HYDRAULICS Flashcards
What are the hydraulic systems of the 737?
The 737 has three hydraulic systems: system A, system B, and a standby system.
How are hydraulic reservoirs pressurized?
Systems A and B are pressurized by bleed air, and the standby system is pressurized and serviced through system B by a fill line.
How are hydraulic systems quantity and pressure indications indicated on the MDS?
The hydraulic quantity and pressure indications of systems A and B are located on the inboard Display Unit after selecting SYS on the MFD panel.
What does an RF on the HYDRAULIC indicator indicate and when is it valid?
An RF indication next to a quantity indicates the reservoir is below 76% and requires servicing. The RF indication is only valid when the aircraft is on the ground with both engines shut down, or after landing during taxi-in with the Flaps UP.
How does flap operation affect hydraulic fluid quantity indications?
Extension of the leading edge devices may result in up to 20% drop in indicated quantity.
What is the normal pressure of hydraulic systems A & B?
The normal pressurization for system A and B is 3000 ± 200 psi.
When does the STANDBY HYD LOW QUANTITY light illuminate?
LOW QUANTITY: indicates the standby hydraulic system has less than 50% quantity in the reservoir
Which precaution(s) should be taken when turning on the electric hydraulic pumps?
Placing both ELEC HYD PUMPS switches to ON simultaneously may create an amperage surge, resulting in hydraulic pump motor circuit breakers tripping in the E/E compartment. Staggering switch selection ON avoids this possibility.
A minimum of 1675 lbs in the related main tank is required for the heat exchangers to be fully submerged. Minimum fuel for extended ground operation of the EMDP is 1675 lbs.
What does moving a FLT CONTROL switch to STBY RUD do?
• activates the standby electric motor-driven pump
• shuts off the related hydraulic system pressure to ailerons, elevators, and rudder by closing the flight control shutoff valve
• opens the standby rudder shutoff valve
• allows the standby system to power the rudder and thrust reversers
• deactivates the related FLT CONTROL LOW PRESSURE light when the standby rudder shutoff valve opens
• arms the STANDBY HYD LOW PRESSURE light
• illuminates the STBY RUD ON light and the FLT CONT System Annunciator and MASTER CAUTION lights
What causes the automatic operation of the standby hydraulic system?
FLT CONTROL switches positioned ON and the loss of system A and/or B:
• Flaps extended, airborne
• Flaps extended, wheel speed greater than 60
OR
The main rudder Power Control Unit (PCU) Force Fight Monitor (FFM) trips.
What does automatic operation of the standby hydraulic system activate?
Automatic operation of the standby system:
• activates the standby electric motor-driven pump
• opens the standby rudder shutoff valve
• allows the standby system to power the rudder and thrust reversers
• illuminates the STBY RUD ON light and the FLT CONTROL System Annunciator and MASTER CAUTION lights
What is the purpose of the PTU?
To provide hydraulic system B fluid at a flow rate and pressure sufficient to provide normal rates of operation of the leading edge devices (including autoslats) in the event the hydraulic system B EDP output pressure is less than 2350 psi.
What fluid percentage does the standpipe in the system A reservoir preserve in the event of a leak?
With fluid level at the top of the standpipe, the reservoir quantity displayed indicates approximately 20% full.
What fluid percentage does the standpipe in the system B reservoir preserve in the event of a leak?
The quantity decreases until it indicates approximately zero and system B pressure is lost; however, with fluid level at the top of the standpipe, fluid remaining in the system B reservoir is sufficient for PTU operation.
With 0% indicated on the system B quantity indicator, can the PTU still operate?
Yes, with fluid level at the top of the standpipe, fluid remaining in the system B reservoir is sufficient for PTU operation.
