B777 Why is so quiet while turning R demand pump on?

[sm165019117]

i found when we need to pressurize the hydraulic system before pushback, after turning on the R demand pump to auto, there will be quiet in cockpit for a while ( sounds like fans stop working), i am confused...
any logic within the demand pump, fans and noise in that situation. thanks a lot!!!!

[applecrumble]

Originally Posted by sm165019117

i found when we need to pressurize the hydraulic system before pushback, after turning on the R demand pump to auto, there will be quiet in cockpit for a while ( sounds like fans stop working), i am confused...
any logic within the demand pump, fans and noise in that situation. thanks a lot!!!!

ELMS load shedding while the demand pump comes up to speed.

[sm165019117]

Originally Posted by applecrumble

ELMS load shedding while the demand pump comes up to speed.

Thanks a lot, you are right. I checked the electric synoptic during turning the R demand pump to auto, there was a load shed showed. it seems that galley doesn't work or stop working at that moment.