Method and apparatus for concentrating a gas using a single stage adsorption zone

A method and apparatus for operating a pressure swing adsorption process is disclosed that may utilize only a single adsorption stage yet still produce a continuous stream of a concentrated fluid.

FIELD OF THE INVENTION 
This invention relates to a method and apparatus using a single adsorption 
zone for producing an enriched stream of a first gas from a stream 
containing the first gas and at least one second gas. In one embodiment, 
the method and apparatus may be used to obtain a concentrated stream of 
oxygen from air. 
BACKGROUND OF THE INVENTION 
Various different methods have been developed for separating gases and 
producing a concentrated stream of a selected gas. One particular method 
which has been used in industry is the pressure swing adsorption process. 
Generally, these processes use an adsorbent which, under elevated pressure 
conditions, preferentially adsorbs a targeted gas over other gases present 
in a gas stream. Accordingly, the adsorbent could be selected to 
preferentially adsorb an undesirable gas from a gas stream thereby leaving 
a gas stream having an increased concentration of the gases remaining in 
the gas stream. An example of such a process would be the use of a 
pressure swing adsorption process to produce an oxygen enriched air 
stream. The adsorbent would be selected to preferentially adsorb nitrogen 
over oxygen. Thus, after the adsorption process is conducted, the 
pressurized air in contact with the adsorbent contains a higher percentage 
by volume of oxygen. This oxygen enriched air may then be vented from the 
adsorption zone and the adsorbent purged (at reduced pressure conditions) 
to remove the adsorbed nitrogen. Alternately, such a process may be used 
to preferentially adsorb a targeted gas (e.g. oxygen) thereby also 
producing an enriched stream of oxygen. 
Various different processes have been designed to utilize the selective 
adsorption ability of zeolite. Examples of these include, Bansal (U.S. 
Pat. No. 4,973,339), Stanford (U.S. Pat. No. 4,869,733) and Haruna et al 
(U.S. Pat. No. 4,661,125). 
The process and apparatus of Bansal, Stanford and Haruna et al each utilize 
two adsorption zones. The use of two adsorption zones is undesirable as it 
unnecessarily complicates the apparatus since it requires additional 
valving and control means to cycle each adsorption bed through a 
pressurization cycle and a purging cycle. Further, this adds to the cost 
of the apparatus and decreases the reliability of the apparatus. 
Other disadvantages of existing designs is the requirement to use expensive 
valve control means. In particular, solenoids are frequently required to 
switch the adsorption zone from a pressurization mode to a purging mode. 
These controls are expensive and also prone to failure after extensive 
use. 
Further, existing designs utilize electronics (e.g. microprocessors) to 
control the cycling of the adsorption zone. This adds to the cost of the 
equipment and also requires an electrical power source to operate the 
process. Further, the electronic components may be damaged in harsh 
environments and this limits the applications of some existing designs. 
SUMMARY OF THE INVENTION 
Despite the fact the method and apparatus of the instant invention use only 
a single adsorption zone, the instant invention may provide a continual, 
relatively steady, flow of an enriched gas stream while the adsorption 
zone is being purged. Further, this stream of enriched gas may have a flow 
rate which is generally constant throughout the entire cycle of the 
adsorption zone from the pressurization (adsorption) stage to the purging 
(desorption) stage. 
To this end, in accordance with the instant invention there is provided a 
concentrator for obtaining an enriched stream of a first gas from a gas 
containing the first gas and at least one second gas, the concentrator 
comprising: 
(a) a pressurizable adsorption zone having an inlet port and containing a 
member for reversibly adsorbing the at least one second gas to produce the 
enriched stream; 
(b) a storage container; 
(c) a passageway extending between the pressurizable adsorption zone and 
the storage container, the storage container being expandable to an 
expanded position to store at least a portion of the enriched stream when 
the storage container is in flow communication with the pressurizable 
adsorption zone; 
(d) a member positioned in the passageway and moveable between a first 
position in which the storage container is in flow communication with the 
pressurizable adsorption zone and a second position in which the storage 
container is isolated from the pressurizable adsorption zone; 
(e) a purge valve associated with the pressurizable adsorption zone and 
moveable between a closed position and an open position in which the 
pressurizable adsorption zone can be purged; and, 
(f) an outlet port in flow communication with the storage container. 
