AeroElectric - CESSNA Single Engine and Light Twin Pressurization ...

duct it into our capsule, we can produce an "artificial atmosphere" having the same pressure as that of a lower altitude, and thus provide the needed oxygen, regardless of altitude. Obviously, if we introduce compressed air into a sealed capsule, we will increase the pressure, and likewise the oxygen supply, but what happens to the capsule structure? If we OVER-pressurize the capsule, structural damage is likely to occur. To preclude this possibility, we need a means of controlling the pressure. We could provide a means to regulate the air entering the capsule; then the pressure would increase, but the air in the capsule would soon become depleted of oxygen since the air is not moving through the capsule. By adding an OUTFLOW VALVE to our capsule, we can regulate the pressure inside by controlling the outflow of air from the capsule, as well as exchanging the air in the capsule by creating air flow. To increase pressure, the OUTFLOW VALVE would close, and to DECREASE the pressure, the OUTFLOW VALVE would open. We can monitor the pressure inside our capsule by the use of a DIFFERENTIAL PRESSURE GAUGE. It would be referenced to the INSIDE pressure as well as the OUTSIDE pressure, so it would indicate the difference between the two references and thus show cabin differential pressure. The pressure in the capsule is now regulated by the position of the outflow valve. But what would happen if the outflow valve were to stick closed? One of two choices are available. First, we could turn off our compressor, which would eventually lead to our original problem--NO OXYGEN; or secondly, we could install a second outflow valve. This back-up outflow valve is referred to as the SAFETY VALVE. It is merely a redundant feature in our pressurization system for the purpose of insuring safety, and preventing serious damage to our capsule. Now that we can control the pressure in our capsule, what about the task of flying the aircraft? We need a means of automating and selecting our system pressure to relieve the flight crew of manual pressure regulation and monitoring. By adding a CONTROLLER, an ON-OFF SWITCH and a SAFETY SOLENOID in the system, automatic monitoring of pressure and safety is accomplished. The CONTROLLER permits selection of any desired cabin pressure between sea level and 10,000'. It monitors the pressure altitude inside the capsule, and at the same time, controls the outflow valve to a position that maintains a selected cabin pressure altitude. The SAFETY SOLENOID is controlled by an ON-OFF switch, which in turn, controls the safety valve. When the switch is in the "ONII position (PRESSURIZE MODE) the SAFETY SOLENOID is de-energized allowing the safety valve to close and the capsule will pressurize. With the switch in the 1I0FF" position, (NON-PRESSURIZE MODE) the SAFETY SOLENOID is energized, which allows the safety valve to open, thus DE-PRESSURIZING the capsul e. 1. WHAT IS CONSIDERED TO BE STANDARD DAY ATMOSPHERIC PRESSURE AT SEA LEVEL? A. 14.20 PSI, 28.90 IN. Hg. B. 14.70 PSI, 29.92 IN. Hg. C. 4.30 PSI, 8.87 IN. Hg. D. 14.75 PSI, 30.30 IN. Hg. A. As altitude increases, pressure increases B. As altitude decreases, pressure will remain the same C. As altitude increases, pressure decreases D. As altitude decreases, pressure decreases C. Safety valve D. Controller 4. WHAT ARE THE PRESSURE REFERENCES USED TO DETERMINE CABIN DIFFERENTIAL PRESSURE? C. Safety valve pressure and pitot pressure D. Outflow valve pressure and upper deck pressure A. Differential pressure gauge B. Cabin rate-of-climb indicator 6. WHAT PREVENTS ULTIMATE DAMAGE TO THE PRESSURIZED CAPSULE UNDER PRESSURIZED CONDITIONS? 7. WHAT COMPONENT IN THE PRESSURIZATION SYSTEM PHYSICALLY MOVES TO REGULATE CABIN PRESSURE? B. Safety valve C. Outflow valve C. Energized, safety valve open D. De-energized, safety valve closed As this point in your workbook, you should be fairly well acquainted with the pressurization system components and their immediate function. Under- standing WHY pressurization is important, gives you the basis from which the purpose of each component can be further detailed. Previously, we discussed the capsule in which pressurization took place. Let's take a closer look at this capsule, its boundaries, construction, and related components. The pressure capsule is the cabin area of the Pressurized Centurion bounded by the firewall on the front and extending to the aft cabin pressure bulkhead. The cabin floor, just aft of the rear doorpost, becomes the bottom boundary, while the outer skins compose the remainder of our IIsealed capsulell• Like the larger twin Cessnas, the Pressurized Centurion is built on a IIfail-safell construction principle. If anyone structural part in the pressure capsule should fail, the remainder of the capsule would remain intact and functional. Double-row riveting, back-to-back formers, added reinforcement members, and heavier-gauge channels are items that provide the necessary strength to withstand the internal forces of pressuriza- tion. This construction method gives the Pressurized Centurion the same exceptional safety margin as cabin-class twin-engine aircraft. Increased rel iabil ity, safety, and infinite service 1 ife are the resul ts of IIfail-safell construction. 1. Door Seal. 2. Window Seal (Foul Weather) 3. Windshield. Cabi n Pressure C) 1. Rivet 2. Skin 2. Retainer 3. Seal Cabin sealing is accomplished in the same manner as the larger twins. First, the skins and formers are aligned and held in place securely, while all holes are drilled and reamed. The skins are removed and sealant is uniformly applied to the bare formers, then the skins are reinstalled. While the sealant is still workable, the formers and skins are riveted in place, resulting in an air-tight assembly. Should repair to the cabin pressure capsule be necessary, detailed instructions are outlined in the Pressurized Centurion Service Manual. Special types of sealants are used in different areas of the pressure capsule, so consult the Service Manual for proper sealant usage. Not only does the pressure capsule require special sealing, but so does the cabin door and emergency exit. The seals are specially designed to provide pressure retention. They are inflated from the cabin side by pressurized air which enters through holes in the hollow seal. Inflating the seals causes them to expand against the cabin door, emergency exit and fuselage structure for positive sealing. Pressurization has necessitated other changes in the Pressurized Centuiron. Stronger doors, redundant safety latches, and changes in window design Where cables and rods exit the pressure capsule, special labyrinth seals are installed to limit the escape of pressurized air from the cabin. the "unpressuri zed mode", the seal is relaxed and wi 11 allow moi sture to drain from the fuselage. In the "pressurized mode", the seal expands and closes the drain holes to prevent loss of pressurization. 