When it comes to connecting parts of your air system or circuit together, along with the appropriate fittings, you have the choice of using Air Hose or compressed air tubing. This page focuses on air hose. You can find information on air tube on this site as well, linked from the Sitemap page.
Of course, compressed air hose and tube isn’t much good without the fittings to connect them. If you are looking for information on fittings, lots of information about air fittings can be found linked from the Sitemap page as well.
Table of Contents
- Compressed Air Hose
- Compressed Air Tube
- Further Reading on air hoses and air tubes:
Compressed Air Hose
This page focuses on air hose which is just one type of air line that brings compressed air to the air tool, air valve, air cylinder or other compressed air using application.
Sizing Air Hose For Compressor Air Lines
When you are trying to figure out what hose size you need, or even why a 3/4″ hose is well over an inch in diameter, just remember the acronym H.I.D.
The ‘H’ in H.I.D. stands for HOSE. The ‘I.D.” in HID stands for the hose “inner diameter”.
Hose size is measured by its inner diameter.
A 3/8″ hose will have a hole in the center that is exactly 3/8″ in diameter regardless of how the outer diameter of the hose varies. And it does, depending on the type of hose and the manufacturer.
So, will all same size air hoses have the same outer diameter (O.D.)? Nope, they won’t.
Different manufacturers offer air hose with varying wall thickness. Therefore, one 3/8″ hose might be just under 1″ in outer diameter, another might be a 1 1/4″ outer diameter, yet in both cases the I.D. will still be 3/8″, identifying this one as a 3/8″ hose.
It is often the higher priced hose that has a larger O.D. due to more mass in the wall thickness or integrating reinforcement into the hose wall for greater burst strength.
Air compressor hose size chart coming soon…
Is it Air Hose or Air Tube?
Be a bit careful when speaking with folks about air line hose.
First, make sure they are talking about hose and not tubing. Take the time to clarify where the dimension they give you come from.
A technician may provide a hose dimension such as 5/8″ or 3/4″, but they may be talking about the hose O.D.
If you size the necessary fittings based on that information and don’t cross check, and you’ll be making another trip to the hardware store or the tool crib or the industrial distributor for correctly sized fittings.
If it is air hose you are getting fittings for, you need to know the air hose I.D. to get fittings that are sized correctly for that hose.
Air Compressor Hose Types
When you buy a low cost DIY type compressor, it will often come bundled with a low cost, lower quality PVC air hose.
In the photo above, the hose separated from the connector within moments of me adding air to the line. Not a good quality product, at all.
Further, PVC hose gets hard when the weather cools making it quite difficult to orient or coil when it’s cooler out in the workshop.
It were me, even though it’s higher cost, I’d go with a decent quality rubber hose, similar to the one in the photo.
A rubber hose is quite flexible in all but extreme cold weather, and is abrasion resistant. Air hoses often get trod on or have things like fork trucks running over them. Do yourself a favor. Buy a better quality hose if you want it to stand up to this abuse.
Air Compressor Hose Complete With Fittings?
Unless you are buying a bulk hose off a reel, typically your air hose will come complete with male NPT fittings on both ends of the hose.
To use the hose, you will add a connector to the thread on one end, and a coupler to the thread on the other. This creates an “air extension cord” which can be used to bring air to an air tool from the compressor discharge coupler.
If you have two or more air hoses with couplers and connectors installed on them, you can connect one hose to the other, extending your air hose length almost indefinitely.
It is always better to have a longer air hose to the point of use, than it is to use a too long extension cord for the air compressor.
Pressure Drop Across Compressor Hose
Air pressure drops as it moves through a hose. The longer the hose, the greater the pressure drop. That may have issues with the air tool running properly, yet, insufficient air reaching the air tool through a long hose cannot it.
Pressure drop is a concern for your air driven equipment. It might be worth your time to have a review of how pressure drop affects your air tool use.
Power drop through a too long or too light electrical extension cord can harm an electric motor.
Better to ramp up the pressure and enlarge the air hose diameter and length to run the air tool effectively than to run a too long extension cord to the portable compressor and possibly burn out the compressor motor.
Barbed Fittings For Compressor Hose
Barbed style hose fittings will usually have a barbed profile on one side and a “quick connect” – a coupler or connector- on the other side.
The barb will be a specific fractional size, and that is the size that will correspond to the I.D. of the hose.
A specific barbed fitting will only fit a certain size of hose I.D. You would purchase a 3/8″ barb to fit inside the I.D. of a 3/8″ hose, for example.