In accordance with another embodiment of the instant invention, there is 
provided a pressure swing adsorption apparatus for producing an enriched 
stream of a first gas from a gas containing the first gas and at least one 
second gas, the apparatus comprising: 
(a) means for reversibly adsorbing the at least one second gas to produce 
the enriched stream; 
(b) expandable storage means for storing at least a portion of the enriched 
stream; 
(c) outlet means in flow communication with the storage container for 
venting the enriched stream from the apparatus; 
(d) means for alternatingly connecting in flow communication and then 
isolating the expandable storage means and the means for reversibly 
adsorbing the at least one second gas; and, 
(e) purging means for removing at least a portion of the at least one 
second gas from the means for reversibly adsorbing the at least one second 
gas when the expandable storage means is isolated from the means for 
reversibly adsorbing the at least one second gas whereby the expandable 
storage means expands to store at least a portion of the enriched stream 
when the storage means is in flow communication with the means for 
reversibly adsorbing the at least one second gas. 
In one embodiment, the storage container is drivingly connected to the 
purge valve, whereby the purge valve is moved to the open position when 
the storage container expands to the expanded position. 
In another embodiment, the concentrator includes an actuator operatively 
mechanically connecting the storage container to the purge valve. The 
purge valve may be a mechanical valve. 
In one embodiment, the storage container comprises a vessel having 
expandable walls and the vessel defines a reservoir for storing the 
enriched stream, the size of the reservoir increasing as the walls expand. 
In an alternate embodiment the storage container comprises a vessel having 
a moveable member mounted therein and moveable between a first position 
and a second position, the vessel defines a reservoir for storing the 
enriched stream, and the size of the reservoir increases as the moveable 
member moves from the first position to the second position. The 
concentrator may include an actuator drivingly connecting the moveable 
member to the purge valve whereby movement of the moveable member from the 
first position towards the second position actuates the purge valve to 
move to the open position. Alternately, the member may be a pressure 
actuated valve whereby movement of the purge valve to the open position 
causes the pressure actuated valve to move to the closed position. 
In another embodiment, the concentrator may also comprise a biasing member 
to bias the moveable member to the first position. The biasing member may 
be gravity if the moveable member is moved upwardly during the expansion 
mode. Alternately it may be an elastomeric member (eg. if the side walls 
resiliently expand outwardly during the expansion mode or if an 
elastomeric member is compressed during the expansion mode) or it may be a 
spring which is compressed during the expansion mode. 
In a preferred embodiment, the concentrator comprises an oxygen 
concentrator to produce a concentrated stream of oxygen enriched gas. In a 
more preferred embodiment, the gas comprises air, the first gas is oxygen 
and the at least one second gas comprises nitrogen such that the 
concentrator produces an oxygen enriched stream of air. 
In one embodiment, the flow of the enriched stream of the first gas through 
the outlet port is less than the flow of gas through the inlet port. The 
outlet port may be open at all times when the concentrator is in use. 
The member preferably comprises an adsorbent such as a zeolite molecular 
sieve. If a stream of oxygen enriched air is to be obtained from air, the 
member may comprise a nitrogen adsorbent. 
In accordance with another embodiment of the instant invention, there is 
provided a method for producing an enriched gas having an increased 
concentration of a first gas from a gas containing the first gas and at 
least one second gas comprising the steps of: 
(a) the step of introducing the gas into a vessel containing a member for 
adsorbing the at least one second gas; 
(b) the step of pressurizing the vessel for a time sufficient for the 
member to adsorb at least a portion of the second gas to produce the 
enriched gas; 
(c) the step of alternately passing the enriched gas to an expandable 
container having an outlet port to expand the container and isolating the 
expandable container from the vessel; and, 
(d) the step of purging the vessel when the expandable container is 
isolated from the vessel. 