2-3 PRESSURE CAPSULE Pressurization begins with compressed air. The source of this compressed air is the exhaust-driven TURBOCHARGER, located on the lower right-hand side of the engine. The primary function of the turbocharger is to provide the engine with compressed air for high altitude operation. The turbocharger compresses air into the IIUPPER DECK SYSTEW, which is the duct system between the compressor section of the turbocharger and the throttle plate of the induction system. A portion of this IIUPPER DECK AIRII is extracted and routed to the cabin for pressurization. The SONIC VENTURI is the means by which air is extracted from the upper deck. It functions as a fixed bleed-air orifice (flow limiter) to limit the amount of air taken from the upper deck, to prevent a deficiency of air to the engine. Compressing the air causes the temperature of the air to increase. Thus the air from the compressor section is very warm. If this hot air were to be routed directly to the cabin, it would provide a source of heat for the cabin. If heating the cabin is NOT desired, the air can be cooled before entering the cabin by the HEAT EXCHANGER, located on the lower left-hand side of the engine compartment. The HEAT EXCHANGER operates like a radiator. Ambient air flows through the fins of the heat exchanger, around the core, and exhausts overboard. The cool ambient air has thereby cooled the air ~ OVERBOARD PRESSURE CAPSULE inside the core of the heat exchanger, and cool compressed air is allowed to enter the cabin. An air scoop in the lower forward left side of the nose structure, and an exhaust scoop located in the lower side cowl panel assures a high volume of ambient airflow through the heat exchanger. A valve is included as part of the heat exchanger installation to enable the pilot to select either warm or cool airflow through the heat exchanger. In the "warm" position, the valve directs heated air from the engine exhaust shroud through the heat exchanger. A PUSH-PULL control, labeled "CABIN HEAT" is located on the lower right side in the instrument panel. This control operates the "air selector" valve in the heat exchanger assembly for cabin temperature control. After passing through the heat exchanger, 'pressurized air is routed into the cabin through a MANUAL DUMP VALVE PLENUM, located on the forward side of the firewall. When the MANUAL DUMP VALVE is opened, the pressurized air is routed overboard. A push-pull control in the cabin gives the pilot this option. In the event contaminated air enters the cabin, the MANUAL DUMP VALVE should be opened to route the contaminated air overboard. With the MANUAL DUMP VALVE closed, pressurized air enters the cabin through a flapper-type INLET CHECK VALVE installed on the aft side of the MANUAL DUMP VALVE PLENUM. In the event of a loss of incoming pressurized air, the check valve will trap pressurized air in the cabin and prevent back- flow. Loss of pressurized air could be the result of an engine malfunction or if the MANUAL DUMP VALVE is opened. ¢ ¢ RAM AIR FLOW 11I11I1111111111I HEATED RAM AIR FLOW PRESSURIZED AIR FROM TURBOCHARGER PRESSURIZED AIR VENTING FROM CABIN ------- MECHANICAL CONNECTION PNEUMATIC CONNECTION PRESSURIZED AIR DUMP VALVE CONTROL HANDLE CABIN HEAT, DEFROSTER AND VENTILATING AIR CONTROLS TO ALTITUDE SELECTOR CONTROL TO CABIN PRESSURIZATION SWITCH After passing through the inlet check valve, the pressurized air enters a DIVERTER CHAMBER. A valve within the diverter assembly is operated by a push-pull control labeled FLOOR-DEFROST/OVERHEAD. The valve directs the airflow from the diverter assembly to either the floor registers or to the overhead outlets. When the "CABIN HEAT" control is in the "COOL" mode, the air may be ducted to both the floor registers and the overhead outlets. When the control is in the "CABIN HEAP mode, the warm air is ducted through the floor level outlets only. This is accomplished by an interconnect between the "FLOOR/OVERHEAD" control and the "CABIN HEAP control. DEFROST air to the windshield is taken from the floor level distribution system. Fresh air is routed into the cabin when pressurization is not in use. Leading edge openings located in the wings provide cool air which is ducted into the cabin through CABIN PRESSURE CHECK VALVES. There are two valves; one per wing, located above each of the two forward seats along the wing butt line. Their function is to provide fresh air when in the depressurized mode and to automatically close when the cabin is pressuri zed. CABIN PRESSURE PRESSURE ON PRESSURE CAPSULE .• DEPRESSURIZE .