Most of us equate air compressors with spray painting and don't realise what a handy item they are for general maintenance and restoration of our vintage and not so vintage cars.
Air compressors come in a multitude of sizes and shapes ranging from simple little $20 tyre pumps which connect to the cigarette lighter up to huge diesel powered devices you see being used to drive jack hammers on road and building construction sites. They all use the same principle of compressing air and using it to perform a function. Somewhere in between you can make a choice of a compressor which will suit your needs. The criteria or measurement of an air compressors capability is expressed in cubic feet per minute which is generally abbreviated to CFM or sometimes CM. This expresses the compressors ability to produce the amount of compressed air. This by the way has nothing to do with the size of the receiver which is the tank which holds the compressed air after it is produced. I will refer to the combination of the air compressor and the receiver tank as a "unit".
Most air compressors of the type we will talk about generate around 120 pounds per square inch [PSI] air pressure which will then need to be passed through a regulator to control the pressure to lower levels eg 40 PSI for spray painting. They also need a water trap to eliminate water from the compressed air.
The first important principle is to make sure you purchase a unit which will do the job you want it to. Don't buy the cheapest one around as you may be disappointed with the results. The general rule is to buy as large a unit as possible. It is better to have a unit which can handle the load on an intermittent run basis rather than something running flat out all the time and failing to deliver air that is needed.
If you intend to do some spray painting as well as running air tools such as air drills and sanders I recommend you look seriously at a 13 CFM unit. To go any larger generally requires some special wiring in your house or shed as you will need a 15 amp electrical outlet. The standard household electrical wiring system is for a 10 amp outlet. You can pick the difference on the 3 pin electrical plug as the earth pin is significantly wider on a 15 amp plug. It is interesting to note that you can now buy 13 CFM units for around the $800 mark which is over $100 cheaper than the price I paid for the same brand unit about 9 years ago.
The size of the receiver is also important. Even a 13 CFM unit with a small receiver may be a problem to you in that it lacks reserve capacity to keep up with very large intermittent demands placed on the unit when spraying whole cars or operating some air tools for long periods. I note that some of the imported units which appear to be made in Italy have relatively small receivers.
There are numbers of units for sale on the second hand market. Be wary, as a lot of them are pretty well worn out having been used by builders as a source of compressed air for nail guns. Many have had a real flogging having been used for 8+ hours a day for years. The majority of these are 8 to 10 CFM units. There are quite a few of these coming onto the second hand market as the building industry is currently changing over to "gas guns" which electrically ignite a gas charge from a small cylinder held in the gun. [much more portable]. It is better to go for a new unit as it should last a hobby type user for life however you might pick up a bargain unit from a builder.
My own unit is a 3 cylinder 13 CFM Airmac which is Australian made and has not given me any trouble during the 9 years I have had it. There are also a number of imported types on the market at similar prices but I prefer to keep the money in the country and at least spares are available if I ever need them.
When shopping around be a little wary on some of the "deals" which include air tools and spray guns as well as air hoses. Many of the spray guns are cheap and nasty and a lot of the tools are not much better. Remember that in this business you "pays for what you gets". Do make sure that the unit you are purchasing comes complete with a pressure regulator / water trap. You will also have to make a decision on what type of fittings you are going to use on your air pressure hose connection systems and how much hose you will need. Don't be tempted by the self coiling "spring type" hose you used to see in service stations. Unless you have a specific use for it, self coiling hose is a real nuisance when working with spray guns and air tools.
If you need a very long hose they can be an absolute pain to roll up and unroll just like your garden hose. A tip is to install a metal garden hose reel on the wall in your shed or workshop adjacent to the compressor. You can plumb the air through the reel just like water. It sure makes winding up and unwinding hoses simple We have used them for years in the aviation industry.
Now onto spray guns and tools. Spray guns come in several types and several prices. The panel beating industry standard is the Japanese IWATA series but they don't come cheap starting at around the $130 mark and going up of course. There are a few other types in competition such as the Binks made in the USA which are good but pricey. DeVilbiss and Wagner are also well known. As a general guide in guns you will need a 1.2 mm orifice nossle for spraying enamels, a 1.8 mm for 2 pack paints and a 2.2 mm for lacquers. For more information on spray guns talk to an automotive paint retailer. I also recommend Al. Probert's book "Spray Painting And Panel Beating In Australia".
In the cheaper guns there is low pressure/ pressure pot gun which typically retails for around the $30 mark which is very useful for spray putty, underbody coat and spraying fences with acrylic fence paint. Super cheap also sell a general purpose high pressure gun for about $69 which is quite good for undercoat and reasonable on lacquer. Their $39 high pressure gun is not recommended. Their touch-up gun around $55 is satisfactory.
Some of the air tools I have accumulated and found very useful over the years include-
Tyre inflation tool - built in pressure gauge - just like your local service station
Air duster gun - to blow dust and rubbish off the job. Blow out the workshop floor etc.
Kerosene pot gun. - degreasing engines; cleaning down major parts; spraying anti-rust. Also useful for spraying the weeds in the yard
Air ratchet spanner - really speeds up pulling things apart - be wary about use in assembly
Air impact wrench - wheel nuts off and on in a zip and very useful when removing head bolts or trying to undo large nuts on the suspension etc.
Air orbital sander - speeds up the bodywork process.
Air powered grease gun - simplifies the process when lying under a car. Better than trying to use the old mechanical grease gun in confined areas. Be careful as you can blow out seals on universals and rubber boots on steering components such as tie rod ends and ball joints.
Air chisel - invaluable for the serious restorer and I also use it to cut out the tops from drums etc. It can also be equipped with a bit to "buck" solid rivets.
Some other useful tools available include air powered drills and die grinders but as I have electric tools to cover these I haven't bothered to purchase them. I have drilled a few thousand holes in my time with air drills and they are excellent devices but hungry on compressed air. Their main value is in safety particularly working around aircraft where fuel vapours may be present.
A word of WARNING when using compressed air. Never point compressed air nozzles at yourself or any other person particularly in relation to body orifices as permanent damage to the human body can result. In addition small objects can be picked up and blown at high velocity and will penetrate the human body. Do take appropriate safety precautions applicable when using compressed air such as wearing a mask while spray painting and safety glasses when blowing out dirt and dust.
A small tip if you regularly use compressed air tools and then decide to use the same air lines for spray painting. It is worthwhile blowing some 50 mils of methylated spirits or methanol through the hoses prior to spraying to get rid of any possible moisture in the lines. The high pressure use of airlines associated with air tools appears to allow hot air from the compressor to bypass the typical water trap and carry moisture into the lines where it condenses. I have standardised on this procedure in my workshop and no longer get nasty moisture surprises when spray painting.