:: Air Compressor Parts ::

If you are one of the many folks that have purchased or are considering purchasing a home compressor, you do want to have a bit of information about compressed air filters.

Compressing air generates a reservoir (receiver / air tank) full of wet, dirty, hot compressed air.

As the air leaves the tank, it carries the crud and free water along with it. It also carries a great deal of water vapour. As the compressed air travels to your appliance (air drill / air grinder / blow gun / air brush - what have you?) the compressed air in the air line cools, and some of the water vapour will condense into free water.

That’s why just having a small compressed air filter at the discharge of the compressor tank may not be enough. Even though the unit at the compressor will take much of the debris and free water from the air there, it can’t remove the vapour. Even though you think your air is being filtered, by the time the air gets to your application, water may flowing out of the exhaust ports and onto your work piece, along with the used compressed air.

Of course, if water flowing or blowing onto your work bothers you just a tad :~} , you’ll want to add another compressed air filter just before you use the air.

Many standard compressed air filters have 5 micron filter elements. If you want to know how big that is, check out the details in the Filter page on my web site.

You can purchase compressed air filters with much finer elements, and you can purchase elements that are coarser, allowing much larger particulates through. Much larger is a relative term. We’re still dealing with pretty small bits here.

If you decide that your application needs extensive air filtration, get a micro-filter element for the additional air filter you will need. The new one might filter particulates down to .005 micron, and if you don’t have a 5 micron unit upstream from it to take out the larger bits, the finer element will plug up really quickly, which is why you’ll need the additional filter housing.

You can purchase compressed air filter elements that will strip oil from the compressed air, these known as coalescent filters. Some piston / reciprocating, and other types of compressors too, let oil “blow by” the piston seals into the compressed air tank, and this oil will get blown downstream as you use compressed air. Compressor oil is not good for most tools that have Buna-N type seals. The compressor lubricating oil might ‘eat’ the seals.

Each compressed air filter you install has a negative affect on the available air pressure at your tool. Pressure drop is a reality in compressed air plumbing. You could supply compressed air at 100 PSI into the discharge air line from your tank, and by the time it gets to your tool, all you have available might be 85 PSI. The flow of compressed air through the air lines, the elbows, the ‘T’s and yes, the air filters, all create pressure drop.

If you are using your compressor a lot (make sure you know it’s duty cycle so that you don’t burn it out) then it would be beneficial to have an auto-drain of some sort on the air filter. A float type will open up and let water and crud flow out when the water in the bowl gets to a certain level. An electric auto-drain will be plugged into a 120 Volt outlet, and will open the bowl drain at preset intervals for a preset length of time. You set the electric auto-drain to the interval necessary to keep the filter bowl fairly empty.

If the water and debris in the filter bowl gets above a certain level in the bowl of the filter, it floods the element, and now your compressed air supply is pumping water and debris through the element downstream to your tool.

Did you know that water rusts metal air tool innards, and that water droplets on your work piece will not allow the beautiful paint job you are air brushing on to it to adhere? Of course you did! That’s why you need a compressed air filter.

One more thing. If your air consumption is great enough then even a filter at your tool may not stop the water vapour streaming along with your compressed air from condensing onto your work piece or in your air tool as the air cools. If that is a problem for you, you will need an air line dryer.

Drop me a email from my site if you have any questions. I’ll be happy to respond.

Bill Wade’s experience in compressed air and other industries spans decades; from field sales positions through to the corporate presidential office. His sales agency represents a select group of industrial firms. Mr. Wade writes about all facets of compressed air at http://www.about-air-compressors.com.

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Compressors fall into three general areas; Small portable units like the Porter-Cable “Job Boss” often with one pancake or two small storage tanks, Mid-size units like Campbell-Hausfield, which normally have wheels, and large compressors have fixed bases for shops and industrial sites. In terms of capacities, smaller units start around 1.5 horse and larger unites can exceed 6 horse power motors. The pumps themselves are either oil-less or oil-lubricated and the pumps are one or two cylinder and singe of two-stage compressors …. and this last statement is the reason most wood workers don’t have an air compressor, because they sound complicated.

Some of the useful terms that you should know about when looking for a compressor include: PSI - Pounds per square inch, CFM - Cubic feet per minute, Duty Cycle - is the amount of time a compressor can run compared to the amount of rest time (storage tank) over a 30 minute period … such as it can operate for 10 minutes, then rest for 20 without creating significant head wear, Single Stage - is where the compression piston compresses all the air in one stroke, Two Stage - is where there are two pistons that work together to compress the air. (Generally a two stage requires less horse power, and produces less heat).

As a rule, the types of tools that are harder on air volumes are those which run continuously like sanders, and grinders and cutters. Tools that require less cycling are tools that run intermittently like nailers, staplers and in some cases drills or even sprayers.

If you are planning on running some continuous tools like sanders, buffers, grinders and so on you will want to consider something in the mid-size or even large shop size of compressors like. In a case like this you should probably have a 25 gallon storage tank and around a 4 horse rating like a Makita or Craftsman. You will probably be looking at a 220 Volt version as well.

If you are planning on using a number of tools, some of them continuous draw, like grinders, sanders and buffers, you will want to consider a large fixed base compressor like Campbell - Hausfeld or Ingersoll-Rand. These will have around 6 horsepower and a storage tank of 50 gallons or more.

If you are a hobbyist woodworker, who is looking for a nailer or stapler, one of the small portable compressors is probably ideal. Manufacturers like Porter-Cable or Delta will work fine.

The real trick to buying a compressor is to know ahead of time what you are going to use it for and what the air-tool rating is in PSI and CFM. This will give you a better indication the duty cycle you will need. But this isn’t end all either, because your need to look CLOSELY at the air tools you are considering because the same tool an vary widely in the amount of compressed air it will consume. For example a series of six inch random-orbital sanders have cfm differences of of 8 to 24. That’s huge, and it means the difference between buying a mid-size compressor or large fixed compressor. It pays to examine the tools you will be using and select the appropriate ones.

A compressor and associated air powered tools can be a real time saver, even for the hobbyist’s work shop. In many cases a simple brad nailer is almost like having a second set of hands around in assembling and gluing projects together. The other consideration in selecting a compressor is, what other uses will you find for it? For example if you do select one of the portable units, it is conceivable that you can carry this around to odd jobs, in the house, for friends or other areas. This is less of an option of the mid-size and out of the question for the large units … but then the portables will not likely be suitable for sander/buffers … SO … in the end you will have to make that tough decision, but what ever you do, make sure you make sure get a nice selection of tools designed for your compressor. It will make your woodworking more fun, quicker and even more enjoyable than it is now.

Copyright Colin Knecht of WoodWorkWeb.com. This article may be freely distributed and reprinted as long as you leave the article fully intact, including the links.
Visit Woodworkweb.com - woodworking resource for more great woodworking information.

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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

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.

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