•. PRESSURIZE To this point, we have discussed how air is INTRODUCED into the cabin providing cabin pressurization. How pressurization is regulated and controlled will be the topic of the next discussion. To provide an effective means of controlling cabin pressurization, an OUTFLOW VALVE is installed in a recess in the upper aft cabin pressure bulkhead. By locating the outflow valve in the aft section of the cabin, we produce a more effective exchange of air. Air enters the front of the cabin and exits the rear. When the outflow valve is mentioned, the SAFETY VALVE should also be recalled. The function of the SAFETY VALVE is to relieve cabin pressure should the outflow valve malfunction. It is located next to the outflow valve on the aft cabin pressure bulkhead. It also incorpor- ates a means of keeping the cabin de-pressurized when pressurization is not desired. A SAFETY SOLENOID is incorporated in the SAFETY VALVE itself, thereby directly controlling the position of the safety valve. When the cabin pressurization switch located to the left of the controller is in the "0FF" position, the SAFETY SOLENOID is energized, opening the SAFETY VALVE, and thereby maintaining an unpressurized cabin. Conversely, when the switch is in the "0N" position, the safety solenoid is de-energized, allowing the safety valve to close and the cabin to pressurize. DO NOT CONFUSE THE TWO VALVES! The safety valve incorporates a safety solenoid and the outflow valve is connecteG ~l the con troll er by a polethylene tube. Both valves are accessible by removing the interior panel at the aft pressure bulkhead. A cabin pressurization CIRCUIT BREAKER is provided to protect the elec- trical portion of the pressurization system. To select cabin altitude and meter reference pressure to the outflow valve, a CONTROLLER is installed on the lower left instrument panel within easy reach of the pilot. This is the IIBRAINS" of the pressurization system . To monitor the pressurization system, there are two gauges that indi- cate cabin pressure altitude, cabin altitude rate~of~climb, and cabin differential pressure. .'I';:'~' "-',' '-' I '---TO PRESSURIZED AIR DUMP VALVE ......._---_._-_ _------------- --- ..... .--------- ._--- ..------- .- ------- •••••_..-_...- 9: ... ~~ ..,- --------------------,---------_. __ .._--~----••....-.-::--...... ,.----"'\- 0 .- .~ : .. ",.. ". ",' ". ",.-...... ..- :-""-'...-" ' I - .'" - - .. \ .. :"", . .,',_ t',' \ ~,' ~" I. I : • :j..... ,,_ : : Ii , : ~ ~ ~ I -, ~oJ.O ..,,: ~\ : ~ .~~ :~ .~:.tf ..•.. '..... .,/ t' ./:.' ,/:~ ,'::~.- --'.- .'- .- '" - " , ' ~ c::..,.' 0 -~ ..•.•• __.' _-.. ~.:...._ .•.• ~_.. : I , ----, ',.--, I.·::;::---"-'~ ,'.---" ,.,~..;..".•..-- I : ..: ' \ ~ ,,: . ':/ " : , '. , t • • " " : - ' ~ il •• :: :- '" ' " ,~ \ : ~ ,It : , ....1 ~... ,.,1:" ",' I,' .",~ : -- '-'. ~-_.~_.' :> _ •• - "~--"":-': CABIN ALTITUDE and DIFFERENTIAL PRESSURE are combined into one instrument. The large needle indicates cabin pressure altitude, or the artificial altitude created by the pressurization system. The smaller needle indicates cabin differential pressure. DIFFERENTIAL PRESSURE is the difference in pressure between the inside and outside of the pressure capsule. A source from each pressure is referenced to the differential pressure gauge. The MAXIMUM CABIN DIFFERENTIAL PRESSURE is indicated by a "red-l ine" at 3.35 PSI. The second instrument associated with cabin pressurization is the CABIN RATE-OF-CLIMB INDICATOR. It is located on the left side of the instrument panel above the dump valve control handle. It is vented directly to the cabin and senses changes in pressure within the ) cabin to show cabin rate-of-climb or descent. A CABIN ALTITUDE WARNING LIGHT is incorporated to indicate when the cabin pressure altitude reaches and exceeds 12,400 ± 100 ft. The light is controlled by a barometric pressure switch locateJ forward of the instru- ment panel. When this light illuminates, it reminds the pilot of OXYGEN REQUIREMENTS necessary when the cabin altitude is in excess of 12,400 ft. The switch will reset at an altitude of approximately 11,700 ft. 1. WHAT PREVENTS PRESSURIZED AIR FROM ESCAPING PAST THE CABIN DOOR AND EMERGENCY EXIT? A. Rubber o'ring seals B. Seals inflated by upper deck pressure C. Hollow rubber seals inflated by cabin pressure D. Solid rubber seals 2. WHAT LIMITS PRESSURIZED AIR FROM ESCAPING AROUND CONTROL CABLES GOING THROUGH THE PRESSURE CAPSULE? C. Dyno-seals D. Labyrinth seals C. Heat air for the cabin only D. Cool air for the cabin only A. To dump cabin pressure if desired B. To dump cabin pressure when the outflow valve malfunctions C. To route pressurized air overboard D. To pressurize the cabin A. Wing leading edge openings routing air through the cabin pressure check valves B. Ram air from the heat exchanger C. Bleed air from the sonic venturi B. Aircraft altitude above ground C. Cabin rate of descent or climb 8. WHAT IS THE PURPOSE OF THE CABIN ALTITUDE WARNING LIGHT? A. To warn the pilot when the aircraft goes over 10,000 feet B. To warn the pilot when the cabin pressure altitude goes over 10,000 feet C. To warn the pilot when the aircraft goes over 12,400 feet D. To warn the pilot when the cabin pressure altitude goes over 12,400 feet 9. AT WHAT PRESSURE IS THE MAXIMUM CABIN DIFFERENTIAL PRESSURE RED LINE MARKED ON THE DIFFERENTIAL PRESSURE GAUGE? A. 3.45 PSI B. 3.50 PSI C. 3.35 PSI D. 3.30 PSI In this section, you will be able to relate the components of the Pressur- ized Centurion to those of the Pressurized Skymaster with only a few minor differences. The major difference becomes immediately apparent when comparing the two aircraft. The Pressurized Skymaster utilizes airflow from TWO engines. One can basically assume that there will be TWO of each component in the DUAL AIR DISTRIBUTION SYSTEM. The Pressurized Skymaster has a pressure capsule beginning at the forward firewall, and extends to the forward side of the rear firewall. The outside skins are the boundaries for the pressure capsule in all areas, except the area directly over the main landing gear strut wells. In this area, the cabin floor becomes the boundary. PRESSURE DRAIN SEALS are located in the lower skin of the fuselage. The pressure capsule of the Pressurized Skymaster is constructed in the same manner as the Pressurized Centurion in that IIFAIL-SAFEIImethods are employed, and sealing techniques are the same. LABYRINTH SEALS are used wherever cables exit the pressure capsule. Cabin pressurization is provided by both the front AND rear engines in normal operation, but pressurization can be easily maintained from the airflow produced by only one engine. PRESSURIZED SKY MASTER PRESSURE CAPSULE CHECK& - - CHECK & _ •••••••••••••.• DUMP •••••!