Sealing efficiency, service life, and seal loading limits of lip seal for rotating shafts are analyzed. Construction of seal and areas of application are described. Specific advantages of improved lip seal over conventional seals are listed

Endicott, D. L.

English

NASA Technical Reports Server

October 1972	 B72-10672 
NASA TECH BRIEF 
Lewis Research Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Improved Lip Seal for Rotating Shafts 
An improved lip seal has been designed which is 
simpler and less expensive than conventional lip seals. 
Both axial and radial seal loading is provided by an axial 
spring, eliminating the separate radial loading ring con-
ventionally required. The seal can be used in very small or 
inaccessible areas without limitation as to the size of the 
loading spring which can be utilized. A wide range of seal 
loading is available by selective design of the components. 
As shown in Figures 1 and 2, the axial spring forces the 
seal loading ring of the spacer into the formed cavity of 
the seal so that a controllable lip seal pressure can be 
maintained. The ring height is designed so that the flat 
portion of the spacer bottoms on the seal body when a 
predetermined seal load is obtained, and potential over-
loading of the seal is prevented. Varying amounts of 
seal-loading spring force can be applied to the sealing lip 
by changing the nose radius of the loading ring or the 
contour of the flank portions of the spacer or both. 
Additional control of the seal-loading forces can be 
obtained by varying the angle of the seal recess in the seal 
which receives the loading from the spacer. Additionally, 
the stand-off height of the spacer loading section can be 
varied to provide different limits in seal radial loading due 
to the fact that the base of the spacer will bottom on the 
flat portion of the inner seal under predetermined 
spring-loading conditions, and additional spring loading 
beyond this level will be absorbed in compressing the 
body of the inner seal. By matching the modulus of 
elasticity of the inner seal material (plastics such as 
polytetrafluoroethylene, polyiniide, etc.) with the axial 
loading provided by the external spring, a fixed limit in 
seal radial loading is obtained. This feature allows the 
designer to select the desired seal radial loading regardless 
of the size of the external spring. It is possible to design 
the seal such that the same seal load can be obtained with 
a very heavy spring or a light spring; however, different
inner seal and spacer configurations will be required if the 
spring loading variations are very large. The normal 
considerations of sealing efficiency, service life, and seal 
loading limits apply to this seal design; however, a much 
broader range of loading is possible within the same space 
limitations. 
Since the seal radial forces are generated through the 
use of an external spring instead of the conventional 
internal spring, a largerselection of spring-loading rates is 
possible. This is particularly important where the size of 
the seal cavity is limited to small sizes, but where 
relatively large seal radial loading is desired. 
This seal is easier to install than a conventional seal due 
to the fact that the seal is not spring loaded when 
installed, but is loaded after the return spring is installed. 
Less seal damage will occur to the sealing surface of the 
seal during installation with this design. The seal and 
spacer are both installed in the same manner as a plain flat 
washer and then loaded after installation. 
The following are specific advantages of this seal: 
1. This design is less expensive than conventional seals 
due to the fact that the internal seal expansion spring is 
eliminated and the return spring serves this function. 
2. This seal can be loaded to a higher sealing load 
without danger of overloading due to the design arrange-
ment of the spacer. 
3. This seal provides for the compensation of seal 
wear during service like that of spring loaded seals without 
requiring a special spring for this service. 
4 The seal can be used on any shaft and housing 
point where a return spring exists, such as the intake 
valves on an automotive internal combustion engine. 
5. This seal arrangement provides a much greater 
range in lip sealing forces than can be obtained with 
conventional type of lip seals. This will provide better 
sealing on all small sizes of seals.
(continued overleaf) 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting iTh'the use of the 
Aeronautics and Space Administration. Neither the United States	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately owned rights.	 -
https://ntrs.nasa.gov/search.jsp?R=19720000671 2020-03-17T03:42:37+00:00Z
Figure 1. 
Shaft 
Sealing 
Lip 
Seal	 Seal Loading 
Angle [	
("—__.f___Rin Recess
so 
Seal U L 0. External Spring Force 
SIacer 
Stand Off 
Height
Figure 2. 
Patent status: 
Title to this invention has been waived under the 
provisions of the National Aeronautics and Space Act [42 
U.S.C. 2457 (f)], to McDonnell Douglas Corporation, 
3000 Ocean Park Boulevard, Santa Monica, California 
90406 (Attention: Mr. Donald Royer). 
Source: Donald L. Endicott of 
McDonnell Douglas Corp.

under contract to
Lewis Research Center
(LEW-11602) 
B72-10672	 Category 07


Improved lip seal for rotating shafts

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