DOs and DON'Ts in Hydraulic Hose Fitting Repair

Written by Baneet Grover | 290/10/2023

Hydraulic hose fittings are integral to hydraulic systems, connecting hoses to cylinders, pipes, valves, pumps, actuators and joining hoses together. Selecting and installing the correct components allows the system to be airtight, free from leaks and maintain system integrity.

Leaking hydraulic fluid can be the cause of system failures and negative environmental impacts. System downtime due to leaks is very costly. Across the globe, more than 370 million litres of hydraulic fluid leaks into the environment each year.

It's not uncommon for hydraulic fittings to be the source of system leaks. Leaks can come from improper fitting selection, installation, cracks, missing or damaged O-rings and many other causes. Repairing a fitting is not always as simple as replacing it. It's first important to identify why the leak is occurring. Was the fitting improperly torqued, is it leaking from a bad O-ring, has dirt entered the threads, is it cracked, or is the source of the leak from somewhere else entirely? There are a number of ways fittings can leak and there are some basic steps for determining the problem and fixing it, as well as things NOT to do.

What NOT TO DO when fixing hydraulic fitting leaks

Safety first: Don't stick your face and hands near the leak without proper protection. Use protective gear such as a faceguard or goggles, gloves and be sure your arms are protected. Hydraulic fluid can be extremely hot, often over 82 degrees Celsius, and can discharge from the system at very high pressure. Extremely hot fluid discharging at a high velocity can produce severe burns known as hydraulic injection which can be very dangerous. What starts out as feeling like a bad bee sting can rapidly get into the blood stream and even lead to amputation.

Illustrating a prime example, a worker was inspecting a suspected fitting leak in an enclosed area of the plant without depressurizing the system. He attempted to loosen the fitting, which when it became loose enough it blew free and the hose flailed back and forth against the walls of the enclosed space literally whipping him to death.

Identify the actual source: The drip point is not always the leak point, so be sure the leak is coming from the fitting and not somewhere else such as the hose. It is sometimes difficult to identify the source of a leak. Like any liquid, hydraulic fluid follows gravity. It's like a leaking roof. You may have a water spot on your ceiling that started from a leak two metres up your roof. In the same respect, hydraulic fluid can leak from another fitting connection at a valve two metres up the hydraulic hose but start dripping from a fitting lower down the line.
Don't just retighten the fitting. This can cause threads to strip or crack. Overtightening a hydraulic fitting is a very common cause of leaks and can also make an existing leak even worse. Instead, be sure the system has been depressurized and disassemble the fitting. Check for debris, cracks, damaged O-rings or anything that can indicate the fitting is the cause of the leak. Cracked fittings or stripped threads are a sure sign the fitting is not repairable and should be replaced. Don't just use a thread sealant hoping that will fix the problem.
Do not just ignore the leak. In some online forums people ask if a leaking fitting will take care of itself. No! What may start off as a minor leak will usually grow into significant, costly issues and even personal injury.

What TO DO when fixing hydraulic fitting leaks

Let's face it, you really shouldn't try to repair a fitting that's been cracked, or the threads are stripped. Instead, they should be replaced if it's the cause of a leak. However, in some cases they can be repaired or reinstalled.

If the leaky fitting is an O-ring face seal or O-ring boss, after depressurizing the system, carefully disassemble the connection and check if the O-ring is still in good condition. If it's cracked, misaligned, dried out or damaged in any way, it should be replaced. First, make sure you're using the correct O-ring size and material type, and ensuring it's properly lubricated. The proper lubrication of O-rings is imperative, as it will reduce surface friction to prevent cracking, pinching or abrasion during installation and while in service.

If your leaking fitting is an O-ring boss or face seal and the O-ring is damaged, simply make sure the threads are still in good shape, clean and free from debris and replace the O-ring. This is a common situation where the fitting "can be fixed".

The most popular non-O-ring hydraulic reusable fitting in the UK is the BSP straight reusable female and male style, where the male fitting has a 60-degree cone seat thread. These reusable fittings are fastened to a compatible hydraulic hose using a wrench instead of crimping.

In some instances, such as with NPT or JIC fittings, if the threads have only minor nicks, they might be able to be repaired with a crosscut and depth proportional thread file or triangle needle file. But you need to be sure the file will not skip or jump out of fine pitches. Plus, keep in mind removing and retightening fittings can further strip the threads, resulting in a new hydraulic fluid leak path. Though repairing threads in this manner is sometimes successful, one runs the danger of removing too much material, making the thread out of alignment, or causing other damage. That being said, we caution and do not necessarily recommend attempting to "fix" threads.

If you encounter leaking NPT or JIC style fittings, it's important to know their intended design is to be leak tight when initially installed. They are not designed to be removed and reinstalled because the threads might be stripped during reinstallation or retightening, which will cause leaks and insufficient connection. Instead, if NPT or JIC fittings are leaking or otherwise damaged they should be replaced.

A Short Conclusion

If you have a leak, be sure to depressurize the system before diagnosing the problem. If the cause is an O-ring style fitting, and the threads are in good shape, properly lubricate and replace the O-ring before reinstalling. If the fitting is NPT or JIC you should probably replace it. If the connection will accept a BSP straight reusable female and male style - go for it!

Just be sure not to mix fittings from different manufacturers or use a fitting that looks "close enough" ... and NEVER over torque when installing. It's like trying to fit a square peg into a round hole- you'd just be "cutting corners".

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