In accordance with another embodiment of the instant invention, there is 
provided a method for producing an enriched gas having an increased 
concentration of a first gas from a gas containing the first gas and at 
least one second gas comprising: 
(a) introducing the gas into a vessel containing an adsorbent for adsorbing 
the at least one second gas; 
(b) pressurizing the vessel for a time sufficient for the adsorbent to 
adsorb at least a portion of the second gas to produce the enriched gas; 
(c) opening a flow valve to connect the vessel in flow communication with 
an expandable container; 
(d) allowing the expandable container to expand to store at least a portion 
of the enriched gas; 
(e) opening a purge valve to purge the vessel and closing the flow valve 
after the expandable container has expanded by a preset amount; 
(f) purging at least a portion of the second gas from the vessel; and, 
(g) contracting the expandable container to release at least a portion of 
the enriched gas stored in the expandable vessel. 
In one embodiment, the method further comprises the step of venting the 
enriched gas from the expandable container when the expandable container 
is isolated from the vessel. 
In one embodiment, the method further comprises the step of venting the 
enriched gas from the expandable container at all times during the 
operation of the method. 
In one embodiment, the method further comprises the step of automatically 
passing the enriched gas to the expandable container when the vessel 
reaches a preset pressure. 
In one embodiment, the method further comprises the step of automatically 
purging the vessel when the expandable container expands by a preset 
amount. 
In one embodiment, the method further comprises the step of automatically 
isolating the expandable container from the vessel upon the commencement 
of the step of purging the vessel. 
A further advantage of the instant invention is that the expansion of the 
storage container (i.e. the reservoir for storing the enriched gas) may be 
used to actuate the purging cycle when the storage container expands to a 
desired level. Accordingly, an electronic controller is not required to 
time the process. Further, no gas sensors are required to determine when 
to actuate a particular part of the cycle of the adsorption zone. 
A further advantage of the instant invention is that the expandable 
container may be drivingly linked to the purging valve. In this 
embodiment, simple actuation means may be used to move the purging valve 
to the open position so as to initiate the purging cycle. Accordingly, 
solenoids and other complicated switching apparatus are not required. 
Further, the expandable container may be operatively connected to the 
purge valve by mechanical linkages and, in addition, the purge valve may 
be a simple mechanical valve (e.g. a seat valve). Accordingly, no 
electrical power supply is required to initiate the purging cycle. 
It will be appreciated that, according to the instant invention, a 
concentrator, and in a preferred embodiment an oxygen concentrator, may be 
designed wherein a source of pressurized gas (eg. air) which is fed to the 
adsorption zone is the driving source of the entire apparatus. 
Accordingly, the resultant device, which uses only an external motive 
force, may be manufactured as a lightweight reliable unit. 
In accordance with the instant invention, the apparatus may be designed to 
trigger the end of the purging cycle and thereby commence the 
pressurization (adsorption) cycle as the expandable storage container 
contracts to a pre-determined position. This position may be 
pre-determined based upon the volume of the adsorption zone and the time 
required to complete the purging cycle as well as the flow rate of 
enriched gas from the reservoir. In this way, a continual flow of enriched 
gas may be produced by the apparatus. Further, the apparatus is energy 
efficient since the timing of the cycles is based upon the actual 
completion of a cycle (i.e. the contraction of the expandable reservoir) 
as opposed to an electronic timing means which would initiate a cycle 
regardless of the concentration of the enriched gas exiting the apparatus.

DESCRIPTION OF PREFERRED EMBODIMENT 
Concentrator 10 comprises inlet port 12, outlet port 14, adsorption zone 16 
and expandable container 18. Passageway 20 extends between adsorption zone 
16 and expandable container 18. Passageway 20 is provided with purge valve 
22 and valve 24. 
Adsorption zone 16 may be of any particular construction which is known in 
the art for pressure swing adsorption apparatus. In the preferred 
embodiment, the adsorption zone 16 comprises a vessel distinct from 
expandable container 18 that may be subjected to an increased pressure 
during which a selected fluid is adsorbed into adsorption media provided 
in adsorption zone 16 leaving a fluid having an increased concentration of 
the remaining (unadsorbed) fluids in adsorption zone 16. It will be 
appreciated that adsorption zone 16 may comprise a bed containing the 
adsorbent material through which the fluid flows as it passes through 
adsorption zone 16. 
