Re: A320 and Noisy Hydraulic Pumps

From:         bradg@io.org (Brad Gillies)
Organization: Internex Online
Date:         15 Apr 95 11:38:20 
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showie@uoguelph.ca (Steve Howie) wrote:
>George Hull (geohull@ditell.com) wrote:

>I'll add the 767 to the list with noisy pumps. I was seated about halfway
>down, aisle seat in the middle row on an Air Canada flight from SFO to
>YYZ.  When we were on our descent to Toronto, the hydraulic pumps would
>make a low-pitched but LOUD "ZZZZSSSSHHHHHH" noise when we were
>manuevering, seemingly only when we were banking. When the flaps were
>extended for landing, a much higher-pitched, but quieter pump seemed to be
>working. Are there different pumps for different control surfaces??

What you actually heard is the centre system demand pump. there are
two pumps in the centre system one is air driven and one is electric.
you heard the electric one.  The other sound was the flap motor
running. the flap motor is driven by hydraulic flow from the centre
system. Usually those pumps are much quieter than those on other
aircraft.

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Brad Gillies    Bradg@io.org
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