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The local tire store had a special on recently. If you went in for routine service, they'd give you an air compressor, free of charge! I took advantage of that offer as I do most times when something is "free".
Well, the unit shown in the picture just below is the type of portable compressor similar to my “free” one. It plugs into the car's 12 volt power outlet, and will put out compressed air up to 125 PSI.
Of course the flow rate is very low. So low that it might take what seems like forever to fill up a tire or air mattress. But...it is portable!
When looking for portable-compressors, you have to first decide what the applications for are.
Those applications will tell you the capacity of the portable unit that you will need. Not sure about air tool consumption? Click here.
The little compressor shown in this picture is a bit of a toy,
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That is, assuming it works. I tried to use it the other day, and the darn thing wouldn't cycle, and burnt the fuse. Lesson: test your equipment periodically. Don't assume that just because you've got it with you for years in the “boot” of the car, that it will work when you need it.
When using it, you want to be careful too, as some of these low flow, compact compressors can put out 250 PSI, and with enough time might blow the the tire, or an air mattress or beach ball to smithereens!
Once you've figured out the capacity you'll need, (another way of saying capacity is...how many CFM of air at what pressure will you need? )give some consideration to what's going to drive the portable air compressor.
While the unit above will need a special power receptacle to plug it into the car, this next picture shows a portable unit that can be carried from place to place, and plugged into a standard 120 volt outlet.
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Regardless of what portable compressor you choose, you'll face all the same issues relating to compressed air as if your compressor were a 100 HP unit supplying the air to a commercial establishment. Watch out for water problems relating to it's use.
If the portable unit you choose doesn't come with an in-line compressed air filter you'll definitely need one, along with a regulator.
A compressed air filter is a very useful accessory, as without it, you'll likely have water spraying all over your application.
A regulator, set 10-15 PSI below the compressor’s low pressure set point (also known as "kick-in" pressure point) should ensure that your application will see a steady stream of compressed air at a non-varying pressure.
As the pressure in the receiver peaks and wanes due to compressed air use, with the regulator set below the compressor’s lowest pressure setting, your application should never experience a change in that constant, lower pressure.
That is, unless the air tool's demand outstrips the ability of the compressor to keep up. In this case, the pressure coming from the receiver will continue to decay down past the regulator setting, and it will keep dropping as long as more compressed air is being used than your compressor can compress.
If you are running an air tool with your portable compressor, consider adding a lubricator to the filter and regulator. The lubricator will deliver measured amounts of oil from it's bowl to the application.
On the other hand, if your application is, for example, air brushing, then you don't want oil spraying out with the paint.
More on portable-compressors here.
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