The fluid may be a liquid or a gas. If the fluid is a liquid, then 
concentrator 10 may be used, for example, to selectively remove an 
impurity from a liquid stream (eg. the fluid selectively adsorbed into 
carbon) such as water or a pesticide. The concentrator may also be used 
for pressure swing fractional distillation. 
In a preferred embodiment, the fluid is a gas and, more preferably, the 
concentrator is an oxygen concentrator. The following description is based 
upon the use of concentrator 10 as an oxygen concentrator; however, the 
concentrator may be used for other pressure swing operations of fluids. 
If concentrator 10 is an oxygen concentrator, then the feed gas which is 
introduced into adsorption zone 16 via inlet port 12 comprises an oxygen 
containing gas and, more preferably, air. The adsorbent material in 
adsorption zone 16 accordingly comprises a material which selectively 
adsorbs nitrogen (the largest constituent of air) thereby leaving air 
containing an enriched level of oxygen in adsorption zone 16. Such 
adsorbent material are known in the art. Examples of such material are 
zeolites and, in a particularly preferred embodiment, the adsorbent is 
clinoptilolite. 
It will be appreciated that, in an alternate embodiment, the desired 
product may be the fluid adsorbed onto the adsorbent media. In such a 
case, the product exiting purge valve 22 could be fed to a container or 
other apparatus as may be desired. 
The remaining part of this description of the preferred embodiment is 
premised upon concentrator 10 including an adsorbent to remove nitrogen 
from air thereby producing a stream of oxygen enriched air. It is to be 
understood that the feed gas stream fed to adsorption stream 16 may 
comprise at least any two gases and the adsorbent material may be selected 
to adsorb the one or more of such gases leaving a gas stream having an 
enhanced concentration of the remainder of such gases. 
Adsorption zone 16 operates under pressure. Accordingly, means must be 
provided to raise adsorption zone 16 to the desired pressure. In the 
preferred embodiment, the air fed to inlet port 12 comprises a stream of 
pressurized air (eg at a pressure of 5 to 30 psig). It will be appreciated 
that, in an alternate embodiment, a compressor or other means may be 
provided as part of apparatus 10 to feed an air stream into adsorption 
zone 16 and to pressurize adsorption zone 16 to the required pressure. The 
exact pressure which is required for the adsorption media to adsorb the 
targeted gas, and the length of the adsorption cycle, will depend on the 
thermodynamics of the adsorption media. 
Valve 24 is provided in passageway 20 to alternately (i.e. cyclicly), 
connect adsorption zone 16 and expandable container 18 in flow 
communication and to then isolate adsorption zone 16 from expandable 
container 18. Valve 24 may be any member which is movable between a first 
position in which adsorption zone 16 is isolated from expandable container 
18 and an open position in which adsorption zone 16 and expandable 
container 18 are in flow communication. Further, valve 24 may be 
positioned at any point between the two vessels. For example, valve 24 
could be positioned as part of outlet port 26 of adsorption zone 16. 
Further, if adsorption zone 16 and expandable container 18 are a single 
unit separated by a wall (not shown), valve 24 may be positioned in the 
wall. 
While adsorption zone 16 is undergoing the adsorption portion of the cycle, 
adsorption zone 16 is sealed sufficiently such that adsorption zone 16 
will be raised to the required pressure. Preferably, no gas flow out of 
adsorption zone 16 is permitted during this part of the method. 
Accordingly purge valve 22 is preferably in the fully closed position 
shown in FIG. 1 and valve 24 is preferably in the fully closed position 
shown in FIG. 2. Adsorption zone 16 is thus isolated so as to allow 
pressure to build up therein. Due to the inflow of air through inlet port 
12, pressure will build up in adsorption zone 16 and nitrogen will be 
adsorbed in the adsorbent media. 
Based upon the volume of adsorption zone 16, the adsorption characteristics 
of the adsorbent in adsorption zone 16 and the rate of air input into 
adsorption zone 16, the length of time required to achieve the desired 
concentration of oxygen in the free gas in adsorption zone 16 may be 
calculated. Further, a person skilled in the art will be able to determine 
the pressure at which this desired oxygen concentration will be achieved. 
