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-   -   737ng Fuel/spar Valves... (https://www.pprune.org/tech-log/393540-737ng-fuel-spar-valves.html)

spudgunjon 25th Oct 2009 09:45

737ng Fuel/spar Valves...
My understanding is (according to the FCOM v.2 chapter on Fuel system) that the "Spar Fuel Shut Off Valves are DC Motor operated from the hot battery bus. The Engine Fuel Shut Off valves are fuel actuated, solenoid controlled valves powered from the battery bus."

However two questions (essentially the same with different answer options) I have come across are confusing me a little...

From Smartcokpit...

The Engine Fuel Shut Off valves:

A) Are AC operated to OPEN and mechanically closed by the engine start lever or fire switch - GIVEN AS CORRECT
B) Are Hot Battery Bus powered and may be closed by the engine start lever or the respective engine fire switch
C) Are cable operated to CLOSE or OPEN
D) Are cable operated to CLOSE


From B737.org.uk

The Engine Fuel Shut Off valves
A)Are AC operated to OPEN, and mechanically closed by the engine start lever or fire switch.
B)Are cable operated to CLOSE or OPEN.
C)Are Hot Battery Bus powered and may be closed by the engine start lever or the respective engine fire switch. GIVEN AS CORRECT

Can someone please clarify this for me as it doesn't seem to quite add up.

The fcom is claiming the engine shut off valve is on the battery bus which to me would rule out being AC powered EVEN though under normal conditions the battery bus is powered by TR3 (?)...yet the correct answer given at 737.org is stating the engine shutoff valve is on the hot battery bus, wheras the fcom quoted above claims the battery bus???:confused:

Very confused.

Rainboe 25th Oct 2009 11:35

The Spar Valve is upstream of the engine. It is a DC motor Hot Battery Bus powered. The engine mounted EFSOV is fuel operated, solenoid controlled Battery Bus powered. That is as complicated as you want to make it, don't go into it any deeper than that. You will be vastly overqualified and not concentrating on the right stuff while you are learning to fly the plane, and not a bundle of laughs to fly with! The EFSOV is definitely Battery Bus powered. Beware using outside agencies for official Tech stuff. FCOM B Systems 12.20.2

spudgunjon 25th Oct 2009 12:28

Many thanks for the contribution, very much appreciated. Can I just clarify then that both of the given answers as above are, as assumed, technically incorrect?

*And whilst I have no interest in turning the flight deck into a comedy club, I'd just like to state that in my very limited "career" thus far the flying part has been (in relative terms) the easy bit and knowing systems inside out like this has been the thing that has challenged me most. In essence what I am trying to say is that, whereas I have no desire to be a bundle of laughs to fly with, I would suggest that the more I know about this sort of thing the more spare capacity I have to talk about boobs, football and slagging off the company. :ok:

Plus I donít wish to be RHS forever twiddling the MCP!

Rainboe 25th Oct 2009 16:51

The total depth of your knowledge needs to be what I wrote, and no more. Not sure at what stage your career is at, but probably you need to spend the time now at the procedures manuals, rather than the systems manuals. Reading up about RVRs, CAT3, MSAs and what cold temperatures do to them, winds across mountain ranges and what effect it has on you, fuel regulations, checklists and checklist construction.....and a million other things. Then come and tell me all about them.
Both answers are wrong according to Part B as stated. One of the injustices in life is that once a question has been 'passed' by the appropriate authority as OK, it becomes the new truth, even if the answer is plainly wrong. Once it goes on the answer sheet as that answer, there is no changing it unless said 'appropriate authority' authorises it. That costs money. So we end up in a situation where some questions are wrong, and are known to be wrong. I suspect that is the case we have here.

stue 26th Oct 2009 14:49

Rainboe knows exactly what he is talking about, and hands out some very good advice. Boeing FCOM Part B Vol 2, Page 12.20.2 is your guide. It states what both yourself and Rainboe have said, Smartcockpit and B737.org.uk are good, but not to be fully relied upon.

Have fun flying her!

BOAC 26th Oct 2009 17:42

Has anyone let CaptainSandL know?

CaptainSandL 27th Oct 2009 09:46


Good spot, I have been back into the AMM and the engine shutoff valves are 28V DC BAT BUS powered, not HBB as my quiz states.

For info, I first posted those quizzes up almost 10 years ago and nobody else has spotted that yet. I occasionally get queries about the quiz answers but they all seem to be correct after the inevitable initial errors which were ironed out early on. This leads me nicely onto Rainboes point that any website, book or other source may have errors and you should always go by your company FCOMs. That said even Boeing material has errors!

Finally, note that my quizzes are for Classics. At the foot of the quiz page is a section on NG differences which could be significant in a fuel valve question.


theshed 27th Oct 2009 13:26

There is a reasonable difference between the classic and the ng's when it comes to fuel valves the classic only has one!

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