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NO MORE LEAKS, PART 2: Fixing a Port End Connection

We're back with our second installment in our NO MORE LEAKS series to help you identify and fix your hose and fitting leaks. In our first post in the series, Troubleshooting Fluid System Connection Leaks, we gave an overview of how to troubleshoot a system that’s leaking, and the connection areas to focus on.

Now that the leak has been located and the probable causes are narrowed down, what should you do to fix it? In part 2 of the series, we’re going to take a deeper dive into what a leakage from the port end means, and what you can do about it!


When it comes to leaks, you should make no assumptions. It is worth your time to at least consider every possible cause before jumping in and fixing a leak because often, only the symptom is what is most visible, and if a fix is completed based solely on that, the true cause could be missed; this can lead to even more costly leaks and fixes in the near future.

In the last post we outlined the following probable causes for a leakage coming from a port end as the following:

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

  • Damaged fitting

  • Damaged port

  • Inadequate torque/improper assembly

  • Loose or deformed washer

  • Pipe threads

At this point, you have narrowed your leak issue to the port end connection. Now, how do you determine which of the above is the root cause? You will want to investigate all of these probable causes, because in some cases, you may have more than one problem. Since the system is already being investigated, don’t just assume that you found the root cause before eliminating every probable cause. To get the most accurate picture of the leak cause, you may find it helpful to take the connection apart where the leak is located. As always, it's imperative to use proper safety measures and be sure to lockout and power down the system. If you are not sure what safety measures are needed, ask someone for guidance. For additional reference, read our blog post 10 Things Not to Do When Your Hydraulic Fitting Leaks.

Damaged or missing O-ring or seal

There is a large range of what a damaged O-ring/seal could look like. What you are looking for is anything that looks out of the ordinary. Are there pieces missing? Is it frayed? Does the O-ring look pinched and/or deformed? Look very closely at it, as the damage might be small. Examples of damaged O-rings are in Figure 1. Again, damage may not be as obvious as what is shown, so please inspect your O-ring/seal carefully.

Figure 1. Damaged O-rings. Left shows damage from extrusion and right shows damage from installation (circled area).

With a damaged O-ring, the obvious answer is to replace it. Care should be taken when installing the new O-ring to prevent it from being damaged by the fitting threads. It is recommended to use a small amount of lubricant to guide the O-ring to the proper seat on the port end of the fitting.

Another possibility is that the O-ring is missing and was forgotten during assembly. If the O-ring fell out during shipping or assembly, it may not have been an obvious error. Two examples of where O-rings should be are: in an O-ring groove or paired with a retaining ring. If you have an O-ring groove with no O-ring in it or have a retaining ring with no O-ring, then you are missing a critical sealing feature. In figure 2, there are two examples illustrating where the O-ring is supposed to be located but is missing. If you suspect an O-ring is missing or are not sure if one is missing, check with the fitting manufacturer to see if one should have been used.

Figure 2. Examples of areas where O-ring/seal is missing

When replacing a damaged or missing O-ring, be sure to select the correct replacement. Just because an O-ring fits, does not always mean it’s the correct one for the job. Three critical items with O-rings are size, material, and durometer. For size, never assume that the O-ring is the correct size. If it’s too small or too large the O-ring won’t do its job. For O-ring material, you may need a specific material type for your application. You wouldn’t want to use material only to find out afterward that it is incompatible with your system media and/or temperature. For durometer (hardness), softer O-rings tend to get damaged or be extruded out of the fitting. In most cases, 90 durometers are needed. If you are unsure of what O-ring to use, we will will be able to point you in the right direction: ( , call 410-686-1200, or visit

Pro Tip: If you find yourself frequently replacing an O-ring, it may be that you didn't find the true cause. In some cases, a damaged O-ring is a symptom, not the cause. This is why we encourage you to investigate all of the probable causes listed at the beginning of this post, ensuring your investigation was thorough enough to find the true cause(s).

Damaged fitting

What does a damaged fitting look like? Some fitting damage is easy to spot, like a large crack or scratch. In some cases, though, minor damage may be missed or overlooked. Take a critical eye to your fitting, paying special attention to the sealing surface and the threads. Even a small scratch in the right location can prevent a seal from forming. If there is any damage to the sealing surface or threads, you may need to replace the fitting. Figure 3 points out examples of sealing surfaces where you will want to pay special attention.

Figure 3. Sealing surface location examples

If the fitting is damaged, replace it with a good quality fitting. Fittings often get nicks and scratches during handling or storage if they are not properly protected. Damage on a sealing surface or on the threads is irreversible. It is best practice to examine a fitting before assembly to ensure that no damage happened during shipping or handling. Looking at the fitting over first will prevent headaches in the future. As well, be careful when assembling fittings as damage can often occur in the process of assembly.

An important safeguard is to always keep any shipping caps and plugs on fittings until they are installed. This practice helps to prevent damage during storing and handling.

Damaged port

Spotting port damage is very similar to looking for fitting damage. You’re looking for scratches on the sealing surface or thread damage. If the port is damaged you can either replace it, or where applicable, you can try to refinish a damaged port. Refinishing, however, is a process for skilled machinists and should not be done by someone who has not been trained. Be sure to take a critical eye over the sealing surfaces of your port, as nicks and scratches on the sealing surfaces of a port can cause leaks (see the post linked to in the paragraph above for complete details on identifying port nicks and scratches).

If the port has pipe threads, make sure to read the section below addressing them specifically, as they have more issues than outlined here.

