What is Carbon Molecular Sieve (CMS)?
Carbon Molecular Sieve (CMS) is the filtration media inside a PSA (Pressure Swing Adsorption) nitrogen generator. It separates oxygen from compressed air, allowing the system to deliver high-purity nitrogen.
How much CMS is lost each year?
Under normal operating conditions, a PSA generator will lose about 2–5% of its CMS per year. This gradual loss happens naturally as the sieve undergoes repeated pressurization and regeneration cycles.
Most systems require a partial top-off of 10–15% every 3–5 years, depending on operating hours, air quality, and maintenance practices.
Why is it important to keep the sieve beds topped up?
Maintaining proper CMS levels ensures that the generator can achieve and sustain target purity. If CMS volume drops too low, the generator:
- Has to work harder to reach purity, leading to longer cycle times.
- Consumes more compressed air, reducing efficiency.
- May be unable to consistently reach its rated purity.
Keeping sieve beds topped up prevents excessive strain on the system, lowers energy costs, and extends the lifespan of other components.
What happens if large voids form in the sieve material?
When CMS levels drop too much, voids or empty spaces can form inside the sieve beds. These voids allow air to channel unevenly through the bed rather than being evenly distributed.
The result is:
- Purity instability: Nitrogen output may fluctuate or drop below specification.
- Higher oxygen slip: Oxygen “breaks through” early since parts of the bed are no longer effective.
- Premature media failure: Uneven airflow causes additional stress and accelerates CMS degradation.
What about CMS dusting?
As CMS ages and breaks down, fine carbon dust particles can be released into the system. This is known as “dusting.” If not managed, dusting can lead to:
- Valve failure: Dust buildup causes valves to stick or wear prematurely.
- Muffler clogging: Carbon fines collect in exhaust mufflers, reducing efficiency and increasing back pressure.
- Filter element damage: Downstream filters can become overloaded, requiring more frequent replacement.
Proper CMS maintenance not only protects gas purity but also safeguards critical system components from avoidable wear and tear.
How can I maximize CMS lifespan?
- Maintain clean, dry, oil-free compressed air with proper filtration and drying equipment.
- Follow preventive maintenance schedules for filters, drains, and dryers.
- Schedule periodic CMS top-offs (every 3–5 years, depending on usage).
- Monitor system performance (purity stability, cycle times, and efficiency) to catch early warning signs.
Bottom Line
A PSA nitrogen generator will always lose some CMS each year—it’s part of the normal operating cycle. But by keeping sieve beds topped up, preventing dusting, and maintaining your air system, you’ll protect your investment, ensure stable purity, and avoid costly downtime.