Aux 1 Unit 11 Q1

Main propulsion shaft hydraulic sleeve-type couplings, often simply referred to as hydraulic couplings, are specialized devices used to connect sections of a ship’s main propulsion shafting system, such as the intermediate shaft to the gearbox or to another intermediate shaft.  

1. Hydraulic coupling – Bosun Marine

Key Features:

• Keyless Connection: They eliminate the need for traditional keyed or tapered connections, simplifying installation and removal of shaft sections.   1. HYDRAULIC COUPLINGS – Maucour www.maucour.fr
• Hydraulic Actuation: They utilize hydraulic pressure to create a tight interference fit between the coupling halves, ensuring secure and reliable torque transmission.   1. HYDRAULIC COUPLINGS – Maucour www.maucour.fr
• Axial and Radial Movement: They allow for some degree of axial and radial movement between the connected shafts, accommodating misalignment and thermal expansion.

Components:

• Inner Sleeve: A thin-walled sleeve with a tapered outer surface, fitted onto the shaft.
• Outer Sleeve: A thicker sleeve with a tapered inner surface that fits over the inner sleeve.
• Hydraulic Chamber: An annular space between the inner and outer sleeves where hydraulic fluid is injected.
• Sealing Rings: O-rings or other seals prevent fluid leakage from the hydraulic chamber.
• Hydraulic Fittings: Connections for injecting and releasing hydraulic fluid.

Operation:

1. Assembly: The inner sleeve is first mounted onto the shaft. Then, the outer sleeve is positioned over the inner sleeve, leaving a gap between them.
2. Hydraulic Injection: High-pressure hydraulic fluid is injected into the annular chamber between the sleeves.
3. Interference Fit: The hydraulic pressure forces the outer sleeve to expand radially and contract axially, creating a tight interference fit with the inner sleeve and the shaft. This friction-based connection transmits torque efficiently.
4. Disassembly: To disconnect the coupling, hydraulic fluid is injected into the chamber again, but this time at a lower pressure. The outer sleeve is then hydraulically pushed off the inner sleeve.

Advantages:

• Easy Installation and Removal: Eliminates the need for time-consuming and labor-intensive processes like heating or hammering required for traditional keyed connections.
• Accommodates Misalignment: Allows for slight misalignment between the shafts, reducing stress on the system and improving reliability.
• No Keyways: Keyways can weaken the shaft and are prone to stress concentrations. Hydraulic couplings eliminate this weakness.
• Reduced Vibration: The hydraulically tightened connection provides a smooth and vibration-free transmission of torque.
• Suitable for High Torque: Can handle high torque loads encountered in main propulsion shafting systems.

Disadvantages:

• Requires Hydraulic System: Needs a dedicated hydraulic system for operation, adding complexity.
• Potential for Leaks: Hydraulic systems can develop leaks, requiring regular inspection and maintenance.

Applications:

• Widely used in marine propulsion systems to connect intermediate shafts to gearboxes or other intermediate shafts.
• Also used in other industrial applications requiring high-torque, keyless connections.

Overall, main propulsion shaft hydraulic sleeve-type couplings offer a reliable, efficient, and convenient solution for connecting shaft sections in demanding marine environments. Their keyless design, hydraulic actuation, and ability to accommodate misalignment contribute to the smooth and safe operation of the vessel’s propulsion system.

Let’s outline the procedure for removing a main propulsion shaft hydraulic sleeve-type coupling:

Safety Precautions:

• Isolation: Ensure the propulsion system is completely shut down and isolated, with appropriate lockout/tagout procedures in place.
• Depressurization: Release any residual pressure in the hydraulic system associated with the coupling.
• Lifting Equipment: Use proper lifting equipment and techniques to handle heavy components safely.
• Personal Protective Equipment (PPE): Wear appropriate PPE, including safety glasses, gloves, and steel-toed boots.

Removal Procedure:

1. Preparation:

• Access: Gain access to the coupling, which might involve removing any surrounding covers, guards, or insulation.
• Cleaning: Clean the coupling and surrounding area to remove any dirt, grease, or debris that could interfere with the removal process or contaminate the hydraulic system.

2. Disconnect Hydraulic Lines:

• Identify Lines: Identify the hydraulic lines connected to the coupling’s injection fittings. These lines supply the hydraulic fluid for tightening and loosening the coupling.
• Depressurize: Ensure the lines are depressurized before disconnecting them.
• Disconnect: Carefully disconnect the hydraulic lines from the coupling, using appropriate tools and taking care to avoid spills or contamination of the hydraulic fluid.

