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Fellow listers
(especially Lorn, Pat, Chris, Jack and Vern ) ;
I went out and did
some gear retract/extension tests and recorded the results: here they are (it's
confusing, and doesn't jive with what one would expect, so follow
closely):
1. The last
time I went out the plane, I took a lap around the pattern. The gear
wouldn't retract, so I returned to ground, checked the pressure reading (about
1300 PSI), and went home to research the problem.
2. Returned to
the plane today - pressure was down 900 - NOTHING had changed except the
temperature was significantly cooler and it was cloudy vs. blazing
sun.
Here's the sequence
of what I did next:
3. Turned on
the Master. NO pump blip.
4. Put the plane on jackstands
5. Bypassed the "squat" switch
6. Raised the
gear lever - and, as expected, the gear retracted perfectly.
7. Pressure on
the gauge read 0 as soon as I raised the handle, and stayed there after the
gear was retracted and the pump shut off. This indicates it is reading the
low side.
8. Lowered the
gear handle.
9. The gauge
read about 0 the entire lowering process, then, at the last second before the
pump shut off, it went to about 800 PSI.
10. Turned off
the master
11. Opened the
dump valve, and the pressure dropped - but only to about 400
PSI.
12. Closed the dump valve
(pressure stayed the same).
13. Turned on the master - the
pump "blipped" and the pressure went to about 900 PSI.
14. Raised the gear (same
results as 6 - 7).
15. Pulled the
pump CB.
16. Opened the
dump valve. Result - IMMEDIATE freefall, gauge read 0 the entire
way.
17. Lowered
the gear handle.
18. Pushed in
the CB.
19. Pressure
ran up to about 700 PSI.
20. Master
off.
21. Opened the
dump valve - pressure dropped to about 300 - 400 PSI.
22. Turned on
the master - bump blipped up to about 900 PSI.
I repeated this
process several times and got virtually identical results.
Oh, one more thing. When the gear retracts, it sucks up to the
point of the gear doors being almost closed, then the pump cycles off and
back on, quickly, usually twice, before the gear doors completely close and the
pump stops for good. And again, I've never experienced (or noticed) my
pump turning on during flight).
I then decided to
adjust the low pressure switch (it is the adjustable type). I baced the
adjustment screw out 1 turn and then repeated steps 14 - 21. This time,
when I turned the master on, the pump didn't blip. This suggests my low
pressure set point was now below 400 PSI. I played around with this
process several
times before getting
the pressure to 550 PSI, then turning the screw just until the pump
blipped. Before I think the pump was set about 650 - 700 PSI, and now I
think it is about 550 PSI. That may help matters, but it's not the real
problem.
An interesting
conclusion is that the low pressure limit may be set to 550 PSI, but the pump
can't seem to shut itself off quickly enough, so the pressure can still get as
high as 800 or even 900 PSI.
Based on what some
of you had told me, I've got something funky going on with the dump valve.
It drops to zero on free fall tests, but does NOT drop to zero when the
gear is already extended. Any thoughts? Can any of you confirm what
your planes do in this situation?
At this point I am
very confused, still, about why my pressure is increasing on those hot days to
over 1200 PSI, and why it can also decrease later (as I witnessed today vs. two
days ago). I'm also very confused about this whole dump valve thing.
Please
help!
Sincerely,
Matt
Hapgood
919-933-3295
ps. I haven't
removed the spool valve, but it doesn't look that difficult to do - it is
accessible without removing the pump.
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