"OUTFLOW VLV L" advisory message

[Hardy Heinlin]

Another effect I noticed regarding the real-world AC bus 1 short circuit currently discussed in other threads.

The real deck shows OUTFLOW VLV L.
PSX doesn't.

PSX does have the cabin pressurization ICU L power on AC bus 1,
but PSX doesn't have that item in its OUTFLOW VLV L message logic.

In PSX, the OUTFLOW VLV L message appears if:

Left manual outflow valve control is selected on
OR
Left manual outflow valve control is not powered (main battery bus)

That's all.

Maybe I should add OR ICU L not powered?

Same for the right valve accordingly.


Cheers,

|-|ardy


P.S.: OUTFLOW VLV R wasn't shown on the real deck. So I think they didn't select any manual control, otherwise this would have been symmetrical, pair-wise. I guess OUTFLOW VLV L was a consequence of the AC bus 1 short circuit. Or even the cause of it!? If so, all is fine in PSX :-)

[John H Watson]

PSX does have the cabin pressurization ICU L power on AC bus 1,

Correct (as well as DC 1). The ICUs convert the digital signals from the cabin pressurisation controllers to analog signals for outflow valve motor control during Auto operation. The internals of the ICU look a lot like the SRMs, so hopefully we won't have to go too deeply into the logic.  Anyway, the ICU sends an ac signal to the motor which is used during normal ops.

The valve has various types of position feedback. The overhead panel and EICAS valve displays are DC-driven (with various power supplies for redundancy). There is also ac-driven feedback system for motor control (using the AC power sent to the ICU).

I don't think ICU talks directly to the EIUs, but the pressurisation controller should be getting status data from the ICU and the controller should tell the EIUs that something is wrong.

The QRH does specify that only the faulty valve be put in manual. The pilot then fully closes it manually using the valves backup DC motor. It's interesting to note that the pack selection procedure is affected by whether or not the aircraft has an NGS (Nitrogen Generation System for fuel tank vapour inerting)

I guess OUTFLOW VLV L was a consequence of the AC bus 1 short circuit. Or even the cause of it!?

Very unlikely. That's what CB's are for. There are probably quite a few CBs inbetween the AC Bus and the ICU. If all the CBs didn't work, the ICU power wiring would probably melt long before the AC bus tripped off 

[Hardy Heinlin]

Ah, OK, that makes sense. So it's correct in PSX. I just rechecked the left outflow valve automatic behaviour in PSX when AC bus 1 fails. The valve won't move anymore. So the crew selected asymmetric manual control indeed.

Thanks for the refresher :-)


|-|ardy

[John H Watson]

 

The valve won't move anymore. So the crew selected asymmetric manual control indeed.

So you've modified PSX? I don't see the fault message appearing in my version of PSX causing the crew to select the manual system.

I'd say the ICU will be continuously reporting its status to the pressure controller (on a data bus). If the AC  loss doesn't kill the fault/voltage sensing circuits in the ICU, the ICU should report the failure to the pressure controller. If AC bus 1 failure kills those fault/voltage sensing circuits, the pressure controller should sense this also.

[Hardy Heinlin]

I didn't modify it. As expected, the message doesn't appear during an AC bus 1 short circuit (which keeps DC bus 1 intact in PSX 10.43). DC 1 still powers the ICU control. The message will only appear when the crew selects manual control.

Even if I open the BTB 1 switch manually to kill DC bus 1 as well, the message will not occur in PSX because all ICU L stuff (AC and DC) is not involved in my message logic (see first post above).

"Outflow valve control L" check is a direct check if C548 MAIN BATTERY BUS - P6 L06 is powered.


So does it require a modification? Like this?

Left manual outflow valve control is selected on
OR
Left manual outflow valve control is not powered
OR
Left ICU AC is not powered
OR
Left ICU control DC is not powered

[John H Watson]

ICU Left gets both DC and AC power.
[P6 J30] 28Vdc Bus 1 CB C10267 and [P414 M8] 115ac Bus 1 CB C3165.

The 115ac voltage is 3 phase. One phase bypasses the ICU and goes through an auto/manual relay to the AC motor on the outflow valve. The other two phases go to the ICU where it is:
1) converted to +5V & +-/15V (like the PSM). I'd say this is used to power the microprocessors in the ICU.
2) redirected out of the ICU to an AC tachometer on the outflow valve (seems to be part of a servo rate system)

The 28V dc voltage is a little harder to follow. It goes to a power supply in the ICU. It may be used by the ICU altitude trips (11,000' and optional 14,500'). It may also be sent from the ICU to provide power for a position feedback potentiometer in the outflow valve (not to be confused with potentiometer for the valve position sent to the cockpit). This may be part of valve control.

I can't see the ICU operating properly without either of these voltages.

ICU R uses [P6 J31] 28Vdc Bus 2 CB C10268 and [P414 B8] 115ac Bus 2 CB C3166.

"Outflow valve control L" check is a direct check if C548 MAIN BATTERY BUS - P6 L06 is powered.

This is just for the auto/manual relay. No power on this stops the auto control of the outflow valve (EDIT: Let me check this, there are multiple CB's feeding this relay.

[Hardy Heinlin]

The AC and DC stuff for the ICUs is already implemented in all PSX versions. As you can see, the valve won't work automatically when the ICU fails.

It's just the message logic that needs an ICU check. I can add that in 3 seconds.

[John H Watson]

As you can see, the valve won't work automatically when the ICU fails.

Understood, but it must generate a message to tell the pilots to switch to manual control (You don't want the airplane to reach overpressure or cabin altitude warning limits before taking action)

This stuff is endlessly complicated.... I don't remember checking any of this stuff before.

For Auto Control, the manual switch must be deselected:

This allows power from either C548 [P6 L6] (Main Bat Bus) or C549 [P6 J28] (28Vdc Bus 1) power to:
1) activate a relay which allows [P414 M8] C3165 AC Bus 1 (phase C) power to go to the Left outflow valve motor (for automatic pressurisation control)
2) activate a relay which allows [P83 C4] C124 APU BAT HOT BUS power to reach the ICU (This lets the Left ICU know that the pressurisation system is in Auto mode).

This allows power from either C547 [P6 L7] (Main Bat Bus) or C549 [P6 J28] (28Vdc Bus 2) power to:
1) activate a relay which allows [P414 B8] C3166 AC Bus 2 (phase C) power to go to the Right outflow valve motor (for automatic pressurisation control)
2) activate a relay which allows [P83 B4] C381 APU BAT HOT BUS power to reach the Right ICU (This lets the Right ICU know that the pressurisation system is in Auto mode).

[Hardy Heinlin]

I just added the ICU check to my message logic and the message works now when a related AC/DC bus fails, like on that real 744.


I didn't change the usual ICU power sources; they are still these:

ICU L is powered by AC bus 1 (no flight deck CB) and the control is powered by P6 J30.
ICU R is powered by AC bus 2 (no flight deck CB) and the control is powered by P6 J31.


The valve motor automation requires AC power in any case, correct?

[John H Watson]

I just added the ICU check to my message logic and the message works now when a related AC/DC bus fails, like on that real 744.

Thanks!

The valve motor automation requires AC power in any case, correct?

Correct (but not in manual mode).

[Hardy Heinlin]

OUTFLOW VLV () message logic modification is now available in PSX 10.43:

http://aerowinx.com/board/index.php?topic=4191.0


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