Any valve mechanism (either mechanically or electrically operated) may be 
used for valve 24. Preferably, valve 24 is a pressure actuated member 
which will open to bring adsorption zone 16 into flow communication with 
expandable container 18 when adsorption zone 16 reaches the pressure at 
which the required oxygen concentration will have been achieved (eg. a 
check valve). One advantage of this approach is that valve 24 may open, 
and the adsorption cycle therefore terminate, when a desired preset 
pressure is achieved. Thus no sensors are required to monitor the progress 
of the adsorption cycle. The adsorption cycle automatically terminates 
when the requisite pressure is reached. Preferably, valve 24 is a 
mechanical member which is biased (eg. by a spring) to the closed position 
and which will open when the pressure upstream thereof (i.e. in adsorption 
zone 16 and in passageway 20) reaches a preset pressure (which may be the 
pressure at which the desired concentration of oxygen is achieved in the 
free gas in adsorption zone 16). 
When valve 24 is in the open position shown in FIG. 1, oxygen enriched air 
will pass from adsorption zone 16 through passageway 20 and into 
expandable container 18. 
Outlet port 14 is in flow communication which expandable container 18. When 
valve 24 is in the open position shown in FIG. 1, outlet port 14 is also, 
indirectly, in flow communication with adsorption zone 16. When valve 24 
opens, expandable container 18 expands so as to receive at least a portion 
of the oxygen enriched air which exits adsorption chamber 16. Accordingly, 
outlet port 14 provides a flow of oxygen enriched air when valve 24 is 
open and the oxygen enriched air is passing into expandable container 18. 
Further, when valve 24 closes and adsorption zone 16 is isolated from 
expandable container 18, expandable container 18 preferably will have by 
then stored a sufficient supply of oxygen enriched air so that outlet port 
14 may still provide a flow of oxygen enriched air even while adsorption 
chamber 16 is undergoing a purge cycle. 
In a preferred embodiment, outlet port 14 has an aperture 28 which is open 
at all times when concentrator 10 is in operation. Aperture 28 is 
preferable of a pre-set opening size so as to provide a generally 
continuous flow of oxygen enriched air through outlet port 14. It will 
also be appreciated that, if desired, aperture 28 may have a variable 
opening size so as to vary the flow rate of oxygen enriched air through 
outlet port 14. This may be desirable if, for example the apparatus is 
used for medical purposes, eg. providing a source of oxygen enriched air 
to a patient. Further, aperture 28 may be operable so as to seal outlet 
port 14 (or alternately a valve to close outlet port 14 may be provided). 
This may be desirable if, for example there is backpressure from 
downstream equipment. 
Preferably, expandable container 18 and aperture 28 are sized so that 
outlet 14 provides a generally constant flow rate of oxygen enriched air 
during both the adsorption cycle and the purge cycle of adsorption zone 
16. To this end, outlet port 14 preferably has a reduced flow rate of gas 
therethrough than the flow rate of air into adsorption zone 16 via inlet 
port 12. Preferably, the flow rate of gas through outlet port 14 is about 
half that of the flow rate into inlet port 12. For example, if inlet 12 
has a flow rate of 6-8 liters per minute of air, then outlet port 14 
preferably has a flow rate therethrough of 2-4 liters per minute of oxygen 
enriched air. This flow rate may be achieved by, for example, selecting 
the cross sectional area of outlet port 14 or including a flow 
restriction, such as aperture 28, in outlet port 14, to achieve this 
result. It will be appreciated that two or more adsorption zones 16 may be 
connected to one or more expandable containers 16. A regulator could also 
be used to control the output rate from port 14. 
Expandable container 18 may be any storage container for storing a gas 
which has an expandable reservoir 30 for storing at least a portion of the 
oxygen enriched gas produced in adsorption zone 16. In one preferred 
embodiment, expandable container 18 may be a storage vessel having 
expandable walls. In this embodiment, container 18 may have at least one 
wall which will expand when container 18 is subjected to an increased 
pressure. For example, one or more of the walls of container 18 may be 
composed of an elastomeric material. Alternately, in another preferred 
embodiment, container 18 may have a flexible side wall which is movable 
between a first, compacted position and a second expanded position when 
reservoir 30 is filled with oxygen enriched air. For example, expandable 
container 18 may be in the shape of a bellows. 
