Troubleshooting Fluid System Connection Leaks

Find the origin of your fluid system connection leak and determine the probable causes.Leaks can cause a multitude of issues both big and small. At a minimum, leaks cause a system to perform below its capacity which may lead to issues in rate of production or premature wear on the system. Leaks can also mean needing to stop production to perform an immediate fix and, really, everything in-between those things. The issues with a system leak can be far-reaching and costly. You know you need to get it fixed as fast as possible, but where do you start? This is a question we are asked quite frequently. 


The right path to finding and fixing a leak

This post will outline some common areas to get you on the right path towards finding and fixing a leak.The first section will help you locate the source of the leak. After the source is found, use the second section as a guide to further analyze what is going on. This is the first post in a series and is meant to be a quick reference. Later posts will go into more detail on each probable cause and give further tips on corrective actions. It may be helpful to review our post: 10 Things Not to Do When Your Hydraulic Fitting Leaks before starting your search. 

With most leaks, the steps to resolve it are the same. Approach the problem fresh leaving any assumptions at the door, because the true issue may surprise you. To start, below are the three steps that will be outlined.  

  • Detect the origin of the leak 

  • Narrow down a probable cause 

  • Where possible, resolve the issue 


Detecting the origin of a connection leak 

The origin of a connection leak is not always obvious. The tube, hose, and fitting are your best witnesses for determining the source. Keep in mind though, oil can run down tubes or hoses and pool in an area far away from where the actual leak is.  

Before getting too close to the system, be sure to use correct safety measures, and shut down and lockout the system. Once the system is locked out it may be helpful to clean off the system to identify the origin. You may find it necessary to turn the system back on and watch the entire assembly to try to pinpoint where the leak starts. Again, use proper safety procedures when watching for the leak, and don’t get too close or don’t touch anything.  

For hydraulic fluid applications, if you can’t spot the leak using the method above, you may be able to detect the leak with a special fluorescent dye. If your system allows it, add the dye to the fluid in the reservoir. Then using an Ultraviolet light, you should be able to detect the source of the leak. 

In pneumatic applications, it can be even more difficult to pinpoint the origin of the leak. Specialized equipment exists for detecting gas leakages. However, in some applications, it can be helpful to brush a special soapy solution onto your suspected connection and then watch for bubbles to appear. 

We cannot emphasize this enough, use proper safety procedures when troubleshooting your system. Never assume something is safe when dealing with high-pressure systems. They look calm on the outside but are incredibly dangerous under pressure. If you are not sure what the proper safety procedures are, ask someone. Ideally, any work or inspection should be done with a depressurized, powered-down, and locked out system. If you find that you need to have the system on in order to narrow down the leak origin, please do so with extreme caution. 

Leak problems and probable causes 

Once the origin of the leak has been located, you can better understand what might be causing it. Below you will find five common leak locations along with a list of what might be the cause. This list of problems and causes is not all-inclusive, but it is a great place to start. You can also download a guide of these leak problems and probable causes to keep handy.

Causes of connection leaks from the port end.
1)  Leakage from the port end as shown in Figure 1. The probable causes for a leak in this area: 

  • Damaged or missing O-ring/seal (on fittings/adapters using O-rings/seals) 

  • Damaged fitting 

  • Damaged port 

  • Inadequate torque/improper assembly 

  • Loose washer (on adjustable fittings) 

  • Pipe (taper) threads (more explanation to come on this in a later post because pipe threads can have unique problems) 

Causes of connection leaks from the front or back of the nut.

2)  Leakage from the back and/or front of the nut as shown in Figure 2. The probable causes for a leak in this area: 

  • Inadequate torque 

  • Misalignment of fitting and tube 

  • Missing O-ring/seal (on fittings/adapters using O-rings) 

  • Damaged O-ring /seal (on fittings/adapters using O-rings) 

  • Braze overflow on sealing surface (on connections that have brazed connection) 

  • Damaged fitting 


Causes of connection leaks from braze joints.3)  Leakage from the braze joint as shown in Figure 3. This figure is showing a braze sleeve used on an O-ring Face Seal (ORFS) fitting, but the causes listed below apply to any type of brazing joint. The probable causes for a leak in this area: 

  • Incorrect/Inadequate braze alloy 

  • Too little heat during brazing 

  • Too much heat during brazing 

  • Inadequate/improper cleaning 

  • Improper joint clearance 

  • Inadequate/improper flux 


Causes of a circumferential tube crack4)  Circumferential tube crack as shown in Figure 4. The probable causes for a leak in this area: 

  • Excessive system vibration 

  • Inadequate/improper clamping of tube 

  • Tube line misalignment 

  • Improper routing of lines 


Causes of a longitudinal tube crack
5)  Longitudinal tube crack as shown in Figure 5. The probable causes for a leak in this area: 

  • Poor quality welded tube 

  • Excessive cyclic pressure 

  • Tube wall too thin 



There is usually not a quick answer to the question: “Why is my fluid connection leaking?” To answer this question, you always need to start further upstream. Find out the “why is this happening?” before you try to answer the “how do I fix it?” in order to ensure it doesn’t happen again. 

To review, use these steps to get you down the right path: 

  • Detect the origin of the leak 

  • Narrow down what could be causing a leak from the origin you found 

  • Where possible, resolve the issue 

These steps may seem implied, but when you’re in a pinch and something needs to be fixed immediately, there is often a temptation to assume you know your problem. The reality is you only know step one.  If only the symptom is fixed, you may find your system and yourself in the same boat shortly after the first repair. For example, if you assume your problem is a bad O-ring and replace it. Afterward, you may find that further investigation would have revealed the true cause of the leak was incorrect assembly. That “bad O-ring" that was replaced was just a symptom, not the true cause.   

Now that we’ve covered some ground on what key areas to look at and the possible causes, the next posts in this series will detail what some possible solutions or next steps are for fixing the leak. Listen to what your leak is telling you, it is often pointing right at what you need to fix. 

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, Parker Tube Fittings Division, and Burleigh Bailey, retired senior project engineer of Parker Tube Fittings Division.




Burleigh Bailey, retired senior project engineer at Parker Tube Fittings Division,






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

A Dollars and Sense Approach to Preventing Hydraulic Oil Leaks

How Many Times Can I Reassemble a Hydraulic Fitting?

Metric Ports: Which Fitting Goes With Which Metric Port?

Leaking Ports? Troubleshooting for SAE J1926 and ISO 6149 Ports

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