----t- DUMP VALVE VALVE . t OUT. t OVERBOARD FLOW SAFETY OVERBOARD VALVE VALVE The front turbocharger is located on the lower right side of the engine, and is accessible by removing the lower right cowl panel. Compressed air is routed from the turbocharger into the "upper deck system", extracted by the SONIC VENTURI (flow limiter) and routed through the front AIR SELECTOR VALVE. The AIR SELECTOR VALVE permits selection of either cool or warm pressur- ized air to enter the cabin, depending on the position of the front IIPRESS AIR TEMplI control located on the instrument panel. If the control is in the "COOL" mode, the air is directed through the HEAT EXCHANGER, where it is cooled by ram ambient air and then routed to the cabin. The scoop for ram air to the heat exchanger is located in the left cowl nose cap. When the IIPRESS AIR TEMplI control is in the IIWARW mode, the CABIN AIR SELECTOR routes pressurized air through the cabin combustion heater, rather than through the heat exchanger. The heater can then be operated if additional cabin heat is desired. After the air passes through either the cabin heater or through the heat exchanger, the air is then routed through the front MANUAL DUMP VALVE PLENUM, through the FIREWALL INLET CHECK VALVE, and into the cabin through the defrost network and cabin floor outlets. Standard equipment ~lso includes a recirculating blower located beneath the instrument panel on the left side of the forward firewall. The only purpose of the blower is to circulate cabin air back through the heater when operating in the IIHEATIImode, or through ventilators above the radios 3-3 22 ~ ~23 1. Blower 10. Adapter 17. Selector Assembly 2. Firewall Shutoff 11. Air Selector Valve 18. Overhead Outlets Valve 12. Venturi 19. Air Scoop 3. Diverter Valve 13. C opHot Outlet 20. Diverter 4. Inlet Valve (Heater) 21. Air Dump Valve 5. Recirculation Tube 14. Defroster Outlet 22. Outflow Valve 6. Heater Assembly 15. Auxiliary Ventilation 23. Safety Valve 7. Adapter Outlet 24. Stop 8. Inlet Duct 16. Floor Level Outlet 25. Control Assembly 9. Heat Exchanger 26. Control Cable when operating in the (ICOOL" mode. It also incorporates a FIREWALL SHUT-OFF VALVE which closes to prevent loss of pressurization when the front DUMP VALVE is opened for rear engine ~ operations. All the selector valves are manually operated by slide controls, located on the lower mid-right instrument panel. The front and rear dump valve controls are located on PRESSURIZED AIR DUMP VALVE CONTROLS (-- ----...., I I t:::dI I I LfRONT-J ICABIN PRESS AIR 'I PUll TO , DUMP I I r REAR --, I I ) \ , ---- PRESS AIR TEMP fR 0 NT REAR COOL fWD PASS AUX AIR HIGH ~ lOW Off @Off WARM1 I I I I 1---- TO FRONT PRESSURIZATION AIR SELECTOR VALVE I L TO REAR PRESSURIZATION AIR SELECTOR VALVE ------- TO FRONT PRESSURIZED AIR DUMP VALVE AND FIREWALL SHUTOFF VALVE -- -- -- -- TO REAR PRESSURIZED AIR DUMP VALVE RAM AIR FLOW STATIC AIR PRESSURIZED AIR FROM FRONT TURBOCHARGER PRESSURIZED AIR FROM REAR TURBOCHARGER RECIRCULATING PRESSURIZED AIR FROM CABIN PRESSURIZED AIR VENTING FROM CABIN ELECTRICAL CONNECTION MECHANICAL CONNECTION PNEUMATIC CONNECTION AI R FLOW CHECK VALVE __ COMBUSTION HEATER COOL AIR BYPASS TUBE GROUND PRESSURIZATION PORT PRESSURE TEST PORT FLOOR LEVEL OUTLET (FORWARD OF RUDDER PEDALS) CONTROLLABLE FLOOR LEVEL OUTLET (UNDER PILOT'S SEAT) CONTROLLABLE FLOOR LEVEL OUTLET (UNDER FRONT PASSENGER'S SEATI TO ALTITUDE SELECTOR CONTROL I "HEAT EXCHANGER RAM AIR INTAKE (INSIDE REAR ENGINE AIR SCOOP) PRESSURIZED AIR FLOW FROM COMPRESSOR SECTION OF TURBOCHARGER The rear distribution system is the same as the front, with the exception of the ducting. The ducts are modified to match the rear engine mounting. The distribution network within the cabin is the overhead ventilation system. Note that the front engine supplies air to only the floor ducts and rear engine supplies air to just the overhead ducts. The turbocharger for the rear engine is mounted below the engine on the left side of the engine compartment. Compressor discharge from the rear engine is routed up across the engine through the SONIC VENTURI (flow limiter) to the CABIN AIR SELECTOR VALVE. The REAR cabin air selector valve diverts the air around the heat exchanger when the control is in the "WARM" mode. Air is directed through the heat exchanger when the control is in the "COOL" mode. Ambient ram air for cooling the heat exchanger is ducted through the rear engine air scoop. There is no combustion heater on the rear engine assembly. Pressurized air is then routed to the rear MANUAL DUMP VALVE PLENUM and through the rear FIREWALL INLET CHECK VALVE. The air then enters a DIVERTER ASSEMBLY in the cabin which distributes the air through the overhead outlets. If all overhead outlets are closed, a RELIEF VALVE in the DIVERTER ASSEMBLY "OPENS" and allows air to enter the cabin at the rear firewall. The OUTFLOW and SAFETY VALVE on the Pressurized Skymaster are located on the lower half of the rear pressure bulkhead. The function of these valves is the same as for the Pressurized Centurion; to control the amount of air that leaves the pressure capsule or aircraft cabin, and as a safety back-up, should the outflow valve stick closed. The CONTROLLER for the pressurization system is located to the lower left of the pilot's instrument panel. The "ON-OFF" switch, CABIN RATE- OF-CLIMB INDICATOR, and CABIN ALTIMETER/DIFFERENTIAL PRESSURE INDICATOR are also located to the pilot's lower left. A CABIN ALTITUDE WARNING LIGHT on the instrument panel is also included as a means of monitoring cabin altitude. Oxygen should be used when this light is on. The light is automatically turned on by a barometric switch at a cabin altitude of 12,500 ± 500 feet. The light will go out at approximately 11,500 feet. 1. WHEN THE FRONT PRESSURIZED AIR TEMPERATURE CONTROL IS IN THE "WARM" MODE: A. Pressurized air is routed through the heat exchanger and cabin combustion heater B. Pressurized air bypasses the heat exchanger and cabin combustion heater C. Pressurized air bypasses the heat exchanger and is routed through the cabin combustion heater B. Provides air to overhead ducts only C. Provides air to floor ducts and defroster D. Closes to prevent loss of pressurization when the front dump valve is opened for rear engine only operations A. Diverts air through the heat exchanger when in the WARM mode B. Diverts air around the heat exchanger when control is in WARM mode C. Route fresh air into cabin 6. IF ALL OVERHEAD AIR OUTLETS ARE CLOSED, WHAT PREVENTS PRESSURIZED AIR FROM DAMAGING THE DUCTS? A. Air will enter cabin through the floor vents B. Air will enter through the defroster vents C. A relief valve in the diverter assembly opens and allows air to enter at the rear firewall A. On the bottom fuselage skin B. On the rear pressure bulkhead C. On the forward pressure bulkhead D. In the forward bulkhead of the right tail boom ~ Aft press~~e Bulkhead ,------, : : CONTROLLER I I ~.