Filter Maintenance - It's Time To Change

In previous posts, we talked about in-line compressed air filters.

In the large majority of them there is an element that you need to change every 6 months to a year - sometimes less.  Keeping those elements changed is very important to the quality of your compressed air.

If you don't change them in a timely manner, then it's like you don't have them at all.  All of the junk you were trying to keep from getting in your equipment will get through.

If that wasn't reason enough to change them, there's another reason.

Occasionally we have customers that will hold off ordering the elements as long as they can, even if the differential pressure gauge on the filter is showing it's time to change.  That's understandable, because often the elements can be expensive.  It's like a bill that's due every six months - if you could pay that bill every eight months and get the same service, you'd probably do it.

However, with clogged filters it doesn't work that way.  Many of the filters have a differential pressure gauge to show the filter needs changing.  So what is that showing and why is it important?

The differential pressure gauge simply measures the pressure before the filter and the pressure after the filter.  That shows you the pressure drop across the filter.

PRESSURE DROP

We're not talking about the 1969 Jamaican Rocksteady hit. 

If that's the Pressure Drop you have, no problem.

However, pressure drop in your compressed air system is bad.  We went into why in an earlier blog post, but it bears repeating.

Every 2 psi increase in pressure is about a 1% increase in energy use.

So let's look at the cost of not changing a clogged filter.  Every filter has a pressure drop - it's inherent to all filters.  A clogged filter, however, will often be 10 psi or more above and beyond your normal filter pressure drop. That's means the compressor or compressors upstream will be using 5% more energy.   So let's look at the numbers on that.

We'll take a look at an average installation in the USA:  30hp air compressor running about 60 hours per week.  The motor has a 1.1 service factor, 91% efficiency, and the electrical cost is 12 cents per kWh.  In that scenario not changing a clogged filter costs about $10 per week, $40 per month, and $520 per year.  The filter element in question probably costs about $150 for OEM or half that for an aftermarket.  So holding off another two months changing the filter will cost them about $80 on the electrical bill.

If you have a large manufacturing plant, you probably have between 100-300 hp worth of air compressors and you likely run 80 hours per week.  Not changing the filter costs about $43 per week or $170 per month for every 100hp (using same electrical cost, motor efficiency, and service factor).  

Also, these numbers are just for one filter.  It is typical to see two or three filters in the line.  If you have a desiccant dryer, there are usually two filters before and two filters after.  A big plant with a 300 hp worth of compressors would use an extra $2000 per month in electricity by not changing them. 

You can't afford not to change them.

So holding off hold off on filter maintenance will:

1.  Contaminate your process.
2.  Run up your electrical bill.

It doesn't make sense to not change the elements when it's time.  If you don't, problems "soon come,"  as they might say in Jamaica.