Pressure drops from filters are a normal occurrence. Even when installing a new filter, some pressure will be lost as compressed air passes through it. This should be considered at the time of purchase and factored in to compressor system performance. However, increasing pressure drops over a filter’s lifetime can rack up higher power bills. Knowing how to select system filters and when to replace them can help you save money in the long run.
Operators often make filter selections based solely on the type or structure of their compressor system. This is a mistake. Contaminants in a compressed air system come from a variety of sources, including piping corrosion, bacteria and mold growth, ambient air and compressor lubricants. Including these factors in filter selection will lead to cleaner air. Knowing the required purity of air at the point of use should also be considered when selecting a filter. This will depend on the application, as air used in pneumatic conveyance of machinery may not require the same level of purity as air used in food or pharmaceutical production environments.
Types of Filters
Coalescing filters remove water and aerosols from air. They can also remove particulates. High efficiency may require a general purpose filter further upstream. While they remove most contaminants, these filters can produce large pressure drops.
Vapor removal filters operate on the principal of adsorption. They typically remove lubricant aerosols using activated carbon granules, carbon cloth or paper. Vapor removal filters work well after coalescing filters, as they can catch and remove gaseous lubricants that will go through the coalescing filter.
Dry particulate filters are usually employed to remove desiccant particles after an adsorption dryer. They can also be implemented at point of use. Dry particulate filters operate in a manner identical to a coalescing filter.
Pressure drops can indicate a filter needs to be replaced. However, filters should not be replaced based on pressure issues alone. When considering changing a filter, answer these four questions:
Is the manufacturer’s service life expired?
Has an air audit revealed that air quality is below acceptable limits?
Are pressure drops exceeding acceptable levels?
Are pressure drops exceeding the manufacturer’s change point?
Answering yes to any of these questions indicates it’s time for a new filter. You many also consider replacing filter elements before the recommended pressure drops or air quality issues occur, as the increased energy cost from reduced air pressure could be more than that of a new filter.
Understanding what kind of filter your system needs is the first step to ensuring your air is pure and at the proper pressure. Regularly monitoring and replacing filter elements can reduce pressure drops and contaminants in your system, keeping energy costs low and air purity high.