•......---,I I ----, / The construction of the outflow valve begins with a diaphragm and housing which creates an internal chamber. As the diaphragm expands, the outflow of cabin air is restricted. As the diaphragm contracts, the air is allowed to flow out freely. The natural shape of the diaphragm tends to open the valve. In order to control the position of the outflow valve, we can install a valve labeled lithe CONTROLLER". The purpose of the controller is to control the air pressure inside the outflow valve chamber. But, unless we provide some means to allow a flow of air through the outflow valve chamber, the pressure in the chamber will be trapped, the valve will close and we will not be able to open it. By installing a bleed line to ambient air and incorporating an orifice in the line, an air flow is created. Now we can expand the chamber and close the outflow valve by opening the controller completely. Although some of the pressure will bleed off through the overboard vent, the remaining pressure will be more than sufficient to close the valve. By closing off the controller, air pressure in the chamber will bleed over- board, and the natural shape of the diaphragm will open the outflow valve. Thus, we control the position of the outflow valve by the amount of air pressure we direct to it through the controller. ,------, : ~ CONTROLLER I I •..... ~ I I ------~ The outflow valve will operate to maintain a selected cabin altitude. However, we must incorporate some means of providing safety when maximum cabin differential pressure is reached (3,35 PSI). Since cabin differential pressure is determined by the difference between the pressure inside the aircraft compared to the pressure around the outside of the aircraft, we will utilize these sources to automatically control maximum differential pressure. Utilizing the same outflow valve, we place a cylinder in the middle of our valve. Down the center of the cylinder we drill a passage to ambient air. Additional passages lead from the outflow valve chamber to the center passage. To isolate the chamber air from ambient air, install a differential valve, but spring load the valve to the open position. A diaphragm is also installed between the differential valve and housing. ,------" : ~ CONTROLLER I I .--/ ~ I I I I \_-----~ Above the differential valve, we create a diaphragm chamber, spring -loaded to hold the valve closed. On one side of the diaphragm we will vent cabin air pressure. On the other side of the diaphragm we vent ambient air pressure through a line called a PICCOLO TUBE. Thus, we have a differential pressure regulator. When at altitude, ambient air pressure is low and cabin pressure is high. At maximum differential pressure, the force created across the diaphragm compresses the larger spring, allowing the smaller spring to lift the differential valve, and bleeding outflow valve chamber pressure overboard. The natural shape of the outflow valve diaphragm opens and thus maintains 3.35 PSI maximum differential pressure. POPPET VALVE TO OUTFLOW VALVE THREADED SHAFT SPRING ! r-----~------)-~---)-----/-------I I I I I I I ' I 11 --- : AIR FILTER I --~ i ~ L ~---------~-------~------- In its simplest form, the controller is an altitude sensitive valve. By opening and closing the valve, we control the amount of air pressure directed to the outflow valve. In order to make it responsive to altitude change, we control the valve position with a sealed bellows (29.92 IN. Hg. - Sea Level Pressure Altitude). An increase in altitude causes the bellows to expand, opening the poppet valve, and thus closing the outflow valve. Likewis~, a decrease in altitude contracts the bellows, closing the poppet valve, and allowing the outflow valve to open. The controller now operates, but we are unable to select cabin altitudes. By incorporating a knob, spring and screw mechanism, we can set and adjust the amount of tension or preload on the bellows, and thus select the point at which the poppet will begin to open. The last component we need to install is an air filter to prevent contamination to the system. VERNIER DRIVE 5:1 GEAR RATIO The outflow valve/controller system is now complete. Remember the controller is altitude selectable and altitude sensitive. Also, the outflow valve is referenced to three different levels of air pressure. The highest of these pressures is cabin air pressure in the differential pressure regulator lower section. It enters the chamber through a micron wafer filter in the side of the differential control section of the valve. The second highest pressure in the outflow valve is metered control pressure from the controller to the main diaphragm chamber. The lowest pressure reference is in the differential pressure regulator upper section, which is ambient air pressure obtained from the piccolo tube. The final component in the pressurization system is the safety valve. The safety valve is installed to limit cabin pressure in the event the/ / The safety valve is very similar to the outflow valve in construction. It consists of a chamber created by a diaphragm and a housing with an overboard bleed and solenoid control valve. The same type of pressure regulator utilized on the outflow valve is also used on the safety valve. The safety valve is designed to be fully open, or fully closed. During normal pressurized operation the pressurization switch is placed bleed valve, and blocking off the small bleed passage on the left. Cabin air pressure then enters the diaphragm chamber and closes the valve. Remember, the safety valve is not connected to the controller or outflow valve! In the event the outflow valve malfunctions, and fails to regulate maximum cabin differential pressure, (3.35 PSI) the safety valve pressure regulator will open the safety valve. At 