Alternative O-Rings for Hypergolic Propellant Systems

O-rings are used in many NASA propulsion systems to seal high pressure lines that contain liquid engine 

propellants and gases. Production of a widely-used commercial O-ring, compatible with these liquids 

and gases, was discontinued due to lack of a key compound ingredient. The NESC engaged O-ring and 

material manufacturers and performed extensive materials compatibility testing to find suitable replacements. These replacement candidates are still awaiting qualification to NASA design and construction 

standards (e.g., NASA-STD-6016, etc.).

NASA Engineering and Safety Center Technical Bulletin No. 20-04

National Aeronautics and Space Administration

www.nasa.gov

Background

Parker-Hannifin has stopped making O-rings with 

E0515-80, an ethylene propylene diene monomer 

(EPDM) material often used in hypergolic propellant 

systems. Production was halted due to a supplier of an 

E0515 compound ingredient unexpectedly and suddenly 

ceasing operations in late 2018. The O-rings are used in 

many NASA programs. An NESC assessment team was 

formed and planned to test several candidate replacement 

materials to avoid future dependence on a single material. 

While the E0515 O-rings are used in multiple applications 

across NASA, the use of the rings in hypergolic propellants 

is of particular interest. Parker-Hannifin suggested 

another in-house material, EM163, as the replacement for 

E0515. EM163 is a Shore M 80-durometer EPDM material, 

certified to NAS1613 Rev. 6, a specification for use in 

hydraulic fluid systems. Note that E0515 was certified to 

NAS1613 Rev. 2. The main difference between Rev. 2 and 

Rev. 6 is the requirement to be compatible with additional 

hydraulic fluids. Parker-Hannifin expects EM163 to 

perform similarly to E0515 but did not perform testing for 

hypergolic propellant compatibility. 

Replacement Materials Testing

and Results

The NESC assessment team chose six candidate 

materials for testing as possible E0515 replacements. 

The assessment team also contacted several material 

compounding firms in the event none of the six candidate 

materials were found to be compatible. Short and longduration tests were performed in accordance with 

standard testing procedures. Figure 1 shows unexposed 

and exposed Park-Hannifin E0515 O-rings from the shortduration testing. Two of the candidate materials, including 

the EM163 material suggested by Parker-Hannifin, were 

eliminated from consideration after short-duration testing.

Three materials, Parker E0540, Precix E152, and Parco 

5778-80, successfully completed short- and long-duration 

testing and are considered compatible replacements 

for Parker E0515 in hypergolic propellant applications. 

One material, Freudenberg-NOK E458, gave mixed 

results during the short- and long-duration testing and is 

considered a compatible replacement for Parker E0515 in 

limited hypergolic propellant applications.

References

1. ASTM D395, Standard Test Methods for Rubber 

Property—Compression Set.

2. NASA-STD-6001B, Flammability, Offgassing, and 

Compatibility Requirements and Test Procedures,

April 21, 2016.

3. Parker O-Ring Handbook, ORD-5700, Parker Hannifin 

Corporation, Cleveland, OH, 2018. 

For information, contact Daniel J. Dorney at daniel.j.dorney@nasa.gov.

www.nasa.gov Author: Daniel J. Dorney. For information, contact Jonathan Jones at jonathan.e.jones@nasa.gov 05/01/2020 05/18/23