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Repairing leaks part 2 - Repairing a port end
In our first blog post in the article series ”Troubleshooting and repairing leaks in hydraulic and pneumatic systems”, we gave an overview of how to locate faults when a leak has occurred in an application, and we went through methods for narrowing down the visible causes of the leak. Now the question is simply what to do to remedy the problem?
In this article we will take a deeper look at what leakage from port ends means, and what can be done about it. When it comes to leaks, you must never assume anything. Time is therefore well spent investigating all the possible causes before the leak is fixed.
In our first article we outlined the likely causes of a leak coming from a port end.
- Damaged or missing O-ring/seal. (on fittings/adapters that have an O-ring/seal)
- Damaged fitting
- Damaged port
- Incorrect torque / incorrect assembly
- Loose or deformed washer
- Pipe thread
The problem has now been narrowed down to the leak occurring at a port end connection. The task now is to work out which of the above causes is responsible for the leak. Be sure to investigate all the likely causes, as in some cases there may be more than one problem. To get the most accurate picture of the leak, it can be a good idea to disassemble the connections where the leak has occurred. Always remember to shut the system down and observe the safety precautions.
Damaged or missing O-ring or seal.
A damaged O-ring or seal can look many different ways. Is the O-ring or seal missing altogether? If it is there, is it frayed? Does it look pinched or deformed? Remember to look closely, as the damage can be very small. See image 1 for examples of damaged O-rings.
If the O-ring is damaged, it must be replaced with a new one. When installing the new O-ring, it is important to take care during the replacement process to avoid damaging the thread. We recommend using a small amount of lubricant to help the O-ring into place.
Image 1
If the O-ring is missing, it has most likely been forgotten during assembly. The O-ring may have fallen out during shipping or assembly, which means it has not been an obvious fault. Image 2 shows two examples where it is obvious that an O-ring is missing. On one fitting you can clearly see that the groove where the O-ring should sit is empty. The other fitting also clearly shows that the O-ring is missing against the sealing face. Always contact your supplier if you are unsure whether an O-ring is missing or not.
Image 2
When a new O-ring is to be installed, it is important to find the right replacement. Just because an O-ring fits does not always mean it is the best fit. There are three factors that are important to be aware of when finding a new O-ring: size, material and hardness (durometer).
It is important to choose the right size, as both an O-ring that is too large and one that is too small will not seal optimally. When choosing the right material, it is important to select a material that can withstand the media running in the application, as well as the temperature present in the application. When it comes to hardness (measured in shore durometer), softer O-rings tend to be damaged or extruded out of the fitting. In most cases, shore 90 is suitable. If you are unsure which O-ring to use, we are always ready to help you.
You can search all of Hymatik's O-rings here
Damaged fitting
What does a damaged fitting look like? Some damage is easy to spot, such as large cracks or scratches.
Small damage can often be hard to spot and is therefore often overlooked. Put on your critical glasses and examine the fitting closely. Pay particular attention to the sealing face and the thread. Even the tiniest scratch in the right place can prevent the O-ring or seal from sealing.
If there is damage to the sealing surface or the thread, it may be necessary to replace the fitting. See image 3 for examples of sealing faces that require special attention.
Image 3
If the fitting is damaged, it must of course be replaced with a new one of good quality, as damage to sealing surfaces and threads cannot be repaired. Fittings can often pick up nicks or scratches during handling or storage if they are not properly protected. You should always check the fitting before it is installed in an assembly, to make sure it has not been damaged during transport or storage. Also be careful that the fitting is not damaged during assembly. To avoid damage to fittings, it is a good idea to store them with caps on.
Damaged port
Identifying damage on port ends is very much the same as with a damaged fitting. Look for scratches on the sealing surface and on the thread.
If the port is damaged, it can either be replaced or reworked. Reworking is, however, a process for skilled professionals and should not be carried out without the relevant education/training. As with the inspection of a fitting, it is important to put on a critical eye when the sealing surface of the port is to be examined for nicks and scratches.
(If the port end has a pipe thread, read the section further down).
Incorrect assembly
A correct assembly is crucial for a leak-free connection.
