Last week's discussion of hydraulics prompted me to fire up the test stand I
use for trouble shooting and testing to record some scenarios discussed.  One
topic that comes up every so often is the loss of pressure while climbing and
the gain in pressure while descending.  If you don't have pressure gauges you
may take the pump blip during a climb to 18k as a leak. With a gauge you can
watch pressure follow temperature.  Of course, in our planes we have the nose
gear hydraulics warming from engine heat and the main gear hydraulics being
influenced by ambient temperatures so the relationship between ambient and
pressure gets a little distorted.  Trapping hydraulic fluid and heating it can
build enormous pressure and it should be respected.  The embedded photos show
a time history of a single cylinder being warmed and than cooled.  After the
first pump blip during the cooling cycle, I turned the pump off so pressure
could continue to fall.  Heating is from a hobby heat gun and cooling is done
with a hand full of ice.

Chris,

 

What a super experiment!  It certainly helps as a basis for understanding some of the exotic lock-ups that have been described here.

 

Thanks.

 

Scott