NESC tech bulletin

National Aeronautics and Space Administration

www.nasa.gov

Applicability

NASA and industry frequently use 

pyrovalves in propulsion systems 

and other types of applications.

Background

In 2008, the NESC investigated 

four instances when normally 

closed pyrovalves did not actu-

ate after simultaneous firing 

of dual NSIs failed to ignite the 

booster charge. In each anomaly, 

an Al PCA with NSI flame chan-

nels in a Y configuration (Y-PCA) 

was used to direct the output

energy to the booster charge. The 

booster charge generates most 

of the force to actuate the ram

and open the pyrovalve. 

Based on assessment findings that the Al PCA chan-

nels eroded during firings, reducing energy for booster

initiation, and that the “Y” flow passage had potential flow

issues, the Mars Science Laboratory propulsion system team 

chose a new SS PCA with independent V-shaped flow passages 

(see figure). The NESC conducted an additional independent

assessment to compare the booster interface temperature for 

the two configurations and quantify the improvements.

Findings and Conclusions 

Based on testing to date, the SS V-PCA produced an aver-

age temperature of 2300°F at the booster interface versus 

1400°F for the legacy Al Y-PCA during a single initiator firing

indicating that both are reliable in this firing mode. However, 

the SS V-PCA did not improve the pyrovalve performance during 

simultaneous firings (skew within 5 microseconds). Although 

the NSI firings were nominal, neither configuration produced 

a temperature at the booster 

that was significantly above the

auto-ignition temperature of 

the booster propellant. Doubling 

the diameter of the flow pas-

sages in the SS V-PCA above 

the standard diameter (four 

times the cross-sectional area) 

was also evaluated and did 

not eliminate the simultaneous

firing anomaly.

As in the legacy Al Y-PCA, test

results for the SS V-PCA indicated

firing commands for the two

initiators should be separated by 

at least 2 milliseconds (ms) to 

guard against potential opera-

tional failure. When separated by 

2 ms or more, both the legacy 

Al design and the new SS design produced booster interface

temperatures adequate for reliable booster ignition.

References

NESC Technical Bulletin No. 09-01, Failure of Pyrotechnic Oper-

ated Valves with Dual Initiators. NASA Engineering and Safety 

Center.

Jet Propulsion Laboratory, Disclosure for the Steel Primer 

Chamber Assemblies for Dual Initiated Pyrovalves. New Tech-

nology Report #46302, California Institute of Technology,

July 7, 2008.

CONAX Y-PCA Booster Anomaly Investigation Report, NESC Doc-

ument Number RP-08-111, NASA Technical Memorandum (TM) 

Number TM-2008-215548.

Potential Failure of Dual Simultaneously

Initiated Pyrotechnic Operated Valves

The NASA Engineering and Safety Center (NESC) Technical Bulletin No. 09-01 reported an independent

investigation of four pyrovalve failures that occurred while using aluminum (Al) pyrovalve primer chamber 

assemblies (PCAs) during ground testing. The investigation revealed that simultaneous firing (within a few 

microseconds) of the NASA Standard Initiators (NSIs) was the primary reason why the booster charge failed 

to ignite and the pyrovalves subsequently failed to operate. A second investigation of a new stainless steel 

(SS) PCA design with separate flame channels was completed in 2010. The new SS configuration was found 

to be improved in most respects; however, no improvement was noted in the temperature delivered to ignite 

the booster during dual simultaneous NSI firings. Simultaneous firings should be avoided when using either 

the Al or the SS PCA design.

For more information contact the NESC at www.nesc.nasa.gov

NASA Engineering and Safety Center Technical Bulletin No. 10-02

Diagram of a Normally Closed (NC) Pyrovalve Block