Troubleshooting leaks in hydraulic and pneumatic systems

Leaks in a system can cause a range of problems, both large and small – for example the system running below its capacity, which causes problems with production speed. It can also cause very premature wear in the system, meaning the system has to be replaced much earlier than expected.

If a leak occurs, you may have to shut down the entire system in order to repair it, which can be both extensive and expensive for a company.

When the leak occurs, the problem has to be solved as quickly as possible – but where do you start?

Most leak problems follow the same approach: first and foremost you should approach the problem without any kind of assumption, because the real cause of the leak will most likely surprise you.

The right way to find and repair a leak

In this article we go through the process of troubleshooting a leak using the three steps described below:

• Find out where in the system the leak has occurred
• Determine the real cause of the leak
• If possible, solve the problem.
  
  

Find out where in the system the leak has occurred

It is not always obvious where in the system the leak has occurred. The tube, the hose and the fittings are the best witnesses when determining the source of the leak. Always remember that oil can run down tubes and hoses and end up far away from where the leak has occurred.

Before you start inspecting and getting too close to the system, make sure to use the correct safety precautions and follow the correct safety procedures, which include shutting the system down and not touching anything until this has been done. If this is not done, fatal consequences can arise both for the system and for those standing close by.

Once you have shut the system down, it can be an advantage to clean the system, as this can help make it easier to find the leak. It may be necessary to switch the system back on along the way in order to try to find the point where the leak starts – here it is again very important to follow correct safety procedure and not touch anything.

If the application is a hydraulic system and you still cannot find the leak using the method above, you may be able to identify the leak by using a special fluorescent dye. If your system allows it, you can add a dye to the fluid in the tank.

In pneumatic applications it can be much harder to locate the source of the leak. For this, special equipment is available to identify a gas leak. In some applications, however, it will be possible to brush a special soap solution onto the suspected leak point and watch for small bubbles appearing.

It cannot be stressed enough how important it is to have the safety procedures under control when a fault in a system has to be found. If you are working with a high-pressure system, for instance, you should never assume that the system is safe. A high-pressure system can look completely calm on the outside, but is extremely dangerous under pressure. If you are in doubt about what the correct safety procedures are, ask someone who knows. Ideally, any work or inspection close to the system should take place with the system switched off. If it is necessary to have the system switched on in order to identify the leak, we recommend doing so with extreme caution.

Leak problems and possible causes

Once you have found the leak, you can better understand what caused it to occur. Below we have listed five common leaks and a list of what may have caused them. The list does not cover all leak problems and causes, but it is a good place to start.

1. Leak from a port connection

The likely causes of the leak are:

• Damaged or missing O-ring/seal. (on fittings/adapters that have an O-ring/seal).
• Damaged fitting.
• Damaged port.
• Incorrect torque/incorrect assembly.
• Loose sealing washer (on adjustable fittings).
• Taper threads.
  
  
  

2. Leak before and/or after the nut

The likely causes of the leak are:

• Incorrect torque.
• Incorrect alignment between fitting and tube.
• Missing or damaged O-ring/seal (on fittings/adapters that have an O-ring/seal).
• Incorrect brazing (for fittings that require a brazed joint).
• Damaged fitting.
  
  
  

3. Leak from a brazed joint

The picture shows a braze ring used on an ORFS (O-Ring Face Seal) fitting, but the list below applies to all types of fittings that have a brazed joint. The likely causes of the leak are:

• Incorrect/insufficient brazing alloy.
• Too much or too little heat during brazing.
• Insufficient cleaning.
• Incorrect clearance between the surfaces to be brazed.
• Insufficient/incorrect flux/brazing paste.
  
  

4. Cracks across the tube (see picture 4)

The likely causes of the leak are:

• High vibration in the system.
• Insufficient/incorrect clamping of the tube.
• Incorrect/misaligned tube routing.
  
  
  

5. Cracks along the tube

• Poor quality welded tube.
• Excessive cyclic pressure.
• The wall thickness of the tube is too thin.
  
  
  

Summary

There is rarely a quick answer to the question: "Why is my application leaking?"
To answer it, you must always start with: Why is it happening? Before you move on to "how do I fix it?" to make sure it doesn't happen again.

Use this approach:

• Find out where the leak has occurred.
• Narrow down what may be causing the leak.
• If possible, fix the problem

These steps may seem obvious, but when the problem occurs and needs to be solved immediately, many are tempted to assume that they already know what the problem is. In reality, they only know step 1. If only the symptom is fixed, there is a high probability that the problem will reoccur shortly afterwards.
For example: it is assumed that the problem is caused by a faulty O-ring, which is therefore replaced with a new one. A closer inspection, however, reveals that the true cause of the leak is incorrect assembly. The "faulty" O-ring that was replaced was merely a symptom, not the true cause.

Troubleshooting and leak repair article series

Did you find this article interesting? The next blog post – 'Leak repair – Repairing a port connection part 2' is published in May and is a follow-up article describing in more detail the likely causes of a leak and the repair of a port connection.

Hymatik's Thread Identification Chart

A frequent cause of leaks in your system can be choosing the wrong thread type. If you are unsure how to identify the correct thread type and sealing method on your fittings and components, we have created a thread identification chart so you can easily and clearly determine the correct components and fittings.

Read more about our thread identification chart here!