To provide flared tubing and hose connections for high-pressure hand tightened cryogenic service, a 1/4-inch male AN seal was modified by machining to receive a special, double-truncated-cone-shaped Kel-F washer between it and the flared flex hose connector

Meyer, W. A.

English

NASA Technical Reports Server

Double Truncated 
Cone-Shaped Kel-F 
Washer
--	 Double Truncated 
Cone-Shaped Kel-F 
Washer 
Union 
Flared F 
Connece
5/8 Marmon Clamo 
December 1968
	 Brief 68-10417 
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. 
Hand-Tightened, High-Pressure Seal 
This Surface 
Altered 
The problem: 
A heed existed to provide flared tubing and hose 
connections for high-pressure (10,000 psi) cryogenic 
service that could be assembled without the use of 
tools. 
The solution: 
Modify existing high-pressure fittings to provide 
hand-tightened, leak-proof connections. 
How it's done: 
A 1/4-inch male AN union was modified by ma-
chining to receive a special, double-truncated-cone-
shaped Kel-F washer between it and the flared flex 
hose connector as shown in the left figure. This modi-
fied fitting with the insert can be hand tightened. 
The insert design provides sufficient compression of 
the Kel-F material to allow a metal-to-metal fit be-
tween the flared tube and the AN union. Tests were 
conducted at 10,000 psi, ambient temperature, and at 
3000 psi, —320°F, using liquid nitrogen. These tests 
were conducted with fittings tightened by various per-
sonnel having different hand strengths. All tests were 
successful, and no leakage was experienced. 
A 3-5/8-inch-diameter, double-truncated-cone-
shaped seal, used in conjunction with a Marmon 
clamp modified with wing nuts, as shown in' the right 
figure, was successfully tested at room temperature, 
but leaked excessively at —320°F. Total shrinkage 
of a Kel-F seal for a given diameter and temperature 
can be computed by subtracting from the diameter the 
product of the constant K and the diameter. From 
these computations, it can be determined that the seal 
will shrink 0.034437 inch at —320°F, which is more 
than the compressibility of the material. Therefore, 
a leak would be expected at that temperature. Con-
versely, at a 0.750-inch diameter, the seal will shrink 
0.007 125 inch. Compressibility of the material is great-
er than the shrinkage at this temperature, and a sealed 
fitting without leakage can be achieved. 
The use of this type of hand-tightened seal, for use 
on cryogenic lines to —320 0 F, is limited to seal diam-
eters of 3/4 inch and less. Indications are that there 
(continued overleaf) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19680000417 2020-03-12T06:01:59+00:00Z
would be no limit to the size of this seal design, for 
use at ambient temperature. 
Notes: 
I. Areas in which this type of fitting and seal could 
be used to advantage are (I) laboratory instrumen-
tation, (2) flow bench hookups, and (3) hydraulic 
connections. 
2. No additional documentation for this invention is 
available. 
3. Questions concerning this invention may be di- 
rected to:
Technology Utilization Officer 
Marshall Space Flight Center 
Huntsville, Alabama 35812 
Reference: B68-10417
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to NASA, Code 
GP, Washington, D.C. 20546. 
Source: Wilbur A. Meyer 
of North American Rockwell Corporation 
under contract to
Marshall Space Flight Center
(M FS- 18416) 
Brief 68-10417	 Category 05


Hand-tightened, high-pressure seal

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