Often nicknamed manufacturing’s fourth utility alongside electricity, gas and water, compressed air is used in over 90% of the world’s manufacturing facilities. As with the other utilities, it is a critical cog in production processes. Its proper application and maintenance have a profound impact on the productivity, financial results and successful operation of businesses.
Facilities and maintenance personnel strive to assure that their compressed air systems operate in a safe, efficient and cost-effective manner. To do this, purification systems are installed to ensure a continuous supply of high quality compressed air, and filtration is at the core of any purification system. Filtration technologies for compressed air treatment use replaceable filter elements that must be changed periodically. However, there is often confusion over why and when the filter element needs to be replaced.
Here, we will examine the types and sources of contamination, filtration technologies and their function, frequently asked questions, myths surrounding differential pressure monitoring, and recommendations for changing filter elements.
For complete information on the benefits of regularly changing filter elements, answers to more questions about compressed air filtration and maintenance, and the use of differential pressure indicators download the full white paper "Why should I change my compressed air filter element?".
Compressed air contamination comes from a variety of sources:
- Atmospheric contamination entering the compressor.
- Contamination introduced by the compressor.
- Contamination introduced by the air receiver and distribution piping.
There are 10 contaminants that require treatment in a typical compressed air system:
- Water vapor
- Atmospheric dirt
- Oil vapor
- Water aerosols
- Condensed liquid water
- Liquid oil
- Oil aerosols
Coalescing filters are one of the most important types of purification equipment as they treat the majority of these contamination types whilst water separators, dry particulate filters and adsorption filters address the others. The table below shows how each technology is used to ensure clean compressed air.
Filter elements do not last forever
All of these filter technologies (with the exception of water separators) use a replaceable filter media, typically in a cartridge, or element form. These elements are subject to extreme, dynamic conditions in the compressed air stream, including:
- Wide pressure variations.
- Pulsing air demand.
- Temperature variations.
- Humidity ranges from 100% saturated air to sub-zero dewpoints.
- Chemical attack.
Over time, these conditions lead to the degradation of the filter media and subsequent loss of its contamination removal integrity. Hence, the filter elements should be replaced periodically to assure optimum contamination removal performance.
Parker recommends an annual (12 month) replacement of its coalescing and dry particulate filters and float drains to ensure proper contaminant removal. Parker’s domnick hunter OIL-X coalescing filters and dry particulate filters come with an Air Quality Guarantee that is based upon annual filter change-outs using genuine parts.
While Parker makes a clear statement on maintenance requirements, their remains a great deal of uncertainty on when and why compressed air filter elements should be changed. This is understandable, as every compressed air system is different. However, conditions, even within the same system, can change rapidly, so it is best to adopt a preventative position when it comes to maintenance.
Frequently asked questions
Why should I change my compressed air element?
As discussed above, the effects of the arduous conditions in which coalescing and dry particulate filter elements operate will eventually degrade their performance.
What happens if a filter element gets damaged?
In time, the contaminants will weaken the media and cause leaks or holes to form. Once this happens, their leak area will rapidly grow and contamination will bypass the filter element.
What if my facility only operates part-time. Will I get a much longer life out of the filter elements?
As noted, the filter elements will be affected by the contaminants in the compressed air stream, and this constant exposure will weaken them. To preempt carryover, an annual filter change-out is considered a best practice. Parker guarantees the performance of filters that have annual filter change-outs.
Can I wash filter elements?
No, it is not possible to wash contamination out of the filter media. Subjecting the filter media to hot soapy water or solvent will result in damage.
My filter element doesn't look dirty. Do I need to change it?
First, the part of the filter element you can see is the drainage layer which is responsible for preventing coalesced liquids from being carried downstream. The main filtration media is below this layer and is not visible without dismantling the filter element. Second, coalescing and dry particulate filters capture aerosols and particles down to sub-micron size - undetectable to the human eye.
Myths surrounding differential pressure monitoring
Many filter housings are supplied with differential pressure monitors. It is a common mistake to base filter change-outs on these devices. DP Monitors are non-calibrated and typically indicate a pressure change from the upstream side to the downstream side with a substantial margin of error. While they might give an indication of maintenance required due to a blockage on the filter media, they will not give an accurate depiction of the filter’s ability to remove contamination. Thus, they are not to be relied upon to determine filter element maintenance.
Differential pressure is an indication of air quality.
Differential pressure is the result of the filter element collecting contamination, but there is no correlation to the delivered air quality.
The filter is fitted with a DP Gauge to indicate when to change the filter element.
These devices offer a general idea of pressure reduction. They are not calibrated and have an accuracy margin of +/- 25%. They should not be relied upon as a service indicator. The manufacturer’s recommendation should be followed instead.
Compressed Air filter elements should only be changed when differential pressure rises.
While keeping differential pressure low is a good practice, it does not have a comprehensive impact on contamination carryover. Hence, it should not be used as an indicator of when the element should be changed.
Filter elements must be replaced periodically to ensure a continuous supply of high quality compressed air is always available. Other benefits include:
- Protection of adsorption dryer beds.
- Protection of downstream equipment, personnel and processes.
- Reduced operational costs.
- Increased productivity and profitability.
- Continued peace of mind.
Download the full white paper "Why should I change my compressed air filter element?" for complete information on the benefits of regularly changing filter elements, answers to more questions about compressed air filtration and maintenance, and the use of differential pressure indicators.
This article was contributed by Mark White, compressed air treatment applications manager, Parker Gas Separation and Filtration Division EMEA