Below is a list of the assembly faults that may have occurred during make-up:
- The O-ring is stuck in the thread, which indicates that the O-ring was not seated correctly before installation.
- A cut O-ring, which indicates that the O-ring has been pinched during assembly.
- A damaged backup washer on an adjustable fitting, which indicates a damaged or missing O-ring, or over-tightening of the torque. (See more details in the next section).
- A leak at low pressure occurring right after installation, with no other problems present, indicates an incorrect tightening torque.
It is also important to make sure that all the components that should be on the fitting are actually there. Missing components can cause leakage. Make sure the O-ring/seal, washer and nut are where they should be, if they are supposed to be there - see picture 4.
Loose or deformed backup washer
Adjustable SAE and ISO O-ring boss (ORB) port end fittings use a backup ring to retain the O-ring under pressure. If the backup ring does not fit properly, as can be seen in picture 5, it can cause leakage or lead to O-ring extrusion during prolonged system use.
When the removed fitting is to be inspected for leakage, the backup ring should be examined more closely. Is the backup ring loose or able to move in any way? Is the washer deformed (the washer must be flat or concave, see picture 5)? Is the O-ring damaged on the side closest to the backup ring? If one of your answers is yes, then the backup ring is the cause of the leak.
Damage to an O-ring fitted on an adjustable fitting can be due to a loose or deformed backup ring. This damage looks as if someone has taken a bite out of the O-ring. The damage may also be a cut on the top side of the O-ring, which can be caused by the washer. In addition, a deformed washer can cause the O-ring to extrude through, causing damage. To make sure this does not happen, it is important to follow the correct assembly instructions.
Guide to assembling ORFS fittings Guide to assembling 37° flare fittings
Another common problem with adjustable port ends is that the O-ring gets pinched when the nut is not in the right position. This happens because of an exposed thread beneath the nut. This causes the backup ring to deform during assembly. If this happens, the O-ring cannot seal.
When the backup ring is inspected, it must not be too loose and must sit in the position shown in picture 5. If it is loose, or not seated correctly, the fitting cannot be used. A loose backup ring can be due to various things: poor quality, previous use, over-tightening of the torque, or incorrect assembly.
Another thing that is important when inspecting the backup ring on a new or used fitting is to look at its shape. It must either be flat or have a slightly convex shape pointing towards the port end in order to seal properly. It should not have a concave shape (pointing towards the fitting). Picture 6 shows in an exaggerated way what is meant by the backup ring being convex (in reality it should not be that convex).
Picture 5
Image 6
Pipe (tapered) thread
Although pipe threads are available, they are not a popular choice. This is because pipe threads tend to leak when exposed to high pressure, temperature fluctuations, impact loads and/or high vibration levels. Leakage can therefore be due to many different causes.
Typical problems with connections using pipe-thread ports:
- Circumferential cracks at the root of the thread, often caused by high vibration or impact loading.
- The fitting works loose due to large temperature fluctuations or high vibration levels.
- Cracks in the internal thread, often caused by over-tightening.
- Leakage due to missing sealant, a fitting that has been used before or a poor threaded connection.
- Leakage due to incorrect installation.
When pipe fittings are to be inspected for possible damage, the old thread must be completely cleaned of dirt and tape residue. Once this has been done, it is possible to inspect the pipe fitting for corrosion, cracks, thread damage or other signs of damage. If you find any of these faults, the fitting must be discarded.
If the fitting is being replaced, it is important to inspect the new fitting for damage – pay particular attention to damage to the thread. To ensure a proper seal, read the manufacturer's installation instructions. Almost all pipe threads require some form of sealant in order to create a tight connection. Choose the right sealant to avoid contaminating the system.
Summary
Leakage in an application can be a costly and time-consuming affair. The cause of a leak is not always obvious, and if the wrong assumptions are made, the leak can quickly reappear. This article should make it easier to identify the cause(s) of leakage from a port end, so the damage can be repaired and does not happen again. Just remember that a leak may have several causes.
If you are experiencing leakage problems or need a part to repair your leak, you are always welcome to contact us, and we will give you our best advice and guidance.
