Two types of polyimide seals are developed for hydraulic actuator rod in low pressure second stage of two-stage configuration. Each seal melts test objectives of twenty million cycles of operation at 534 K. Analytical and experimental study results are discussed. Potential applications are given

Johnson, R. L.

Lee, J.

Loomis, W. R.

English

NASA Technical Reports Server

A. 450 V-Seal, Original Design 
Loading 
Springs 
Outhoard P"I
B. 30 0 V-Seal with Split Load Ring 
Gland 
Housing 
Inboard 
May 1971	 Brief 71-10098 
S	 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-Temperature, Long-Life Polyimide Seals for Hydraulic Actuator Rods 
Two new types of polyimide seals have been 
developed for an hydraulic actuator rod in the low 
pressure second stage of a two-stage configuration. 
The first stage is subjected to full hydraulic system
Present seals in the hydraulic systems of com-
mercial, subsonic, jet aircraft operate satisfactorily for 
more than 1000 hours at temperatures in the range 
of 344° to 356°K (160 to 180°F); but seals in 
Outboard
Gland	 Loading Backup Ring 
Housing	 Springs 
Inboard 7\(
Load Ring Gland 
Assembly Housing 
Inboard 
Loading Backup Ring 
Springs 
Bearing	 -*- Rod --.	 Sealing Elements	 Bearing	 4-Rod-ø- Sealing Elements 
"	 Spacer	 eauIng	 Load Ring Bearing	
...m-Rod-ø Elements 	 Assembly. 
C. Tapered Leg V-Seal with Split Load Ring 
Rod Seal Designs with Polyimide Sealing Elements 
pressure of 20.7 to 28 MN/m 2 (3000 to 4000 psi),	 Mach 2 military fighters are limited to less than 
and leakage past this seal is returned to a res- 	 1000 hours of operation at the higher temperature 
ervoir. The second stage is subjected to a return	 of 409°K (275°F). Previous laboratory work es-
pressure of about 0.69 to 1.38 MN/m 2 (I00to 200 psi). 	 tablished that elastomeric rod seals are restricted to 
Each seal met test objectives of 2 x 10 cycles of 	 several hundred hours of service at 478°K (400°F), 
operation at 534°K (500°F). The severity of this 	 and that the best nonelastomeric seals are limited 
testing was equivalent to 3000 hours of operation	 to less than 500 hours at 590°K (600°F) due to 
in an advanced aircraft.	 limitations in seal design and/or seal materials. 
continued overleaf) 
	
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https://ntrs.nasa.gov/search.jsp?R=19710000097 2020-03-17T02:22:06+00:00Z
The selection of unfilled polyimide plastics as seal 
material for a second-stage actuator rod was based 
on an evaluation of numerous materials, including 
plastics, soft metals, and hard metals. Characteristics 
evaluated were: compatibility with various high-tem-
perature fluids at temperatures of up to 590°K 
(600°F); sliding friction; tensile modulus of elasticity; 
tensile yield strength; percent elongation; and hard-
ness. An extensive analytical and experimental study 
was made to find the most promising combination 
of seal designs and materials. Those selected for 
endurance tests included the polyimide V-seal, the 
cobalt-molybdenum lip seal, and a tool steel-silver 
reed seal. Of the seals evaluated, the polyimide 
V-seal demonstrated the best potential for meeting the 
requirements. 
Two modifications, of the original V-seal design 
were evolved (see fig.). The original ir/4 rad (45°) 
V-seal design configuration is shown in A. 
• Design B is a reconfigured V-seal with 7r/6 rad 
(30°) leg angles. Changing the angles of the seal-
ing legs from ir/4 to 7r/6 rad resulted in longer 
legs, which permitted greater leg deflections for a 
given load, thus reducing the sealing stress and 
increasing the life of the seal. The initial applica-
tion of the axial load by the outboard loading 
springs causes the inner load ring to make contact 
with the outer seal leg. The use of this dual loading 
arrangement resulted in a more uniform and con-
trollable seal load. 
Another modification of the original V-seal con-
figuration is shown in C. This design further im-
proved the original V-seal designs by incorporating 
linearly tapered sealing legs to minimize the bending 
stresses at the transition surfaces of the seal. In 
effect, the tapered leg configuration relocated the 
maximum bending stress away from the notch-
sensitive area of the seal, thus minimizing cracking. 
This configuration also gave seal deflections equiva-
lent to those obtained with the 7r/6 rad V-seal, 
but with an approximate 35% lower seal circumfer-
ential loading. This resulted in lower contact stresses 
at the seal contact surface between the polyimide 
element and the actuator rod.
Both the r/6 rad V-seal and tapered leg V-seal 
with split load ring assemblies successfully completed 
the 2 x 107 cycle test at temperatures to 534°K 
(500°F), with a leakage rate of less than one drop 
per minute. Test fluid was a chlorinated phenyl 
methyl silicone at a pressure of 0.69 to 1.035 MN/m2 
(100 to 150 psig). The actuator cycling rate was 
maintained at 5 cps with a total piston-rod stroke 
length of 0.51 ±0.051 cm (0.20 ±0.02 in.). 
Notes: 
1. This seal could be directly applied to flight and 
engine control actuators for high-performance air-
craft. It may also have potential application as a 
low pressure, high temperature rotary shaft seal 
for other types of equipment. 
2. The following documentation may be obtained 
from: 
National Technical Information Service 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.95) 
References: 
NASA-TM-X-52888 (N70-40903), High-Tem-
perature Polyimide Hydraulic Actuator Rod 
Seals for Advanced Aircraft 
NASA-CR-72563 (N70-10905), Development of 
High-Temperature Polyimide Rod Seals 
3. Technical questions may be directed to: 
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B71-10098 
Patent status: 
No patent action is contemplated by NASA. 
Source: John Lee of
Fairchild Hiller Corp. 
under contract to
Lewis Research Center, and 
William R. Loomis and Robert L. Johnson
Lewis Research Center
(LEW-1 1212)
C 
-0. 
Brief 71-10098	 Category 04,07


High-temperature, long-life polyimide seals for hydraulic actuator rods

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