Detection delay defects are omitted by using helium mass spectrometer leak detector combined with several known procedures. Technique combines carbon dioxide purging, cryogenic separating helium accumulation, and use of carbon dioxide as carrier gas

Camarillo, R. G.

Moore, B. C.

English

NASA Technical Reports Server

July 1972 B72-10354 
NASA TECH BRIEF 
Marshall Space Flight Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tecr 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. 
Helium Leak Measurements Using CO 2 as a Carrier 
The problem: 
Present methods to accurately detect the presence 
and level of gas leakage often incur long delays in 
detection. 
The solution: 
Leak detection is accomplished by using a helium 
mass spectrometer leak-detector and, by combining 
several known procedures, omits those defects in present 
techniques that result in delay of detection. 
How it's done: 
The improved leak-detection technique combines car-
bon dioxide purging, cryogenic separating helium accu-
mulation, and the use of carbon dioxide as a carrier gas. 
Helium leak-detector sensitivity using the 3pecimen 
evacuation technique is better than 1 x 10-9 std. cm3 / 
sec. The difficulty in locating leaks using this technique 
occurs when the specimen is a large volume-low conduc-
tance system such as the plumbing of a typical cryogenic 
shroud used in vacuum chambers. The controlling factor 
for locating leaks in such a system is the system time-
constant rather than the leak-detecter sensitivity. 
The specimen pressurization technique, i.e., sniffmg 
technique, is used as an attempt to circumvent the time 
constant effect. This method reduces the effective leak-
detector sensitivity to 1 x 10 .... 6 std. cm3/sec. at best. 
When using the sniffmg technique, the controlling factor 
becomes the effective sensitivity rather than the system 
time-constan t. 
This study deals with the development of a technique 
that retains the basic leak-detector sensitivity while cir-
cumventing the specimen time-co)1stant. The technique 
uses CO2 as a carrier gas. The leak-detector liquid nitro-
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States 
gen trap is used as a cryogenic pump fOT the carrier gas. 
The permissible throughput of the leak-detector is a 
nominal 5 x J(f4 std. cm3/sec. for air. The leak-detector 
throughput using CO2 may be maintained at 10 .... 1 std. 
cm3/sec. without compromising the leak-detector ioni-
zation chamber vacuum level. 
A continuo~s CO2 purge is maintained through the 
specimen. Helium is introduced into the specimen at a. 
rate of 2.7 x J(f8 std. cm3/sec. The leak-detector re-
sponse is recorded and compared to the response when 
no CO2 purge is used. The helium leak is valved 'off, 
and the "cleanup" rates with and without the CO2 
purge are recorded. Using the CO2 purge, the response 
rate shows a significant increase without loss in the 
effective sensitivity. 
Notes: 
1. Information concerning this innovation may be of 
interest to manufacturers and users of pressure ves-
sels, cryogenic hardware, or vacuum hardware. 
2. Requests for further information may be directed to: 
Technology Utilization Officer 
Marshall Space Flight Center 
Code A&TS-TU 
Huntsville, Alabama 35812 
Reference: B72-10354 
Patent status: 
No patent action is contemplated by NASA. 
Source: B. C. Moore and R. G. Camarillo of 
McDonnell Douglas Astronautics Company 
under contract to 
Marshall Space Flight Center 
(MFS-21742) 
Category 03 
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights . 
https://ntrs.nasa.gov/search.jsp?R=19720000353 2020-03-17T03:30:03+00:00Z


Helium Leak Measurements Using CO2 as a Carrier

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