1. Oxygen
2. Function
3. Filters
4. Internal Alarm
5. Maintenance
6. Repair
7. Specifications
8. Sources and Additional Informations
An oxygen concentrator produces oxygen by filtering the oxygen out of the ambient air. This technology is cheaper, safer and easier to handle than tank systems with compressed oxygen.
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In Europe oxygen concentrators are used by patients at home for long term oxygen therapy. In developing countries concentrators are find in operation theatres and ICU when no central gas supply exist. |
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Usually the oxygen is supplied through a nasal cannula. The connecting tube can have several meters. The patient breathes normal air through the nose which is enriched with pure oxygen through the nasal cannula. |
Oxygen
The ambient air consist of 21% of oxygen (O2) and 78% of nitrogen (N2) but only the oxygen is vital for all living beings. Absorbed by the lungs, transported with the blood and pump by the heart all our body cells get the needed oxygen. The waste product of the cells is carbon dioxide which again is transported with the blood and pumped through the heart back to the lungs where it is exhaled.
The oxygen concentration can be measured with an oxygen meter.
Medical doctors measure the oxygen concentration of the blood with a pulse oximeter.
Function
The compressor pumps air into two sieve cylinders. The cylinders are filled with a material which absorbs the nitrogen of the air. Because this filtering only works under high pressure and the filters are saturated with nitrogen after some seconds the cylinder has to be flushed out with oxygen regularly. Therefore the pressure has to be released and a small amount of the produced oxygen is used to clean the filter. In order to provide a continuous oxygen flow to the patient a second cylinder and a oxygen reservoir is needed. The two cylinders work alternating in cycles and the reservoir tank stores the produced oxygen.
A complete cycle consists of:
1. Inlet valve of tank 1 opens. Outlet valve is closed.
2. Sieve tank 1 is filled with air. Pressure increases.
3. Filtered oxygen gets through a valve into the reservoir tank. Nitrogen is absorbed by the
filter.
4. Inlet valve closes. Outlet valve opens. Pressure decreases. Nitrogen passes out through a
muffler. A part of the created oxygen is used to flush the rest of the nitrogen out of the
tank. Meanwhile tank 2 is filled with air.
5. Circle starts again. Tank 2 delivers oxygen into the reservoir tank.
A typical cycle takes between 10 and 20 seconds and the pressure of the sieve tanks and the reservoir can reach 1.4 – 1.8 bar (20 – 26 PSI), depending on the manufacturer.
An oxygen concentration of 96 - 98% can be expected.
The reservoir tank is connected with a pressure regulator and a flow meter. Here the oxygen flow can be set between 1 and 5 liters per minute through the user. The value is shown by a little ball floating in a glass tube.
After the flow meter a humidifier follows. It is just a closed plastic bottle with distilled water. The oxygen passes through the water and gets humidified. This is important for the patient because the oxygen is very dry and irritate the rhinitis.
The inlet and outlet valves of the sieve tanks are controlled by the control unit. This electronic board creates the needed signals for the valves. The valves can be electrical solenoid valve (e.g. Weinmann) or air pressure valves (e.g. Healthdyne).
After switching on the concentrator needs a few minutes to provide oxygen. Some cycles have to be done before the reservoir tank is filled and oxygen under sufficient pressure and concentration is available.
Filters
Beside the two big molecular sieve filters there are some more small filters in the air way of the concentrator. At least one filter is find directly in the inlet. This is a foam filter which filters the dirt out of the ambient air. Sometime a second fine bacterial filter follows. Often another bacterial filter is in the outlet between the reservoir tank and the flow meter. This filter does not only protect the patient but also the concentrator by humidity from the outlet.
A third filter is used as a muffler at the nitrogen outlet. It just reduces the noise of the escaping nitrogen.
Internal alarm
Usually an internal oxygen measurement with an alarm function is connected to the outlet. In case the concentration drops under some 80% a buzzer will make an alarm.
In the first minute(s) when the concentrator do not deliver sufficient concentration the alarm function is deactivated.
A 9 V back up battery provides the power for the alarm unit during times of power blackouts.
Maintenance
The inlet filter always is a foam filter which should be cleaned regularly but at least once a month. The filter can be taken out easily by the user and can be washed with soap water. The filter has to be dry before replacing.
The patient filter is a single use bacterial filter. It has to be changed once a year or every 5.000 hours.
For a function check the best procedure is to switch on the concentrator while humidifier and tubes are still connected. Bubbles must be created immediately and the little ball of the flow meter must float. If not the humidifier or the tubes are blocked.
Humidifier and tubes always have to be clean and the distilled water has to be changed daily.
Then disconnect the humidifier and connect a oxygen meter. The measurement equipment itself has to be checked before connecting (21%). 2 – 5 minutes after switching on the concentrator must deliver full concentration. The concentration decreases after some year but should be more than 90%.
The alarm function and the battery also have to be checked. Therefore the concentrator simply has to be disconnected from mains and switched on. An alarm must be heard.
Every concentrator has a hour meter. The working hours should be written down in the service report.
After maintenance the concentrator should run for some hours to clean the system from humidity (see below).
Repair
In principle two problems can occur. First, there is no oxygen flow, second there is oxygen flow but the concentration is too low.
A flow is visible by the floating ball in the flow meter and the bubbles in the humidifier. very often the airway is blocked by dirt or water drops in the tube. If you are not sure disconnect the humidifier and check the pressure at the outlet with your finger. With open outlet the ball must float with closed outlet the ball must fall down.
If the the airway is free but the concentration is too low the concentrator itself has a problem. A concentration lower than 90% is poor, below 85% not acceptable.
Listen to the sound of the concentrator. The valves and the escaping nitrogen of the muffler can be heard.
A complete cycle takes 10 – 20 seconds, time enough to check the function of all valves.
Look at your oxygen meter. The concentration must increase after switching on continuously. If concentration increases and decrease alternately, only one sieve tank works. Listen to leakages. You can make leakages visible by applying soup water with a brush to the suspicious area. Bubble will create then.
In general concentrators must run once in a while for some hours. The sieve filters are sensitive against humidity. Once they get humid the filters are blocked and do not work anymore. They have to be replaced than which often is not economical. This is a big problem specially in coastal areas where the humidity of the air is very high.
It is a good practice to let the concentrator run for some hours after maintenance and repair.
Specifications
Time of one cycle: 10 - 20 seconds
Internal pressure: 1.4 – 1.8 bar (20 – 26 PSI)
Maximum concentration: 96 - 98%
Alarm: less than 80 – 85%, no main power supply
Flow: adjustable, 1 – 5 liter per minute
Lifetime: some 10.000 hours
Weight: 15 - 20kg
Price: 600 – 1.500 ?/font>
Sources and additional informations
https://en.wikipedia.org/wiki/Oxygen_concentrator
https://en.wikipedia.org/wiki/Oxygen
https://en.wikipedia.org/wiki/Nitrogen
https://en.wikipedia.org/wiki/Oxygen_saturation
https://en.wikipedia.org/wiki/Oxygen_sensor
