NIFE Engines 3-5-1 Hydraulic Systems

Question 1

Explain how Pascal’s Law governs the forces and pressures associated with a confined liquid

Answer 1

Pressure applied to a confined liquid is transmitted equally in all directions without the loss of pressure and acts with equal force on equal surfaces. The shape of a container has no effect on the pressure or force relationships

Question 2

Explain the relationship between linear displacement and the change in force between the input and output pistons of a closed hydraulic system

Answer 2

Linear displacement is inversely proportional to the multiplied force

Question 3

Describe a basic aircraft hydraulic system

Answer 3

The main purpose of a hydraulic system is to multiply force. Create a mechanical advantage.

Question 4

Reservoir

Answer 4

A storage tank for the hydraulic fluid required in the system. Also serves as an overflow basin for excess fluid caused by thermal expansion, allows air bubbles to be purged, and separates foreign matter

Question 5

Non-pressurized reservoirs

Answer 5

vented to the ambient air to prevent a vacuum from being formed as the fluid level in the reservoir decreases - used in utility, cargo, and patrol aircraft that are not designed for violent maneuvers

Question 6

Pressurized reservoir

Answer 6

Pressurized by bleed air from the compressor or by hydraulic system pressure. Ensures positive fluid flow for any aircraft attitude

Question 7

Types of pumps

Answer 7

1. Hand pumps
2. Power pumps
   - Variable displacement
   - Constant displacement

Question 8

Hand pumps

Answer 8

used in hydraulic systems to supply fluid under pressure to subsystems such as the landing gear, flaps, canopy, cargo doors, bomb bay doors, and to charge brake accumulators (normally classified as emergency systems)

Question 9

Power pumps

Answer 9

normally driven by the engine but may be electrically motor driven - they either displace a variable amount of fluid or a constant amount of fluid

Question 10

Variable displacement pump

Answer 10

Regulates volume delivery in accordance with system flow demands

Question 11

Constant displacement pump

Answer 11

delivers a constant fluid output for any given rotational speed.

Question 12

Pressure regulator/unloader valve

Answer 12

Always paired with a constant displacement pump. Maintains a set pressure in the system by diverting excess pump flow back to the reservoir when the preset is reached

Question 13

Check valve

Answer 13

Allows one-way flow in a system. Allows the free flow of fluid from pumps, but prevents back flow of system pressure

Question 14

Accumulator

Answer 14

• Absorbs pressure surges in the system
• Supplements the pump’s output by storing fluid under pressure
• Stores fluid under pressure for emergency operations

Question 15

Filters

Answer 15

Ensure the delivery of contaminant free hydraulic fluid.

Question 16

Relief valves

Answer 16

a pressure limiting device - a safety valve installed in the system to prevent pressure from building up to a point where seals might burst or damage may occur to the system

Question 17

Pressure gauge

Answer 17

Indicates the amount of pressure in the hydraulic system

Question 18

Pressure switches

Answer 18

used to indicate a hydraulic pressure drop that falls below allowable limits (will illuminate a light in the cockpit when low)

Question 19

Hydraulic fuses

Answer 19

safety devices installed at strategic locations throughout a hydraulic system - designed to detect or gauge ruptures, failed fittings, or other leak-producing failures/damage

Question 20

Selector control valves

Answer 20

Used in a hydraulic system to direct the flow of fluid

Question 21

Actuators

Answer 21

Converts fluid power to mechanical power