The Diesel Effect in Hydraulic Systems: Material Damage is the Consequence

A loud cracking, a brief loss of power – and suddenly the machine stops. The cause? Invisible. The diesel effect has struck.

What sounds like a fringe phenomenon in theory can lead to costly failures in practice. In hydraulic systems, the diesel effect causes microscopically small explosions that thermally and mechanically stress components. Seals deform, valves wear out faster, and the hydraulic oil loses its function. Therefore, it is all the more important to understand the causes – and to prevent them intentionally.

How does the diesel effect occur?

The diesel effect occurs when air bubbles in the hydraulic oil are compressed under high pressure. This process often happens when air enters the system through leaky seals or during maintenance. When this air is compressed by a sudden pressure increase, the temperature in the enclosed bubbles rises rapidly. The oil droplets contained within can ignite, similar to what happens inside a diesel engine's cylinder. This process occurs within milliseconds and is not visible to the naked eye.

Typical causes during operation

Leaks and maintenance work

The most common causes of the diesel effect are leaks in the system, for example at sealing points or threaded connections. Poorly vented systems after maintenance or commissioning also carry a high risk.

Rapid pressure changes

Sudden changes in volume flow or quick valve switching can cause pressure spikes that favor the compression of trapped air bubbles.

Cavitation-like conditions

Pressure drops that form vapor bubbles which later collapse also create conditions similar to the diesel effect and can further intensify it.

Consequences for the system

Damage to seals

High temperatures cause seals to lose elasticity, harden, or partially burn, leading to leaks and further malfunctions.

Wear of components

Valves, pumps, and other metallic components can be mechanically damaged or eroded by temperature peaks and explosive pressure rises.

Degradation of hydraulic oil

The oil ages faster, loses its lubricating properties, and can be contaminated by residues such as soot particles.

Signs of the diesel effect

The effect often goes unnoticed until visible failures occur. However, there are some signs to watch for:

Discolored hydraulic oil

A dark or black coloration may indicate combustion residues.

Unusual noises

Knocking or banging sounds during operation indicate micro-explosions in the system.

Loss of performance

Reduced efficiency or irregular actuator movements may indicate internal damage in the system.

Measures to prevent

To avoid the diesel effect, targeted measures in maintenance, design, and operation should be considered:

Regular system venting

The system should be fully vented of trapped air after maintenance or commissioning.

Prevent cavitation

A sufficiently high suction pressure and streamlined piping can help prevent the formation of vapor bubbles.

Use suitable materials

Seals and other components should be temperature-resistant and suitable for hydraulic operation.

Use sensors for monitoring

Temperature and pressure sensors can detect changes early and enable targeted intervention before damage occurs.

Conclusion

The diesel effect is a often underestimated hazard in hydraulic systems. Understanding the causes and taking appropriate precautions can prevent failures, extend the lifespan of components, and increase operational safety. A combination of systematic venting, preventative maintenance, and robust component design forms the basis for safe and efficient operation.