Avoiding Dieseling in Hydraulic Cylinders: Causes and Prevention Tips

Nov 18

Dieseling, also known as "diesel effect," in hydraulic cylinders is a phenomenon that occurs when air or other gases mix with hydraulic fluid inside the cylinder and ignite, producing excessive heat and even causing potential damage to the equipment. Understanding the causes and implementing prevention strategies is crucial to maintaining safe, efficient, and durable hydraulic systems. Below you’ll find the causes of dieseling in hydraulic cylinders, its negative effects, and effective prevention methods.

What is Dieseling in Hydraulic Cylinders?

Dieseling occurs in hydraulic systems when a mixture of air and hydraulic fluid within a cylinder ignites due to compression, similar to how a diesel engine operates. The hydraulic cylinder itself essentially becomes a combustion chamber, and the rapid compression of the trapped air within the hydraulic fluid generates heat. This heat can be intense enough to ignite the oil molecules, producing micro-explosions that may compromise cylinder components, seals, and other parts of the hydraulic system.

Causes of Dieseling in Hydraulic Cylinders

Dieseling in hydraulic cylinders can occur for several reasons, often stemming from improper maintenance, incorrect system design, or operational issues. Here are the primary causes:

1. Air Entrapment in Hydraulic Fluid

One of the most common reasons for dieseling is air trapped within the hydraulic fluid. This air can enter the system through leaks in the hoses, fittings, or valves, or during the filling process. When the trapped air is compressed under high pressure, it can reach temperatures that cause the oil to ignite.

2. Sudden Cylinder Movement and High-Speed Operation

Hydraulic systems subjected to abrupt and high-speed operation can experience rapid compression of hydraulic fluid and trapped air. This compression generates heat, potentially leading to the diesel effect. In applications where hydraulic cylinders operate quickly and with high-frequency movements, the risk of dieseling increases.

3. Low-Quality Seals

Worn or low-quality seals can cause air to leak into the cylinder. Seals play a vital role in keeping the hydraulic fluid pressurized and free from contamination. When seals degrade over time, small air pockets may form in the hydraulic cylinder, allowing the diesel effect to occur.

4. Low Hydraulic Fluid Levels

When the hydraulic fluid level is too low, air can be drawn into the system, increasing the likelihood of air entrapment. This issue is more prevalent in systems that experience fluid leaks or are inadequately maintained.

5. Inappropriate Hydraulic Fluid Type

Using a hydraulic fluid that is not compatible with the operating temperatures and pressures of the system can exacerbate the potential for dieseling. Low-quality or incorrect fluids may contain impurities that can increase the chance of combustion, especially under the high temperatures generated during operation.

Effects of Dieseling on Hydraulic Cylinders

Dieseling can lead to a series of issues that reduce hydraulic system efficiency, reliability, and longevity. Some common effects include:

Damage to Seals and Components
The extreme heat generated during the diesel effect can cause seals to harden, crack, or degrade more quickly. Over time, this leads to leaks and potential breakdowns of other cylinder components.
Reduced System Efficiency
Dieseling can impair system efficiency, leading to sluggish or erratic cylinder movement. The loss in efficiency affects the system’s overall productivity and increases energy consumption.
Increased Maintenance Costs
Hydraulic systems experiencing regular dieseling may require frequent repairs or replacements, escalating maintenance costs and increasing system downtime.

Preventing Dieseling in Hydraulic Cylinders

Now that we understand the causes and effects, let’s dive into practical prevention methods. Here are some effective ways to prevent dieseling in hydraulic systems:

1. Properly Bleed the Hydraulic System

When installing or servicing hydraulic components, make sure the system is properly bled to remove any trapped air. This can involve:

Opening bleed valves while circulating hydraulic fluid to purge air pockets.
Operating the cylinder through its full stroke to release trapped air in the chamber.
Monitoring pressure levels as the system is bled to prevent over-pressurization.

Bleeding the system thoroughly during installation and maintenance helps eliminate air pockets that might otherwise cause dieseling.

2. Use High-Quality Hydraulic Seals

Seals play a critical role in maintaining pressure and preventing air from entering the hydraulic system. Choose high-quality seals that are specifically designed for the pressures, temperatures, and fluids used in your hydraulic system. Regularly inspect seals for wear, and replace them as necessary to avoid leakage that could allow air to enter.

3. Maintain Appropriate Hydraulic Fluid Levels

Keeping hydraulic fluid levels at the correct level helps ensure that air is not introduced into the system. Regularly check and refill the fluid reservoir, especially in high-demand applications where fluid levels may fluctuate. Using a sight gauge or level indicator can make it easier to monitor fluid levels consistently.

4. Avoid Abrupt Cylinder Movements

In applications where the hydraulic cylinder must operate at high speed, consider adjusting the system controls to minimize rapid acceleration and deceleration, which can lead to high compression of the fluid and trapped air. Gradually accelerating and decelerating cylinder movements reduces the chances of generating the excess heat necessary for dieseling to occur.

5. Use Anti-Cavitation Valves

Installing anti-cavitation valves can help prevent air pockets from forming within the hydraulic cylinder. These valves allow for the proper return of hydraulic fluid, reducing the chance of low-pressure areas that could result in cavitation (formation of air pockets). Anti-cavitation valves are especially useful in high-speed or high-demand hydraulic systems where rapid cylinder movements are common.

6. Select the Right Hydraulic Fluid

Choosing the correct hydraulic fluid is essential for system performance and safety. Look for fluids designed for high-pressure and high-temperature applications if your system operates under such conditions. High-quality fluids are formulated to reduce the likelihood of combustion when exposed to high temperatures. Additionally, opt for fluids with anti-foaming agents to help eliminate air entrapment.

7. Regularly Inspect and Maintain the System

Preventative maintenance is key to identifying potential problems before they become significant issues. Regularly inspect all components, including hoses, fittings, valves, and cylinders, for signs of wear or leaks. A well-maintained hydraulic system is less likely to experience the conditions that lead to dieseling.

Consider a maintenance schedule that includes the following actions:

Inspecting seals and replacing them as necessary.
Checking for leaks or worn components.
Ensuring the hydraulic fluid is clean and at the proper level.
Inspecting for proper valve function to prevent cavitation.

Additional Tips to Prevent Dieseling

Here are some additional strategies to keep dieseling at bay in your hydraulic system:

Use a Quality Filtration System: Particulate contamination can lead to seal degradation and increased wear in the hydraulic cylinder. Regularly replace filters to prevent contaminants from entering the system and potentially contributing to dieseling.
Monitor System Temperature: Keeping the hydraulic system within the recommended temperature range prevents overheating, which can exacerbate the diesel effect. Use temperature gauges to monitor and address any signs of excessive heat.
Invest in Training: Equip operators and technicians with knowledge about the risks and prevention techniques for dieseling. Well-trained personnel are more likely to operate equipment within safe parameters and catch issues early.

Dieseling in hydraulic cylinders can lead to serious damage and costly repairs if left unaddressed. By understanding the causes of dieseling and implementing preventative measures, you can keep your hydraulic system running smoothly and extend its lifespan. Regular maintenance, proper bleeding, choosing the correct hydraulic fluid, and using quality seals are all essential practices to prevent the diesel effect. With these steps in place, your hydraulic system will be safer, more efficient, and more reliable in the long run.

Photo by Sandeep Singh: https://www.pexels.com/photo/back-hoe-getting-dirt-11824185/

Jenn Garman