Improper assembly

Proper assembly is critical with fittings. A certain amount of torque is required to provide enough clamping load at the joint to resist the forces of internal pressure and vibration loosening. The Parker Catalog 4300 Assembly/Installation section provides the recommended torque for each thread type and size.

A few giveaways that assembly errors may have been made are:

  • O-ring jammed into threads, indicating that the O-ring was not seated properly

  • Cut O-ring, indicating the O-ring was pinched during assembly

  • Damaged backup washer on adjustable fittings, indicating damaged or missing O-ring, or over torque (see the next section for more specifics on assembly damage)

  • Leaking at low pressures right after install when no other issues are present, indicating incorrect assembly torque

Making sure that all the required components are on the fitting is also critical. Ensure you have O-rings/seals where you need O-rings/seals, washers where you need washers, and adjustable locknuts where you need adjustable locknuts. Missing components cause leaks. Figure 4 details two types of fittings with their required components called out. If you find components are missing, you will need to replace them. Reference our detailed assembly instructions in the Assembly/Installation section of the Parker Catalog 4300. A helpful ssembly instruction video is below:

Figure 4. Seal ring groove (right) and straight adjustable O-ring boss (left) shown with required components

Loose or deformed backup washer

Adjustable SAE and ISO O-ring boss (ORB) port end fittings use a backup washer for securing the O-ring under pressure. If the backup washer does not have a proper fit onto the undercut of the fitting, as shown in figure 5 (below), then this may cause a leak path or lead to O-ring extrusion during prolonged system usage.

When you are inspecting the disassembled fitting for the root cause of your leak, take a close look at the backup washer. Is the washer loose or movable in any way? Is it deformed (the washer should be flat or concave see figure 6)? Is the O-ring damaged on the side closest to the backup washer? If any of these answers were yes, then one of your leak causes is the backup washer.

O-ring damage on an adjustable fitting can have a root cause of a loose or deformed backup washer. This damage could look like a nibbling of the O-ring. It could also be a cut on the top side of the O-ring, which is most likely caused by the washer. Additionally, a deformed backup washer can lead to an O-ring making its way through the gap thus causing damage. To ensure these issues don't happen, be sure to follow proper assembly instructions when assembling or re-assembling.

Another common problem on adjustable port ends is the O-ring getting pinched when the locknut is not in the correct location. This happens due to thread exposure below the locknut. Thread exposure leads to a deformed backup washer during assembly. If this happens, an O-ring extrusion gap will open with the potential to leak.

Note: Parker’s fittings with SAE and ISO adjustable ORB port ends come standard with our Robust Port Stud, which was created to alleviate this issue during assembly.

When inspecting the backup washer, note that the washer should not be loose and should be seated in the position shown in figure 5. If the washer is loose or not properly seated, the fitting cannot be used. The backup washer needs to be tight against the fitting and preferably in the uppermost position (near the locknut threads). A loose backup washer may be an indication of a poor-quality, previously used, over torqued, or improperly assembled fitting. Remember to inspect the replacement fitting too, as these rules apply to every fitting with a backup washer, whether new or used.

Figure 5. Partial cutaway of an adjustable ORB port end showing correct placement of backup washer

Another important step when examining a back-up washer on a new or used fitting is to look at its shape. It needs to be either flat or have a slightly convex shape pointing toward the port end in order for it to properly seal. The backup washer should not have a concave shape (pointing towards the fitting), and it should not be free to move by gravity in the undercut area. We have shown an exaggerated version of what we mean by slightly convex shape in figure 6, the shape should not be quite this convex.

Figure 6. Partial cutaway of an adjustable ORB port end showing an exaggerated convex-shaped backup washer

Pipe (taper) threads

Though pipe threads are available, they are not a popular choice. Pipe threads on a whole have a very high tendency to leak when subjected to high pressures, temperature variations, shock loads, and/or excessive vibration. Leakage can be due to any number of different reasons which would need to be verified and remedied accordingly.

Typical problems in pipe threaded port connections include:

  • Circumferential crack in the root of thread, usually caused by excessive vibration or shock loads

  • Loosening of fitting, due to temperature variation or excessive vibration

  • Crack on the internal thread (especially cast material), usually due to over-tightening

  • Leakage due to lack of sealant, previously used fitting, or poor thread connection

  • Leakage due to improper installation

Pipe threads are not easy to work with and often cause headaches, so where possible they should be avoided during the design stage. While pipe fittings can be re-used, it is not recommended to do so.

When examining a pipe thread for possible damage, you will want to remove the old tape or paste. After this has been removed, look the fitting over for corrosion, cracks, thread damage, or other signs of damage. If you find any of those issues you will want to discard the fitting.

If the fitting is being replaced, be sure to inspect the new fitting for damage on the threads. Refer to the manufacturer’s assembly instructions for a proper seal. Almost all pipe threads require some form of sealant to create a seal. Care should be taken as not to contaminate the system by improperly applying the sealant.

If you must use pipe fittings, ensure correct assembly is done by reviewing our assembly instructions and video: How Tight Is Tight? Assembling Tapered Threads


Leaks cost a lot of downtime and money. With the details included in this post, you should be able to identify the root cause(s) of a port end leak, and ensure that you do not have the same issue again. Although inspecting your fittings and ports as outlined above is time-consuming, it's necessary to avoid additional system leakage, delays, and money.

If you are unsure about a leak's cause or what you should do about a leak once you find the cause, contact your fluid system experts at your local Colliflower ParkerStore. We’ve often seen the issue before and can get you pointed in the right direction. We are here to help.

Remember - subscribe now to learn more as we continue this important, time and money-saving series to receive the product expertise you need to get back to work - FAST!


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