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Let's not forget this thermal influence causing
non-function can also happen in reverse. It has been reported that a thermal a
soak on the ground after a cold night can and has caused a failure to retract
after take off.
A while back I offered a solution of bumping the
pump automatically whenever both pressure switches, HI and LO, are open due to
high pressure. This would put the system back in normal operation mode
without the need for pilot intervention
Wolfgang
----- Original Message -----
Sent: Tuesday, September 04, 2012 7:53
PM
Subject: Re: [LML] Re: Thermal influence
on Hydraulic Pressure
Fred,
I wish we had an easy way
of bleeding just a wee bit of pressure without
momentarily dumping the gear in cruise.
The 320/360 pumps use a non-adjustable thermal relief
valve rated at 2,500 psi. The actual cracking pressure is 2,500 to 2,900
psi. This is the lowest set-point Parker has available. 2,900
psi is a lot of pressure for a system that nominally operates at 1,200
psi. Hopefully the design margin for the cylinders etc. was
chosen large enough.
The first time I saw a 2,000+ excursion was on the test
bench. I was leak checking a cylinder. The test stand was near the
hangar door. The sun swung around and hit the pressurized
clyinder. I dont' know what the max pressure was since that gauge only
went to 2,000 psi.
Chris
Chris Zavatson
N91CZ
360std
From: Frederick Moreno
<frederickmoreno@bigpond.com>
To: lml@lancaironline.net
Sent: Monday, September 3, 2012 11:54
AM
Subject: [LML] Re: Thermal
influence on Hydraulic Pressure
I have an MPV-50 engine monitor that includes continuous
reading of the hydraulic system pressure on my Lancair IV/
I have seen the same thing, particularly on a flight that started
on a cool morning departure from my home drome and took us to the desert
for a 110+F day. On descent, pressure rose from its customary 1250
to 1500 psi at which point Bitching Betty started to complain so I
bumped my speed brakes which are hydraulic, and lowered pressure
back down to my customary range. Same thing sometimes
happens in reverse, a hot soak on the ground, then a climb to 10-11,000
feet for a cool soak, and at some point the hydraulic pump kicks on
to restore pressure to the desired level. My TR-182 used to the
the same thing routinely when departing Phoenix in the summertime.
It is a real effect, and makes one wonder about very high pressure
events arising from FL 270 (say) cold soak terminating in Phoenix on a
July afternoon. Hmmmm....
Fred
-------Original
Message-------
-took this photo after a descent from 16.5k to 1,500 ft.
OAT went from 42 to 94 degrees.
High Pressure gauge is pegged at 2,000+ psi
-Didn't get a photo, but the opposite happened on the ramp in
Spokane. After sitting for an hour, the low pressure gauge was
pegged at 1,200 psi+. Spokane might not be the warmest spot in the
country, but at 85 deg F, it was 55 degrees warmer than the cold soak on
the previous leg.
Temperature changes have a big impact on system
pressure.
Chris Zavatson
N91CZ
360std
http://www.n91cz.net/
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SENDER_EMAILfrederickmoreno
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