pressurizing hydraulic's ?

[soul112 0]

so basiclly i was watching the 747-400 ITVV video (EGLL _KSFO) and in the pre engine start up, the captain says. i see you have taken away ground power. is it okay to pressureize hydraulics, you then see the F/O presss a button on the overhead. what button does he press ? and what is he really doing ?.

 

 

alex b

[PHXMD-11 86]

what button does he press ? and what is he really doing ?.

 

Probably setting the DEMAND SYS 4 selector to AUX and the other three selectors to AUTO. Hereby pressurizing the hydraulic system.

 

Maybe turning on the APU generators.

[scandinavian13 5,192]

Probably setting the DEMAND SYS 4 selector to AUX and the other three selectors to AUTO. Hereby pressurizing the hydraulic system.

Yep.

 

Maybe turning on the APU generators.

Nope. If he pulled the ground power without the APU gens on, you'd have larger issues than pressurizing the hydraulics.

[dmwalker 603]

soul112,

 

As the captain is asking the ground personnel for clearance to pressurise the hydraulics, I imagine it is a safety check to ensure that personnel and equipment are clear of any hydraulically powered external moving parts.

 

I think the only switches you see the First Officer switching on are just before the “Before Start checks below the line”. They can't be the Demand Pump Selector Switches or the APU generators because the First Officer is reaching directly above and not to his left, so he's presumably switching on the beacon prior to startup, plus one other switch in that panel and then pressing Recall on the EICAS.

[maxfly1 0]

First when you ready disconnect Grnd Pwr, you need to switch to APU Pwr.

 

When Capt asks if we're clear to pressurize hydraulics and gets positive response from the Ramper, FO will turn #4 Pump to AUX and Pumps #1, #2 and #3 to AUTO for steering for push back. Than you push Fuel Pumps.....

[dmwalker 603]

The video doesn't show the Demand Pump Selector Switches being switched. It shows only the following views about 35 seconds after asking for clearance to pressurise the hydraulics:

 

I think the OP is asking about these.