Leaking cylinders: causes, consequences and prevention

In practice, as a hydraulics expert, I speak with many customers about hydraulic cylinders. Common topics include leaks and repairs. I often hear the remark: “Oh, but the cylinder isn’t leaking, is it?” Appearances can be deceiving in high-pressure hydraulics. The scratches that cause leaks are difficult to see. Why is that?

First, the scratches are located only on the inside of the cylinder. Second, they are as thin as a hair. We are talking about micrometers here. What causes these tiny scratches? How can you recognize a leak? And, most importantly, how can you prevent scratches and leaks? I explain this in this blog.

The origin of scratches

The number one causes of scratches are sand particles (or other dirt), metal shavings (for example from welding near the cylinder), and side loading of the plunger. In any workshop, sand, metal shavings, and other debris can easily become airborne. Hydraulic cylinders are sensitive to this contamination.

A plunger that is in use — and therefore extended — is always greasy due to the hydraulic oil. If employees are not careful, airborne particles can stick to the plunger. When the plunger retracts into the cylinder housing, it carries these particles inside. This causes scratches, which will eventually lead to leakage.

Warning: contaminated hydraulic oil

Sand, metal shavings, and other debris can also enter the cylinder through the hydraulic oil. That is why it is important to handle the oil carefully. For example, do not fill the hydraulic pump with oil while a colleague is welding nearby.

Characteristic scratch patterns

When my colleagues or I open a cylinder housing, we can immediately identify what caused the scratch. The scratch patterns are very distinctive.

Sand and metal shavings create one or more deep, isolated scratches.

In the case of side loading, the plunger sits at an angle inside the cylinder housing, causing it to rub against the side. This results in a half-circle scratch pattern on one side of the housing.

Consequences for colleagues

Scratches can occur anywhere inside the cylinder, which sometimes makes them difficult to detect. For example, if scratches are located at 50% of the plunger’s stroke length, they will not be noticed if you only use 25% of the stroke.

But imagine a colleague needs the cylinder tomorrow and requires 50% of the stroke. The plunger seal will then pass over the scratches under full pressure. The cylinder will start leaking, and your colleague will no longer be able to use it. That is why it is important to have cylinders periodically tested with a dynamic test. In another blog, I explain the importance of dynamic testing.

Using leaking cylinders

Nevertheless, it often happens that employees continue using leaking cylinders. I sometimes hear them say: “As long as my cylinder doesn’t leak faster than I can top up the oil, I’m fine with it.” I have even seen customers reassemble rejected cylinders that we returned to them.

This decision is often made by employees who do not use the cylinders themselves in practice. I find this the worst part, because it can be dangerous for colleagues. A leaking cylinder can cause an oil injection injury. This is something you absolutely want to prevent.

Motivations

Companies often have their own reasons for continuing to use rejected cylinders. It saves money. A new cylinder can easily cost more than €1,000. If you have just received several large invoices, new cylinders are expensive. And if an urgent job needs to be completed, there may be time pressure. You cannot wait for a repair or the delivery of new cylinders.

However, if companies continue to use rejected cylinders for these reasons, they are taking a significant risk. My urgent advice: work safely — or don’t work at all.

Recognizing a leak

To avoid this risk, it is important to discard leaking cylinders. But how can you tell if a cylinder is leaking?

First, you may notice a pool of oil around the cylinder when you take it out of storage. That is already a sign that something is wrong. This check can easily be included in your user inspection.

In addition, a leak becomes visible during operation: you pump oil into the cylinder, but the pressure does not build up. Or the plunger fails to extend.

Prevention is better than cure

Ideally, you want to prevent leaks altogether. You can do this by placing the cylinder on a stable surface to prevent side loading of the plunger. Also ensure a clean working environment where no one is welding nearby. This prevents sand, metal shavings, or other debris from entering the cylinder or the hydraulic oil. Proper maintenance is also essential to delay cylinder failure as long as possible.

Safe working with hydraulics

Handling scratches and leaks responsibly — and preventing them — are key principles for working safely with hydraulics. The foundation of this is simply using your common sense (“BRAIN”).

Mennens and our hydraulic partner Holmatro make it easier for you to work safely with hydraulics, for example through inspection, certification, and maintenance services.

Want to know more? Contact a Mennens branch near you.