Aux 1 Unit 11 Q2

Main propulsion shaft hydraulic sleeve-type couplings, often simply referred to as hydraulic couplings, are specialized mechanical devices used to connect sections of a ship’s main propulsion shafting system. These couplings are crucial for transmitting the immense torque and power generated by the engine to the propeller, enabling the vessel to move through the water.  

1. Hydraulic coupling – Bosun Marine

Key Features and Function:

• Keyless Connection: They provide a keyless connection between the shaft sections, eliminating the need for traditional keyed or tapered connections. This simplifies installation and removal, reducing downtime during maintenance or repairs.   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 Shaft Coupling | Marine Support Equipment Supplier | HJ ship-machinery.com
• Misalignment Compensation: They allow for some degree of axial and radial movement between the connected shafts, accommodating misalignment caused by thermal expansion, ship flexing, or manufacturing tolerances. This reduces stress on the shafting system and enhances its reliability.

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 slides 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 mounted onto the shaft, and the outer sleeve is positioned over it, leaving a gap.
2. Hydraulic Injection: High-pressure hydraulic fluid is injected into the chamber between the sleeves.
3. Tightening: The hydraulic pressure expands the outer sleeve radially and contracts it 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 again at a lower pressure, and the outer sleeve is hydraulically pushed off the inner sleeve.

Advantages:

• Easy Installation/Removal: Eliminates the need for time-consuming and labor-intensive processes like heating or hammering required for traditional keyed connections.
• Misalignment Compensation: Accommodates slight misalignment, 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: Provides a smooth and vibration-free transmission of torque.
• Suitable for High Torque: Can handle the 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:

• Primarily used for connecting intermediate shafts to gearboxes or other intermediate shafts in marine propulsion systems.
• Can also be used in other industrial applications requiring high-torque, keyless connections.

Overall, hydraulic sleeve-type couplings are essential components in modern marine propulsion systems. They offer a reliable, efficient, and convenient solution for connecting shaft sections, contributing to the smooth and safe operation of the vessel.

Here’s a breakdown of the tightening procedure for a main propulsion shaft hydraulic sleeve-type coupling:

Safety and Preparation

• Safety First: Ensure the propulsion system is completely shut down and isolated. Employ proper lockout/tagout procedures to prevent accidental activation.
• Access and Cleaning: Gain clear access to the coupling and ensure all mating surfaces (shaft, inner sleeve, outer sleeve) are clean and free of any debris or contaminants.
• Hydraulic System Preparation: Ensure the hydraulic system used for tightening is in good working order, with the correct type and quantity of hydraulic fluid. Check for leaks and ensure all connections are secure.

Tightening Procedure:

1. Install Inner Sleeve:
   • The inner sleeve is first mounted onto the shaft section. It might be a light press-fit or a slip fit, depending on the design.
   • Ensure proper alignment and orientation based on any markings or instructions.
2. Position Outer Sleeve:
   • The outer sleeve is then carefully slid over the inner sleeve, leaving a gap between them.
   • Alignment marks on the two halves should be matched.
3. Connect Hydraulic Lines:
   • Connect the high-pressure hydraulic lines from the pump to the designated injection fittings on the coupling.
   • Ensure the connections are tight and leak-free.
4. Apply Hydraulic Pressure:
   • Gradually increase the hydraulic pressure using the pump or control system.
   • Monitor the pressure gauge to ensure it stays within the manufacturer’s specified range.
5. Observe Loading Ring:
   • As the pressure increases, the outer sleeve will expand radially and contract axially, creating the interference fit.
   • Observe the loading ring or indicator on the outer sleeve. It will gradually retract as the fit tightens.
6. Reach Target Pressure and Hold:
   • Continue increasing pressure until the loading ring is fully retracted and flush with the coupling body, indicating a complete fit.
   • Once the target pressure is reached, hold the pressure for a specified duration (usually a few minutes) to allow the coupling to settle and ensure a secure connection.
7. Release Pressure and Disconnect:
   • Once the hold time is complete, slowly release the hydraulic pressure.
   • Disconnect the hydraulic lines from the coupling.
8. Final Checks:

• Visual Inspection: Visually inspect the coupling to ensure there are no gaps or misalignment between the halves.
• Torque Check (if applicable): If the coupling has bolts, tighten them to the specified torque using a calibrated torque wrench.

Key Points:

• Controlled Pressure: The hydraulic pressure must be increased gradually and monitored closely to avoid over-pressurization and potential damage.
• Manufacturer’s Instructions: Always follow the specific instructions provided by the coupling manufacturer, as procedures and pressure requirements may vary.
• Cleanliness: Maintain a clean working environment to prevent contaminants from entering the hydraulic system or affecting the coupling surfaces.
• Qualified Personnel: The tightening procedure should be performed by qualified personnel with experience in handling hydraulic systems and large shaft couplings.

By following these steps and adhering to best practices, you can ensure the proper and safe tightening of a main propulsion shaft hydraulic sleeve-type coupling, leading to a reliable and efficient connection for transmitting power from the engine to the propeller.

In the context of hydraulic sleeve-type couplings, the completion of the push fit (the secure connection between the shaft and coupling halves) is determined by a combination of visual indicators and pressure monitoring during the tightening process.

Key Indicators of a Complete Push Fit:

1. Loading Ring Position:

• Visual Indicator: Most hydraulic sleeve couplings feature a loading ring or indicator on the outer sleeve. This ring is visible when the coupling is not fully tightened.
• Retraction: As hydraulic pressure is applied to expand the outer sleeve and create the interference fit, the loading ring retracts into the coupling body.
• Flush Position: When the loading ring is fully retracted and flush with the coupling body, it signifies that the outer sleeve has expanded sufficiently to achieve the desired interference fit. This is a primary visual cue that the push fit is complete.

2. Hydraulic Pressure:

• Pressure Gauge: The hydraulic system used for tightening typically has a pressure gauge that monitors the pressure applied to the coupling.
• Target Pressure: The coupling manufacturer specifies a target pressure that must be reached to ensure the proper interference fit.
• Pressure Hold: Once the target pressure is achieved and the loading ring is fully retracted, the pressure is held for a specific duration (usually a few minutes) to allow the coupling to settle and ensure a secure connection.
• Pressure Drop: Any significant pressure drop during the hold period may indicate a leak or an incomplete fit, requiring further investigation and corrective action.

Additional Checks:

• Visual Inspection: Beyond the loading ring and pressure monitoring, a visual inspection is crucial. Ensure there are no visible gaps or misalignment between the coupling halves.
• Torque Check (if applicable): Some couplings might have bolts that require tightening to a specific torque value. A torque wrench can be used to confirm that these bolts are adequately secured.

Importance of a Complete Push Fit:

• Torque Transmission: A proper push fit guarantees efficient and reliable torque transmission between the shaft sections.
• Prevents Slippage: An incomplete fit can result in slippage, leading to vibration, wear, and potential damage to the shaft or coupling.
• Avoids Over-tightening: Excessive pressure during assembly can damage the coupling or shaft. Monitoring the pressure and using the loading ring indicator help prevent this.

In Conclusion:

The completion of the push fit in a hydraulic sleeve coupling is determined by visually confirming the loading ring’s fully retracted position and monitoring the hydraulic pressure during the tightening process. Ensuring a proper interference fit is critical for the coupling’s integrity, efficient power transmission, and the safe operation of the propulsion system.