hydraulic systems

Pascals law

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

pressure

force per unit area

what is exchanged for the change in force in a hydraulic system

linear displacement / distance traveled

main purpose of a hydraulic system is to

multiply force

aircraft hydraulic systems consists of

power system and any number of actuating subsystems

what does the power system generally include

fluid supply, power supply, and all other components not including selector valves

current aircraft have two hydraulic power systems. what are they

one for flight controls only

supplies fluid pressure to the utility system in addition to other flight controls

what do manufacturers refer to when talking about the power control systems

systems supplying pressure only for the flight controls

reservoir

storage tank for the hydraulic fluid required in the system and serve as an overflow basin for excess hydraulic fluid forced out of the system by thermal expansion, allow bubbles to be purged, and separate some foreign matter from the system

non-pressurized reservoirs

vented to the ambient air to prevent a vacuum from being formed as the fluid level decreases

pressurized reservoirs

pressurized by bleed air from the compressor or by hydraulic system pressure

hand pump

used in hydraulic systems to supply fluid under pressure to subsystems such as the landing gear, flaps, canopy, etc

power pumps

normally driven by the engine but may be electric motor driven. displace a variable or constant amount of fluid

variable displacement pump

regulates volume delivery in accordance with system flow demands

constant displacement pump

delivers a constant fluid output for any given rotational speed

pressure regulator or unloader valve

maintain set pressure in the system by diverting excess pump flow back to the reservoir. works in conjunction with the constant displacement pump

check valve

allows one way flow in a hydraulic system

accumulator

• serves as a cushion or shock absorber by absorbing pressure surges in the system

• Supplements the pump output when the pump is under peak load by storing energy in the form of fluid under pressure

• stores enough fluid under pressure to provide for emergency operation of certain actuating units

Filters

ensure delivery of contaminant free hydraulic fluid by preventing dust, grit, and undesirable impurities from entering the system

relief valves

pressure limiting device

pressure gauges

indicate the amount of pressure in the hydraulic system

pressure switches

used to indicate a hydraulic pressure drop that falls below allowable limits

hydraulic fuses

safety devices that are installed at strategic locations throughout a hydraulic system to detect ruptures, failed fittings, or other leak producing failures

selector control valves

used in hydraulic system to direct the flow of fluid

actuators

convert fluid under pressure into linear or reciprocating mechanical motion