Why should you use caution with emergency compressors?

This cooler is set up to condition incoming emergency air.

In the heat of summer, it is common to have heat-related problems in an industrial facility. When these problems include the failure of the air compressor, the only option is often to bring in a motor-driven portable rental compressor. The use of these gas or diesel units can cause huge problems in a plant unless proper preparations are made.

There are usually lots of fuel-driven compressors of all sizes at the local equipment rental store; typically a unit can be obtained that is about the same size as your failed unit. However, you should be aware that these units are often missing a very important component — an aftercooler. The compressed air produced by any compressor is very hot when it leaves the compression element, but typically stationary compressors have an internal air- or water-cooled aftercooler that removes most of the heat in the compressed air — and lowers it from about 200° F to a temperature slightly higher than ambient.

Portable compressors without aftercoolers inject this very hot air into your plant, often overloading the air dryer and causing moisture problems if adequate secondary cooling is not provided.

Compressed air at 120° F or higher entering the plant from a diesel compressor with no aftercooler contains more than four times as much moisture as compressed air at 70° F (room temperature). This excess water is far more than can be processed by an ordinary air dryer, often resulting in dryer failure and excess condensed moisture forming in the pipes and machinery inside the plant. At best, this water, lubricant, dirt and rust mixture will be drained out by well placed condensate drains located at low points in your plant piping system; at worst, it will deposit on your finely produced product, causing contamination.

Some plants plan for emergency diesel compressors by installing permanently mounted coolers (see photograph above) through which hot emergency air is passed, lowering the temperature and removing moisture so the air dryers can work properly. Others will rent coolers or pass the emergency air through large receiver tanks to provide cooling — something to think about on hot summer days.