Alternately, or in addition, container 18 may comprise a vessel having a 
movable member mounted therein and movable between a first position and a 
second position. The size of reservoir 30 increases as the movable member 
moves from the first position to the second position. An example of such a 
construction is shown in FIGS. 1 and 2. In these Figures, the movable 
member comprises piston 32. 
In the embodiment of FIGS. 1 and 2, expandable container 18 is a 
longitudinally extending member and, is preferably vertically oriented. 
Piston 32 may be movably mounted in container 18 by any means known in the 
art. Further, piston 32, and the means for movably mounting piston 32 in 
container 18, preferably isolate reservoir 30 from upper portion 34 of 
container 18. In this way, the oxygen enriched gas which enters container 
18 will remain in reservoir 30 instead of passing upwardly by piston 32 to 
upper portion 34. Piston 32 preferably moves upwardly into upper portion 
34 of container 18 due solely to a pressure of the oxygen enriched stream 
passing through valve 24. Piston 32 may be so mounted by a plurality of 
O-rings 36 which are positioned between piston 32 and side wall 38 of 
container 18. The O-rings, in conjunction with piston 32 seal reservoir 30 
from upper portion 34. However, it will be appreciated that other means, 
such as a bellows, bearings or a cam may be used to movably mount piston 
32. 
When the adsorption cycle of adsorption zone 16 is completed, valve 24 will 
open allowing a stream of oxygen enriched air to pass into container 18. 
At this time, piston 32 may be in approximately the position shown in FIG. 
1 (i.e. in a contracted position towards the bottom of container 18). 
Oxygen enriched air will enter container 18 and pass through aperture 28 
through outlet port 14. However, as the flow of oxygen enriched air 
through aperture 28 is restricted, pressure will build up in container 18 
which will force piston 32 into upper portion 34. As additional oxygen 
enriched air enters container 18, the pressure will be maintained in 
container 18 and piston 32 will continue to move into upper portion 34, 
for example until the position shown in FIG. 2 is reached. 
As oxygen enriched air exits adsorption zone 16, the pressure in adsorption 
zone 16 will decrease. For example, the pressure in adsorption zone 16 may 
reach 20 to 30 psig at the end of an adsorption cycle. As the pressure is 
reduced, for example to about 5 psig, nitrogen will commence being 
released by the zeolite thus decreasing the concentration of oxygen in the 
air exiting adsorption zone 16. At this time, it is desirable to purge the 
zeolite in adsorption zone 16. Advantageously, in one embodiment of the 
instant invention, the purge cycle may be commenced automatically. 
In particular, apparatus 10 may include an actuator which drivingly 
connects the expandable container (e.g. piston 32) to purge valve 22 
whereby movement of piston 32 from a first contracted position (as shown 
in FIG. 1) to a second expanded position (as shown in FIG. 2) actuates the 
purge valve to move it to the open position. As the flow rate of oxygen 
enriched air through aperture 28 may be predetermined and as the volume of 
container 18 is predetermined, a person skilled in the art may determine 
the distance through which piston 32 will travel as the oxygen enriched 
air exits adsorption chamber 16. By designing container 18 so as to permit 
piston 32 to move this distance, piston 32 may be in the upper position 
shown in FIG. 2 when the oxygen enriched air has been vented from 
adsorption zone 16 and the pressure in adsorption zone 16 has been reduced 
to a point wherein it is desirable to purge adsorption zone 16. 
Preferably, piston 32 is drivingly connected to purge valve 22 so as to 
actuate purge valve 22 when piston 32 is in the upper position shown in 
FIG. 2. At that time, purge valve 22 will be in the open position allowing 
air to exit therethrough (as shown in FIG. 2). When purge valve 22 opens, 
the pressure in passage way 20 will drop to a sufficient degree such that 
valve 24 (which is preferably pressure operated) will close thus isolating 
reservoir 30 from adsorption zone 16. In this position, the pressurized 
air entering inlet port 12 may pass through the adsorbent material in 
adsorption zone 16, exit adsorption zone 16 via outlet port 26 and exit 
passageway 28 via the purge valve thereby removing the nitrogen which was 
releasable adsorbed by the adsorption media from apparatus 10. 
