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Technical Tip – Purge Gas 101

Technical Tip – Purge Gas 101

We hope this article helps you better understand the purge requirements of your laser system. With proper purge gas setup and consideration, your lasers performance and lifetime will be improved.

KT laser


Kern’s 250 watt and greater laser systems require a purge gas connection. This includes Kern’s CO2 and fiber laser systems.


The purge gas serves two ultimate purposes. First, is prevents component damage by creating a positive pressure inside the laser tube housing. This reduces the chance for dust, smoke and other contaminants to enter the laser housing. Secondly, the laser purge gas will reduce high humidity inside the laser housing. When solely considering CO2 lasers reducing the humidity will also reduce water vapors that can distort the laser beam by optical absorption. Ultimately, a clean and dry environment is optimal for peak laser performance.


Kern’s lasers can use one of two purge gases, compressed air or nitrogen. The purity of the purge gas is a very important factor and will extend the life and reduce maintenance costs. In general, purge gas needs to be clean and dry. The purge gas should be filtered to remove particles that are larger than 1 micron. The gas should be dried so that the dew point is 18 degrees Fahrenheit lower than the chiller’s inlet cooling fluid temperature. The purge gas should also be oil free to better than 99.995%.


If a nitrogen purge is being used a simple 1 micron filter in-line with the laser system will suffice. When considering compressed air (notorious for moisture and oil), there needs to be a “line-of-defense” and “last-line-of-defense” in place. A good quality compressor with an after-cooler and separating condenser make up a good “line-of-defense”. The images below show a standard purge gas configuration.

purge diagram

Closer to the actual laser source a “last-line-of-defense” filter system will be required. For compressed air users, Kern recommends utilizing our purge filter setup shown below and available on

purge image

For nitrogen users, Kern recommends our nitrogen filter setup. Please follow this link to


Kern’s laser systems feature a simple ¼” push connect fitting at the back of the laser system for the connection of the purge line. There is also a purge flow gauge at the rear of the machine to set the proper flow rate.

back of machine


Once the proper purge system is in place, it is just as important to perform ongoing maintenance. This includes replacing filters and draining water traps as required. Kern suggests checking your filter weekly, keeping spares in stock and replacing dirty filters immediately.

If your purge system becomes contaminated with excessive moisture or oil, all filters, tubing, and fittings should be replaced with new parts. This will ensure that all contamination is removed from the system that could potentially harm the laser source.


In short, if you have a laser from Kern that is greater than 250 watts, you will require a purge gas. Compressed air or nitrogen are acceptable purge gases. Ensure the correct purge configuration and “last- line-of-defense” filter system are in place. Do not ignore maintenance!