Rephasing Cylinders: A Complete Guide for Mobile Hydraulics

When equipment operators notice their hydraulic cylinders drifting out of sync or failing to extend evenly, the culprit is usually a misunderstood component: the rephasing cylinder system. These specialized hydraulic systems play a critical role in maintaining synchronized movement across multiple cylinders, ensuring equipment operates smoothly and safely.

Whether you're managing a construction fleet, agricultural equipment, or forestry machinery, proper knowledge of these systems can save thousands in repairs and lost productivity.

How Rephasing Cylinders Work

A rephasing cylinder system enables multiple hydraulic cylinders to extend and retract in near-perfect unison, creating synchronized movement across an entire hydraulic lift system. The key to this synchronization lies in the rephasing passageway.

Located at the position of full extension, this passageway allows a small amount of hydraulic fluid to bypass the cylinder piston when fully extended. This bypass mechanism is what enables the cylinders to "rephase" or resynchronize themselves during operation.

When hydraulic fluid is applied to the cylinders, they extend together. However, over time, factors like internal leakage, air ingestion, or varying loads can cause the cylinders to fall out of sync. The rephasing passageway corrects this by allowing fluid transfer between cylinders at full extension, bringing them back into alignment.

This design eliminates the need for complex mechanical connections or additional flow control devices, making rephasing cylinders an elegant solution for applications requiring synchronized movement across multiple lifting points.

Advantages of Rephasing Cylinders

Rephasing cylinder systems offer several compelling benefits that make them ideal for mobile hydraulic applications:

• Enhanced System Stability: By maintaining synchronized movement, rephasing cylinders provide superior load distribution and equipment stability. This is particularly crucial for applications like agricultural implements or construction equipment where uneven lifting can cause damage or safety hazards.

• Simplified Design Requirements: Unlike traditional synchronized systems that require mechanical connections or complex flow dividers, rephasing cylinders achieve synchronization through their internal design. This eliminates additional components that could fail or require maintenance.

• No Parasitic Power Loss: Traditional flow divider systems often experience constant power losses due to pressure drops across flow control devices. Rephasing cylinders avoid this inefficiency, providing better overall system performance.

• Improved Operational Control: The ability to self-synchronize gives operators better control over complex hydraulic systems, reducing the skill level required for effective operation while improving overall equipment performance.

• Cost-Effective Implementation: While initial costs may be higher than single-cylinder systems, rephasing cylinders often prove more economical when considering the eliminated need for additional synchronization hardware and reduced maintenance requirements.

Disadvantages of Rephasing Cylinders

Despite their advantages, rephasing cylinder systems do present certain challenges that operators should be aware of:

• Increased System Complexity: Rephasing systems are inherently more complex than single-cylinder applications, requiring a deeper understanding of hydraulic principles for effective troubleshooting and maintenance.

• Higher Initial Investment: The specialized design and manufacturing requirements of rephasing cylinders typically result in higher upfront costs compared to standard hydraulic cylinders.

• Maintenance Requirements: The increased complexity translates to more sophisticated maintenance needs, often requiring technicians with specialized knowledge of rephasing system operation.

• Potential for Fluid Leakage: The rephasing passageways, while essential for operation, create additional points where internal leakage can occur, potentially affecting long-term system performance.

• Lack of Inherent Position Control: Rephasing systems excel at maintaining relative synchronization but don't provide absolute position control, which may be required for certain precision applications.

Rephasing cylinder systems operate using a master-slave configuration that ensures coordinated movement across multiple cylinders. Understanding this relationship is essential for proper system design and troubleshooting.

• Master Cylinder Function: The master cylinder receives hydraulic fluid directly from the system's pump and initiates movement for the entire system. It sets the pace and pressure for all connected cylinders, acting as the primary control point for the rephasing system.

• Slave Cylinder Operation: Slave cylinders receive hydraulic fluid through interconnected lines from the master cylinder. They follow the master cylinder's movement patterns, extending and retracting in response to pressure changes initiated by the master cylinder.

• Series vs Parallel Systems: Rephasing cylinders can be configured in either series or parallel arrangements. Series systems feature different bore and rod sizes across cylinders, while parallel systems use identical cylinder specifications. Series configurations are more common in applications requiring different load capacities across lifting points.

