pneumatics

Aircraft Pneumatic SystemsPneumatic systemA fluid power system that uses a compressible fluid, air to transmit power.purposeFor major functionsTo perform the same type of operations performed by hydraulic systemsUsed to operateLanding gearFlapsBrakesDoorsDriving pumps ,starters and water injection pumpsFor emergencyAs a back up system to be used when hydraulic (other main) system failsTo operate emergency devices

advantagesAir is universally availableIs inexhaustibleAir is compressible-can be used to store pressureNo return lines, reservoirs and hand pumps are required - simple and light in weight.Relatively Free from temperature problemsNo fire hazardMinimum contamination disadvantagesAir is highly compressible-energy is lost compressing the airWater might condense when air is compressedThis water might freeze when temperature and pressure are very lowNeeds water (moisture) separator componentsSource of compressed airAir bottleRelief valveControl valveCheck valvesRestrictorsWater separatorFilterShuttle valveChemical drierLines and tubing

Source of compressed airMulti-stage piston compressorEngine bleed airVane type air pumpMulti stage piston compressorAir is compressed with piston type compressors with many stages used to recharge high pressure bottles with compressed airThe drive shaft is driven with the engine or electrical motors

Vane type pumpConsists of sliding vanes in a rotor that is eccentrically mounted in a cylindrical housing.Rotation of the rotor creates a low pressure chamber to suck air and ,traps the air between the vanes and compresses the air in the chamber whose volume decreases with the rotation of the rotor. Is widely used for low pressure systems.

Types of vane type pumpWet dryWet type pumpUses vanes made of steelLubrication is obtained by engine oil flowing into the compressor through the mounting flangeThe air should pass through an oil separator before it can be used for the desired purpose.Dry type pumpUses vanes made of carbonDoes not need a lubricant The vanes provide the required lubricationThe vanes are breakablecan be easily damagedDry type pump

Wet type pump

Jet engine bleed airAir is bled (tapped) from the compressor section of a jet engine or an auxiliary power unit.The pressure is regulated and supplied to user systems.Widely used for medium pressure systems.

Air bottleIs used for storage of compressed air at system pressure in high pressure systemsHas two valvesCharging valve Compressed air source can be connected here to charge the cylinder on groundControl valve acts as a shut of valve until the air is required for use.

Relief valvePrevents damage to the system by limiting the pressure in the system.Has a valve that is closed by a spring at normal pressures.The excess pressure overcomes the spring force opening the valve and the surplus air is exhausted into the atmosphere. The valve remains open until the pressure returns to normalRelief valve

Control valveA shut off valve that is used to control the flow of compressed air between the source and the system.

control valveControl valve

Check valvesAre used both in hydraulic and pneumatic systems.Is a one way flow control valve

Check valve

filtersMicronic filters are widely used to protect the system from dirt and dust.Consists of Ports Filter element Micronic type-cellulose, replaceableScreen type-wire mesh ,cleanableA relief holeFilter-micronic type

Filter -screen type

restrictorIs a flow control valve that reduces rate of airflowReduces speed of operation of an actuating unitHas a wide inlet and a narrow outlet to reduce rate of flow.restrictor

Variable restrictorIs similar to the restrictor except that the dimension of the outlet can be adjusted for desired performance.Variable restrictor

Shuttle valveIs used to direct either normal operating pressure or alternate emergency pressure for actuating a unit.

