front 43

will a "closed center, plug type" selector valve relieve the pump of its workload when no demands are on the system?

Back 43

No; this type of selector valve requires the use of an unloading valve or regulator elsewhere in the system

Front 44

would an engine driven pump that has an unloading valve downstream be a constant or variable displacement pump?

Back 44

constant

Front 45

besides manually, how else are selector valves operated?

Back 45

electrically (solenoids)

or

pneumatically (compressed air backup)

Front 46

how are solenoids checked with a multimeter?

Back 46

check for power between ground pin and one of the others when retracting, and ground pin and the remaining pin when extending

Front 47

why might selector valves have an air inlet line?

Back 47

so the system can be activated pneumatically in case of electrical failure

Front 48

what is periodically required for landing gear systems with a pneumatic backup?

Back 48

they must be tested, by "blowing the gear down" while the airplane is on jacks

Front 49

what must be done if air is introduced into a hydraulic system?

Back 49

the system must be bled