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EDM Today Magazine Need answers for the toughest EDM questions?
You’ve come to the right place!
O-ring Basics
Per Wikipedia, “An O-ring is a mechanical gasket in
round cross-section.” O-rings are characterized by the
QD3 DI Tank Connector Leakage
diameter of the O-ring cross section and the I.D. of
the O-ring as shown in Figure 3. In our application, the
I use DI tanks that utilize the QD3 style quick discon- the shape of a torus; it is a loop of elastomer with a
O-ring effects a seal by being compressed between the
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nect heads and have persistent leakage issues at the
bottom of the groove in the QD3 head boss and the I.D.
connection. Any suggestions?
of the hole in the tank head as shown in Figure 4.
- Edward
Roger Kern’s reply:
Before answering this question, I need to digress to
expound briefl y on two topics:
• QD3 Details
• O-ring Basics
QD3 Details
Figure 4
Figure 3
The QD3 head system (See Figure 1) is a two port
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quick disconnect system that allows resin tank
O-rings are usually available in standard inch or metric
changeover in less than one minute.
cross-section sizes and a variety of inside diameters.
O-rings are normally installed in an O-ring groove that
has a diameter somewhat larger than the O-ring I.D.,
which means the O-ring operates in a stretched state.
The amount of stretching effectively reduces the
O-ring cross section, but this is accounted for in O-ring
application design standards.
QD3 Joint Leakage Cause
Both the QD3 head and the tank head are molded
polymer components. As a result of shrinkage and
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other issues, the center distance between the bosses
on the QD3 head and the bores in the tank head can
vary somewhat. That variance can reduce the O-ring
squeeze on one side of the bores and increase it on
the other side of the bores, resulting in leakage on the
Figure 1
sides that have the reduced squeeze.
The QD3
head (See
QD3 Joint Leakage Fixes
Figure 2)
connects
This fi rst thing to try, and the simplest fi x, is to apply
the inlet and
outlet deioniz-
Toolbox Treasures feature in the Winter 2023 issue
ing hoses
of EDM Today available at www.edmtodaymagazine.
from the a thickened silicone grease to the O-rings. (See the
com.) The thickened grease is often viscous enough to
machine to
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stop the leak, as the pressure in this portion of the DI
the resin tank
system is relatively low.
by means of
If that doesn’t work, it will be necessary to change the
two cylindri-
O-rings to a different size. Since O-ring cross sections
cal bosses
are limited to standard sizes, the only way we can
that simulta-
increase the sealing squeeze between the boss groove
neously mate
bottom O.D. and the bore I.D. is to procure an O-ring
with corre-
with a slightly larger I.D. This will reduce the instal-
sponding
lation stretch and slightly increase the O-ring cross
receiver holes
Figure 2
in the tank
experimentation to fi nd the correct size (too small an
head, and
I.D. increase may not stop the leak and too large an I.D.
the connection is sealed with O-rings that sit in O-ring
increase may not allow the parts to fi t together), this
grooves in the bosses. The QD3 system is my personal section, restoring the seal. While it may take a bit of
fi x has always allowed me to successfully resolve this
favorite for this application.
EDM Today Magazine
EDM Today Magazine EDM Today Magazine EDM Today, Spring 2024 Issue
particular leak issue.
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