Compressed air pipe sizing

Avoid pressure drop in your compressed air piping, with our easy to understand compressed air pipe sizing information.

Compressed air pipe sizing: the art of calculating the right pipe size for your compressed air needs. Of course, you want to know the best size of pipe to install in your compressed air system. You don't want to spend too much on a too big pipe, but you also don't want any problems with too small pipes.

Let me help you to find the best pipe size for your compressed air system.

Pressure drop

Air that flows through a pipe always creates a pressure drop. What does this mean? You will lose pressure because the air has difficulty to pass through the pipe.

Say you set your compressor at 7 bars pressure. You connect a long, small pipe to it and install your air-tools at the end of the pipe.

If you don't use any air and you would measure the pressure at the compressor and at the other end of the pipe, you would measure 7 bars pressure at both ends of the pipe. Of course! Common sense tells us that since they are connected, the pressure is the same.

Now you operate 1 of your air tools, a big one.. say an air-grinder (any air tool that rotates, like grinders, hoists, drills, etc always use a lot of air). You will notice that the pressure at your compressor stays at 7 bar, while the pressure at the air-tool drop to maybe 5 or 6 bar.

What's happening? Do you need a bigger compressor (greater capacity)? No, you need bigger compressed air pipes! The long pipe in our example is creating a pressure drop, because the air has trouble traveling through the pipe so fast. It's like a traffic jam on a busy highway!

A pressure is always measured at 1 point. A pressure drop is always measure between two points. It's the difference in pressure between point A and point B.

The more air tools you will use at once, the more air will have to travel through the pipe and the bigger the pressure drop over the pipe will be.

Compare it with breathing through a straw. The longer and narrower the straw is, the harder it is for you to breath. If you would breathe through a very long and narrow straw, that would be quite difficult, right?! Now, if you would breath through a very big straw, more like a pipe, say 5 cm (or 2 inch) in diameter.. that would be very easy, right!

Same goes for compressed air systems, the bigger your pipes are, the better.

How to calculate pressure drop?

That's very easy! If you can count and know 1+1 = 2, you can calculate the pressure drop and/or the best size of compressed air piping for your system!

How it's done? There are tables that tell you exactly how much the pressure drop will be for a given air-flow and pipe diameter. No need to calculate anything, just look it up in the table.

It's easy as that! You should aim for a maximum air drop of 0.1 bar only!

(In practice, I've seen anything between 0 and 2 bar pressure drop... people are just throwing money away every day! )

Check out our pipe sizing calculation page for tables and examples.

What about other bends, couplings and other stuff?

We learned that pipes create pressure drops, which we try to avoid. But what about other obstacles, like bends, couplings, valves, hoses, etc.? They create pressure-drops too!

Each of the things listed above is an obstacle in your compressed air system. Air has trouble to flow through it. If the pipe in our example has a hundred bends in it, it would be harder for the air to pass through the pipe.

Remember our comparison to rush hour traffic on the high way? If there are a lot of sharp bends in the highway, you wouldn't drive that fast, would you? Same goes for compressed air..

The same is true for any object that restricts air flow. If you install a coupling with a very small diameter in between two pipes, that's a mayor pressure-drop creator, because the air will have trouble passing through it.

There are tables available that will tell you the pressure drop over bends, coupling and other things. To make it easier for you, they are usually expressed as 'equivalent pipe length'.

The equivalent pipe length tables can be found on our pipe sizing calculation page (including examples).

Pressure drop.. What's the big deal?

So you installed too small and long piping and now you have a 2 bar pressure drop. What's the big deal, you can just increase the pressure on your compressor, right?

Right, that's true! If your equipment needs at least 6 bars and you have a 2 bar pressure drop in your system (which is huge!), just set the pressure on your compressor at 8 bars and you will be fine (you will have 8 bars at your compressor, 2 bar pressure drop over your piping, resulting in 6 bars pressure at your air-tools).

But, that increase in pressure will cost you a lot of money in the long run! Why? Compressing air to 8 bar requires far more energy than compressing it to just 6 bar. Second, if you have air-leaks, far more (expensive) air will escape your system at 8 bar, when compared to 6 bar).

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