Hydraulics Flashcards
What are the Hydraulic Systems of the 737:
- System A
- System B
- Standby Hydraulic System.
How are the hydraulic reservoirs pressurized?
- System A and B reservoirs are pressurized by regulated bleed air.
- The Standby Hydraulic reservoir is pressurized by the System B reservoir.
How are the hydraulic systems quantity and pressure indications indicated on the MDS?
The hydraulic quantity and pressure indications of system 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?
- Hydraulic quantity below 76% when:
o on the ground with both engines shutdown or,
o after landing with flaps up during taxi in.
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 and B?
- 3000 psi +/- 200psi.
- 3500 psi maximum.
When does the STANDBY HYD LOW QUANTITY light illuminate?
- The STANDBY HYD LOW QUANTITY illuminates when the standby reservoir is approximately half empty.
- System B continues to operate normally, however the system B reservoir fluid level indication decreases and stabilizes at approximately 70% full.
Which precautions, should be taken when turning on the ELEC HYD pumps?
- Verify there is more than 1675 lbs of fuel in the respective main fuel tank.
- System B First ON last OFF to avoid hydraulic fluid migration.
- Placing both ELEC Hydraulic Pump switches to ON simultaneously may create an amperage surge resulting in hydraulic pump motor circuit breakers tripping in the E&E Compartment.
o Staggering switch selection to ON avoids this condition.
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 by closing the:
o Flight Control Shutoff Valve:
§ Ailerons
§ Elevators
§ Rudder
- Opens the Standby Rudder Shutoff Valve
- Deactivates the related FLT CONTROL LOW PRESSURE light when the Standby Rudder Shutoff Valve opens.
- Allows the Standby system to power the Rudder and the Thrust Reversers.
- Illuminates:
o STBY RUD ON
o FLT CONT
o Master Caution
What causes the automatic operation of the Standby Hydraulic System?
- Automatic operation is initiated when the following conditions exist:
o Flaps extended, and
o airborne, or wheel speed greater than 60 knots, and
o loss of System A or B, with the respective FLT CONTROL switch positioned to ON
OR
o The main PCU Force Flight Monitor trips (FFM).
What does automatic operation of the standby hydraulic system activate?
- 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?
The purpose of the PTU is to provide Hydraulic System B fluid at a flow rate and pressure sufficient to provide normal rates of operation for the Auto-slats and Leading-Edge Devices in the event the Hydraulic System B Engine Driven Pump output pressure drops below a specific value (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. System A hydraulic pressure will be maintained by the Electric Motor Driven Pump EMDP.
What fluid percentage does the standpipe in the system B reservoir preserve in the event of a leak?
0%, however the fluid at the top of the standpipe still allows operation of the PTU.
With 0% indicated on the System B quantity indicator, can the PTU still operate?
Yes. With the fluid level still at the top of the standpipe, fluid remaining in the System B reservoir is sufficient for Power Transfer Unit operation.
