Posted for TOM GARDINER
<n20087@yahoo.com>:
Folks,
I thought I would take some time here to outline my recent experience with
the
parker oildyne pump so that it would save some of you the same time and
expense
i have had to deal with
recently. My pump had been sitting in the aircraft
for
a number of years through the early construction phase without
exercise.
Once I
began swinging the gear and flying I experienced various issues:
1. Gear would not
retract - despite operation of the dump valve
2. Gear would not lower unless dump valve was actuated
3. Pump would screech
and make various noises
4. Pump would turn on and off frequently during flight
After experiencing all of these
issues I decided to make it my mission to
learn
as much about the system and eliminate all of the failure modes. Lessons
learned:
1. The pump has many applications in the marine industry for which there is
some excellent
documentation
2. The two way dump valve supplied with the kit is poor quality and cannot
be
trusted (can leak internally and
externally)
3. It is a very good idea to install pressure gauges in both up and down
hydraulic lines
4. The original
pump is slow to raise and lower the gear
5. Nobody knows more about the equipment than Parker/Oildyne
6. Heat will cause pressure
increases in the lines to the point that the
pressure switches will drop out
7. Seals inside the pump will eventually leak through
wear and tear
especially
after sitting for a long period
8. There are numerous failue modes to the system, the goal is to
eliminate
as
many of them as possible
Following 2 instances of not being able to raise my gear in flight I had had
enough. After studying all of the related posts on this site I then elected
to
call Oildyne. The people there were
kind enough to share with me their
engineering drawings and their recommendation of the correct configuration
for
the pump
internals for the LNC2 application. Contrary to some of the posts
to
LML the preferred spool type is a symmetrical one that is
centered using two
additional springs. The attached drawings provide a good understanding of
how
the spool, check valves
and relief valves work. Armed with the data I set
about modifying my hydraulic system as
follows:
1. Removed the original pump adapter from the pump motor - Parker p/n781021
2. Removed the relief valves
from the pump adapter and installed on a new
adapter - Parker p/n 781047
3. Replaced the gear pump module for the high output
upgrade - Parker p/n
634218
4. Replaced the dump valve with a high quality swagelok 3 way valve that
dumps
to
the tank B-42XHF2=BKB
5. Replaced one of the pressure switches for another (was replaced under
warranty - had a 500psi
hysteresis)
6. Installed a small pressure gauge for diagnostic use
7. Installed a new fluid reservoir. New design does
not have the mounting
hole
in the bottom
A 781021 can be converted to a 781047 by performing the following
steps
1. Remove the asymmetric spool in the pump adapter and replace it with the
symmetric one along with the
two centering springs
2. Remove center relief valve as shown in drawing - it is unnecessary
Net
results:
1. All gear legs move together and at about the same rate
2. No screeching - sounds smooth with positive
cut off - I believe the
center
relief valve to be responsible for the occasional screeching
3. Emergency dump valve
dumps pressure on both sides of the pump to zero
with
return to the tank
4. No internal leaks - Hence no cycling of
the pump in flight
5. 100% reliability on gear operations
All mods to pump done for
$250
Notes:
To inspect the check valve poppet as a possible leak
down cause, remove the
hex
plug, on whichever side of the power unit is having the problem. Inside there
is
the spring and
the poppet. Check the rubber face seal of the poppet for any
chips which might be embedded. On a rare occasion the face seal itself,
which
has a 'stepped' design, may delaminate, which can cause a leak. When
finished
doing all this, retorque the hex
plug to 450-600 in-lbs.
Parts can be sourced from
Western Fluid Power, 2759 South 300 West, Suite H, Salt Lake
City, Utah
84115.
Talk to Boyd Ottenstein at 801-486-6500
Oildyne Sales contact
larry.fern@parker.com
Tom Gardiner
LNC2 826CT
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