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.
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.
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.
Sudden changes in volume flow or quick valve switching can cause pressure spikes that favor the compression of trapped air bubbles.
Pressure drops that form vapor bubbles which later collapse also create conditions similar to the diesel effect and can further intensify it.
High temperatures cause seals to lose elasticity, harden, or partially burn, leading to leaks and further malfunctions.
Valves, pumps, and other metallic components can be mechanically damaged or eroded by temperature peaks and explosive pressure rises.
The oil ages faster, loses its lubricating properties, and can be contaminated by residues such as soot particles.
The effect often goes unnoticed until visible failures occur. However, there are some signs to watch for:
A dark or black coloration may indicate combustion residues.
Knocking or banging sounds during operation indicate micro-explosions in the system.
Reduced efficiency or irregular actuator movements may indicate internal damage in the system.
To avoid the diesel effect, targeted measures in maintenance, design, and operation should be considered:
The system should be fully vented of trapped air after maintenance or commissioning.
A sufficiently high suction pressure and streamlined piping can help prevent the formation of vapor bubbles.
Seals and other components should be temperature-resistant and suitable for hydraulic operation.
Temperature and pressure sensors can detect changes early and enable targeted intervention before damage occurs.
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.