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Spray painting - The compressor.

Which compressor do you need?.


If you decided to paint your car, or parts of it, with a spray gun you just go out and buy one, right? Not quite, there is some more to it I'm afraid.

To start with you will need a compressor, spray guns need compressed air to work. Not all of them, there are spray guns which will run on electricity. I'm not going to discuss those for the simple reason I have never used one. So, a compressor it is. The first thing you'll have to decide is how much capacity you need. Every air-tool needs a specific amount of CFM (Cubic Feet per Minute) of air capacity, spray guns are no different. For small jobs you can get away with a relatively small compressor and a spray gun that will use about 5CFM / 140L per minute. I'll give you examples of spray guns which are within that range in another chapter. A 1HP compressor with a tank of 50 liters will do.
Note: The US gallon is defined as 231 cubic inches (3.785 liters). In contrast, the imperial gallon, which is used in the United Kingdom, Canada, and some Caribbean nations, is defined as 4.54609 liters. Hence 100 liters = 26.4 US-gallons and 22 Imperial gallons.

If you are planning on spraying a whole car you will have different needs, first off you need another spray gun and they most likely will consume up to 10CFM / 285L per minute. You need a larger compressor to "feed" that spraygun. So, will a compressor twice the size do? No, compressing air is not a linear process. You will need something in the 150 to 200 liter range with a 3hp motor on it, most probably a 2 cylinder.

Why is this so important? You don't want the compressor to run out of air every few minutes while painting, when you start a paintjob you just want enough capacity to finish it in one go. Waiting for a compressor to get the pressure you need is no problem when you're inflating your tires but when you're spray painting you definitely don't want that.

How much pressure should a compressor be capable to deliver for a spray gun? Not very much, most spray guns run off of 2 to 3 bar / 29 to 44 PSI. HVLP (I will explain this later) guns may take just up to 2 bar or 29 PSI. Most compressors will give you anywhere in between 6 and 10 bar / 87 to 145 PSI. The maximum pressure a compressor can build up is not that important. If you can find one cheaper that goes up to 8 bar instead of the more expensive one that will give you 10 bar, go for the cheap one!

Here is a picture of my compressor, it's in another part of the building to begin with. You can see it's producing 96dB of noise which is a lot, on top of that it has got fans on it which will circulate the air. Unless you got a proper paintboot you don't want any turbulence while spraying. It will kick up dust from wherever, you want your paintjob as clean as possible so having it in the garage is a no go. This compressor is a 200 liter 4HP model, capable of delivering about 11.7CFM / 330 liter/minute and yes, it builds the pressure up to 10 bar / 145 PSI.


Bigger compressors are lubricated by oil, to maintain your compressor it's mandatory to change the oil let's say once a year. If you are running your compressor daily there will be an indication of running-hours determinated by the manufacturer after which you have to change it. Same goes for the intake air filter(s). Only use products the manufacturer indicates, having said that, you can use any oil which is made to lubricate compressors. Keep an eye on the level on a regular base as well, depending on how much you use it.

If you're not using your compressor every day depressurize it, that way the 10 bar / 145 PSI are not putting any strain on all the parts involved, especially couplings. Be aware there is water / moisture in the air that's sucked in. You will find there is water in your tank over a period of time, no exact span of time here but whenever you depressurize the compressor let the water off which has accumulated in the tank. First off you don't want any water to get into your spray gun! Other pneumatic tools are not liking it eigther. Overall, you should let the water in your compressor off at least once a month. If you're in a very damp climate even more often.

A compressor of a bigger size is not cheap, maintaining it will pay off! You'll get many years of error-free operation from it when you do.

You will need some air hoses (also called air-lines) too! Don't go for the least expensive ones, they normally don't last very long, are stiff and the couplings may not be what you want. Meaning leaking out air. A decent inner diameter is important as well, the cheap stuff has an inner diameter of probably 6 mill / 1/4 inch or even less. You want to have air-hoses that have an inner diameter of like 8 mm / 5/16th inch. A smaller diameter reduces the air pressure at the end of the line. If you're on like 75 feet of air line you'll loose about 2 bar / 30 PSI using those. Getting around a car you will need the length, especially if your compressor (like mine) is located at the other side of the wall.

I do hope this will give you some guidelines on which compressor you may need or want and how to maintain it.
A good compressor is a precious thing to have, be sure you'll be using it with other air-tools as well! There is a wide range of those, from drills, wrenches, chissles, impact guns up to dual action sanders. Actually everything you can imagine power-tool wise.

Last update : August 29th, 2018