Note: Descriptions are shown in the official language in which they were submitted.
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A Pneumatic Controlled Pressure
Swing Adsorption Oxygen Concentrator
Background of the Invention
The present invention relates to a medical oxygen
producing equipment, and more particularly to an automatically
controlled oxygen concentrator by pressure swing adsorption
method.
A small medical oxygen concentrator by pressure
swing adsorption is very popular, which has entered into many
families of European and American countries for their medical
care. For example, each of the 5-6 largest manufacturers in
the United States, manufactures 10,000-30,000 small-sized
oxygen concentrators annually.
A small oxygen concentrator with pressure swing
adsorption is generally equipped with two tanks filled therein
with molecular sieves. The molecular sieves have uniform
pores with molecular dimensions. These pores can selectively
adsorb nitrogen molecules, but do not adsorb oxygen molecules.
Therefore nitrogen and oxygen can be separated from air by the
adsorption process, and yield oxygen gas with high purity.
A typical pressure swing adsorption process for
producing oxygen is as follows: Firstly the indoor air is
compressed by a medical oilless air compressor to a pressure
of 0.15-0.30 MPa. By a pneumatic circuit consisting of
pneumatic components, the compressed air is led to the first
molecular sieve tank and contacted with the molecular sieves,
and the nitrogen molecules in the compressed air are adsorbed
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in the molecular sieves, the remaining oxygen molecules are
discharged from the other end of the tank. The first
molecular sieve tank is in an "adsorption process". A part of
the discharged pure oxygen enters into an oxygen storage tank,
after pressure regulated, filtered and supplied to patients
for breathing. Another part of oxygen enters into the second
molecular sieve tank. The second molecular sieve tank is
controlled by a pneumatic circuit, now it is connected to the
atmosphere with no pressure inside. The nitrogen molecules
adsorbed in the previous cycle in the molecular sieve of the
tank is promptly in a free state. The input pure oxygen
"purges" and strips the nitrogen molecules adsorbed into the
air and results in the air having low concentration of oxygen,
which is discharged from another end of the second molecular
sieve tank into the atmosphere. At this stage, the second
molecular sieve tank is called a "desorption process".
After about 10-15 seconds, the first molecular sieve
tank is "saturated", while the second molecular sieve tank is
already "purged" and regenerated. Consequently the air flow
controlled automatically by pneumatic circuit is reversed, the
compressed air is switched into the second molecular sieve
tank, wherein the molecular sieves conduct adsorption
processes and produce oxygen. At the same time the first
molecular sieve tank is changed into air-discharging with no
pressure inside. A part of oxygen discharged from the second
molecular sieve tank enters into the first molecular sieve
tank to conduct the desorption process. An independent oxygen
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storage tank receives oxygen coming alternately and
uninterruptedly from two molecular sieve tanks, which can be
supplied to the oxygen breather. The two molecular sieve
tanks adsorb and desorb in endless cycles for separating
oxygen continuously from the atmosphere. They consume no
other substances but electric power.
There are two kinds of control methods for pneumatic
control circuit in the new commercial small oxygen
concentrator. One of them is a timing control circuit, i.e.,
controlling the direction of air flow by switching on and off
the valves according to the timing, which is divided into
controlling valves mechanically and by electronic components.
The second one is to control the direction of air
flow according to the pressure in the circuit by selecting an
optimum shifting pressure in the pneumatic circuit. When this
given shifting pressure is reached, the direction of the air
flow is changed. In the circuit an electronic pressure sensor
sends out signals in response to the given pressure, and the
signals are magnified via electronic components and then
electromagnetic valves are controlled to change the direction
of the air flow.
Since the output of the air compressor varies in
different circumstances, the mode with pressure controlling
can result in steady performance of the oxygen concentrator.
Factors, such as different elevations, thin air, voltage
change, compressor ware-and-tear, or greater resistance to
inlet air due to unclean air filters result in the output of
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air compressor reduced, and the control circuit may prolong
the working cycle automatically, maintain until the given
optimum shifting pressure is approached and then the direction
of air flow in the pneumatic circuit is changed. However the
first timing control circuit has no such advantage.
Therefore, the pressure control is a tendency of development
at present.
Many kinds of oxygen concentrators with high
pressure swing adsorption have been disclosed in references;
some patent and patent applications are listed below:
U.S. Patents: 5,183,483; 4,545,790; 3,659,399;
CN Patents and Patent Applications:
95244068.7; 95190507.4;
94115637.0; 91214831.4
872064250 and 872060760.
A part of the above references involves large-size
oxygen manufacturing devices with complicated structure, huge
volume and high cost, so they are not suitable for use in
small-size oxygen concentrators.
