BEFORE YOU GET STARTED - SKILLS AND TOOLS

While repairing O2 concentrators is not a highly complex activity, it does need some minimum level of understanding, skill and tools.

SKILLS

• Patience and aptitude
• Basic “handy-man” skills - ability to use mechanical, electrical and electronics hand tools
• Meticulous note keeping - keeping paper notes or photos/videos of the disassembly so it helps you while doing the reassembly.

TOOLS & SUPPLIES

• Set of Allen Keys for hex socket head fasteners
• Set of screwdrivers for slotted and phillips head fasteners
• Set of spanners
• Some pliers of various types - flat, nose etc.
• Teflon Tape, Electrical insulation tape
• Plastic container or magnet base metal bowl for holding all removed fasteners
• Multimeter

COMPRESSOR

• The compressor is a critical part of the concentrator. 
• It MUST be of “oil free” design - meaning there is no need to lubricate the pistons with oil. This ensures hydrocarbon emissions from the compressor do not mix with the oxygen output from the concentrator. Also, from flammability and fire safety issues, it is best to avoid having any oil, oil residues or hydrocarbon products present within the concentrator.
• Oxygen comprises about 21% of ambient air. To get a specific amount of flow rate (litres per minute aka LPM), the compressor must be capable of pumping 5 times the desired output LPM. So, if the machine is designed for 10 LPM, the compressor must be able to produce a flow rate of at least 50 LPM. Considering additional in-efficiencies of the process/system, it is recommended to double that figure. So, the compressor must be rated for 10 times the desired output oxygen LPM.
• Pay attention to Compressor datasheets where you can get the output pressure v/s flow rate graph. As working pressure increases, the compressor flow rate decreases. Compressor rating must be selected based on this “de-rating“ curve to get the desired output LPM.
• To reduce noise and vibration, most compressors are mounted on flexible spring mounts. While this is useful during normal operation, it can cause severe problems during transit/transportation if not taken care of. Shocks and impacts during transport can cause compressors to get jammed, or worse, broken. So, it is important to have a system of “lock bolts” to securely hold the compressor during transit, which are then removed prior to installation.
• Keeping the compressor cool by using forced air cooling is also important, especially in hot, tropical regions. Many low end machines do not have adequate cooling, which causes the compressors to seize or burnout due to over temperature. Compressors with builtin thermal cutouts can mitigate such problems. 

COOLING/DEHUMIDIFYING THE COMPRESSED AIR

• Since ambient air contains a lot of moisture, especially in tropical regions, it needs to be removed before it reaches the molecular sieves. This is necessary since the zeolite has an equal, or sometimes even greater, affinity for capturing moisture compared to nitrogen. Also, compressed air becomes quite hot, and must be cooled in order to condense the moisture from vapor to water for later extraction. The cooling coil system in the PSA process helps cool down the hot air, making it easier for the next water separation stage to work.
• Moisture removal after the cooling coils is done using Moisture separators. The separator is attached to an automatic drain system that allows it to periodically empty out the collected water and discharge it from the machine. Many commercially available machines use a minimal cooling coil, and do not have a moisture separation stage. This often results in the zeolite getting saturated with water vapor, and the machine can no longer trap nitrogen in the molecular sieves.

ZEOLITE MOLECULAR SIEVE

• PSA Oxygen concentrators rely on Zeolites to perform their work. Commonly used Zeolites are either Sodium 13X or Lithium X. Sodium 13X is cheaper, but not very efficient. Lithium X is much more expensive, but is also three times more efficient compared to Sodium 13X. Many cheap low end machines, which produce >90% O2 only at 1-2 LPM, and <80% O2 at 4-5 LPM, may likely have Sodium 13X molecular sieves. Replacing with LithiumX may improve performance, but it may also require some tweaking of the PSA timing cycles or adjusting parts such as the orifices.

ELECTRONICS

• Usually, this is the most tricky problem to solve, since each machine will have its own custom controller board whose documentation is not publicly available.
• Look for blown fuses, disconnected wiring, tripped thermal cutouts or thermal fuses and other obvious signs of failures.
• It may be possible for a skilled technician to identify electronics/electrical faults. And if spare parts can be obtained, then such faults can be easily fixed.
• Other failures, such as a microcontroller or custom part fault can only be solved by replacing the PCB completely

Example of a job card -