3.45 PSI differential pressure, the differential valve will allow the diaphragm chamber pressure to bleed overboard through the center drilled passage. The natural form of the safety valve diaphragm will open the safety valve, and cabin air will be vented overboard. Summarizing what we have learned, we have an outflow valve modulating to control cabin pressure. The outflow valve is repositioned by the controller in the instrument panel. The controller is altitude sensitive as well as being adjustable. If the outflow valve should malfunction, the safety valve will limit maximum differential pressure before structural damage can occur. I '---TO PRESSURIZED AIR DUMP VALVE I AIRCRAFT ALTITUDE I I I I I I I I I I I I I I : GU:PJ : _ DIFFERENTIAL MODE ISOBARIC MODE UNPRESSURIZED MODE Now that we have an overall picture of the pressurization system as applied to the Pressurized Centurion and Pressurized Skymaster, let·s take a more in-depth look at the control system from a total operational view. The controller allows the pilot to select a pressure altitude at which the cabin will begin to pressurize, as shown on the outer scale. The inner scale represents the altitude at which maximum differential pressure will be reached. The difference between the outer scale and the inner scale is referred to as the "ENVELOPE". We can best illustrate the envelope by assuming that the controller is selected to hold a 4,000' pressure altitude in the cabin--as shown on the outer scale. The maximum differential pressure altitude will then be 12,000' as shown on the inner scale. So the lIenvelopell in this case has a base of 4,000' and an upper limit of 12,000'. As long as the aircraft is flown at an altitude inside this envelope, the controller will influence the outflow valve to regulate cabin pressure altitude at a constant pressure equivalent to 4,000'. As the aircraft climbs and descends within the envelope, the differential pressure increases and decreases accordingly, in order to maintain a constant absolute pressure altitude of 4,000' in the cabin. Remember, AS ALTITUDE INCREASES, AMBIENT PRESSURE DECREASES. In order to compensate for the decrease in ambient pressure as we climb, we must compress more air into the cabin to build up the differential pressure to keep a constant cabin altitude. Upon descent, the opposite is true. As long as the aircraft is BELOW the envelope as selected on the control- ler, the outflow valve remains open and the cabin is unpressurized. When the aircraft climbs and penetrates the lower limit of the envelope, the outflow valve is positioned to restrict outflow which causes pressure to start building inside the cabin. As the climb continues within the envelope, the outflow valve slowly closes to maintain preselected cabin altitude as the outside ambient pressure decreases. Thus, cabin absolute pressure remains constant, keeping cabin pressure altitude at the value selected on the controller. If the airplane levels off at any altitude within the envelope, the outflow valve will stabilize, and differential pressure stops building. The outflow valve will then modulate, only as necessary, to hold that particular differ- ential pressure. But if the climb continues through the envelope above maximum differential pressure altitude, the outflow valve will open to prevent the cabin from exceeding 3.35 PSI maximum differential pressure. Now the system has shifted from isobaric control by the controller to differential pressure control by the outflow valve differential pressure regulator. Once the cabin is pressurized to maximum differential pressure, a continued climb will LOWER ambient pressure. As a result, cabin pressure also decreases at the same rate in order to maintain a 3.35 PSI maximum differential between the cabin pressure and ambient pressure. In review, the outflow valve position is influenced by the controller while the aircraft is being operated BELOW the envelope and INSIDE the envelope. When the aircraft is operated ABOVE the envelope, the outflow valve has a built-in maximum differential pressure regulator, or limiter, which overrides the influence of the controller when "red-line" (3.35 PSI) differential pressure is reached. A. Controlling the pressure in the safety valve chamber B. Adjusting the size of outflow valve orifice C. Controlling the air pressure inside the outflow valve chamber D. Adjusting spring tension on the outflow valve A. Controller selector knob and the piccolo tube B. Outflow valve and controller D. Cabin pressure, ambient atmospheric pressure and the pressurization "ON-OFF" switch and safety solenoid A. At 3.35 differential pressure B. At .10 PSI above outflow valve maximum differential pressure setting 4. AS YOU CLIMB THROUGH THE ENVELOPE ABOVE MAXIMUM DIFFERENTIAL PRESSURE ALTITUDE, THE OUTFLOW VALVE WILL: B. Open, to prevent the cabin from exceeding 3.45 PSI maximum differential pressure C. Open, to prevent the cabin from exceeding 3.35 PSI maximum differential pressure D. Close, to prevent the cabin from exceeding 3.35 PSI maximum differential pressure 4-21 A. the highest is cabin air pressure B. the second highest pressure is metered control pressure from the controller to the main diaphragm chamber A. the solenoid on the safety valve is de-energized B. the controller is controlling the position of the outflow valve as altitude increases C. the safety valve solenoid is energized D. Both A and B are correct 7. WHEN A PRESSURIZED CENTURION CLIMBS UP THROUGH THE PRESSURIZED ENVELOPE, CABIN DIFFERENTIAL PRESSURE WILL BE CONTROLLED BY: B. The outflow valve differential pressure regulator C. Controller and outflow valve 8. WITH THE CONTROLLER SET AT 4,000 FT. AND THE FLIGHT ENVELOPE ALTITUDE EXCEEDED, THE CABIN PRESSURE WILL BE: 9. THE CONTROLLER IS BOTH SELECTABLE AND ALTITUDE SENSITIVE. WHICH PART OF THE CONTROLLER MAKES IT ALTITUDE SENSITIVE? B. The isobaric poppet valve C. The sealed bellows 10. WHAT POSITION WILL THE OUTFLOW AND SAFETY DIAPHRAGMS TAKE WHEN AIR PRESSURE IS REMOVED FROM THE DIAPHRAGM CHAMBER? A. Outflow valve open, safety valve closed B. Safety valve open, outflow valve closed C. Outflow valve open, safety valve open D. Outflow valve closed, safety valve closed