Couplers and Connectors

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Couplers and connectors are to compressed air and air compressor plumbing, what a wall plug and wall socket are to electricity.

To further that metaphor, the wall socket performs a similar function for electricity as the coupler does for compressed air. Both require something to be plugged into them for flow to take place.

The cord plug performs a similar function for electricity as the compressed air connector does for the flow of compressed air. By inserting them into the appropriate receptacle, flow can take place.

Like their electrical counterparts, the couplers and connectors you will acquire for plumbing your compressor, air hose and air tools have certain standards. Not paying attention to them may create problems, not as serious as trying to plug a 120 volt plug into a 220 volt socket for sure, but problems with air leaks, poor air flow and so on.

Compressed Air Couplers

Air compressor discharge coupler

Think of the compressed air coupler as the “cup” into which you “pour” the connector. That will help you remember which of the dynamic duo – the couplers and connectors – is which.

A discharge coupler, one of which is shown in the photo,  is the device at the end of the pipe from the air tank on your air compressor.

The discharge coupler keeps the air pressure in the tank until you need to use it. It can do this because most couplers are “checked”. This means that the air coupler has an internal one-way valve that could be spring, air-pressure or both, forced closed to stop the compressed air from flowing through it.

You will normally see a compressed air coupler on one end of each air line as well as on the discharge from your air compressor. The air line coupler will be checked as well.

Compressed Air Connectors

Compressed air connector

The compressed air connector is the other half of the compressed air connection team.

When an air connector is inserted into a mating discharge coupler on the air compressor, the connector unseats the coupler’s internal check valve. This allows the compressed air to flow from the compressor tank, through the discharge coupler, through the connector, and into whatever the connector is attached to.

Usually the connector is attached to an air hose. By inserting the connector into the discharge coupler, air flows into the air hose.

At the other end of the air hose there is typically another compressed air coupling. This stops the air from flowing out of the air hose to atmosphere, as this coupling will be checked too.

Couplers and Connectors Make Air Extension Cords

Compressed air is power. Just like you would use an extension cord to conduct electrical power over a longer distance, air hoses provide the same function. If we use the electrical model for comparisons sake, the air connector would emulate the plug on the electrical extension cord, and the coupler would emulate the socket. If there is nothing plugged into the socket on the extension cord, power does not flow, even if the plug is connected to the wall socket.

Installing Couplers and Connectors

Odds are good that the discharge coupler on your air compressor is one equipped with a female thread. The end that turns onto the pipe from the tank has internal threads, and the pipe has a male thread that matches the internal thread in the coupler.

Or, less likely, your discharge coupler has a male thread – one that sticks out of the end of the coupler – and the coupler is turned into a female thread on a bushing on the compressor discharge pipe.

That covers two the most common attachment configurations for air couplers.

Air connectors also have male thread and female thread configurations, and they, too, come also with a barbed fitting.

The barbed fitting allows the barb to be inserted into an air hose, and with a gear clamp or compression clamp on the outside of the hose over the barb, the connector is firmly connected to the hose.

The air connector can come equipped with a barbed end as well, also for inserting into an air hose.

Air hose with male fitting.

Air hoses often come equipped with male threaded fittings on each end, so the connector and the coupler would need to be female threaded to be installed.

Regardless of the choice of fitting – female / male / barbed – when you wish to install a new coupler, it is necessary to ensure that the thread on the receptor end is the same as the thread on the inside or outside of the coupler or connector.

Incompatible Couplers and Connectors

Your air compressor came with a discharge coupler already installed. When you wish to use air from your compressor, you will want to plug an air connector into that coupler. Which one?

Unfortunately, there are a number of standards for couplers and connectors. If you purchase connectors for your compressor and they are not of the same standard as your coupler, they may not insert.

Or, if they insert, they may not be firmly installed, and may blow out when least expected.

If the connector isn’t correct, even if installed and locked in, it may not open the check valve all the way, thus impeding flow of compressed air to your air tool.

In the connector photo, an ARO 210 connector is shown. That style of connector may not fit your coupler. There are military specifications for some couplers and connectors, and different companies have their own designs and standards. It can be a bit confusing.

Coupler and Connector Kits

Coupler and connector kit

One solution to the confusion over which connector fits which coupler is to buy coupler and connector kits.

In the kit depicted in the image above – and looking at the contents from the left – the kit has one coupler with a female thread, one connector with a female thread, one connector with a male thread, and one bushing to allow connecting two items with female threads together.

This kit contains couplers and connectors with an “M” style configuration, as can be noted at the top of the package. This means that as long as you acquire couplers and connectors that have this “M” style designation, they will work together, regardless of where you acquire them.

Other coupler and connectors kits may contain just one coupler and multiple connectors, since you will likely use more connectors than couplers, so that’s why some kits have only one coupler but many mating connectors.

Using your couplers and connectors

If you are not familiar with how the coupler and connector works, and particularly when you decouple one of them, be prepared for a  blast of air from the connector.

Depending on what the connector is threaded into, that blast of air might be just a bit, or if it were a large air cylinder or long hose, that blast of air can be quite long and violent. When you decouple  a coupler connector, keep the connection away from your face, and hold firmly to both parts until the pent up compressed air has dissipated to atmosphere.

