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* Airplane in the air
* Trailing edge flap position between up and 15
* System B EDP low pressure.
Inputs
Two air/ground relays supply air/ground information.
These two flap position switches on the flap control unit in the
main landing gear wheel well supply flap position signals:
* TE FLAPS UP switch
* TE FLAPS LANDING WARNING switch.
The EDP pressure switch is on the hydraulic system B pressure
module. It supplies a system B EDP low pressure signal when
the pump pressure is less than 2350 psi for more than 0.5
seconds.
Control
The PTU control circuit receives power from two 28v dc circuit
breakers. The control circuit can use power from one or the
other circuit breaker. Each of these power inputs go through an
air/ground relay.
Both signals from the air/ground relays combine and supply
input to flap position switches. If the trailing edge flaps are
between up and 15 units, the flap landing warning switch sends
a signal to the HYD SYS B EDP relay.
When the pressure from system B EDP is less than 2350 psi, a
ground goes to the HYD SYS B EDP relay. When the relay
energizes (0.5 seconds after the relay receives power and a
ground), power goes to the PTU control valve. This opens the
valve and system A hydraulic pressure operates the PTU motor.
The HYD SYS B EDP relay has a hold-on circuit after the ground
from the low pressure switch energizes the relay. The hold-on
circuit maintains the ground on the relay after the system B EDP
pressure goes high again. The hold-on circuit also stops
intermittent operation of the PTU system if the EDP B pressure
increases more than or decreases less than 2350 psi.
PTU Automatic Shutoff and Inhibit
The PTU control valve moves to the closed position for either of
these conditions:
* Airplane is on the ground
* Airplane is in the air and the trailing edge flaps move to the
up position, or are more than 15 units.
HYD POWER TRANSFER UNIT SYSTEM - FUNCTIONAL DESCRIPTION - ELECTRICAL
EFFECTIVITY
GUN ALL 29-25-00
Page 14
D633A101-GUN Jun 10/2006
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
29-25-00-005
PTU Manual Shutoff And Inhibit
The PTU control valve moves to the close position when the
ALTERNATE FLAPS arm switch is moved to the ARM position
and the ALTERNATE FLAPS control switch is moved to the
DOWN position. This energizes the LE standby drive shutoff
valve relay and sends 28v dc to the standby shutoff valve
indication relay. When the standby shutoff valve indication relay
is energized, power to the hydraulic system B EDP relay is
removed. This stops operation of the PTU.
Training Information Point
During a system test of the PTU system, you operate the PTU
system and put the airplane in the air mode.
Obey these warnings when you put the airplane in the air mode:
WARNING: MAKE SURE THE DOWNLOCK PINS ARE
INSTALLED ON ALL THE LANDING GEAR.
WITHOUT THE DOWNLOCK PINS, THE LANDING
GEAR COULD RETRACT AND CAUSE INJURIES
TO PERSONS AND DAMAGE TO EQUIPMENT.
WARNING: MAKE SURE THAT PERSONS AND EQUIPMENT
ARE CLEAR OF RUDDER, THRUST REVERSERS,
AND LEADING EDGE SLATS BEFORE YOU
SUPPLY HYDRAULIC POWER. RUDDER, THRUST
REVERSERS, AND LEADING EDGE SLATS CAN
MOVE QUICKLY WHEN YOU SUPPLY HYDRAULIC
POWER. THIS CAN CAUSE INJURY TO PERSONS
AND DAMAGE TO EQUIPMENT.
WARNING: MAKE SURE THAT PERSONS AND EQUIPMENT
ARE CLEAR OF THE LEADING EDGE FLAPS AND
SLATS. THE LEADING EDGE FLAPS AND SLATS
CAN MOVE AUTOMATICALLY. THIS CAN OCCUR
WHEN THE HYDRAULIC SYSTEM I S
PRESSURIZED, THE TRAILING EDGE FLAPS ARE
IN POSITION 1, 2, OR 5, AND THE NOSE OR MAIN
LANDING GEAR AIR/GROUND RELAYS SENSE AN
AIRBORNE CONDITION. THIS CAN CAUSE INJURY
TO PERSONS OR DAMAGE TO EQUIPMENT.
WARNING: KEEP PERSONS AND EQUIPMENT CLEAR OF THE
FLIGHT CONTROL SURFACES. THESE
COMPONENTS CAN MOVE SUDDENLY WHEN
YOU PUT THE AIRPLANE IN AIR MODE. THIS
CAN CAUSE INJURIES TO PERSONS AND
DAMAGE TO EQUIPMENT.
HYD POWER TRANSFER UNIT SYSTEM - FUNCTIONAL DESCRIPTION - ELECTRICAL
EFFECTIVITY
GUN ALL 29-25-00
Page 15
D633A101-GUN Oct 10/2002
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
29-25-00-005
WARNING: OBEY THE PROCEDURE THAT PREPARES TO PUT
THE AIRPLANE IN THE AIR MODE. IN THE AIR
MODE, MANY OF THE AIRPLANE SYSTEMS CAN
OPERATE. THIS CAN CAUSE INJURIES TO
PERSONS AND DAMAGE TO EQUIPMENT CAN
OCCUR.
　
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