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MAINTENANCE MANUAL

AIR CONDITIONING SYSTEM SHUTOFF AND FLOW REGULATOR VALVE — SYSTEM DESCRIPTION
1. Description
A. General
This valve is designed to shut off and also regulate the flow of air for the air conditioning system.
The valve is normally open and is pneumatic in actuation with an internal electrical solenoid which
is used to cause valve to pneumatically close when electrical energy is applied to it. See Figure 1
and Figure 2.
The valve consists of three major sub-assemblies bolted together and interconnected with
pneumatic tubing. The sub-assemblies are the servo, actuator and venturi body.
2. Major Components and Sub-Assemblies
A. Servo
The servo consists of a filter, pilot regulator, a relief valve, two solenoid switcher valves, a
differential pressure servo and an altitude bias servo, all of which are contained in a housing.
The filter is a cartridge-type replaceable element located in the cover of the differential pressure
servo by a fitting. On Aircraft 1432 and subsequent, the filter is located in the manifold downstream
of the venturi. See Figure 1 and Figure 2.
The pilot regulator consists essentially of a ball valve, diaphragm, springs and cover assembly. The
ball valve is essentially a spring-loaded ball, a valve seat and rod. The diaphragm is retained
between a guide and cover assembly which is attached to the servo housing. The cover assembly
contains a calibration adjustment screw, spring retainer and spring. The diaphragm presses against
the ball valve rod which has a spring retainer and preloaded spring.
The relief valve is an assembly threaded into the servo housing consisting essentially of a spring-
loaded ball, seat and housing. The relief valve input is from the actuator pressure line, the output is
open to ambient.
The solenoid switcher valves consist essentially of a ball valve and a solenoid attached rigidly
together. The ball valve is essentially a ball housed between two seats. The solenoid consists
essentially of a spring-loaded armature, a rod, an electromagnetic assembly, a housing and a
connector. The rod links the armature at solenoid with ball of the ball valve. The spring presses the
armature against the rod and the rod presses the ball valve against a seat.
The differential pressure servo consists essentially of a diaphragm, springs, a retainer and a slide
valve. The diaphragm is retained between the servo housing assembly and cover assembly which
has a calibration adjustment screw, spring retainer and spring. The diaphragm presses against a
slide valve which has a spring retainer, preloaded spring and adjustment screw.
The altitude bias servo consists of a sealed aneroid bellows and lever arm assembly. The bellows
is attached to the servo housing by a screw at one end. The other end of the bellows is attached to
a lever arm which pivots to change tension on the preloaded spring that moves the slide valve.
B. Actuator
The actuator consists essentially of a spring, a diaphragm, a housing and a cover. The spring
presses the diaphragm against an adjustable open stop which is threaded into the cover. The
diaphragm is connected by a rod to an arm attached to the butterfly shaft. The arm rests against the
adjustable closed stop threaded into a bracket assembly which is attached to the actuator housing.
The housing has a vent to atmosphere.

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C. Venturi Body
The venturi body consists essentially of a butterfly which is bearing-mounted in a venturi section.
One end of the butterfly shaft protrudes above a venturi mounting flange and has an attached arm
which connects to the actuator diaphragm. The arm is actuated by the actuator. The venturi has
threaded ports at the inlet and the throat and is flanged for aircraft installation. Index marks
indicating OPEN and CLOSED positions are provided adjacent to the actuating arm on the bracket
assembly.
D. Test Fittings
Test fittings incorporated in the valve assembly plumbing are used for overhaul bench checking
only.
3. Operation
A. Electrical
This unit is a normally spring-loaded open, dual schedule, venturi flow control and shut-off valve.
See Figure 1 and Figure 2.
Upstream pressure is sensed through a filter to a pilot regulator which supplies the actuator with a
regulated air pressure source. A relief valve is provided to protect the control elements from over
pressure in the event the pilot regulator fails.
The shut-off function is accomplished by energizing the solenoid valve, allowing control pressure to
bypass the servo slide valve and pressurize the actuator causing the butterfly to close. When the
solenoid is de-energized, the pressure is cut off, the actuator vents to ambient via the vent orifice
and the butterfly opens again.
The servo slide valve responds to two different signals. One is the inlet to venturi throat differential
pressure (delta P). This signal is sensed across the delta P servo diaphragm which is balanced
against a calibrated spring force.
This portion of the control maintains a fixed relationship between inlet to venturi throat delta P. Any
increase in flow increases the inlet to venturi throat delta P signal. Increasing the signal makes the
diaphragm assembly move the slide valve toward the open position, allowing regulated pressure to
enter the actuator chamber. As the pressure in chamber A increases, it generates a force on the
actuator diaphragm assembly. This force overcomes the actuator return spring and modulates the
butterfly toward the closed position controlling the flow through the venturi.
The other signal comes from an aneroid bellows (altitude bias servo) through a lever arm and
preloaded spring to the slide valve. The aneroid responds to ambient pressure and generates a
force directly proportional to ambient pressure. This force is added to the force generated by the
delta P servo and increases the controller venturi delta P linearity with decreasing ambient
pressure. These two functions together control the airflow through the unit to the desired flow.

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Air Conditioning System (Aircraft 1000 thru Aircraft 1431) Shut-off and Flow Regulator Valve
Figure 1

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MAINTENANCE MANUAL

PILOT
REGULATOR RELIEF VALVE

P SERVO

ALTITUDE
STOP
ALTITUDE
BIAS SERVO PRELOADED SPRING

AMBIENT LEVER ARM

BLEED ORIFICE

SOLENOID

TEST TEST
FITTING FITTING CHAMBER "A"

OPEN
ACTUATOR
VENT
CLOSED

AIR FLOW BUTTERFLY

OPEN STOP CLOSE STOP

TIL-02914C-

Air Conditioning System (Aircraft 1432) Shut-off and Flow Regulator Valve
Figure 2

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