Compressors make compressed air, so far, so easy. However, while almost all workshop compressors deliver 10 bar, the suction and delivery capacities are more complex. Here the manufacturers like to write actually completely meaningless numbers in large digits on the device because they sound better. And then there is the completely underestimated tank, which can allow a compressor that is actually too weak to grow beyond itself.
transcript of the video
(Note: This is bonus content for people who cannot or do not want to watch the video above. The video track information is not reflected in the transcript.)
To have compressed air you need a compressor. And they can be a little confusing with all those numbers and dates all written on them. What that means in each case and how big the compressor has to be for typical maker projects – we explain everything in this video. Have fun!
Compressed air in the workshop is a super useful thing! First of all, it gets dirt out of corners where it would otherwise be difficult to remove. Then you can also use it to operate tackers and nail guns, you can paint with it – and sandblasting, for example, opens up completely new possibilities. Well, and even if you don’t have any big plans: Compressed air is also extremely practical for cleaning vacuum cleaner robots.
The most obvious value for a compressor is the pressure, measured in bar. You know that from filling car tires. Such a car tire typically has a good 2 bar, and as long as the compressor provides more pressure than this 2 bar, the air flows towards the tire when filling and pumps it up.
The compressors that are of interest to makers are in the so-called low-pressure range and can generate 8 or 10 bar of pressure, industrial devices of course even more. But for the home workshop, 8 to 10 are quite enough. For most work you reduce the pressure anyway, my spray gun, for example, only needs 2-3 bar, so there’s a pressure reducer on the compressor for that, you can adjust it.
The next value is the air output per minute. And there are now two pieces of information: First, the intake power. This tells you how much air a compressor sucks in from the environment per minute in order to then compress it. This value is simply calculated. And then there’s the power output. This is actually measured on the discharge side of the compressor. If it is measured according to the standard, it is called the “Effective Delivery Quantity”. This indicates how much air is available per minute after compression. Since losses occur in compressors, this delivery quantity is always less than the calculated intake capacity and this loss varies in size depending on the compressor. Unfortunately, however, the intake power is the megapixel of the compressor seller: the number says little, but it sounds good. So the intake power is often given prominently, not the delivery quantity. As a rule, these can be found in the technical data or on the type plate. It is ideal if you are given the “Effective Delivery Quantity”, which is then the standardized measurement and can therefore be easily compared.
So now, of course, the question is: how much air do I need per minute?! Yeah – it depends on what you want to do. Here are a few typical uses:
A small nail gun or staple gun takes about a liter per shot. For a spray gun you need at least 100 liters per minute. A random orbital sander with a compressed air drive needs at least 250 liters per minute and it gets really intense when sandblasting, you can quickly reach over 500 liters per minute and then you need a correspondingly powerful compressor. At least in theory.
After all, it is not the case that the air is routed directly to the tool after it has been compressed. Instead, it first lands in a tank. Unlike electricity, air can be stored very easily. And that’s why almost all compressors have a built-in tank, that’s this big thing here. The air is pumped in there after compression, and when we remove air, we do it from this tank. Now that has advantages and disadvantages.
Let’s start with the benefit. This compressor can generate 10 bar. If you switch it on, it fills the tank until there is 10 bar in the tank. The compressor cannot build up more pressure, so it switches itself off. If we now remove air, the pressure in the tank drops and if it falls far enough, it automatically starts up again until there are 10 bar in the tank again.
If we now assume that we have a compressor that has an effective delivery volume of 200 liters per minute. And we take 100 liters per minute with a spray gun, then the compressor can build up the pressure in the tank faster than we take air. That means: while we are painting, the compressor keeps going out because there is still enough air in the tank to be able to paint without interruption.
If we connect a nail gun and shoot a nail every 15 seconds, we’re only removing 4 liters per minute. Then the compressor only kicks in occasionally to refill the tank, so a fairly small compressor is enough for nailing.
If I were to connect an eccentric sander that needs 250 liters per minute, it would work at first. There is enough air in the tank to provide 250 liters per minute. But not for long, because there are only 50 liters in the tank of my compressor, so that only lasts a few seconds. Then the compressor would start and try to fill the tank. But he wouldn’t be able to cope with that because he delivers 200 liters while I take 250 liters. So my compressor is not enough for a random orbital sander.
So, and now to the sandblasting gun. It needs a REAL amount of air, even more than the grinder! But the big advantage is that I can easily wait a little while sandblasting. It doesn’t matter, it just takes me longer to finish. When painting, for example, you wouldn’t want to take a break because you could see it in the paintwork if you had to wait a minute for the compressor in between.
So if I want to sandblast now, I can do it with my compressor. Then I have to wait again and again until there is enough air in the tank that I can remove quickly enough, then I can sandblast a bit and then wait for the compressor again. The larger the tank that I can empty quickly, the longer I can sandblast in one go before I have to wait for the tank to be filled again. That sounds really annoying, but I don’t think it’s a problem for small parts. After all, you also save yourself a significantly larger and more expensive compressor. And unless you’re restoring vintage cars, you don’t sandblast them every day.
The tank therefore ensures that the air flow remains constant, regardless of whether the compressor is running or not. And ideally, the tank also gives the compressor a little breather, whenever there is enough pressure in the tank.
But now the tank also has disadvantages. Our ambient air also contains water. When compressed, this water liquefies and collects at the bottom of the tank. There is a small drain plug on the bottom and you can drain the water from there. You should too, because otherwise the tank can rust from the inside if there is permanent water in it. However, not all the water stays in the tank, a little of it also goes in the form of drops into the hose and thus into our tool. It doesn’t matter if I clean the chain saw, but when you paint you don’t want water in the air. Then there are water separators that take the water out of the air and also have a drain plug to drain the collected water.
However, compressors now have even more properties than just pressure and delivery volume. Volume, for example, is also an issue. Cheap compressors are usually really loud.
SCREAMING: “It’s usually on the nameplate too, and often really big on the tank too, because at that volume you DEFINITELY need to wear hearing protection.”
And even then, I find it awkward being in the same room as the compressor. I get scared every time it starts automatically. So it’s great if you can put the compressor in the next room, in my case it’s in the boiler room right next to the workshop and I put the hose through the wall. I have a switch in the workshop that I can use to turn the compressor socket on and off, so the compressor doesn’t bother me in the workshop. Alternatively, there are also so-called whispering or quiet compressors. They are quite a bit quieter, really good ones are hardly any louder than a fridge. But these things are also significantly more expensive if they are to produce the same delivery quantity.
With that we would have covered the most important performance data. Now there are still oil-free compressors and oil-lubricated compressors. Oil-free ones are often louder than their oily counterparts and also wear out a little faster. But the compressed air is oil-free and you don’t have to pay attention to the oil level. Compressors with oil are therefore often quieter and last longer. And they always have a tiny bit of oil in the air. Some tools, such as a pneumatic nail gun, really like this. Paint guns but again not. It doesn’t matter what kind of compressor you use: you can filter out oil from the air afterwards with so-called oil separators or add it by simply putting a drop of oil in the compressed air connection of the nailer, for example.
That’s it from me for this week, happy crafting and… compressing? Until next week! Bye!
(yom)
