Counter lung, incorporated in closed-loop rebreathing system, accommodates user's breathing tidal volume so that the loop pressure is relatively constant during breathing cycles

Babinsky, A. D.

Kiraly, R. J.

English

NASA Technical Reports Server

1972	 B72-10219 
NASA TECH BRIEF 
Ames Research Center	 -4r 
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. 
Counter Lung 
In a closed-loop rebreathing system, it is necessary 
to maintain the loop pressure relatively constant as 
the pilot inhales and exhales. A counter-lung is incor-
porated in a closed rebreather loop to accommodate 
a user's breathing tidal volume so that the loop pres-
sure is relatively constant during breathing cycles. 
Orifice Bleed Vent Hole Pressure Breathing	
Pressure Breathing Aneroid 	 Safety vent 
Exhalation PressureA  Altitude Antisuffocation Valve o	 Exhalationsnat Pressure o Supply	 Compeed Valve7 ir —2 Compensat ion
-. ) 
.Conter Demand
Regulator	
\	 ----------	 (Ba I. 
-	
t Disconnec Seal	
Io	
\___, 
N2 Purge ., 
Rebreather 
N1__
, f Loop 02 Demand 
Regulator 
Rebreather 
Bag
0 In 
Variable	 Container 
Volume Control 
The counter-lung is a flexible bag within a rigid 
container. The inside of the bag is connected to the 
breathing loop; the outside is pressurized with air at 
about one inch of water pressure above cabin pressure 
to prevent cabin air from leaking into the system. At 
altitudes where the rebreathing loop must be operated 
at pressures over ambient, the counter-lung is pres-
surized to the standard breathing schedule starting 
at 11.6 km cabin altitude. 
The counter-lung pressure control regulator sup-
plies gas pressure to the outside of the bag from an 
available aircraft source during the inhalation portion 
of the breathing cycle; the pressure is controlled 
according to a prescribed pressure schedule by an 
aneroid control. A pressure-compensated valve allows 
venting of air from the pressurized container during 
exhalation in order to maintain a fixed operating 
pressure. 
Loss of air supply pressure to the demand regulator 
of the counter-lung would result in the lack of control 
of counter pressure on the outside of the bags; this 
would cause the counter-lung to be virtually inopera-
tive, and the oxygen demand regulator would then be 
forced to supply the full tidal volume needs of each 
breathing cycle with the pilot's exhalation escaping 
from around the mask. If the demand regulator fails 
to operate, because of loss of air supply pressure, the 
anti-suffocation valve shown in the diagram permits 
exposure of the outside of the bag to ambient pressure 
and thus provides normal breathing action without 
benefit of pressurized breathing conditions. The anti-
suffocation valve is spring-loaded so that it is normally 
open, but a diaphragm at the back of the valve is 
referenced to the inlet air supply pressure and this 
forces the valve into the closed position as long as 
normal supply pressure is available. When the pres-
sure falls below a selected value, the valve opens 
and restores ambient pressure into the space sur-
rounding the counter-lung. 
The demand regulator is so located that its di-
aphragm is referenced to the counter-lung container 
(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=19720000219 2020-03-17T03:33:31+00:00Z
pressure which, in turn, is already altitude compen-
sated. Thus, this method of diaphragm reference 
eliminates the need for an additional altitude aneroid. 
The nitrogen vent shown in the figure is designed 
to remove nitrogen continuously from the rebreather 
loop; during operation with 100% oxygen feed, nitro-
gen may be released from body cavities, liquids, and 
tissues. The amount of gas vented during each breath-
ing cycle is the difference in volume between the 
fully-inflated counter-lung and the pilot's tidal vol-
ume; thus, each pilot can set the volume control to 
suit his tidal volume. During each exhalation, the 
vent valve will open when the bag becomes fully 
inflated and the loop pressure begins to rise above 
the air pressure in the container. Conversely, on in- 
halation, when the rebreather bag becomes fully col- 
lapsed and the loop pressure begins to fall below the 
air pressure, the demand regulator will open to supply 
oxygen from the electrolysis cell. 
Notes: 
1. The following documentation may be obtained 
from: 
National Technical Information Service 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.95)
Reference: 
NASA CR-73396, Aircraft Oxygen System 
Development, Laboratory Breadboard 
System Test Report. 
2. With few modifications, the counter-lung can be 
adapted for underwater breathing in a ditched 
aircraft; no electrical or mechanical power is re-
quired. 
3. Requests for further information may be directed 
to:
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California 94035 
Reference: TSP 72-10219 
Patent status: 
No patent action is contemplated by NASA. 
Source: Andrew D. Babinsky and 
Raymond J. Kiraly of 
TRW, Inc./Mechanical Products Division 
under contract to 
Ames Research Center 
(ARC-10248) 
B72-10219	 Category 05


Counter lung

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