In the small-size oxygen concentrators disclosed in
the prior art, more valves are used in all pneumatic control
circuits, in which electronic components control the pilot-
valve and the pilot-valve controls the main valve. The
following shortcomings exist in these devices:
a) More pneumatic components, more pressure pipes and
joints which increase the possibility of leakage;
b) More electric controlling circuits and joints which
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lead to disturbances readily;
c) Complicated electronic and electric controlling
circuits, which are more difficult for maintenance and repair.
The above said drawbacks enhance the cost of
manufacturing and the difficulties for maintenance and repair.
In particular, the reliability of oxygen concentrators
decreases.
The commercial oxygen concentrators by three famous
companies in the United States are as follows:
Oxygen Concentrator Model 590 (Puritan Bennett Co., US);
Oxygen Concentrator Newlife (Air Sep Co., US); and
Oxygen Concentrator Alliance (Healthdyne Technologies
Co., US, U.S. Patent 5,183,483).
One of the famous brand names of oxygen
concentrators in the market gives high concentration of oxygen
with low noise and good appearance. Its pneumatic control
circuit contains a Sensym electronic pressure sensor which
measures the air pressure in the circuit. When a given
pressure is reached, the pressure sensor sends out signals,
which are magnified by an electronic integrated circuit board,
and result in controlling a pair of clippard electromagnetic
pilot-valves controlled in order. The electromagnetic pilot-
valve controls two air operated Hamphrey two-position three-
way valves, which permit the main air flow into and out of the
two molecular sieve tanks for producing oxygen. The following
illustration shows the change of working medium for automatic
control.
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circuit Electronic Electric Controlling System I~Pneumatic Control Valve
Components ~ I
The reliability of oxygen concentrator is affected
due to using many pneumatic components and complicated
pipelines and electric controlling circuits. For example,
before delivering the apparatus from Hong Kong, to Tianjin
Harbor, 200 of the apparatus were found out of order during
routine examination. Having been delivered to Beijing, a
further 5% of the apparatus needed repairs after being
checked. Due to long distance transportation in China and
serious conditions in the Qinghai-Xizang Plateau, etc., it is
even more tiresome for agents going back and forth to repair
them.
The Durable-Cassia Co., Ltd., from 1994 to 1997,
handled more than 50 % of oxygen concentrators imported to
China.
After selling and doing maintenance for several
years, people realized that a small-size oxygen concentrator
is necessary to be developed for China and other developing
countries. It shall have high reliability under various
unfavorable conditions. Its price should be reasonable and
acceptable by common families, and it must also be convenient
for maintenance.
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The object of the present invention is to overcome
the drawbacks in said references and commercial products, and
to provide a small-size oxygen concentrator, which is
controlled by a new pneumatic device, suitable for use in
various unfavorable conditions, simple and compact in
structure, few components and pipelines, high in reliability,
cheap in price, as well as convenient for maintenance.
SUMMARY OF THE INVENTION
The present invention provides an oxygen
concentrator with pressure swing adsorption, comprising a left
molecular sieve tank and a right molecular sieve tank with
molecular sieves filled inside, an oxygen storage tank
connected with the said two molecular sieve tanks, an air
compressor, and an automatic control device controlling the
direction of air flow and linking pipelines, wherein the said
automatic control device is a full-pneumatic pressure control
apparatus.
The said full-pneumatic pressure control apparatus
is a pneumatic combined valve.
The said pneumatic combined valve consists of two
pilot-pilot two-position five-way valves, a one-way cylinder
and a mechanical two-way valve, the said pneumatic components
connected by drilling holes on the valve body to eliminate
pipelines.
One of the said two-position five-way valves is a
control valve, used for controlling the air feed to and air
discharge from the molecular sieve tanks.
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Another of the said two-position five-way valves is
a distribution valve, which is connected with the control
valve, used for distributing the air flow paths on both sides
of the control valve.
The said mechanical two-way valve is connected with
the distribution valve, used for supplying air flow to the
distribution valve and the control valve during pressure
shifting.
The said one-way cylinder plays a role of
displacement or pressure sensor, and locates at the same
horizontal level as that of the mechanical two-way valve,
which sends out signals to the mechanical two-way valve.
The one-way cylinder contains a spring and a piston
inside, and the length of rod part of the piston is
adjustable.
The said three tanks are connected via pipes, in
which two air pipes connected with the said oxygen storage
tank are equipped with two one-way valves respectively, and
the said connecting pipe connected with the said two molecular
sieve tanks is equipped with a throttling orifice in the
middle.
The air flow required in the invention is supplied
by an air compressor.
