Design adds gas thrust bearing to face of conventional face seal. Bearing lifts seal's carbon face out of contact after startup and establishes thin gas film between sealing surfaces. Operating pressure and speed capabilities are greater than those of conventional face seals

Johnson, R. L.

Ludwig, L. P.

Zuk, J.

English

NASA Technical Reports Server

August 1972	 CORRECTED COPY	 B72-10114 
NASA TECH BRIEF 
Lewis Research Center 
NASA Tech Briefs announcenew 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. 
High Speed, Self-Acting, Face-Contact Shaft Seal

Has Low Leakage and Very Low Wear 
The problem: 
To devise a gas turbine engine shaft seal capable of 
operating satisfactorily at 200 psi (138 N/cm 2 ) sealed 
pressure, 400 ft/sec (122 rn/see) sliding velocity, and 
1000°F (811K) sealed gas temperature. Conventional 
labyrinth seals have high speed capability, little to no 
wear, but too high a leakage rate. Conventional face-
contact seals wear rapidly at these operating conditions; 
at higher pressures, temperatures, or sliding speeds, 
both wear and leakage are excessive. 
The solution: 
Add a gas thrust bearing to the face of a conventional 
face seal. The gas thrust bearing lifts the carbon face of 
the seal out of contact soon after startup .and establishes 
a thin gas film between the sealing surfaces. Rubbing 
occurs only at startup and shutdown substantially re-
ducing wear. Operating pressure and speed capabilities 
are significantly greater than those of conventi&nal face 
seals.
COMPRESSOR 
DISCHARGE
How it's done: 
Figure 1 is a schematic of a gas turbine engine shaft 
seal. The head assembly with the carbon sealing ring does 
not rotate but is free to move axially and is pressed 
against the rotating seat face by the springs. Good contact 
between these parts inhibits hot gas leakage from the 
inside of the seal, across the sealing face, and into the 
bearing compartment Because of rubbing contact between 
the seal ring and seat face (which at severe conditions 
will be in vibratory contact), conventional face seals in 
turbine engines are limited to operating conditions of 
about 125 psi (86 N/cm 2 ) pressure differential and 350 
ft/sec (107 rn/see) sliding velocity at 800°F (700K) sealed 
gas temperature. Adding a gas thrust bearing to the 
carbon face establishes and maintains a gas film between 
the sealing surfaces. Because the gas film is very thin 
(0.0001 to 0.0004 inch) (0.0003 cm to 0.0010 cm), 
leakage across the sealing face is limited. Because the 
self-acting lift pads develop high separating forces at 
operating speeds which prevent rubbing contact, wear 
is minimized. The positive stiffness of the gas film due 
to the lift pads allows the carbon face to track the move-
rents of the rotating seat face without being in contact,
400 FTISEC SEAL	 400	 10000 F 
200 PSI BEARING
RELATIVE 
EAT	 200 WEAR RATE 
	
_ 	
NONE LU 
10	 10.0 
RELATIVE 
LEAK RATE
	
	 1.0
RUBBING LABYRINTH SELF-
GAS THRUST' cs-56861	 FACE	 ACTING 
BEARING	 CARBON SEALING RING 	 SEAL	 FACE 
(LIFT PADS)	 si 
	
is Figure 1. - Self-acting face seal.	 Figure 2. - Seal performance comparison. 
(continued overleaf) 
This document was prepared under the sponsorship of the National	 Government assumes any liability resulting from 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=19720000114 2020-03-17T03:31:23+00:00Z
Figure 2 shows leakage and wear rates for the self-acting 
seal compared to conventional face seals and labyrinth 
seals. The self-acting seal has about 1/10 the leakage of 
labyrinth seals, and less leakage and substantially less 
wear than conventional face seals. 
Notes: 
1 The lift pads provide the following important features 
generally missing in conventional face seals: 
a. High-gas film stiffness that allows the head to 
dynamically track the seat face motions without 
rubbing contact. 
b. The ability to operate with divergent face defor-
mation (due to thermal, centrifugal, etc, distortions). 
2. Over 320 hours of successful performance at a multi-
tude of operating conditions was achieved with one 
seal assembly with little wear. The severest operating 
condition was at 300 psi (207 N/cm 2 ) sealed pressure, 
500 ft/sec (153 m/sec) sliding velocity, and 1200°F 
(922°K) sealed gas temperature. 
3. This seal should be of interest to manufacturers of 
commercial compressors and gas turbines: 
4. A similar concept is employed in NASA Tech Brief 
B72-l0447. 
5. The following documentation may be obtained from: 
National Technical Information Service 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.95)
Reference: NASA TN-D-5744 N70-24256j 
Design Study of Shaft Face Seal with Self-
Acting Lift Augmentation, I - Self-Acting 
Pad Geomerty 
Reference: NASA TN-D-7006 (N71-11579) 
Design Study of Shaft Face Seal with Self-
Acting Lift Augmentation, II - Sealing Dam 
Reference: NASA TN-D-6164 (N71-20392) 
Design Study of Shaft Face Seal with Self-
Acting Lift Augmentation, III - Mechanical 
Components 
6. Technical questions may be directed to: 
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B72-10114 
Patent status: 
No patent action is contemplated by NASA. 
Source: J. Zuk, L. P. Ludwig, and R. L. Johnson

Lewis Research Center 
(LEW-1 1598) 
B72-10114
	
Category 07


High speed, self-acting, face-contact shaft seal has low leakage and very low wear

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