Installing a Barbed Fittings On Compressor Hose
First you slide a gear clamp over the hose, then insert the fitting barb into the hose I.D. Some folks use a little soap to make this easier. If I find that the barb is tight, generally I just use some good ‘ol spit!
Once the barb is inside the hose, slide the gear clamp back up the hose until it’s well over the barb inserted inside the hose. Tighten securely.
On the other side of the barbed fitting could be another barb, it might be a coupler, it might be a connector, it could be a male or female thread. You acquire the barbed fitting that suits the air hose installation requirements.
A reminder that though they both are used to transport compressed air, air hose is not the same as nor is measured the same way as compressed air tubing.
Compressed Air Tube
Compressed air tube is an inexpensive and quick to install compressed air supply line for almost any compressed air using application.
On earlier pages I’ve talked about the various types of fittings for plumbing your compressed air to your tools and cylinders and other air-using applications.
Now, let’s talk a bit about the air tube that you will use these compressed air fittings on.
What’s The Difference Between Air Tube & Other Air Lines?
What’s the difference between air tube and air hose?
One difference between compressed air tubing and air hose is how the size of each is measured as mentioned above.
Sizing Air Tube For Compressed Air Lines
When Measuring Tube Size – remember TOD
The ‘T’ in TOD stands for TUBE.
The O.D. in the acronym TOD stands for outer or outside diameter.
So, you measure compressed air tube by its outer dimension, not the hole in the middle.
A 1/4″ poly tube (the compressed air industry workhorse air line) will be exactly 1/4″ on the O.D.
Want to check?
If you take a 3/8″ hose and then you take a piece of 3/8″ P.E. (polyethylene) tube, the 3/8″ P.E. tube will slide inside the 3/8″ hose perfectly.
The same for 1/4″ tube into 1/4″ hose, 1/2″ tube into 1/2″ hose, etc.
Air tube applications
The vast majority of air lines used in industry are polyethylene or polyurethane tube.
Polyethylene is the most common as it is least expensive, easily obtained, usually is purchased in 100 foot rolls, is easily cut, and quickly attached to an instant type fitting.
If you are contemplating doing a lot of compressed air plumbing, talk to your supplier. You can purchases compressed air tube in 1000′ plus rolls if you need that much.
Air Tube For Tools?
I would not normally hard poly air tube to supply an air tool. The fittings used for poly tube do not lend themselves to any kind of sideloading with a hard or rigid tube.
An air tool is in constant motion, and in moving an air tool to do work, you would be sideloading the tube-to-fitting connection all the time. It might not be too long before the connection failed or started to leak.
Hard poly tube does not take to bending in a too tight coil. The right poly tube for an air tool is the “coil hose” type which is designed to stretch as the tool is being used, and have fittings suitable for the side loading using an air tool commonly imparts to the connection.
As I mentioned earlier, you normally use poly tube with instant type fittings, though sometimes mini-barbed type fittings are used as well.
The mini-barb is just as it sounds. One side has a barb that is sized to fit inside the tube. The other side has a fitting to connect to the boss. When using a mini-barb on tubing, typically hose clamps are not used. The “sticktion” inside from barb to tube is normally sufficient to keep the barb inside the tubing.
The instant fitting, into which you insert a square-cut end of poly tube, has some type of “O” rings inside it. The “O” ring seals on the outside of the tube to render the tube-to-fitting connection air tight.
This is why an accurate O.D. is critical for tube. Once I blamed a vendor for a batch of fittings that I thought were out of specification. Further investigation revealed that the whole lot of poly tube was undersized by a couple of thousandths of an inch. That was enough to allow continuous leaking in the tube-fo-fitting connection, and even allowed “blow off” of the tube from the fitting periodically.
Inside the tube orifice of the instant fitting there will also be a ring with teeth, a collet. When the tube is inserted, these teeth penetrate the surface of the tube lightly to hold the tube in the fitting.
When compressed air is introduced to the poly line, it expands the poly tube slightly, and the teeth grip even harder preventing air line blow out.
The use of an instant fitting then requires a certain surface hardness of the tube to work properly.
Air line tubing that is quite soft or stretches easily may be better installed with a fitting specifically for them.
Since with softer tube the tube O.D. will actually lessen as the tube is stretched for the application, or in dynamic equipment, the stretching may reduce the O.D. of the tube sufficiently for blow off to happen.
Tube To Fitting
Since you measure the tube on the O.D. then the mating connecting hole on the fitting must be the same size as the tube.
A1/4″ tube will have an actual 1/4″ mating size hole in the fitting.
Over recent years, the “instant” style fitting has become the predominant style of fitting to connect air lines in the 10-32 through the 1/2″ tube size.