MRO Today - Inlet air filters

Inlet air filters

by Dan Wise

The inlet air filter is protection against the damages caused by airborne particles. However, the importance or priority of inlet filter maintenance is a site specific issue.

Consider the differences between these two industrial plants.

The first is a manufacturing plant in a suburban area where the prevailing winds blow over a large residential neighborhood before reaching the inlet filters on the roof of the plant. They use metal screens for their inlet filtration with annual maintenance for simple cleaning.

The second is a manufacturing plant located near a coal-fired power plant. The prevailing winds expose their inlet filters to fly ash. This requires a more sophisticated filtration and more maintenance attention.

It is generally understood that a dirty inlet air filter will cost you money by decreasing the efficiency of the compressor. The restriction of air flow will result in less CFM output of compressed air.

In addition, poor filtration of the inlet air will reduce the service life of the valves and piston rings in a reciprocating compressor. Contaminants in the air stream can do even more damage to rotary screw compressors because they operate with closer tolerances.

The inlet air filter can play an important role in maximizing CFM output and improving the service life of the compressor.

Here are some tips from compressor operators.

a) The best way to determine when to change your inlet filters is to measure the restriction in the piping between the filter and the intake of the compressor. This restriction is best monitored by a water manometer, an intake filter indicator or a dial gauge that is calibrated in inches of water.

The idea is to service the filter when the monitor reaches a certain level of restriction. This specification can vary between 10 and 20 inches of water because of the different designs of filters. We recommend that you get a guideline from a filter vendor that is knowledgeable about compressors.

The new compressors being sold today are supplied with a variety of devices to monitor inlet air filters. If your compressor did not come with such a device, you can make a simple modification and take the guesswork out of filter maintenance.

The manometers or restriction indicators can be installed directly into your inlet piping. They are usually found approximately 24” above the connection to the compressor inlet flange.

b) Avoid using visual inspections to “see if the filter is dirty and needs replacing”. An inlet filter that is doing its job will look dirty.

Also, normal eyesight can only see particles at around 40 microns. That means that an inlet filter rated at 10 micron can look dirty and still have useful service life.

c) Always be gentle when removing an inlet filter element from its housing. It will defeat the purpose to drop contaminants into the intake piping because of accidentally bumping the element. This is another reason to avoid opening the filter housing for visual inspections.

d) Use a clean rag (not a burst of compressed air) to wipe out the dirt from the inside of the filter housing before installing a new element. This is especially important for gasket surfaces in the housing.

e) Make sure the gaskets of your element are flexible and will be able to conform to the sealing surface. You should use an element with a compressible gasket that springs back when you test it with finger pressure.

f) Oil bath inlet filters (still operating in some plants) are efficient if you have the time and manpower to keep up with the maintenance. If not, it would be good to upgrade to a style with the replaceable dry element. Maximize your efficiency and protection by picking one size larger than your compressor CFM rating when upgrading to a dry filter system.

You will need to protect the filter housing from vibrations if you make this conversion on a reciprocating compressor. Ask your filter vendor to recommend a device you can install that will dampen the vibrations on your specific application.

Proper inlet air filter maintenance can help you maximize the CFM output of your compressors. This will save you money because it means that you are making efficient use of the energy costs incurred to produce the compressed air. It can also reduce maintenance costs by eliminating contaminants in the compressed air stream.

Compressor inlet filters are best understood by people with experience in the compressor industry. Contact advice@compressorwise.com with a phone number and the best time to contact you for advice on your compressor filtration inlet. This article was provided courtesy of www.compressorwise.com.