Moisture separatorRemoves moisture from the air.It uses deflector baffles in the path of the compressed air to force it into a sharp turn.The air makes a sharp turn and leaves the separator while the water condenses on the baffles to be collected on the bottom of the separator.A dump valve opens to dump the collected water when the pump is not operating. Moisture separator

Dump valve solenoidHeater blanketAir inAir outChemical drierRemoves the moisture left after the air passes through the moisture separator.Consists of a cartridge that contains a desiccant.Tubing and LinesPneumatic tubing and lines can beRigid tubingStainless steel for high pressure and/or high temperature areasAluminum tubing- for medium pressureFlexible hoseTypes of systemsHigh pressureMedium pressureLow pressureHigh pressure systemsCompressed Air is stored in metal bottlesPressure range is from 1000-3000 PSIThe air bottle has two valvesCharging valveControl valveThe bottle is light in weightCannot be recharged during flightOperation is limited by small supply of bottled airsupply is reserved for emergency operationSome aircraft use compressors to charge the bottles during flight

Types Full systemsBack up systemsFull systemsSome aircraft use pneumatic power to operate flaps, doors, landing gear and brakes.

4300-4950 PSI1750 psiSENSING LINEcomponentsFour stage radial compressorDriven by engine accessory driveUnloading valveMaintains 2900-3300 PSIShuttle valveAllows ground charging by isolating the compressorMoisture separator-removes 98% of the waterDesiccantfilterBack pressure valveBottlesIsolation valvePressure reducerSafety disc

componentsFilter and relief valvePressure regulatorCompressor Hydraulic motorSolenoid controlled selector valveSafety fittingWater separatorDump valveChemical drierPneumatic manifoldfilter

Back up systemsPneumatic systems are used as emergency systems to extend retractable landing gear and application of brakes.

Medium pressure systemGenerally obtains compressed air from the compressor section of a jet engine.Pressure ranges from 100-150 PSIUsed for cabin pressurization and thermal anti-icing systems

Low pressure system Used on light reciprocating engine aircraftCompressed air is obtained from an electrically driven or engine driven pumpPressure ranges from 1 to 10 PSI

Dry and wet type pumps

Pneumatic system for deicing

Pneumatic system for driving gyros

Suction driven

Pneumatic power system maintenanceIncludes Servicing ,troubleshooting, component installation and removal and operational testingCompressor lubricating oil - check dailyFiller cup must be torqued and safetiedPurging periodically, to remove water and other contaminantsMight require removal of units and linesDraining air bottlesServicing air bottlesOperational check

Where does the air used in a medium pressure system come from? It comes from the jet engine compressor. It comes from an air bottle that is recharged before takeoff.it comes from an electric driven compressor connected to the main gearbox.It comes from the exhaust system of a jet engine-What is the function of the air compressor? The air compressor regulates air temperature- The air compressor replaces the air pressure and volume lost through leakage and operation. The air compressor discharges air after it has been used by the air conditioning system The air compressor is not used in Pneumatic Systems because it is a component of the Engine. Bottled air is usually reserved for emergency operation- TRUE FALSE What is the moisture separator? It's the Pneumatic System's pressure sensing regulator and relief valve- It's the system that separates water from air. It's a component of the Pneumatic System that acts as a back-up unit for emergency operations It's the component of the Pneumatic System that separates air from the hydraulic fluid. What is used to prevent explosions in the moisture separator? A non-return valve A by-pass valve, A safety fitting. There is no protection against explosions. Pneumatic Systems using air bottles can be operated several times before recharging. TRUE FALSE What are Pneumatic Systems used for? Pneumatic Systems are used for brakes, doors, pumps/ and emergency devices. Pneumatic Systems are used for the main control surfaces. Pneumatic Systems are used in case of extra engine power is needed. Pneumatic Systems are not used in aviation because gases become uncompressible at high altitudes. Which categories can Pneumatic Systems be divided into? High Pressure Systems and Low Pressure Systems. High Pressure Systems/Medium Pressure Systems and Low Pressure Systems. Medium Pressure Systems and Low Pressure Systems. Nitrogen Systems and Air Systems. Why do Pneumatic Systems using eternal air not need a return line? Because they have very big reservoirs that are filled with gas before takeoff. Because the air they use is discharged after use. It is not true! They have return lines. Because the gas when compressed becomes very hot so that it can not be reutilised. Pneumatic systems employ gas together with a liquid to transmit a force. TRUE FALSE