3INTRODUCTIONHydraulics is based on the fact that liquids are incompressibleHydraulic system is a system where liquid under pressure is used to transmit energyIn it a hydraulic pump converts mechanical power to hydraulic powerAn actuating cylinder converts hydraulic power to mechanical power.
5DEVICES USING HYDRAULIC SYSTEMS IN AIRCRAFTS Gun turretsAuto pilotShock absorption systemsDive, landing, speed and flap brakesBomb bay doorsDoors and hatchwaysLanding gears, wing flaps, etc…
6PRINCIPLES OF OPERATION Governed by Pascal’s lawThe oil is in contact with both sides of the piston head but at different pressures. High pressure oil may be pumped into either side of the piston head.The selector valve determines to which side of the actuating cylinder the high pressure oil (red colored side) is sent.
7PARTS OF THE POWER SYSTEM RESERVOIRACCUMULATORFILTERPOWER PUMPSYSTEM RELIEF VALVEPRESSURE REGULATOR
9RESERVOIRFUNCTIONSHolds reserve supply oil to account for normal leakage, emergency supply of oil, volume changes, thermal contraction of oil,Provides pressure head on the pump, a place to remove air or foam from liquid, air space for expansion of the oil due to temperature changesetc
10RESERVOIR CONSTRUCTION Material: 5052 aluminium Size: takes into account all oil volumes in operational requirements, thermal expansion, leakage, etc.Shape: domed cylindrical shape, due to ease of construction & mounting
11ACCUMULATORS PRINCIPLE Gas valve lets in compressed gas at ½ system pressureDiaphragm pops up & oil is sent through systemWhen system pressure>accumulator pressure, diaphragm deploys
12ACCUMULATORSUSESAbsorbs the shocks due to rapid pressure variations in a hydraulic systemHelps maintain a constant pressure within the hydraulic systemHelps the hydraulic pump under peak pressure loadsIt is an emergency source of powerSpherical shape is preferred for accumulators
13POWER PUMPSFUNCTIONIs to change mechanical horsepower to hydraulic horsepowerTYPESGear pumps: move fluid based upon the number of gear teeth and the volume spacing between gear teeth.Piston pumps: move fluid by pushing it through the motion of the pistons within the pump
14POWER PUMPS PRINCIPLES OF GEAR PUMPS The liquid from the reservoir is pushed between the gear teeth.The oil is moved around to the other side by the action of the drive gear itself and sent through the pressure line.
15POWER PUMPS PRINCIPLES OF RECIPROCATING PISTON PUMP As the cylinder block rotates, space between the block and the pistons increase, letting in more oil.As the block rotates from bottom dead center, the reverse occurs and the pistons push oil out through the outlet
16SYSTEM RELIEF VALVE PRINCIPLE The adjustment screw is set for a certain pressure value P2.When the pressure increases, the poppet will move up, forcing the excess liquid in
17Douglass Pressure Regulator High pressure oil from the power pump opens valve C and also act on piston APiston A pushes Ball B off seat D, the oil goes through passage D into the center chamber back to the reservoir.
18Single Action Single Impulse HAND PUMPSUsed for testing on ground and for EmergencySingle Action Single Impulse
19Selector ValvesPosition (1) is the position of the selector valve, for example, upon the extension of the landing gear or the lowering of flaps.Position (2) is the position of the selector valve upon retraction of the landing gear or the raising of the flaps
20ACTUATION CYLINDERThe function is to take the pressure & hydraulic fluid flow & change them into linear or rotary motion.Single piston double rod is an equal displacement cylinder used in aileron system or automatic guidance systemDouble piston-double rod actuating cylinder used in bomb bay doors
21ADVANTAGES It is lighter in weight than alternate existing systems. It is dead beat, that is, there is an absence of sloppiness in its response to demands placed on the system.It is reliable; either it works or doesn't.It can be easily maintained.It is not a shock hazard; it is not much of a fire hazard.It can develop practically unlimited force or torque.
22CONCLUSIONHydraulic systems determine flight worthiness, usability and reliability.