Hydraulic cylinders operating in demanding conditions are vulnerable to a range of failures. The most common sign of damage is a leak, typically caused by seal failure—which itself may stem from something as simple as a scratch on the rod. That’s why installing seals correctly is critical to preventing leaks.
The seal’s job is to keep hydraulic oil inside the cylinder and in the correct chamber. A leak is often due to wear or failure of the piston seal, allowing oil to pass through to the wrong part of the cylinder.
Seal damage is the most common reason for both internal and external cylinder leaks. Below is a breakdown of the most frequent causes behind these issues.
Internal vs. External Leaks
Internal leak: The damage occurs inside the cylinder with no visible oil escaping. Instead, the cylinder “creeps” or sinks under load because it can no longer hold pressure. These leaks are hard to detect without regular inspections and often go unnoticed until performance drops.
External leak: Oil visibly leaks out of the cylinder. If there’s a longitudinal scratch on the rod, it can cut into the seal every time it moves over that spot, quickly causing a leak. If there’s a crosswise scratch, the seal wears more evenly, but the damage can still result in a leak that may not be noticed right away.
The most common causes of hydraulic cylinder leaks:
1. Dirt and contaminants in the cylinder
Dirt and other contaminants inside the cylinder wear down the seals, which often leads to internal leaks. When the seals wear out enough and metal surfaces start to make contact, the cylinder tube and piston become scratched.
Contaminants usually enter the cylinder during hose or valve replacement, or via dirty hydraulic oil. That’s why it’s important to avoid storing hoses and fittings without protection and to ensure surfaces are thoroughly cleaned. It’s also a good idea to replace the system’s filters regularly, as they affect oil cleanliness.
2. Neglecting maintenance
Regular maintenance of hydraulic cylinders is essential to prevent leaks and damage. During servicing, the seals should always be replaced. Old seals can easily be damaged during disassembly or even when opening the cylinder. It’s also crucial to inspect the seal surfaces for scratches or corrosion. The cost of new seals is small compared to the cost of removing and servicing the cylinder—especially if reused seals fail shortly afterward.
3. Dents and impacts
In demanding environments, bumps and knocks are inevitable. Physical damage to the cylinder is a major cause of leaks. A common issue is the bucket or grapple of a machine striking the cylinder rod or tube during lifting or rotation. For this reason, it’s important to follow operating guidelines and take care to ensure nothing sharp hits the cylinder rod during use.
