Crane Hydraulic System Thumping: Causes and Solutions

[MikePhua]

A common issue in cranes and other heavy machinery is the presence of "thumping" or unusual noises in the hydraulic system. This problem is typically accompanied by air in the hydraulic fluid, which can affect the crane's performance, safety, and operational efficiency. In this article, we explore the causes behind hydraulic system thumping in cranes, its potential impact, and how to resolve the issue effectively.
Understanding the Hydraulic System in Cranes
Cranes, whether they are mobile, crawler, or tower cranes, rely heavily on hydraulic systems to lift and move heavy loads. The hydraulic system is responsible for powering the crane’s boom, jib, and other operational parts. This system uses hydraulic fluid to transfer force within the machinery, allowing for smooth, controlled movements.
Hydraulic systems in cranes are complex and consist of various components, including:

1. Hydraulic Pump: Powers the flow of hydraulic fluid through the system.
   
2. Hydraulic Cylinders: Convert hydraulic fluid into mechanical force to move the crane's components.
   
3. Control Valves: Direct the flow of hydraulic fluid to the appropriate cylinders based on operator inputs.
   
4. Filters and Reservoirs: Clean and store hydraulic fluid to keep the system running efficiently.
   
5. Hydraulic Fluid: Transmits force and provides lubrication to the system.
   

Any disruption in this fluid flow, particularly air entering the system, can lead to issues like thumping, loss of power, and erratic movements.
Common Causes of Air in Hydraulic Systems
The presence of air in a hydraulic system, which often leads to thumping or a "chattering" noise, is one of the most frequent problems faced by cranes. There are several potential causes for air entering the hydraulic lines:

1. Low Hydraulic Fluid Levels
   One of the most common reasons for air entering the hydraulic system is low hydraulic fluid levels. When the fluid level is too low, the pump can start to draw in air, which results in aerated fluid. This can cause a variety of issues, including poor pump performance, erratic control, and the characteristic thumping noise.
   • Solution: Regularly check and top off hydraulic fluid to ensure the levels are within the recommended range. Follow the crane manufacturer’s guidelines for fluid specifications.
     
2. Damaged or Leaking Hydraulic Hoses
   Leaks in hydraulic hoses, fittings, or seals can allow air to enter the system, which leads to air pockets and inconsistent hydraulic performance. This can often be heard as a thumping sound when the pump is working harder to force fluid through the system.
   • Solution: Inspect hydraulic hoses, fittings, and seals regularly for signs of wear or leaks. Replace any damaged components immediately to restore system integrity.
     
3. Improperly Bled Hydraulic System
   When the crane's hydraulic system is first filled with fluid or after repairs, it may contain air that needs to be purged (bled). If the system is not properly bled, air pockets can form and disrupt fluid flow, causing thumping sounds and inconsistent hydraulic performance.
   • Solution: Follow the manufacturer’s recommended procedure to bleed the hydraulic system. This typically involves running the crane through its operational cycles while the system is open to allow trapped air to escape.
     
4. Faulty Hydraulic Pump
   A malfunctioning or worn-out hydraulic pump may not be able to maintain the necessary pressure or flow of hydraulic fluid, which can lead to cavitation. Cavitation occurs when the fluid pressure drops too low, causing air bubbles to form within the fluid. These air bubbles can result in thumping noises when they collapse inside the system.
   • Solution: If a faulty hydraulic pump is suspected, test the pump’s performance and replace it if necessary. Pumps that are not producing the correct pressure or volume of fluid should be serviced by a professional technician.
     
5. Contaminated Hydraulic Fluid
   Contaminants in the hydraulic fluid, such as dirt, water, or metal particles, can interfere with the flow and cause air to become trapped within the system. Contaminated fluid can also lead to the degradation of system components, further exacerbating the problem.
   • Solution: Replace hydraulic fluid and ensure that the system is properly filtered to prevent contamination. Regularly check fluid quality and replace filters as needed to maintain system cleanliness.
     

Impacts of Thumping on Crane Performance
When air enters the hydraulic system and causes thumping, it can have several negative effects on crane performance and safety:

1. Reduced Lifting Capacity
   Air in the hydraulic fluid reduces the system’s ability to generate consistent power, which can lead to a decrease in the crane’s lifting capacity. The boom may not be able to lift loads as efficiently, which can delay operations and compromise safety.
   
2. Erratic Boom Movements
   The presence of air in the hydraulic system can cause jerky or uneven movements of the crane's boom, jib, or other lifting components. This can make precise control more difficult, especially in operations that require fine adjustments.
   
3. Increased Wear on Components
   Prolonged air contamination in the hydraulic system can cause increased wear on the pump, cylinders, and valves. This accelerates the need for repairs and maintenance, leading to higher operational costs.
   
4. Potential for System Failure
   If not addressed, air in the hydraulic system can lead to more serious failures, such as pump damage, leaks, or even a complete hydraulic system failure. This can lead to extensive downtime and expensive repairs.
   

Preventing Hydraulic Thumping and Air Infiltration
To minimize the chances of air entering the hydraulic system and causing thumping, operators and maintenance teams should follow these best practices:

1. Regular Fluid Checks
   Regularly check hydraulic fluid levels and quality to ensure that they remain at optimal levels. Low or contaminated fluid should be replaced immediately to prevent air from entering the system.
   
2. Perform Scheduled Maintenance
   Adhere to the manufacturer’s recommended maintenance schedule, including inspections of hoses, seals, filters, and the hydraulic pump. Timely servicing can catch issues before they develop into more serious problems.
   
3. Proper Bleeding Techniques
   After fluid changes, repairs, or system modifications, ensure that the hydraulic system is properly bled to remove trapped air. This is a simple but essential step in ensuring smooth operation.
   
4. Use High-Quality Hydraulic Fluid
   Always use the manufacturer-recommended hydraulic fluid to prevent contamination and maintain system performance. Contaminated fluid can exacerbate air infiltration issues and damage internal components.
   
5. Monitor Hydraulic Pressure
   Keep an eye on system pressure to ensure that the pump is operating within the correct range. If pressure drops significantly, it could indicate the presence of air in the system, which should be addressed promptly.
   

Conclusion
Hydraulic thumping in cranes is a common issue that often results from air entering the hydraulic system. Whether caused by low fluid levels, leaks, or contamination, this problem can have a significant impact on crane performance, safety, and operational efficiency. By understanding the causes of air infiltration and following proper maintenance practices, crane operators can minimize the risk of thumping and ensure that the hydraulic system remains in top condition. Timely detection and resolution of hydraulic issues not only improve machine performance but also help reduce maintenance costs and downtime, keeping your crane operating at full capacity.