AN Fittings – How tight is tight?

Cobra nose with oil cooler

Nothing worse than a new AN fitting connection, spraying oil or fuel all over your new creation. But the more you tighten it, the worse the leak becomes. What to do? This article from Parker Hose outlines the correct procedures to tighten any size AN fitting

Proper Assembly Steps for 37° Flare Fittings Using the Flats Method

Properly assembling your fitting connections help to ensure that your systems install and stay leak-free. This is why we have started a series of assembly posts/videos featuring the proper assembly of the most popular tube and port ends. Today we are talking about the proper assembly steps for 37° flare fittings, which are also known as JIC fittings. Improper flaring or installation causes over half of the leakage with flared fittings. Thus, proper installation is critical for trouble-free operation.

For the 37° flare fitting, the flats method of installation is recommended because it is more forgiving than the torque method. It circumvents the effects of friction due to the differences in plating surfaces, finishes, and lubrication that can greatly influence the torque required to achieve proper joint tightness or clamping load.

Watch the video to learn the proper process for assembly of 37° flare fittings, or follow the steps outlined below.

Proper 37° flare fittings assembly and installation steps:

Step 1: Check your flared tube, if applicable. 
If connecting to a flared tube, start by verifying that the tube end is properly flared. The flare should be reasonably square and concentric with the other diameter of the tube. Ensure that it is free from rust, scratches, splits, embedded chips, and dirt, all of which can compromise the connection. For detailed instructions on proper tube end preparation, please see our blog post and video: Tube End Preparation Best Practices for Leak-Free Hydraulic Tube Fitting Connections.

Step 2: Align the flare ends and tighten.
Next, align the flared tube or hose end with the nose of the fitting. Lightly tighten the nut until you feel wrench resistance, approximately 30-inch pounds will be needed.

Step 3: Mark the nut.
It’s good practice to mark the nut position relative to the body. Using a permanent marker, make a mark on one of the flats of the nut and continue the mark to the body of the fitting.

Step 4: Tighten using recommended flats.
Now tighten the nut further using the number of flats recommended in the Assembly and Installation section of the Parker Catalog 4300.

Fitting Torque Spec chart

A flat is equivalent to one side of the hexagonal nut, or one-sixth of a turn. 

Step 5: Make a second mark on the fitting.
Once properly tightened, use a permanent marker to place a second mark on the fitting adjacent to the previously marked line on the nut. This second mark serves as a check that the connection has been tightened during final inspection and allows for an easy check to see if the nut has come loose and backed off during operation. It also provides a reference for subsequent remakes.

Tech Tip: It’s important not to force or “draw in” a tube assembly that is too short, too long, or misaligned. The misalignment places an undesirable strain on the joint leading to premature loosening/leakage. 

By following these steps, your 37° flare fitting connections will be properly installed. To help you ensure that all of your hydraulic fitting connections are installed properly, Parker Tube Fittings Division has created a series of tube and port end assembly and installation videos for the most common hydraulic fitting connections, which will be shared on over the next couple of months. You can also find detailed assembly and installation information for port end threads and tube fittings in the Assembly/Installation section of our Catalog 4300


What to do if I didn’t read this first?

Ok, you’ve over-tightened the fitting and it won’t seal. Not all is lost. If you know the brand of fitting, they can be replaced – but it isn’t recommended to mix manufacturers. The Flare side of the fitting is the same, but the hose and fitting side varies between different manufacturers.

This Parker article will give you some information on assessing the quality of your part.

How Many Times Can I Reassemble a Hydraulic Fitting?

If the flare face is scratched, maybe you can save the connection by adding a compression washer. Special shaped conical washers are available for this exact purpose.

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