The master-slave relationship makes sure that all cylinders in the system respond uniformly to control inputs, maintaining synchronized movement even under varying load conditions. This configuration also simplifies the hydraulic circuit design by requiring only one primary control valve for the entire system.

Common Issues with Rephasing Cylinder Systems

Rephasing cylinder systems can exhibit several characteristic problems that operators should recognize and understand:

• Cylinder Creep (Drift): One of the most common issues, creep occurs when cylinders gradually move from their set position without operator input. This typically indicates air entrainment in the system or internal seal leakage. If multiple cylinders drift or the system feels "spongy," air is likely the primary culprit.

• Synchronization Failure: When cylinders fail to extend or retract at the same rate, the system has lost its synchronization. This can result from internal leakage, contaminated fluid, or worn seals that affect the rephasing passageway operation.

• Cylinder Bypass: A systematic issue where hydraulic fluid bypasses cylinder pistons inappropriately, causing erratic movement or complete loss of function. This requires methodical diagnosis to identify whether the problem lies with seals, contamination, or mechanical damage.

• Contamination Damage: Scoring of cylinder barrels and piston seals usually indicates that contaminants have entered the system. This can compromise the rephasing passageways and lead to complete system failure if not addressed promptly.

• Air Entrainment: Air trapped in the hydraulic system creates compressibility that interferes with precise cylinder movement and can cause the entire system to behave unpredictably.

Rephasing a Cylinder System

Proper rephasing procedures are essential for maintaining system performance and should be performed regularly as part of preventive maintenance:

Standard Rephasing Procedure: With the cylinder system fully extended, actuate the cylinder valve for 30 seconds. For systems that are rephased frequently, 5-10 seconds may be sufficient. This procedure allows excess air to be purged from the system while permitting fluid transfer through the rephasing passageways.

New System Considerations: New rephasing circuits often require extended rephasing sequences—sometimes several minutes—to bleed excessive air from the system. This process may need to be repeated multiple times until the system achieves proper synchronization.

Diagnostic Rephasing: Before performing maintenance rephasing, check cylinder rod positions by:

• Fully extending all cylinders, then retracting approximately 2 inches from the rephasing position

• Disconnecting all hydraulics from the machinery

• Measuring each extended cylinder rod length

• Allowing the equipment to stand for an extended period

• Remeasuring the rods to identify any drift

• Comparing measurements to identify problematic cylinders

This diagnostic approach helps pinpoint specific cylinders that may require individual attention or repair.

Best Practices for Maintaining Rephasing Cylinder Systems

Effective maintenance of rephasing cylinder systems requires a proactive approach that addresses both routine care and system-specific needs:

• Regular Rephasing Schedules: Establish routine rephasing intervals based on equipment usage patterns. High-use equipment may require weekly rephasing, while seasonal equipment might need rephasing at the beginning of each operating period.

• Fluid Quality Management: Maintain clean hydraulic fluid through regular filtration and replacement schedules. Contaminated fluid is one of the leading causes of rephasing system failure, making fluid quality management critical for long-term reliability.

• System Pressure Monitoring: Regularly check and maintain proper system pressure settings. Incorrect pressure can affect rephasing passageway operation and lead to synchronization problems.

• Environmental Considerations: Protect rephasing cylinder systems from environmental contaminants by maintaining proper seals and covers. Dust, dirt, and moisture can severely compromise system performance.

• Documentation and Record Keeping: Maintain detailed records of rephasing procedures, fluid changes, and system performance. This documentation helps identify patterns that may indicate developing problems before they cause equipment failure.

• Professional Inspection: Schedule regular professional inspections of rephasing cylinder systems, particularly for critical applications. Trained technicians can identify potential issues that may not be apparent during routine operation.

Maximizing Your Rephasing Cylinder Performance

Rephasing cylinders represent a solution for applications requiring synchronized hydraulic movement. While they require more technical understanding than simple cylinder systems, their benefits in terms of performance, reliability, and operational efficiency make them invaluable for many mobile hydraulic applications.

Success with rephasing cylinder systems comes from understanding their operation, recognizing common issues early, and maintaining consistent preventive maintenance practices. When properly maintained and operated, these systems provide the reliable, synchronized movement that keeps mobile hydraulic equipment operating at peak efficiency.

For more on this subject, be sure to check out our YouTube video on Rephasing Tie-Rod Cylinders!