By using the said technical solution of the present
invention, the full-pneumatic control device sends out signals
to various pneumatic components according to the pressure
variation of the pneumatic circuit itself, and then the
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automatic operation of the pneumatic device is controlled by
all pneumatic components. It may be shown as follows:
pneumatic device ~ pneumatic components
The operation and control of the full-pneumatic
device is from pneumatic to pneumatic. There is no
transformation of other media, and the goal of automatic
control is attained similarly. In this manner it prevents
addition of electronic and electric components as that in the
pneumatic control circuit of the prior art leading to increase
of transformation of medium among pneumatic, electronic and
electric components.
Therefore, the pneumatic control is greatly
simplified, the reliability increased, the manufacturing cost
lowered and the daily maintenance easier, and the object of
the invention is accomplished.
Meanwhile, in the present invention, the two two-
position five-way valves, the one-way cylinder and the two-way
valve comprise a very compact pneumatic combined valve,
resulting in the integrated, simple and compact internal
structure of oxygen concentrator, less components, less
pipelines and less electric wires. The detail advantages are
the following:
Reliability improved - The full-pneumatic control
has neither electronic nor electric components, the structure
is simple, shockproof, resistant to temperature, few pipes and
no electric wiring, and disturbance reduced. It has been
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proved that the reliability is good after long distance
transportation test for sample apparatus by bus from the coast
to Qinghai-Xizang Plateau.
Manufacturing cost reduced - Without electronic
components, only one combined valve is used, cost for parts
decreased, labor saved for assembly, allowing the price of
product to be reasonable and competitive, and readily entering
into families.
Maintenance easy - Internal structure may be
10 understood directly through viewing. Technicians can carry
out maintenance work after a short term of training.
The specifications of the small-sized oxygen
concentrator in accordance with the present invention are as
follows:
Oxygen flow 1-5 liters/minute, adjustable
Oxygen purity 1-3 liters/minute, 95~3%
4-5 liters/minute, 90~3%
Power Required <500 watts
The performance of the prototype is the same as
those products of said three U.S. companies.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 shows that the left molecular sieve tank is
in the adsorption process, the right molecular sieve tank is
in the desorption process, and the device is at low pressure
stage (0.05 MPa) ;
Fig. 2 shows that the device is at the intermediate
pressure stage (0.08 MPa-0.12 MPa);
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Fig. 3 shows that the device is at the moment when
air flow is shifting (0.15-0.18 MPa);
Fig. 4 shows the completion of air flow shifting,
the next cycle starts, the left molecular sieve tank is in the
desorption process, whereas the right molecular sieve tank
becomes in adsorption process, and the device returns to a low
pressure stage (0.05 MPa).
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will be described in more
detail below in combination with the drawings.
Fig. 1 is the beginning of a cycle. The compressed
air is carried out of an oilless air compressor 19, passed
through pipe 24, five-way valve 11 and pipe 3 to left
molecular sieve tank 1. Under the pressure, the molecular
sieve in the tank 1 adsorbs nitrogen molecules from the air,
the remaining oxygen is discharged out of the upper pipe 2 of
the molecular sieve tank 1. At this time the tank 1 is in the
adsorption process.
A part of oxygen gas discharged from pipe 2 is
passed through the check valve 4 to the oxygen storage tank 7
for use of oxygen breather. Another part of oxygen is passed
through the throttling orifice 5 and pipe 9 to the top of the
right molecular sieve tank 10, while the bottom of the right
molecular sieve tank 10 is vented to the atmosphere via pipe 8
and five-way valve 11, the tank has no pressure inside. The
nitrogen molecules adsorbed on the surface of the molecular
sieve of tank 10 in the previous cycle become in a free state
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under no pressure. Rinsed and stripped by input oxygen gas,
the nitrogen is mixed and returned to the air with low oxygen
content (oxygen content: 16-18%, close to the content in the
air exhaled by man), which is discharged via pipe 8 and five-
way valve 11 into the atmosphere. The molecular sieve tank 10
is in a desorption process.
Meanwhile, the compressed air is passed through pipe
25, exerts pressure on the left cavity of five-way valve 14,
and tends to push the valve spool to shift rightwards.
However, as it is at a low pressure stage, the air pressure is
0.05 MPa only, the thrust is not enough to overcome the
internal friction of valve 14, unable to push the valve core
to move rightwards.
Another compressed air is passed through pipe 23 to
the one-way cylinder 22, and starts to push the piston 20 to
shift rightwards gradually. The mechanical two-way valve 16
is in a closed position, whereas the compressed air in pipe 18
is cut off by valve 16.