The driving connection between piston 32 and purge valve 22 may be either 
mechanical or electrical but is preferably mechanical. As shown in FIGS. 1 
and 2, extension member 40 extends upwardly from upper surface 42 of 
piston 32. Movable arm 44 is fixedly mounted to extension member 40. 
Accordingly, movable arm 44 moves longitudinal with respect to container 
18 as piston 32 moves longitudinally within container 18. When piston 32 
is in the contracted position shown in FIG. 1, moveable arm 44 is 
positioned adjacent surface 46 of container 18 and, when piston 32 is in 
the expanded position, as shown FIG. 2, moveable arm 44 is spaced a 
distance from surface 46 of container 18. 
Movable arm 44 may be mechanically linked to purge valve 22 such as by 
connector member 48. Connector member 48 comprises a mechanical linkage 
which extends from movable arm 44 to purge valve 22. If container 18 
extends vertically, then connector member 48 may have a first horizontal 
portion 50 and a second vertical portion 52 extending downwardly from the 
end of horizontal portion 50 distal to moveable arm 44. Connector member 
48 has a first end 54 which is operatively connected to purge valve 22 and 
a second end 56 which is positioned to engage and be actuated by movable 
arm 44. 
If container 18 is vertically disposed, then connector member 48 may be 
operatively engaged by movable arm 44 so as to move first end 54 upwardly 
as piston 32 moves upwardly and to move first end 54 downwardly as piston 
32 moves downwardly. This may be achieved by having at least a first arm 
58 provided on second end 56. As container 18 expands, piston 32 moves 
upwardly. At some point, movable arm 44 will engage first arm 58. Further 
movement of piston 32 will cause first arm 58 to move upwardly (due to its 
engagement with movable arm 44). As moveable arm 58 moves upwardly, purge 
valve 22 is moved to the open position. When purge valve 22 has been 
opened a sufficient amount of time, valve 24 will close and adsorption 
zone 16 will be purged. During this purging cycle, piston 32 will move 
downwardly into reservoir 30 thereby forcing oxygen enriched air through 
aperture 28. The movement of piston 32 may be due to the pressure of 
gravity (if container 18 is vertically disposed). In addition, or 
alternately, a biasing member, such as spring 62 may urge piston 32 
downwardly to the contracted position. 
As air exits aperture 28, piston 32 will move downwardly and, accordingly, 
arm 44 will move downwardly. If purge valve 22 is a vertically operable 
valve, then purge valve 22 may cause first arm 58 to move downwardly in 
conjunction with movable arm 44 (such as by the force of gravity and/or a 
biasing means urging purge valve 22 to the closed position) thus closing 
purge valve 22. Alternately, or in addition, second end 56 may have a 
second arm 60. In this embodiment, vertical portion 52 is a generally 
non-compressible member (eg. a rod) and as piston 32 moves downwardly, 
movable arm 44 will engage second arm 60 thereby driving first end 54 
downwardly so as to close purge valve 22. 
Preferably, connector member 48 moves essentially only due to movable arm 
44 pushing up longitudinally outwardly on first arm 58 and longitudinally 
inwardly on second arm 60. Further, arms 58 and 60 are preferably spaced 
apart. In this way, piston 32 will move upwardly a defined amount before 
causing purge valve 22 to open thus allowing reservoir 30 to be filled a 
preset amount before the purge cycle commences. Further, piston 32 may 
move downwardly by a preset amount until it engages second arm 60 thereby 
closing purge valve 22 and completing the purging cycle. The distance 
between the arms is preferably sufficient to allow the purging cycle to be 
conducted while piston 32 is still pumping air from reservoir 30 through 
aperture 28. In a particularly preferred embodiment, by the time piston 32 
is in the contracted position shown in FIG. 1, purge valve 22 has been 
closed for a sufficient amount of time to allow adsorption zone 16 to have 
reached the requisite pressure to have produced an oxygen enriched stream 
and to cause valve 24 to open. Thus, a continuous supply of oxygen 
enriched air through aperture 28 may be obtained. 
