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Old 25th Oct 2009, 09:45
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spudgunjon
 
Join Date: May 2008
Location: The Shire
Posts: 29
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

AND---

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???

Very confused.
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