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I recently purchased an air compressor. When I turn it on without a hose attached, it seems to work fine. It gets up to 140 PSI and shuts off the motor.

As soon as I attach the hose, I can't get it above 60 PSI. I can hear air leaking out both at the quick connect coupling to the air compressor and at the other end where I have an attachment screwed on the hose to fill car tires.

This is similar to the connection on the air compressor (except that the female end is permanently attached to the compressor such that I can't unscrew it): Quick connect air hose

I assume that Teflon tape on the threads would help the screw on connectors, but I'm at a loss as to how to make the quick connect couplers less leaky.

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If the tank gets to 140 and you get 60 at the hose your regulator may be bad. Also I've never seem a quick connect permanently attached to a compressor before, you sure it's not just tight? –  Jason Jan 15 at 20:25
    
When the hose is connected both the tank and the regulated guages only get to 60 PSI. With no hose, both get to 140. I'll double check the quick connect on the compressor to see if it can unscrew. –  Stephen Ostermiller Jan 15 at 20:46
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2 Answers 2

up vote 5 down vote accepted

You are correct that it is a good idea to use teflon tape on the threaded fittings, however no sealant is required or advised on the quick-connect part itself. These are designed to seal using internal o-rings.

There are multiple types of quick-connect air line fittings that at first glance appear similar, but are not necessarily compatible. It is very likely that you have connected two incompatible types, resulting in a leak. This is very common.

The two "main" types are often referred to as "automotive" and "industrial", though each can have sub-types that are typically letter designations, e.g. Industrial can be M, H or G. There's also a type called ARO, and one called Lincoln, but these are somewhat less common (at least in the US consumer market).

air fittings

(image from Legacy Manufacturing)

The documentation for your air compressor may specify exactly which type of fitting you have. Otherwise head to the local big box store with your male coupling that leaks, and look for a similar-while-slightly-different male coupler to try.

Legacy manufacturing has published a very informative guide on the evolution of the various types of quick-connect fittings that lists the common types in use, with some images of each.

Milton Industries has also published a document that may help identify the type of plug you have, though their letter designations may not exactly match those of other manufactuers.

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I have found over the years that the amount of air leakage is proportional to the cost. The cheaper the connectors the more they leak. Be especially leery of the cast "white metal" ones sold at discount stores. –  mikes Jan 15 at 22:55
    
The Teflon tape did wonders for the threaded connections. I don't have any leaks now. –  Stephen Ostermiller Jan 17 at 18:49
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Placing an O-ring inside the socket will stop the leaking between the end and the quick connect. This will also allow you to use an industrial (type D) end with an automotive (type C) Quick Connect socket. It has worked for me many times in a pinch.

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