Coupler and connector operation

Item one on the sketch is the coupler, and it is equipped with a knurled ring. Typically something that comes equipped with a knurled part is meant to be manipulated by hand.

To connect the connector (item two) to the coupler, you need only to insert the probe into the female opening on the coupler. Savvy users know that if you move the knurled ring to the left as you insert the connector, and then release the ring as the connector bottoms out,  that this makes the process easier.

Regardless, forcing the connector into the coupler should allow the two to connect.

I always push the knurled ring on the connector towards the connector after the two have mated, just to be sure they are connected securely. One or two air hose “blow offs” when you are connecting will help you understand why I do that.

To decouple, hold both sides securely and away from your face. Pull the knurled ring to the left with a couple of fingers on the left hand, and make sure you hold on particularly tight to the connector side, as compressed air will bellow out of there.

Hope this helps you better understand couplers and connectors.

You are welcome to add comments and questions using the comment box below. Only comments pertaining to couplers and connectors will be posted on this page.

By Ashley Pearce

As a passionate manufacturing and mechanical engineer, I've had my fair share of run ins with air compressors and compressed air systems. With over a decade of experience in the industry, I have both a fresh perspective and time-served hands and mind to help you with your compressor problems (along with our able community!)

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Real Noob
Real Noob
January 15, 2021 11:06 pm

Here’s a real noob question: how do I size the hose needed to connect the squeeze valve and the tire valve connector? It’s similar to gas station installations, where I always saw them assembled with hose clamps. I’d rather get it right than buy different sizes.

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Real Noob
January 16, 2021 6:41 pm

Hello RN. Sorry, I don’t know for sure what you mean by the “squeeze valve”. If you know the fitting size on the tire chuck then that size is the I.D. of the hose. In other words, if the fitting on the tire chuck is 1/4″ NPT, then you want to buy a 1/4″ or 3/8″ hose, since air hoses are measured on the I.D. Does that help at all?

April 23, 2020 11:35 am

I have a leak from the 1/4″ connector. The female part doesn’t leak, but when I fit in the male part, which is on the air line, there is an air leak. It seems the male to female is not connecting properly, and the leak is fluctuates if I wiggle the plug.
Is it just the male that’s faulty?

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Andrew
April 23, 2020 11:44 am

Hi Andrew. I’ve moved your question to a more appropriate page.

Is the condition new? Is it a new connector and old coupler, or are both new? Please have a read of this entire page and the info there may provide help. If not, please add a comment with more info. Thanks.

Reply to  Fix My Compressor Moderator
April 23, 2020 12:20 pm

I don’t think so. Because I can use the compressor (I’m a joiner and most often use it to pin glued boxes together) I’ve never bothered to question the hissing, but in the interests of efficiency, I think the problem should be cured.

Calvin Babich
Calvin Babich
March 2, 2017 1:08 pm

I am going to Germany in a few weeks to carve stone. I am trying to keep things simple by only taking my air tools instead of electric ones. Will any of the North American quick couplers connect to the German ones? If not, is there somewhere to buy adaptors? I have attached a picture of the air hose and connectors that I will have to deal with.
Thank you,
Calvin Babich

September 28, 2016 9:16 pm

Need to fill air tank with portable battery/air compressor (100 psi). Fitting at end of hose on compressor does not fit onto air tank OR any quickconnect. Any suggestions? I’m open.

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Emily
September 29, 2016 9:49 am

Not being able to see either the compressor hose fitting or the tank fitting, it is difficult to determine a specific answer. We suspect on the end of the compressor is a fitting to allow the hose to connect to a tire valve. What is on the tank we have no idea. You can acquire a tire valve – thread fitting. Google will be your best bet there. Else, it’s time to update the coupler and connector so that your compressor will quick connect to the tank. The problem with that of course is that the compressor may no longer be suited for filling tires.

March 15, 2016 11:21 am

Hi! I am looking for some help identifying the quick snap coupler on the new compressor I bought. Unfortunately the seller doesn’t know what type of fixture it is and in spite of having euro, pcl and uni hi flow snaps, none of them fit! Am hoping to be able to identify and buy the corresponding snap before resorting to a blow torch to break the loctite already in place.

Here is the coupler : (link did not work)

Thanks John

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  John
March 15, 2016 11:24 am

Hello John. Unfortunately, the link in your post to the image of your coupler did not work. As noted in the content of this page, however, in the circumstance in which you find yourself with your air compressor, it would be our typical response to remove the coupler you cannot identify, and replace it with one of the couplers that you use as your standard for your air lines and your air tools.

Cal Driver
Cal Driver
January 21, 2016 6:33 pm

Thanks so much for this post! I haven’t worked with compressed air or the assorted equipment since I was a boy and my father built a potato cannon with my brothers and I. Really brought back some great memories. Thanks for the straightforward information and for the trip down memory lane.

Tell Burke
Tell Burke
May 27, 2015 9:58 pm

Have to say; understood and learned from this presentation!

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Tell Burke
May 27, 2015 10:13 pm

Outstanding. We are glad to contribute to your fund of compressed air knowledge. 🙂