Shaft riding circumferential seal is used with turbine engines under high pressure conditions. Construction of seal is discussed and schematic diagram to show operations is provided

Hady, W. F.

Ludwig, L. P.

English

NASA Technical Reports Server

Lift 
Pads Seal Ring (3 Segments) Figure 1 
The problem: 
July 1972
	 B72-l0447 
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. 
High-Speed, Self-Acting Shaft Seal

(Circumferential Type) 
Pressurizing
Air
Garter 
Spring 
To produce shaft riding circumferential seals which 
are capable of operating satisfactorily at the pressure and 
speed conditions of advanced turbine engines. Con-
ventional circumferential type seals, because of rubbing 
contact and resulting high wear, cannot operate at the 
pressure (up to 138 N/cm 2 ) (200 psi), temperature (810 
to 922 K) (1000°F to 1200°F) and speed (122 to 213 
m/sec) (400 to 700 ft/sec) requirements of advanced 
engines. 
The solution: 
Add gas bearing lift pads to the bore of the cir-
cumferential seals (Figure 1). These lift pads establish a 
gas film between the seal bore and the rotating shaft. 
.	 Thus, rubbing contact only occurs at the start and stop 
and heat generated by rubbing contact is eliminated.
Seal Dam"	 Lift Pads	 'Seal Dam 
Shaft Q 
Figure 2 
This permits the circumferential seal to have significantly 
greater pressure and speed capabilities than those of the 
conventional circumferential seal. 
How it's done: 
Figure 2 shows a conventional seal with carbon ring 
segments that ride on the rotating shaft. The bore has a 
groove pattern that permits the radial pressure forces to 
(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=19720000446 2020-03-17T03:39:43+00:00Z
be partially balanced out. The sealing dam is a.narrow 
ridge as shown in Figure 2. The seal consists of two 
segmented rings pressurized with air. The air leaks from 
the center of the seal across the left segment on the 
bearing side and also across the tight segment on the 
hot gas side. Thus, oil is prevented from leaking out and 
hot gas is prevented from leaking into the bearing 
compartment. 
To create a self-acting seal, a conventional seal is 
modified by adding the gas bearing lift pads. These 
lift pads have a lift force inversely proportional to gas 
film thickness. At small gas film thicknesses, typically 
0.0003 cm (0.0001-inch), significant force is produced 
to separate the rubbing surfaces. As the film thickness 
increases, the lift force drops off rapidly. Thus, the 
seal inherently operates in the thin film regime and 
leakage is low. Such seals have higher speed and pressure 
capabilities than conventional circumferential shaft seals 
because of the non-contact operation. 
Notes: 
1. A similar concept is employed in NASA Tech Brief 
B72-101 14. 
2. 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 (N70-24256), 
Design Study of Shaft Face Seal with Self-
Acting Lift Augmentation, I-Self-Acting Pad 
Geometry. 
3. Technical questions may be directed to: 
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B72-10447 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to: 
Patent Counsel 
Mail Stop 500-311 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Source: L. P. Ludwig and W. F. Hady

Lewis Research Center

(LEW-1 1274) 
B72-10447	 Category 07


High-speed, self-acting shaft seal (circumferential type)

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