3. Install Withdrawal Tooling:

• Withdrawal Stud and Plate: Attach the withdrawal stud and plate to the outer sleeve of the coupling. The stud threads into the outer sleeve, and the plate provides a surface for the hydraulic jack to push against.
• Hydraulic Jack: Position a hydraulic jack between the withdrawal plate and a suitable support point on the vessel’s structure or foundation.

4. Hydraulic Withdrawal:

• Apply Pressure: Gradually apply hydraulic pressure to the jack, pushing against the withdrawal plate.
• Monitor Movement: Carefully monitor the movement of the outer sleeve as it is pushed off the inner sleeve and the shaft.
• Control Pressure: Maintain controlled pressure and avoid excessive force to prevent damage to the coupling or shaft.

5. Complete Removal:

• Outer Sleeve Removal: Once the outer sleeve is completely free from the inner sleeve, carefully remove it using appropriate lifting equipment.
• Inner Sleeve Removal: The inner sleeve can then be slid off the shaft.
• Inspect Components: Visually inspect the inner and outer sleeves, the shaft, and any sealing rings for signs of wear, damage, or corrosion.

Additional Considerations:

• Manufacturer’s Instructions: Always refer to the specific coupling manufacturer’s instructions for detailed removal procedures, as there might be variations depending on the model and design.
• Alignment Marks: If present, note the alignment marks on the coupling halves before disassembly to aid in reassembly and ensure proper alignment of the shafts.
• Cleaning and Storage: After removal, clean the coupling components and store them in a clean, dry environment to prevent corrosion or damage.

By following these steps and taking necessary precautions, the removal of a hydraulic sleeve-type coupling can be carried out safely and efficiently, minimizing the risk of damage to components and ensuring a smooth reinstallation process when required.

During the reassembly of a main propulsion shaft hydraulic sleeve-type coupling, determining that the push fit is complete is crucial to ensure a secure and reliable connection between the shaft sections. This is typically achieved using a combination of visual indicators and pressure monitoring:

1. Loading Ring Position:

• Visual Indicator: Most hydraulic sleeve couplings have a loading ring or indicator on the outer sleeve.
• Fully Retracted: During assembly, as hydraulic pressure is applied to expand the outer sleeve and create the interference fit, this loading ring retracts into the coupling body.
• Complete Fit: When the loading ring is fully retracted and flush with the coupling body, it indicates that the outer sleeve has expanded sufficiently to achieve the desired interference fit. This is the primary visual confirmation that the push fit is complete.

2. Hydraulic Pressure Monitoring:

• Pressure Gauge: The hydraulic system used for assembly typically includes a pressure gauge to monitor the pressure applied to the coupling.
• Target Pressure: The coupling manufacturer will specify a target pressure that needs to be reached to ensure the proper interference fit.
• Pressure Hold: Once the target pressure is reached and the loading ring is fully retracted, the pressure is held for a specified duration (typically a few minutes) to allow the coupling to settle and ensure a secure fit.
• Pressure Drop: If the pressure drops significantly during the hold period, it might indicate a leak or incomplete fit, requiring further investigation and corrective action.

3. Additional Checks:

• Visual Inspection: In addition to the loading ring and pressure monitoring, a visual inspection of the coupling is also performed to ensure there are no gaps or misalignment between the coupling halves.
• Torque Check (if applicable): In some cases, a torque check might be performed on the coupling bolts to verify that they are tightened to the specified torque, further ensuring a secure connection.

Importance of Achieving Proper Push Fit:

• Torque Transmission: A complete and secure push fit is essential for efficient and reliable transmission of torque from one shaft section to another.
• Preventing Slippage: An incomplete fit can lead to slippage between the coupling halves, causing vibration, wear, and potential damage to the shaft or coupling.
• Avoiding Over-tightening: Excessive pressure during assembly can damage the coupling or the shaft. Monitoring the pressure and using the loading ring indicator helps prevent over-tightening.

In Summary

The completion of the push fit in a hydraulic sleeve coupling is determined by a combination of visual inspection of the loading ring and monitoring the hydraulic pressure during assembly. Achieving the proper interference fit is critical for ensuring the coupling’s integrity, efficient power transmission, and the safe operation of the propulsion system.