The pressurizedbleed air is routed into the fuselage, underthe floor area,and through pneumatic
systemlines with check valves to prevent reverseflow to non-operatingengine. The pressurized air
entersa pressure regulator,which regulates pressure to 18 ± 1 psig for deicer boot operation, door
seal operation, operationof the cabin pressure control ejector/regulator, and supplies a source of air
throughthe ejector. This createsa vacuum for gyro instrumentsoperation. A relief valve in the
pressureregulatorrelievessystempressureat 20.5 to 22 psig if the pressureregulatorfails. Air from
the pressure regulator alsogoes to the deicer systemvalves, which are normallyclosed,and provides
a vacuum through an integral ejectorthe holds the deicer boots down. Whenthe deicer timer is
energized,the solenoid valve on the deicer valve opensand allows pressurizedair to inflate the boots.
Pressureswitcheswhich are normally openclose when the boots reach a pressure of 15 + 1 psig,
indicatingboot inflation to the pilot. When the timer de-energizes the solenoid valveson the deicer
valves, boot pressureis dumped and vacuum is reapplied to the boots.
A check valveis installed in the vacuumline from the gyros,preventing a reverseflow in the vacuum
line to the gyros. A vacuum regulator,placed in the gyro instrumentline,regulatesvacuum at 4.5 to
5.4 in. Hg referenced to cabin pressure.An inlet filter is provided at the inlet of gyro vacuum source. Pneumaticpressureand suction gauges are mounted in the instrumentpanel.
Thecabin door seal is controlled by a solenoid valve,whichopens to pressurize the seal when the
door is closed, and dumps pressurefromthe seal when the door is opened.
The bleed airsystemprovidesa regulated supplyof engine bleedairfor aircraft pressurizationand environmentaland pneumaticsystemsoperationsfrom sea level to 35,000 feet. The bleed air is conditionedfor cooling, heating,and ventilatingby an environmental controlunit.
The ECU bleed air supply systemuses two bleed air mixing andregulatingshutoffvalves. These valvesprovidepositivebleed air shutoff for both the high and low enginebleed air flow, and regulate bleedair to two preset pressurelevels (18 psig and 31 psig). One valve is located in each nacelle, forwardof the firewall. The bleed air mixing valves also provide the use of high and low engine bleed air by mixing in an ejector. High pressure bleed air provides the motive flow throughthe ejector nozzle,entrainingthe low pressure bleed air in the mixing throatof the ejector. The valveregulator sectionmaintainsthe outlet pressureselectedby the pilot at 18 psig or 31 psig. The regulator adjusts flow of high pressurebleedair to the minimumamountrequiredto bring bleedair mix up to selected
pressure.
EFFECTIVITY:
Jan10/90
PIPERAIRCRAFT
PA-42-720(Advanced Trainer)
MAINTENANCEMANUAL
A. Distribution
The following is a list of various components used to distribute, control, and regulate the pneumatic air source in this airplane.
1. ComponentDetailed Descriptions
(a)
Bleed Air Shutoff Valve: (Figure 1) The bleed air shutoff valve is located aft of the engine fireseal,on the left side, at station 89.71. Thevalve operates over the range of ambient temperature(-65°Fto +300°F) ataltitude from sea level to 33,000 feet. The valve shu!s off the airflow during engine starts and as desired by the pilot.
(b)
Intercooler:(Figure 1) The intercooler is located aft of the engine firewall, atthe outboard side of station 106.00. The intercoolercoolspneumaticsystembleed air to temperatures below 200°F, using ram airflow for cooling.
(c)
Bleed Air Overtemperature
Switches: (Figure 1) The bleed air overtemperature are located aft of the engine firewall, in the pneumatic
switches lines at station 106.00. These switchesclose at temperatures of 425°F or higher, warning the pilot of overtemperature
conditions.
(d)
PneumaticSystem Check Valves: (Figure 1) The pneumatic check valves are located below the cabin floor at fuselage station 151.30. The valves prevent reverse air into a non-operating
flow of pneumatic engine.
(e)
PressureRegulatorandRelief Valve: (Figure 1) The pressure regulator and relief valve are located below the cabin floor between fuselage stations 151.30 and 162.60. The pressure regulator regulates bleed air pressure to 18 ± 1 psig for deicer boot operation, andsuppliesa source of air through the ejector, creating a vacuum for gyro instrument operation. A relief valve in the pressure regulator is set to relieve system pressureat20.5 to 22 psig, if the pressure regulatorfails.
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