Small units of standard glass apparatus held together by short lengths of transparent heat-shrinkable polyolefin tubing. The tubing is shrunk over glass O-ring type connectors having O-rings but no lubricant

Del Duca, B.

Downey, A.

English

NASA Technical Reports Server

.February 1968	 Brief 68-10040 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Heat-Shrink Plastic Tubing Seals Joints in Glass Tubing 
The problem: 
To develop a lubricant-free seal for joints of glass 
vacuum (or pressure) systems. The systems must con-
tain no metal parts, no grease, and be capable of 
disassembly into small parts for repeated cleanings. 
The solution: 
Small units of standard glass apparatus held to-
gether by short lengths of transparent heat-shrinkable 
polyolefin tubing. The tubing is shrunk over glass 
0-ring type connectors having 0-rings but no lubri-
cant. 
How it's done: 
Short lengths of transparent polyolefin tubing are 
placed over the 0-ring connections containing the 
0-ring. Hot air from a standard 750-degree heat gun 
is directed at the joint from all directions until the 
tubing shrinks about the joint. The tubing is then 
permitted to cool. This operation can be performed in
a short period of time and the polyolelin tubing can 
be easily removed for disassembly of the system by 
heating it again to a higher temperature. 
Notes: 
I. These sealed joint connections were vacuumtight to 
a vacuum of iO mm of mercury for the length 
of time the system was in service (lout two 
months) and worked well at a positive pressure of 
half an atmosphere. Attempts to pull the joint 
apart resulted in glass breakage before the tubing 
split. This connector was also used to connect a 
water distillation flask to a condensor without 
softening under the heat load, and proved service-
able at even higher temperatures by directing a jet 
of cooling air at the plastic tubing. 
2. No other clamp or connector was used in conjunc-
tion with the shrinkable tubing, resulting in a 
lighter and more flexible glass system. No part of 
the polyolefin tubing contacts the contents of the 
system as the tubing compresses the glass end 
connections about the 0-ring.
(continued overleaf) 
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Aeronautics and Space Administration. Neither the United States	 information contained in this document, or warrants that such use 
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3. Care must be taken to choose a brand of polyolefin 
tubing with a shrink ratio of at least two to one. 
This is necessitated by the geometry of 0-ring con-
nectors, since the tubing must be large enough to 
enclose the large center diameter of the glass con-
nector and still shrink tightly around the glass 
tubing of the connector. Tubing heated to too high 
a temperature during shrinkage tends to split but 
this is easily prevented by proper choice of the 
distance between heat gun and connector.
4. hiquiriesconcerning this innovation may be di-
rected to:
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B68-10040 
Patent status: 
No patent action is contemplated by NASA. 
Source: Betty Del Duca and Arthur Downey 
(LEW- 10329). 
Brief 68-10040	 Category 05


Heat-shrink plastic tubing seals joints in glass tubing

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