Fig. 2 is a continuation of Fig. 1. Because the air
compressor l9 supplies compressed air continuously, and the
throttling orifice 5 restricts the passing of oxygen, the
pressure in the pneumatic device is increased gradually. The
thrust of compressed air acted upon the left cavity of valve
14 via pipe 25 is increased gradually as well. When the air
pressure is raised to 0.08-0.12 MPa, the thrust acted upon the
left cavity of valve 14 is enough to overcome the internal
friction of valve 14, and it pushes the valve spool to the
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right side immediately, thereupon the valve 14 is reversing.
Pipe 15 and pipe 13 are connected, while pipe 26 is directed
to the atmosphere.
Now the valve 14 has already connected with the
control air flow path, which pushes the spool of valve 11
leftwards. However, the mechanical two-way valve 16 is still
in a closed position, no pressure is in pipe 15 and pipe 13,
the right cavity of valve 11 obtains no pressure, and the
valve spool still maintains its original position. Valve 14
has only distributed in advance the air flow path of control
valve 11, the reversing of valve 11 does not occur yet. The
molecular sieve tank 1 is still in the adsorption process, and
the molecular sieve tank 10 remains in its desorption process.
The one-way cylinder 22 is exerted by the gradually
increased air pressure via pipe 23, the piston 20 compresses
gradually the spring 21 to shift rightwards. The rod part of
piston 20 is approaching little by little to the two-way valve
16, but does not touch it yet.
In Fig. 3 the pressure of the pneumatic device is
increased continuously, the compressed air via pipe 23 pushes
piston 21 to shift rightwards. When the pressure reaches
0.15-0.18 MPa, the rod end of piston 21 touches the two-way
valve 16 and pushes its valve spool, so the valve 16 opens
immediately. At this moment, the compressed air via pipe 18
is passed through the two-way valve 16, and again via the air
flow path where the control valve 11 is already distributed in
advance by valve 14 (Fig. 2), i.e. passing through pipe 15,
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valve 14 and pipe 13. The right cavity of valve 11 is exerted
by the air pressure via pipe 13, its valve spool is pushed at
once to the left, consequently the valve 11 shifts the
direction of main air flow.
As shown in the figure, the main air flow is passed
through pipe 24, valve 11 and pipe 8 into the right molecular
sieve tank 10 through the bottom. The molecular sieve in the
tank 10 has undertaken a thorough desorption process and
restored its capacity of adsorbing nitrogen molecules, and it
begins to adsorb nitrogen molecules under pressure. The
molecular sieve tank 10 is changed to conduct adsorption
process. After the nitrogen molecules are adsorbed, the
remaining oxygen is discharged out of pipe 9 from the upper of
the tank 10. A part of discharged oxygen is passed through
check valve 6 into oxygen storage tank 7, for use of oxygen
breather. Another part of oxygen is passed through the
throttling orifice 5 and pipe 2 into the top of the left
molecular sieve tank 1. Now the molecular sieve tank 1 is
connected to the atmosphere via pipe 3 and valve 11, with no
pressure inside. The molecular sieve is rinsed and stripped
by oxygen with no pressure, thus the nitrogen molecules
adsorbed on it surface are desorbed. The molecular sieve tank
1 is changed to conduct the desorption process. The oxygen
entered into the tank 1 is mixed with the nitrogen molecules
desorbed, resulting in low oxygen air. It is discharged from
the bottom of the tank 1 and vented to the atmosphere via pipe
3 and valve 11.
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The stable and precise optimum shifting pressure may
be obtained by adjusting the strength of the spring 21 and the
length of the rod of the piston.
In the Fig. 4, as shown above in Fig. 3, the
compressed air enters instantly into the right molecular sieve
tank 10. The tank 10 with no pressure originally, suddenly
intakes a great deal of compressed air, and the pressure of
the pneumatic device is dropped back immediately to a low
pressure of 0.05 MPa. As soon as the pressure of the device
10 falls, the spring 21 in the one-way cylinder 22 pushes the
piston 20 leftwards to its original position. The spring 17
of the mechanical two-way valve 16 also moves the valve spool
to the left side. Valve 16 is closed, while the air flow of
pipe 18 is cut off.
The operation in Fig. 4 is similar to that in Fig.
1, but the direction of main air flow is reversed. The
molecular sieve tank 10 is in the adsorption process, and the
molecular sieve tank 1 is in the desoption process. Hereafter
the pressure in the device increases gradually, when it
approaches the shifting pressure, the air flow is shifted
again. Thus oxygen is produced in endless cycles.
In combination with figures shown as above, a
detailed description is given to the structure and working
process of oxygen concentrator according to the present
invention, and the connection between various components as a
specific embodiment is also disclosed. The specific linkage
embodiments of any forms or any further variations or
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modifications, so long as the technical solution of the
present is concerned, fall within the scope of the present
invention.
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