Leaking Ports? Troubleshooting for SAE J1926 and ISO 6149 Ports

Troubleshoot leaking ports with these steps from Parker.Wondering why your existing SAE J1926/ISO11926 or ISO 6149 ports are leaking? We receive this question quite a bit. It’s important to know what to investigate when looking for the problem. In this post we will address some of the questions you should think about while you are troubleshooting this issue. Then we will address the steps, potential problems and a few possible resolutions. Please refer to our 10 Things Not to Do When Your Hydraulic Fitting Leaks post to ensure you are safely checking your leaks.

Once you depressurize and lock-out your system, there are two important aspects to consider when troubleshooting your port:

  • First, check the internal threads (also called female) of the port. Is it in good working order or is it damaged?   
  • Second, check to see if the fitting is assembled properly.  


Inspection of the port  

Inspect the sealing surface for scratchesThere are a few key items to look at on the port to ensure proper sealing. The first key area to look at is the O-ring sealing surface. This is the counterbored or chamfered area shown in Figure 1. It is very important to ensure there are no scratches on this sealing surface. You may notice concentric or circular scratches on this surface. Concentric scratches are not usually an issue unless they are oblong and/or deep. A perpendicular scratch, on the other hand, will prevent the O-ring from making an effective seal, resulting in a leak path. If your port has a scratch on it in this area that is continually causing a leak, unfortunately your only path forward may be to get a new port.   



Inspect the leading edge for sharp edgesIt is also important to inspect the edge leading in to the counterbore. We have seen instances, where this area is too sharp. When installing the fitting, this sharp edge can cut or pinch the O-ring. In these instances, we have seen success by utilizing lubricant on the O-ring and installing the fitting slowly. This process helps prevent damage to the O-ring. 





A further dive into proper assembly 

Proper assembly is critical, O-ring boss fittings need to be assembled using the torque method. Here are the links to assembly instructions and videos for: Inspect that the fitting is properly seated against the face of the port.Proper Assembly Steps for Parallel Thread Adjustable Style Port End Fittings  and Non-Adjustable Parallel thread Port End Assembly Instructions for Hydraulic Fittings. However, it is important to know that once the fitting is torqued, you are not done. 

After the torque step, to ensure a proper seal, you will need to check that the fitting is properly seated against the face of the port. This can be seen in Figure 3. Make sure that the flat surfaces are in complete contact. If there is even a small gap, this can lead to future issues as the O-ring will likely extrude through this opening during prolonged system pressurization. This extrusion will create a leak path. 



For proper seating, there are two things that we typically see that limit these surfaces from being in contact:  

  1. Port threads being manufactured incorrectly, specifically that the threads were not cut deep enough into the port. There will be another post on this topic coming soon. 
  2. Fittings not fully seating into the port. In this scenario there is something interfering with the fitting, such as another component.

If you find yourself continually replacing an O-ring or you have a port that seems to be leaking for no apparent reason, check to see if the components are seated. An improper seat may not be obvious, so inspect closely. The goal is a proper assembly. 

If these surfaces are not in contact after full torque is achieved, remove the fitting to inspect the port and fitting combination. Check the full thread depth of the internal threaded (female) port as well as the stud length of the external threads (male) on the fitting. Ensure that the internal port depth is longer than the port stud length. 


When it comes to port sealing, there are usually not easy solutions to leaks. While the solution may not be easy, investigating what may be going wrong is not as difficult as you may think. If your port is leaking, it’s best to check the internal (female) port and look for a proper seat. With either of these, the outlook is not good, but at least you have an answer to your troubleshooting question and know what you need to do to fix the leak. 

Refer to our Tube Fittings Division Frequently Asked Questions page,, for a wealth of information and resources. 

If you have any questions or comments, please post them, and we will respond if warranted. To talk to our techConnect engineer team directly, they can be reached at Parker Tube Fittings Division, 614.279.7070. See Parker Tube Fittings Division's full line of tube fittings and hose adapters

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Emily Alexander, senior design engineer, Parker Tube Fittings Division


Contributed by Emily Alexander, senior design engineer at Parker Tube Fittings Division and Nathan Green, Applications Engineer Team Leader at Parker Tube Fittings Division




Nathan Green, Applications Engineer Team Leader, Parker Tube Fittings Division







Additional related content about hydraulic tube, hose and port fitting connections:

How Many Times Can I Reassemble a Hydraulic Fitting?

Metric Ports: Which Fitting Goes with Which Metric Port?

10 Things Not to Do When Your Hydraulic Fitting Leaks

Four Easy Steps to Identify Hydraulic Threads

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