Understanding Tandem Variable Flow Axial Piston Pump Failure

[MikePhua]

The tandem variable flow axial piston pump is a crucial component in hydraulic systems used in a wide range of heavy equipment, from construction machinery to agricultural tools. This pump is designed to deliver variable flow to hydraulic circuits, making it an integral part of systems that demand efficiency and precision. However, like all complex machinery, these pumps are prone to failure under certain conditions. This article delves into the mechanics of tandem variable flow axial piston pump failure, common causes, and potential solutions.
What is a Tandem Variable Flow Axial Piston Pump?
A tandem variable flow axial piston pump is a hydraulic pump that uses pistons arranged in a parallel configuration to provide fluid flow. Unlike fixed displacement pumps, these pumps can adjust the amount of flow they deliver based on the system’s needs, offering greater control and efficiency in a variety of applications.
The "tandem" aspect refers to the pump’s configuration, where two or more pumps are mounted together in a single housing, often used to power multiple hydraulic circuits simultaneously. The "variable flow" allows the pump to adjust the flow rate depending on the system's demands. These pumps are widely used in heavy-duty machines like excavators, cranes, and wheel loaders.
How Does the Tandem Pump Work?
The tandem axial piston pump operates through a series of pistons arranged in a cylinder block. The pistons move in and out in response to rotational motion provided by a swashplate. The angle of the swashplate determines the displacement of each piston and thus the flow rate. The variable flow feature is controlled by adjusting the swashplate angle, allowing for changes in flow without altering the pump speed.
In a tandem configuration, two pumps are typically stacked together, each responsible for supplying fluid to different circuits. The result is more versatility in controlling hydraulic functions, such as steering, lifting, and powering attachments.
Common Causes of Tandem Pump Failure
While tandem variable flow axial piston pumps are built to last, they can fail if not properly maintained or if they are exposed to harsh operating conditions. Here are some common causes of failure:

1. Contaminated Hydraulic Fluid
   One of the leading causes of tandem pump failure is contamination in the hydraulic fluid. Dirt, debris, or water entering the system can cause wear on critical internal components, such as the pistons, seals, and valves. Over time, this contamination can lead to decreased efficiency, poor performance, and eventual pump failure.
   
2. Excessive Pressure
   Hydraulic systems are designed to operate within a certain pressure range. When the pump is subjected to pressures higher than its rated capacity, the internal components can be damaged. This can cause the pump to lose efficiency or fail outright. Common causes of excessive pressure include system overloading or a malfunctioning relief valve.
   
3. Improper Fluid Levels
   Low fluid levels or air in the hydraulic system can cause cavitation, a phenomenon where vapor bubbles form in the fluid and collapse, causing damage to internal components. Cavitation can erode the metal surfaces inside the pump and drastically reduce its lifespan.
   
4. Improper Maintenance or Lack of Lubrication
   Like all mechanical components, axial piston pumps require regular maintenance. Insufficient lubrication or failure to replace worn seals and parts can lead to pump failure. Lack of proper maintenance increases the risk of internal wear, reducing the pump’s efficiency and performance over time.
   
5. Heat Generation
   Excessive heat is a common problem for hydraulic systems. If the hydraulic fluid becomes too hot, it can lose its viscosity and fail to properly lubricate and cool the internal components of the pump. Overheating can result in a breakdown of fluid properties, leading to pump seizure or catastrophic failure.
   
6. Faulty or Worn Components
   Over time, components within the tandem variable flow axial piston pump can wear down, particularly the pistons, valve plates, and seals. This can lead to poor performance or complete failure. Additionally, any misalignment of the swashplate or piston components can cause significant damage.
   

Symptoms of Pump Failure
Recognizing the early signs of pump failure can save time and money in repairs and prevent further damage. Some common symptoms include:

• Decreased Performance: If the system is delivering lower flow or pressure than usual, it may indicate internal wear or contamination in the pump.
  
• Unusual Noises: Grinding, squealing, or whining noises are often signs of worn components or contamination in the hydraulic system.
  
• Overheating: If the pump or the hydraulic fluid becomes too hot, it may indicate excessive pressure or lack of cooling.
  
• Erratic or Slow Operation: If the hydraulic functions are slow to respond or erratic, it could point to a problem with the pump’s pressure control or flow regulation.
  
• Leakage: External leaks or internal fluid loss are also signs that seals or hoses are compromised.
  

Preventing Tandem Pump Failure
Preventing failure requires proactive care and regular maintenance of the hydraulic system. Below are some best practices to prolong the life of your tandem variable flow axial piston pump:

1. Regular Fluid and Filter Changes
   Changing the hydraulic fluid at regular intervals and ensuring that the filter is clean can prevent contamination. Always use the recommended fluid type and check the system for any signs of debris or contamination.
   
2. Monitoring System Pressure
   Regularly check system pressures to ensure that they remain within the manufacturer’s recommended limits. Installing a pressure gauge at strategic points in the system can help monitor pressure levels and detect any irregularities early.
   
3. Proper Lubrication
   Ensure that all moving parts within the pump are properly lubricated. Check and replace worn seals, o-rings, and bearings to keep the system running smoothly. Lubrication should be done according to the manufacturer's specifications.
   
4. Use of Coolant Systems
   Implementing a cooling system to maintain hydraulic fluid temperature within optimal ranges will prevent overheating and help maintain fluid viscosity. Make sure that cooling fans, heat exchangers, and radiators are clean and functioning properly.
   
5. Avoid Overloading the System
   Never operate the machine beyond its specified load capacity. Overloading can lead to excessive pressure in the pump and premature wear. Always adhere to the load limits for both the machine and the hydraulic pump.
   
6. Routine Inspections
   Conduct routine visual inspections of the pump and the entire hydraulic system to check for leaks, wear, and other potential issues. Catching problems early can prevent costly repairs down the road.
   

Repairing or Replacing a Tandem Pump
When a tandem variable flow axial piston pump fails, it can often be repaired if caught early. Repair options may include replacing worn seals, bearings, or valves, and cleaning internal components. However, if the damage is severe, a full pump replacement may be necessary.
Replacement pumps should be carefully matched to the machine's specifications, including flow rate, pressure ratings, and compatibility with the hydraulic system. It's essential to use parts from reputable manufacturers to ensure proper fit and function.
Conclusion
The tandem variable flow axial piston pump plays a crucial role in hydraulic systems, offering variable flow and high efficiency. However, like any mechanical component, it is subject to wear and failure. Recognizing the signs of pump failure and adhering to regular maintenance schedules can significantly reduce the risk of unexpected breakdowns. By following best practices for fluid management, system monitoring, and component upkeep, operators can extend the lifespan of their tandem pumps and maintain optimal performance for their machines.