Generally, maintenance of pressurization components consists of visual inspection, preventive maintenance, and a complete functional test to verify proper operation. Areas that require inspection are covered in detail in the Service Manual. The areas mentioned below are but a few of those items: The controller, outflow valve, safety valve and pneumatic line between the controller and outflow valve should be checked for condition and security. All manually operated valves and various check valves in the distribution systems should be checked for proper operation and sealing. Cabin windows and doors should be inspected around seal areas for possible leakage. The door seal should be inspected for tears and cuts as repairs can be made to this seal. Each control cable which is routed through a bulkhead from a pressurized to a non-pressurized section must be inspected to determine if they are adequately sealed. ~12 \ 1. Tube 2. Union 3. Nylon Elbow 4. Bushing 5. Adjust· 6. Lock lng screw 7 Nut 8.0 sutflOW Valve • nap Ring 1~. Screen n. Spacer 12. Gasket 13· Piccolo Tub . Lock-O S e 14. Nut - eal 15. S 16 snap Ring • creen 17. Safet 18 G Y Valve • asket 19. Spacer 20. Du 21 L mp Solenoid • ock Nut 22. Adusti 23. 0 R. ng SCrew - lng 24. Nut There are special inspection requirements detailed in Chapter 2 of the Service Manual for the pressure capsule. These inspections are to be replacement, replacement of the controller filter, cleaning of the outflow valve and safety valve. The valves should be cleaned with isopropyl alcohol or mild detergent solution. BE SURE TO WIPE AWAY ANY RESIDUE TO PREVENT THE VALVES FROM STICKING! Cleaning of the outflow and safety valve micron wafer filters may be accomplished by using a vacuum cleaner and hose. Do not apply full vacuum or you may damage the micron wafer. Hold the suction hose away far enough to keep the suction low. The micron wafer should not be removed as it fits so snugly, it could be damaged upon removal. 1. Elbow 2. Control Knob 3. Selector Assembly 4. Filter The Labyrinth Seals, used wherever cables exit the pressure capsule, must be install ed with the slant of the "teeth" toward the pressure capsule. This allows air pressure to push the teeth out to form a seal around the cable. These cable seals are packed with MIL-G-81322 grease prior to installation, and the cable is lubricated for the full length of its travel within the seals. At scheduled intervals, the seals must be removed, cleaned, inspected, and repacked with grease. Cabin Pressure C) Q Pressure drain seals located in the lower skin of the fuselage should be cleaned as necessary. Caution should be used when cleaning these drains. Never insert sharp tools or metal objects into the drains as this will puncture the pressure seals. 1. Rivet 2. Skin 2. Retainer 3. Seal When special installations or repairs are being made, care must be taken not to induce leaks into'the pressure capsule. The Service Manual covers structural repairs and should be referenced when making any repairs or installations in or near the pressure capsule. o liffillllliillilim CRITICAL VISION AREA Ii....) NON-CRITICAL VISION AREA Left windows typical for right windows. Left windows typical _ CRITICAL VISION AREA for right windows. 1-::::::::::::::::::::1NON-CRITICAL VISION AREA .0 t, Maintenance of cabin windows is critical. Damaged window panels and windshields should be removed and replaced if the damage is extensive. Windows are sealed with EC-1675B and EC-1675A accelerator (3M Co.). The windshield is sealed with EC-1608B and EC-1608A (3M Co.). Certain repairs to window panels and windshields are allowed and can be made without removing the damaged part from the aircraft. "WARNING" If temporary repairs are made, the aircraft must be operated in the unpressurized mode until replacement of windows can be made. No repairs are recommended on stressed or compounded curves where repairs would affect the pilot's or copilot's vision. Minute scratches may be removed by rubbing with automobile body cleaner or fine-grade rubbing compound. 1. Window 2. Windshield 3. Door 4. Frame 5. Seal 6. Sealer (Type I) 7. Retainer 8. Sealer (Type n) Maintenance of the door includes removal and installation, rigging, door seal repair and replacement, repairs to the cabin upper door lift assist on the Pressurized Skymaster and emergency exit door assist replacement on the Pressurized Centurion. When repairing the cabin door seal the work area must be clean. The door seal need not be removed from the door. Remove only enough damaged seal to allow installation of the rubber mold. Seals with a damaged area of holes or gaps in excess of six inches in length should not be repaired. The seal should be replaced. Ensure that the door frame seal is installed with existing air holes in the seal toward the pressure source. Repairs are allowed to the Pressurized Skymaster door lift assist. It uses a nitrogen air charge in the lower portion and hydraulic fluid in the upper portion. The Pressurized Centurion emergency exit door assist requires only removing and replacing. A B C-C 14 l. Fuselage Structure 2. Sealer 9. Hinge 3. Nut 10. Seal 4. Retainer 11. Door Seal 5. Window 12. Door Skin 6. Screw 13. Lower Door Seal 7. Cabin Skin 14. Lower Door Structure 8. Doubler 15. Air Hole CABIN PRESSURE WILL NOT GO TO MAXIMUM DIFFER- ENTIAL. TROUBLESHOOTING Outflow valve will not control. Outflow valve not regulating properly. Cabin differential gage not indicating properly. Fresh air check valve not sealing. Check position of pressuriza- tion switch; should be ON. Check vent screen, if dirty, clean. Check circuitry to valve solenoid. Check setting of cabin altitude controller. Check screen on altitude controller, if obstructed, clean. Check position of pressurized air dump controls; "Push in" for pressurization. Check engine power settings. Check venturi, ducting, connections, valving and rigging for leaks; repair. Check position of pressurized air dump controls; "Push in" for pressurization. Check engine power settings. Check venturi, ducting, connections, valving and rigging for leaks; repair. Locate leakage areas and repair as required. Inspect valves. Clean or repair as required. TROUBLE PROBABLE