INTRODUCTION
The Learjet models 23, 24, 24B, and 25 are equipped with a pressurization system that
maintains cabin pressure within comfortable limits. At maximum cabin pressure dif-
ferential, the system maintains sea level pressure between 21,000 and 26,000 feet and
an 8,000-foot cabin altitude at 45,000 feet. Cabin pressure is maintained by controlling
the amount of air being exhausted through an outflow valve. Provision is made to pre-
vent over- or underpressurization.
GENERAL
Cabin pressurization is provided by bleed air
taken from the eighth stage of the engine com-
pressor. The air enters the cabin through the nor-
mal air distribution ducts. The level of cabin
pressure is controlled by regulating the dis-
charge of air overboard through the outflow
valve. Control may be either manual or auto-
matic. For automatic pressurization control,
115 VAC is required.
SYSTEM DESCRIPTION
COMPONENTS
The pressurization system (Figures 12A-1
through 12A-5) consists of an outflow valve on
the forward pressure bulkhead, a cabin safety
valve on the aft pressure bulkhead, a pressur-
ization jet pump (on some airplanes), a pres-
surization control module on the copilot’s
instrument panel, and a mechanical pressure re-
lief valve (in some airplanes) located on the for-
ward bulkhead between the pilot’s rudder pedals.
CHAPTER 12A
PRESSURIZATION
12A-1
FOR TRAINING PURPOSES ONLY
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