Choosing a Hobby Level Air Compressor
Perhaps no other tool has empowered the automotive hobbyist more than the air compressor. Armed with a properly sized compressor and the right air tools, there are very few jobs that can’t be tackled.
Want to inflate tires and blow out carburetors? What about powering air guns and ratchets? Plan on cutting or grinding bad body panels with air tools? How about sanding and painting? While each of these processes usually requires the same amount of working pressure (90 psi), the air tools in question all require a different volume of air to work effectively. You’ll need to properly size the compressor for the tools as well as for the amount of time they will be used.
The air produced by a compressor and the amount of air required to run a specific air tool is measured in CFM (cubic feet per minute). For simplicity we’ll just be looking at what you can expect from compressor size “A” powering tool type “B” and any limitation that may arise.
For the average home user there are two basic types of compressors: oiled units that use a pump with a crankcase filled with oil, and the other is an “oil-less” type.
Oil-less compressors are insanely noisy and not as durable as their oiled counterparts. An oil-less unit isn’t something you want running in your basements or attached garage early in the morning. I recommend you don’t buy one. If you do, the good thing is they don’t last forever.
Oil-less units run about half the cost of a comparable oiled unit and they only last maybe 10-20% as long as an oiled unit depending on use. I started out on an oiled compressor built by my grandfather using an old Briggs & Stratton 3-hp and a used Chrysler RV-2 automotive air conditioning compressor. While it was crude and a bit dangerous, it outlasted him, my father and myself. It was later stolen and is no doubt still serving someone today—50 years later. While a good oiled unit will last longer than you really need, it also won’t give you any problems while you own it. With this in mind we’ll mainly look at oiled machines in the $450 to $650 range. These should cover most needs of a hobby-level user. I’m a firm believer that a 220v/60 gallon 10 CFM oiled unit is the minimal compressor a serious hobbyist should consider, and preferably a cast iron unit at that. I’ll explain why.
Prepare for the long run
Oiled compressors basically come in two types of pumps: cast iron and aluminum. I prefer cast iron pumps for their wear resistance. I only like to buy things once, and a good ferrous cylinder unit is only a few dollars more if there is any difference in price at all.
There are two common voltages and tank sizes available for home compressors: 110/220v and 30/60 gallon, respectively. The largest 110v models usually top out at around 30 gallons and about 5.5 CFM. Some 110v units can run air ratchets and impact guns pretty well but the lower output units most likely won’t. Most wrench-type tools require between 4-6 CFM and a proper compressor will have to supply enough air for them to run effectively for the duration of the task. Some folks may get by with smaller units but there may be some extra time spent waiting for the compressor to catch back up. Forget about continuous grinding or sanding/blasting with a small compressor (30 gallons, 5.5 CFM or less) as it won’t be able to keep up with high demand tools for very long.
Don’t pay too much attention to horsepower as the same compressor that was rated 7hp ten years ago is now rated at 3-3.5hp today. What really matters is CFM at the required pressure and tank size.
Most good 30 gallon units put out anywhere from 4.5-6 CFM and maybe a bit higher. These units will run ratchets and impact guns well for most practical single-user applications. Using these compressors for sanding, grinding and blasting is a bit of a stretch. If mobility is important or storage space is limited, a 30-gallon unit may work well for your needs.
Proper work load, proper care
When I purchased my current “7hp”/60-gallon unit, the 30-gallon model was the same price. Space, funds and spouse allowing, I feel it’s better to have and not need, than to need and not have.
If you are undergoing a full restoration and/or have paint or prep work in your future, I strongly recommend a 220v unit of at least 10 CFM and 60 gallons capacity at a minimum. My 60 gallon unit is rated 10.3 CFM @ 90 psi. It will outrun any of my wrench style tools all day long. However, if grinding, cutting, sanding or blasting is required, those tools will demand more than my compressor can continuously supply. I can’t use them non-stop but that really isn’t a big deal. When the pressure drops too low for the tool to work properly, it’s about time for me to take a break anyway. This is especially true with a media blasting cabinet, which can become tiresome.
Whichever compressor you get make sure you change the oil in it regularly with the recommended type. I like to break-in new compressors by running them for 20-30 minutes continuously and then change the oil. It’s a good idea to keep an eye on the condition of the oil and change it when it gets a metallic tinge. This will get you in the habit of checking and changing your compressor oil. Don’t forget to add a good water separator, oil your air tools and drain your tank frequently too. Air tools don’t react well with water, especially un-lubed or during a paint job. Taking care of your compressor like you would your car will ensure it will be around longer than you will. After becoming accustomed to having a high quality compressor around you’ll never be able to live without it.
By Billy Hammell