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Explosive air

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Engineering Articles

Explosive Air

By: Thomas Yoon

Have you considered your air compressor as a potential bomb?

If you have not, then you better!

Although air compressors are built to withstand high pressures, and will have all the necessary relief valves to take care of normal occurring overpressures, explosion involving fire propagation is another matter.

How can a fire occur in an air compressor?

In order to understand the phenomenon of explosion, we have to understand the nature of fire, because, after all, an explosion is a very rapid propagation of fire.

A fire will only start whenever three conditions are met - fuel, oxygen and heat.

An air compressor when operating will have a very rich supply of oxygen already in place - pressurized oxygen.

Where do we get the fuel?

If you use oil lubricated air compressors, the lubricating oil can become the source of fuel. It can also be in the form of carbon dust. Carbon is formed when oil is heated to high temperatures.

How is it possible to have high temperatures to ignite the combustible mixture?

There can be a lot of reasons - lack of lubrication due to oil deterioration, reduced lubricating quality of the oil, oil pump mechanism fault, oil filter choked, worn out parts leading to lessen oil pressures, etc. Whenever there is a hotspot sufficient to ignite the combustible mixture an explosion will occur. That is the extreme case.

Let's see what can happen that can lead to that extreme case of an explosion.

All the above reasons for lubrication failure or deterioration will gradually cause the machine to operate poorly, wear out the moving parts, cause oil spills and carry over of the oil in the air passages and increased heat built-up.

Now comes the cooling part. Is there a lack of cooling? If the high temperatures due to rubbing of parts from the above are not cooled down sufficiently, the heat will build up. The intercoolers play a very important role in removing the heat?

There are also many other reasons for the lack of cooling.

When the heat transfer surfaces have been coated by films of scale or carbon it will definitely affect the cooling process. The heating surfaces may have been reduced due to choked passages for the cooling medium in the heat exchanger. The cooling medium itself may be too hot probably due to a fault in another machine like the cooling tower where the heat can be taken away to the atmosphere.

The flow of coolant can sometimes be the culprit. When the cooling pump fails, or the driving belt snaps there will be a lack of coolant flow. One must also find out whether the valves for coolant have been accidentally closed or not.

Very often, the effects build upon one another in a vicious cycle - poor heat transfer leads to more heat that carbonizes more oil which coats the heat transfer surfaces more...which leads to worse heat transfer...

Therefore use oil lubricated air compressors with caution. If your air compressors have been running for a long time, chances are, your air compressor pipelines may have already accumulated a sizable amount of oil carried over together with the air flow during operation.

Does your air compressor work non-stop? Is the inter-cooler or the after-cooler efficient? Is your compressed air hot? These are the questions you have to ask yourself.

The oil film in the pipes turns to carbon with heat. The oxygen-rich and moist atmosphere inside the pipes can turn the oil into acids that can further deteriorate the oil to form other organic compounds, perhaps some highly flammable products.

It just needs a spark or a hot spot to ignite this.

Boom!!

Did I frighten you?

What you need is good preventive maintenance. An air compressor working at peak condition with good cooling, good lubricating pressures, and good lubricant and good parts should give trouble-free performance throughout its lifetime.

Sometimes the compressor may have reached the point of no return - coated coolers leading to high temperatures that lead to more coated cooling surfaces that lead to higher temperatures... In this case it is safer to discard the compressor altogether and obtain an entirely new compressor unit. It could be more economical - and safer!

If you do that, do ensure that preventive maintenance is done regularly to keep the unit at peak operating conditions all the time.

An explosion in an air compressor can have grave consequences. Don't take any chances. Perform regular preventive maintenance or buy a new unit before an explosion occurs.

Until next time…

Locate good air compressors for your garage and workshop here:

Eastwood
Northern Tools

Many years of working experience in Marine, Facilities, Construction has given the author material for writing e-books and articles related to engineering, and management. Subscribe to facworld ezine at mailto:facworld-subscribe@yahoogroups.com

More information at http://www.free-marine.com and M & E Engineer

 

 

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