In this embodiment, it may be seen that the actuator for purge valve 22 is 
a mechanical linkage comprising member 40, movable arm 44 and connector 
48. Purge valve 22 is accordingly actuated by vertical movement of piston 
32. Purge valve 22 is preferably a mechanical valve that is moved to the 
open position by vertical motion of connector 48. An example of such a 
valve is a seat valve which is lifted upwardly by upward motion of first 
end 54. However, other valves, such as a gate valve or a ball valve which 
may be opened to an open position by vertical motion of first end 54 may 
be utilized. 
In an alternate embodiment, arms 40, 58 and 60 may define electrical 
connections and contact between arms 44 and 58 may actuate a circuit to 
open purge valve 22 and connection between arm 44 and arm 60 may 
consequentially close the circuit to close purge valve 22. For example, 
vertical portion 52 may be composed of a bimetal member or a muscle wire 
which contracts when heated. When movable arm 44 contacts first arm 58, an 
electrical connection may be made causing an electrical current to flow 
through vertical portion 52 thereby heating the vertical portion and 
causing it to contract. This contraction will cause purge valve 22 to 
open. When the electrical connection is broken (i.e. arm 44 is no longer 
in contact with first arm 58 or alternately the circuit is broken when 
movable arm 44 contacts second arm 60) the current flow through vertical 
potion 52 will be terminated thus allowing vertical portion 52 to cool and 
expand thereby sealing purge valve 22. 
An alternate embodiment of purge valve 22 is shown in FIG. 3. In this 
embodiment, the purge valve comprises a bi-metal strip 64 having an outer 
metal member 66 affixed to an inner metal member 68. The two metals have 
different thermal coefficients of expansion. Accordingly, when contact is 
made between arms 44 and 58, an electrical connection may be made causing 
an electric current to pass, eg. via an electrically conductive member 48, 
to and through bi-metal strip 64 thereby heating the strip. If the inner 
metal member 68 has a greater thermal expansion than the outer metal 
member 66, the heating of bi-metal strip 64 will cause the bi-metal strip 
64 to bend inwardly in the direction of arrow A thereby uncovering opening 
70 so that the purge cycle may begin. When movable arm 44 engages arm 60, 
or brakes contact with first arm 58, the circuit may be closed causing the 
electric heating current to terminate and allowing bi-metal strip 64 to 
cool. When bi-metal strip 64 cools, inner metal member 68 will contract 
more than the outer metal member 66 thereby causing the bi-metal strip to 
curve downwardly and close opening 70. In an alternate embodiment, it will 
be appreciated that bi-metal strips 64 may be positioned on the outside 
passageway 20. 
In a further alternate embodiment, valve 22 may be actuated by a solenoid. 
Once again, contact between movable arm 44 and first arm 58 may complete 
an electric circuit so as to actuate a solenoid to open any desired valve 
which may function as a purge valve. When movable arm 44 engages arm 60, 
or brakes contact with first arm 58, the circuit may be closed causing the 
solenoid to move to its starting position thereby closing the purge valve. 
By constructing a concentrator according to the instant invention, a 
concentrator may be constructed whereby the pressurized air fed to 
adsorption zone 16 may be the only motive force to open purge valve 22 and 
valve 24. Further, it provides the requisite motive force to cause 
container 18 to expand. Thus, by using simple mechanical linkages and 
movable or expandable elements, a gas concentrator having a simple, rugged 
construction may be developed. 
In addition, aperture 28 may be in an open position at all times so as to 
provide a continual supply of enriched gas to outlet 14 even when 
adsorption chamber 16 is being purged. This is due to reservoir 30 
contracting during the purge cycle thereby driving the enriched stored gas 
from reservoir 30 to aperture 28. 
Another advantage of the instant invention is that the expansion of 
container 18 may be used to time the purging cycle of adsorption zone 16. 
Accordingly, electronic timers or concentration sensors are not required 
to provide input to a controller to determine when the purge cycle should 
be commenced or terminated.