Comparative tests of modified and unmodified carbon ring seals showed that addition of helical grooves to conventional segmented carbon ring seals reduced leakage significantly. Modified seal was insensitive to shaft runout and to flooding by lubricant

Ludwig, L. P.

Strom, T. N.

English

NASA Technical Reports Server

July 1974	 B74-10062 
NASA TECH BRIEF 
Lewis Research Center	 - 
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Improved Circumferential Shaft Seal 
. 
.
The Problem: 
Conventional shaft seals as used on some aircraft and 
accessory transmissions tend to leak excessively at the 
higher rotational speeds. Elastomeric lip seals are usually 
satisfactory at sliding speeds below 1219 rn/mm (4000 
ft/mm); however, at higher speeds, the temperature of the 
lubricating film exceeds the useful temperature limit of 
the elastomer causing elastomer degradation and leakage 
of the lubricant out of the transmission. Segmented 
carbon ring seals have suitable high temperature operating 
capability, but at high speeds the carbon rings tend to lift 
up and hydroplane on the lubricant, a thick film of 
lubricant develops and the seals leak even at low pressure 
differentials. 
The Solution: 
Add helical grooves to conventional segmented carbon 
ring seals to counter the lubricant build-up and prevent 
leakage. Comparative tests of modified and unmodified 
carbon ring seals showed that addition of the helical 
grooves reduced leakage significantly, and that the modi-
fied seals gave equivalent performance in other respects 
such as wear life. 
How It's Done: 
A conventional segmented carbon ring seal, shown in 
Figure 1, is modified by adding helical grooves to the bore 
of the side cover ring, as shown in Figure 2. The helical 
grooves are oriented to pump against the leakage tend-
ency.
iiI	 'or 5
	
To[, o r RwojS 
EI' 
Figure 1. - Carbon rings for conventional circumferential seal.
Figure 2. - Modified (helix grooved) circumferential seal. 
Bench tests were run with both modified and unmodi-
fied segmented carbon ring seals to determine comparative 
performance with respect to: (a) leakage, (b) torque and 
heat generation, and (c) operation under shaft runout 
conditions to 0.254 mm (0.010 in) total indicated runout. 
The seals were mounted on a 11.258 cm (5.481 in) 
diameter shaft operated at 6600 rpm which provided a 
seal sliding speed of 2880 rn/mm (9450 ft/mm). Pressure 
differential across the seals was varied from zero to 1.38 
N/cm2
 (2 psi), and the seals were tested in both partially 
flooded and fully flooded conditions. 
Test results showed that: 
1. Leakage through the modified seal was significantly 
lower than through the unmodified seal. 
2. Torque of the modified seal was comparable to that 
of the unmodified seal. 
3. The modified seal was insensitive to shaft runout 
whereas the unmodified seal leaked excessively with shaft 
runout. 
4. The modified seal was insensitive to flooding by the 
lubricant; whereas, leakage through the unmodified seal 
increased with flooding. 
Notes: 
1. This innovation illustrates the use of helical grooves to 
reduce leakage and otherwise improve shaft seal per-
formance. Both the modified seal described herein and 
the concept of adding helical grooves to other conven-
tional seals may be advantageously employed in other 
applications.
(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=19740000062 2020-03-17T14:03:14+00:00Z
2. Further information is available in the following 
report: 
NASA TN-D-7130 (N74-14138), Improved Circum-
ferential Shaft Seal for Aircraft Gear Transmission 
Copies may be obtained at cost from: 
Aerospae Research Applications Center 
Indiana University 
400 East Seventh Street 
Bloomington, Indiana 47401 
Telephone: 812.337-7833 
Reference: B74-10062 
3. Specific technical questions may be directed to: 
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B74-10062 
Patent Status: 
Inquiries concerning rights for the commercial use of 
this invention should be addressed to: 
NASA Patent Counsel 
Mail Stop 500-113 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Source: L.P. Ludwig and T.N. Strom

Lewis Research Center
(LEW-1 1873)
S 
S 
B74-10062	
Category 07


Improved circumferential shaft seal

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