CAUSE REMEDY CABIN PRESSURE EXCEEDS Outflow valve not regula ting Replace valve. MAXIMUM DIFFERENTIAL. properly. Cabin differential gage not Replace gage. indicating properly. Safety valve not regulating If more than 3.5 psi, replace properly. valve. CABIN PRESSURE GOES TO Outflow valve controlling Control line plumbing leaking MAX IMUM DIFFERENT IAL immediately. or ruptured. INDEPENDENT OF AIR- CRAFT ALTITUDE. Leak in casting of outflow valve; replace. CABIN ALTITUDE OVER- Poppet valve is sticking in Replace controller. SHOOTS ALTITUDE ON closed position. SELECTOR. CABIN PRESSURE Safety Valve Discrepant Replace Safety Valve. FLUCTUAT ION ON FULL DIFFERENTIAL. CABIN ALTITUDE Cabin leakage rate too high. Verify and pinpoint INCREASES WITH Upper deck pressure too low. discrepant area per REDUC ED POWER. instruction. Faulty turbocharger Troubleshoot turbocharger. controller. CABIN DEPRESSURIZES Switch inadvertently turned Place switch ON; check switch, SUDDENLY OR INTER- to OFF or intermittent wiring or solenoid valve in MITTENTLY. electrical malfunctions. safety valve for operation and security. FOLLO\JING ARE ADDITImAL TRaJBLESHOOTING PROCEDURESFOR THE PRESSURiZED SI<'YrASfER OOLY I -- TROUBLE PROBABLE CAUSE REMEDY CABIN DEPRESSURIZES Front firewall check valve Replace or repair. WITH FRONT ENGINE AIR leak. DUMPED (MAXIMUM POWER REAR ENGINE). Cabin leakage rate excessive. Seal cabin as required. Fresh air check valves not Inspect valves. Clean or sealing. repair. CABIN DEPRESSURIZES Aft firewall check valve Replace or repair. WITH REAR ENGINE AIR leaking. DUMPED (MAXIMUM POWER FRONT ENGINE). Cabin leakage excessive. Seal cabin as required. Fresh air check valves not Inspect valves. Clean or sealing. repair. CABli~ DEPRESSURIZES Heater check valve leaking. Replace or repair. WITH FRONT ENGINE NOT RUNNING - PROP Cabin leakage excessive. Seal cabin as required. IN FEATHER (MAXlMUM POWER REAR ENGINE). Fresh air check valves not Inspect valves. Clean or sealing. repair. CABIN ALTITUDE EXCESSIVE Cabin leakage excessive. Seal cabin as required. WHILE PRESSURIZING WITH REAR ENGINE PROPELLER Fresh air check valves not Inspect valves; clean or FEATHERED . sealing. repair. CABIN FAILS TO DEPRESSUR- Cabin differential pressure Check gage; replace if IZE COMPLETELY WHEN gage not indicating properly necessary. BOTH PRESSURIZATION AIR CONTROLS ARE PULLED. Improper sealing of firewall Repair or replace and shutoff valve and/or pres sur- rig as required. ized air dump valve at rear firewall. THIS Ca'K:WDES SEaIa'~ FIVE. ANSWERTHE FINAL REVIEH blJESTIOOS 00 THE FOLUMHE PAGES, INSTRUCTIONS: CIRCLE THE LETTER BY THE CORRECT ANSWER. 1. MINUTE HAIRLINE SCRATCHES CAN OFTEN BE REMOVED FROM WINDSHIELD OR WINDOWS BY: A. Sanding and rubbing with 200 grit wet and dry sandpaper B. Cutting out a section and installing a repair section C. Rubbing with automobile body cleaner or fine grade rubbing compound D. All of the above can be accomplished 2. THE PRESSURIZED SKYMASTER DOOR SEAL IS HELD IN PLACE BY: A. EC-1675B and EC-1675A adhesive B. EC-1608B and EC-1608A adhesive A. Mild detergent solution or isopropyl alcohol B. MEK applied with a clean cloth B. The diaphragm chamber C. Air filter 5. LABYRINTH SEALS ARE USED TO: A. Seal around the windows of the Skymaster B. Seal around the doors of both the P210 and P337 C. Provide a seal where cables enter the pressure capsule D. Allows water to drain from the bottom of the aircraft 6. WHAT IS USED TO CLEAN THE MICRON WAFER FILTERS: A. Vacuum cleaner B. MEK and soft cloth C. Mild detergent D. Isopropyl alcohol 7. DOOR SEALS ARE INSTALLED WITH: A. The rubber gap facing the outside B. Air holes in the seal toward the pressure source C. Sealant on both the Skymaster and Centurion D. Both A and C are correct 8. Door seals may be repaired up to a maximum of: A. 8 inches B. 4 inches C. 6 inches D. 3 inches 9. IF THE CABIN DIFFERENTIAL PRESSURE GAGE INDICATION EXCEEDS THE RED LINE, A PROBABLE CAUSE COULD BE: A. Outflow valve not regulating properly B. Cabin differential pressure gage not indicating properly C. Safety valve not regulating properly D. All of the above could cause the problem A. By adhesive only B. By rivets and metal strip C. By a channel groove D. By screws and a locking plate B. Routing warm air over the pressurization heat exchanger C. Heat exchanger and combustion heater D. Both A and C are correct 12. THE PURPOSE OF THE ALTITUDE WARNING LIGHT ON THE PRESSURIZED CENTURION IS TO: A. Notify the pilot when to turn on the pressurization system B. Provide a means for troubleshooting the altitude controller C. Let the pilot know that the safety valve is closed D. Let the pilot know when cabin altitude exceeds 12,400 ± 100 feet A. The position of the outflow valve B. The position of the solenoid valve on the safety valve C. The operation of the altitude control D. The amount of air entering the cabin B. With dry rubber lube C. With teeth on the seal pointing toward the pressure capsule D. Without lubricant A. Cabin altitude and differential pressure instrument B. Cabin rate-of-climb indicator C. Air distribution gauge D. A warning light 16. WITH THE AIRCRAFT PRESSURIZED, WHAT WOULD HAPPEN TO PRESSURIZATION IF A COMPLETE ELECTRICAL FAILURE OCCURRED? A. De-pressurize immediately B. De-pressurize slowly C. Continue to operate normally D. Continue to operate only in the differential mode 17. IF THE CONTROL LINE BETWEEN THE CONTROLLER AND OUTFLOW VALVE WAS LEAKING OR RUPTURED, THE PRESSURIZATION SYSTEM WOULD: A. Continue to operate normally B. Depressurize the cabin C. Depressurize the cabin slowly D. Continue to operate only in the differential mode 18. IF THE SAFETY VALVE LARGE DIAPHRAGM WAS LEAKING OR RUPTURED, THE AIRCRAFT WOULD: 19. THE FRONT ENGINE ON A PRESSURIZED SKYMASTER IS OPERATING AT MAXIMUM POWER. UPON PULLING THE DUMP VALVE FOR THE REAR ENGINE, THE CABIN DEPRESSURIZES. TO TROUBLESHOOT THIS MALFUNCTION, WHAT WOULD YOU CHECK FIRST. A. Safety valve B. Outflow valve 20. WHAT WOULD YOU SUSPECT TO BE THE PROBLEM IF THE CABIN ALTITUDE OVERSHOOTS THE SELECTED ALTITUDE? A. An open safety valve diaphragm B. A defective controller C. A sticking firewall inlet check valve D. An open outflow valve diaphragm