To CONF iture, post #1138:
on 757 there was an indication light for SPAR VALVE status. That one was amber as long as its physical condition was not in total accordance with commanded request.
I believe such indication light does not exist on 777 (?)
The 777 has no transit lights. Spar valve positions are displayed on the fuel synoptic and fuel management maintenance page. These have to be selected on the lower MFD (or left/right inboard MFD) to enable monitoring of the spar valves.
My questions:
How long does a spar valve take from fully closed to fully open ?
15 seconds.
What kind of electrical input does it need to operate ?
28V DC
- Is it a continuous input ?
Spar valve control system (fuel control switches and control relays): yes
Spar valve actuators: no. Limit switches remove power from the spar valve actuators after commanded position is reached.
- Is it just a simple impulse which initiate closure / opening ?
Continuous 28V DC power is provided to the control relay.
Fuel control switch moved to RUN energizes the open coil of the control relay which then sends a power signal to the spar valve actuator. When the spar valve reaches the open position, power through the limit switches is removed from the spar valve actuator.
Fuel control switch moved to CUTOFF energizes the close coil of the control relay which then sends a power signal to the spar valve actuator. When the spar valve reaches the closed position, power through the limit switches is removed from the spar valve actuator.
- Can it produce an only partial closure / opening ?
Yes , if a spar valve actuator jams while in transit. This wil generate a fault indication on EICAS due to a disagree between control relay position and spar valve actuator position.
Or (highly improbable but not impossible):
A temporary reverse logic to the control relay. Example:
With fuel control switch in RUN and temporary reverse logic to the control relay, this moves the spar valve actuator from open to closed position. No alert is generated because there is no disagree between control relay and spar valve actuator. Actuator moves to commanded position.
If the temporary reverse logic is corrected in less than 15 seconds, the spar valve moves [open->close->open] and will be in transit for almost but less than 30 seconds without ever reaching the closed position. Result, obvious limitations to the fuel flow. No alerts are presented and no visual indications if fuel synoptic and/or fuel management maintenance page are not displayed at moment of occurrance.
Before going in all kind of studies and theories regarding fuel composition and / or pipe structure, wouldn’t it be common sense to simply test the effect a partial and temporary spar valve closure could produce on HP fuel pump ?
Temporary partial closure of that valve, isn’t it the easiest way to restrict a fuel flow ?
see my post #590 on page 30 of this thread:
Code One . . . .
regards,
Green-dot