Answers - Hydraulics Systems


1. 100, negligible
2. mineral, polyalphaolefin, phosphate ester
3. Skydrol, IV, V
4. seals, gaskets, hoses
5. micron, particle
6. cold start, pump ripples, shock loads
7. engine gearbox, electric motor
8. non‐pressurized, bleed air
9. screening straining, preventing
10. cleaning, replacing
11. differential, operating principle, loaded
12. manually reset, permanent
13. power‐driven, hand, engine driven
14. positive, non‐positive
15, shear, in the middle of, smaller
16. electrically, servo, servo
17. diverts, pressure
18. priority, non‐critical, low
19. burst, preserves
20. failure, rupture, excessive
21. thermal, thermal expansion
22. regulators, pump
23. shuttle, seal off
24. system, components
25. preload


1. false, 3000‐5000
2. true
3. false, all contaminants are bad
4. false, filters cleaned or replaced
5. false, all of the following
6. true
7. false, non‐pressurized
8. false, 5 microns
9. true
10. false, compensator controlled
11. true
12. true
13. true
14. true
15. true


1. Red

2. Material will be damaged, softened and/or peeled

3. A shear section in the pump‐drive shaft

4. All lines should be plugged or capped after disconnecting.

5. A clogged filter

6. Hand pumps, engine‐driven pumps, electrically driven pumps, and air driven (bleed air).

7. Cabin pressurization, bleed air, aspirator and venture‐tee, and hydraulic system pressure.

8. Limit amount of pressure preventing failure of components

9. To manage the output of the pump to maintain system pressure and allow the pump to turn without resistance.

10. An accumulator

11. To control the rate of airflow

12. To remove contamination and moisture

13. Make sure the air or preload has been discharged.

14. No. petroleum base and phosphate ester fluids will not mix. Neither are seals for one fluid useable with others.

15. In a closed center system the fluid is always pressurized when the pump runs and therefore it will be faster then the open center system that needs to be built up pressure. Since most aircraft applications require instantaneous operation, closed center systems are the most widely used.

16. The advantage of the powerpack is that there is no need for a centralized hydraulic power supply system and long stretches of hydraulic lines which reduces weight.

17. required because the reservoirs are often located in wheel wells or other non‐pressurized areas of the aircraft and at high altitude there is not enough atmospheric pressure to move the fluid to the pump inlet.

18. By‐pass relief valve opens if the filter clogs this will permit continued hydraulic flow and operation of aircraft systems.

19. Centrifugal and impeller pumps

20. The angle of the pump starts to decrease when the system pressure reaches about 2850 psi. The output of the pump will decrease to adjust to system demand.

21. System pressure will increase.

22. Some controlled by pressure, some mechanically, some by electric switches.

23. The PTU is able to transfer power but not fluid between two hydraulic systems. For instance if the engine driven pump in the #1 system is inoperative than system pressure in the number 2 can power the PTU to power the number 1 system.

24. EDV solenoid will move up creating a path for the outlet pressure (Ps) to reach the top of the compensator valve. The outlet pressure will push the compensator valve down and the output pressure will act on the yoke actuating piston and reduce the yoke angle and pump output is reduced to zero.

25. Pressure‐reducing valves are used in hydraulic systems where it is necessary to lower the normal system operating pressure a specified amount.

26. a] Dampen pressure surges in the hydraulic system caused by actuation of a unit and the effort of the pump to maintain pressure at a preset level.

b] Aid or supplement the power pump when several units are operating at once by supplying extra power from its "accumulated" or stored power.

c] Store power for the limited operation of a hydraulic unit when the pump is not operating.

d] Supply fluid under pressure to compensate for small internal or external (not desired) leaks which would cause the system to cycle continuously by action of the pressure switches continually "kicking in."

27. To provide electrical and hydraulic power if the aircraft loses electrical or hydraulic power.

28. When pressurized nitrogen is not directly used to actuate the landing gear actuators or brake units, it will apply the pressurized nitrogen to move hydraulic fluid to the actuator.

29. The engine driven pump won’t be able to draw fluid from the tank, and only the AC driven pump can supply fluid to essential systems.

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