Dump Valve(SMACCS)

[Kalmia]

Hi Guys,
When I was looking at the Pack system of B747 Freighter, I found something I couldn't understand exactly.

You may find Dump Valves(SMACCS) in Pack's(No.1 and No.3)
The question is Why Freighter needs Dump valve.

Manual just said Dump valve restrict airflow to Pack's But I just thought FCSOV has this function(Shut off) and I found this valve is related to fire protection system for main deck cargo.

I know that fire in main deck cargo can be removed with depressurizing it.

can anyone explain that to me?:hmm:

[Exaviator]

It is a long time since I last flew the B-747 but if my memory serves me correctly the purpose of the Dump Valve is to over ride the control of the Out Flow valves and drive them to the full "Open" position, thereby depressurising the aircraft.

[dixi188]

Don't know about the 747F, but IIRC on some A300B-4 cargo conversions, (the ones done at Bristol), when a main deck smoke warning occurred, the main deck air supply was shut off and a dump valve opened to divert some of the air into the lower cargo bays to avoid over pressure in the ducts.
Hope this helps.