Hydraulics Flashcards
How many hydraulics systems are on the 737?
3: System A, B, and Standby
Where is the hydraulic fluid stored?
In 3 reservoirs located in the main gear well
What powers the A and B systems?
One engine pump and one electric pump per system
What powers the Standby System?
Motor driven pump powered by the #2 AC Transfer Bus
What pressure do the hydraulic pumps normally operate at?
3000 psi
What is cavitation?
Rapid changes of pressure in a liquid lead to the formation of small vapor-filled cavities in places where pressure is relatively low
What are the A and B reservoirs pressurized by?
Pneumatic Manifold
How many Master Caution Lights does the A and B system have?
Each pump has a low pressure light, and both electric pumps have an overheat light
What causes the Overheat lights to illuminate?
When the fluid in the electric motor pump case drain or pump housing is too hot
When does the low pressure light illuminate?
If the output pressure from the associated pump is too low
When does the RF indication appear on the MFD hydraulic page?
If the quantity is below 76% with both engines shut down OR after landing with flaps up during the taxi in.
Does the Standby Hydraulic Pump have a Low Quantity and Low Pressure Caution Light? If so, where are the located?
Yes; In the top left of the overhead control panel
When does the standby system Low Quantity light illuminate?
If the fluid level is below 50%
How do you check the A and B system reservoir pressures?
By looking at the gauge located on each reservoir during the preflight walk around
What drives the engine driven pump in system A?
The #1 (left) engine
What powers the electric driven pump in system A?
The AC transfer bus #2
What will the pressure in either System drop to if the engine or electric pump were to fail?
The system will maintain 3000 psi
What happens if a leak occurs in the lines associated with the engine driven pump in system A?
The reservoir will drain down to the top of the standpipe where 20% should remain for the electrically driven pump
What happens if a leak occurs in the lines associated with the electric driven pump in System A?
The reservoir will completely drain
How is System A’s hydraulic fluid cooled?
After passing through the pumps, the return fluid is cooled by passing through a heat exchanger in the #1 main fuel tank before returning to the reservoir
How much fuel does the #1 main fuel tank need to hold in order for proper hydraulic cooling on the ground?
1676 lbs
What happens if the engine pump switch is turned off?
A solenoid held shutoff valve is powered and will block the output of the pump
If a loss of electrical power occurs, what happens to the shutoff valve in the engine driven pump?
The shutoff valve opens and the pump fails to the ON condition
What happens if the #1 Fire Switch is pulled?
The shutoff valve will close to stop the delivery of hydraulic fluid to the engine driven pump and the engine driven pump low pressure light is inhibited
What drives the engine driven pump in the B system?
The accessory drive of the #2 engine
What powers the electric motor pump in System B?
AC Transfer Bus #1
What happens if a leak occurs in the lines associated with either pump in system B?
The fluid will drain to the top of the standpipe where fluid will remain for the PTU
How much fluid will remain in the reservoir at the top of the standpipe during a leak in system B?
The quantity will show approximately zero and system pressure will be lost
How is hydraulic fluid cooled for system B?
Same as system A, but with the #2 main fuel tank instead.
What does the Standby Hydraulic pump power?
Thrust Reversers
Rudder
Leading Edge Devices (to extend position only)
Standby Yaw Damper (certain aircraft only)
What powers the Standby Hydraulic System?
One electric motor pump
When is the Standby System used?
When the A or B system has failed
Where does the standby system receive its fluid and pressure?
System B reservoir
What happens if the standby system has a leak?
The B system reservoir will provide fluid to the standby reservoir until the B system reservoir has decreased and stabilized at approximately 72%
