|Contributed by: David Johnson | Published: December 2003 | Views: 63760 | Email this Article
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first glance, setting up a pneumatic retract system
can seem complex and difficult. However, as we go
thru the basics of setup and operation I think youll
agree it couldnt be simpler.
heart of the Robart retract system is the valve. The
spool is the inner portion that slides in and out
under servo control and redirects the pressure to
either of the Air Out ports. The basic principle is
each retract has a cylinder with a port
on either side. The servo slides the spool one direction
and air pressure is routed to one side of the cylinder.
This causes the cylinder to move to the opposite side
and open the retract. When the servo slides the spool
the other direction, pressure is directed to the opposite
side of the cylinder, closing the retract.
are designed so that when in the absolutely open
and closed position, there is a mechanical advantage
so that air pressure alone isnt holding the
The mechanical advantage is similar
to the locking mechanism on a car door. You can
easily turn the key and disengage the lock, but
if someone puts even a little pressure on the door
lock, you cant turn the key. When retracts
are in the locked position, the air pressure simply
holds the lock closed.
first thing to do when you get your Robart Retract
system is to adjust the Needle valves. These valves
allow you to adjust the speed at which the retracts
open and close by regulating how fast the pressure
is released. One needle adjusts the speed of opening,
the other of closing. To adjust, loosen the lock
nut generously and turn in the needle till it is
snug. Do NOT tighten it down
just turn it
in til you know you are bottomed out. Then back
out the needle 2 full turns. This will be a good
starting point. From here turning the needles in
will slow the speed, turning out will speed them
up. Adjust them in 1/8 -1/4 turn increment. You
can even remove them completely for the fastest
Robart pneumatic retract system also comes with
a fill valve and fill chuck
the fill valve
is very similar to a tire valve and you can even
use pumps made for filling tires. To prevent over-pressurizing
the system, Robart offers an optional pressure gauge
that indicates when the system is fully pressurized.
system comes with easy to follow diagrams to assist
in 2 and 3 gear installation. Well cover the
3 gear since that is what were using on our
Top Flight Giant Scale P-51 ARF.
well start with the tank and attach some red
pressure line. We have the pressure gauge, so we
need to tee off the first line with a red tee. Then
well add another tee with the end going to
the fill valve. The other end goes to the valves
Air In Port.
well run red pressure from one of the OUT
ports and first Tee it off to the back end of the
tail wheel retract, then coming off from there,
well tee off again and go to the back end
of each of the main gear retracts. Basically what
weve done is get air into the valve and attach
one side of the retracts to the out port.
already halfway thru. Now lets get the purple line
and setup of the other side of our pneumatic system.
Its setup the exact same way
line comes out of the second valve port and is teed
off with one side going to the FRONT of the tailwheel
retract. The other side of the tee is teed
once more with pressure line going to the FRONT
of both retracts. We now have pressure going to
the opposite side of the cylinders in the retracts.
pretty much it! See how simple? Our last step is
to setup our servo throw for approximately ¼
to slide the spool fully one way, then the other.
the system according to the size air tank being
used, and watch your retracts in action. Sure is
satisfying to see them operate so smoothly and precisely.
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