Aux 1 Unit 6 Q1

Compressed air systems play a critical role in the operation of marine vessels, particularly in two main areas: starting air for engines and control air for various pneumatic systems.  

1. Compressed Air Uses in Marine Industry – Airfilter Engineering

Starting Air

• Engine Starting: The primary use of compressed air on ships is to start the main and auxiliary engines. These large diesel engines require a significant amount of torque to overcome initial inertia and begin rotating.   1. Marine Air Compressors: Types & Uses – Atlas Copco UAE www.atlascopco.com
• High-Pressure Air: High-pressure air, typically stored at 20-30 bar, is injected into the engine cylinders at the right moment to force the pistons down and initiate the engine’s rotation.
• Starting Air System: This system includes:
  • Air Compressors: Compress atmospheric air to the required high pressure.
  • Air Receivers: Store the compressed air until needed for starting.
  • Starting Air Valves: Control the flow of air to the engine cylinders.   1. Air Start Valve Explained – saVRee www.savree.com
  • Piping and Distribution: Delivers air from the receivers to the engine.

Control Air

• Pneumatic Control Systems: Compressed air at lower pressures (typically 6-8 bar) is used to operate various pneumatic control systems throughout the vessel.
• Examples of Applications:
  • Control Valves: Actuates valves for fuel systems, ballast systems, and other critical systems.
  • Engine Control: Controls engine speed and other parameters through pneumatic governors and actuators.
  • Clutch and Brake Control: Operates clutches and brakes in various machinery.
  • Whistles and Horns: Provides the pressurized air needed for sound signals.
  • Pneumatic Tools: Powers pneumatic tools used for maintenance and repairs.
  • Emergency Shutdown Systems: Activates quick-closing valves and other safety systems in emergency situations.

Advantages of Compressed Air Systems

• Safe and Reliable: Compressed air is a safe and reliable source of energy compared to other options like hydraulics or electricity, especially in hazardous areas.   1. Compressed Air | Better Buildings Initiative – Department of Energy betterbuildingssolutioncenter.energy.gov
• Stored Energy: Compressed air can be stored in receivers, providing a readily available source of energy even during power outages or emergencies.
• Simple and Robust: Pneumatic systems are relatively simple and robust, with fewer moving parts compared to hydraulic systems, making them easier to maintain and less prone to leaks.
• Wide Range of Applications: Compressed air’s versatility allows it to be used for a wide variety of control and actuation functions on a vessel.

Key Considerations:

• Air Quality: The compressed air must be clean and dry to prevent corrosion and damage to pneumatic components. Air dryers and filters are essential parts of the system.
• Pressure Regulation: Different systems require different air pressures. Pressure reducing valves are used to provide the appropriate pressure for each application.
• Redundancy: Critical systems, like engine starting air, often have backup compressors and receivers to ensure availability in case of a failure.
• Safety: Proper safety measures, including pressure relief valves and regular inspections, are essential to prevent accidents and ensure the safe operation of compressed air systems.

In summary:

Compressed air systems are integral to the operation of marine vessels. They provide the power to start engines and control various pneumatic systems, offering a safe, reliable, and versatile source of energy for a wide range of applications.  

1. Ship Compressor Systems: Achilles’ Heels on Board

The pressure used for control air is generally kept higher than the minimum pressure required to operate the control equipment for several important reasons:

1. Pressure Loss in the System:

• Friction and Restrictions: As compressed air travels through pipes, hoses, and fittings, it experiences friction and encounters restrictions like bends and valves, leading to pressure drops along the way.
• Ensuring Adequate Pressure at the Point of Use: By starting with a higher pressure at the source, you ensure that there’s still enough pressure left at the control equipment to operate it reliably, even after accounting for these pressure losses.

2. Operational Variations and Demands:

• Fluctuations in Demand: The demand for control air can vary depending on the number of devices operating simultaneously and their specific requirements.
• Maintaining System Responsiveness: A higher initial pressure provides a buffer to accommodate these fluctuations and ensure that all control equipment receives adequate pressure to function properly, even during peak demand periods.

3. Response Time and Performance:

• Faster Actuation: Higher pressure generally leads to faster actuation of pneumatic devices like valves and cylinders, ensuring quick and responsive control actions.
• Improved Performance: Certain control equipment, especially those involving precise movements or heavy loads, may require higher pressures to achieve optimal performance.

4. Leakage and Wear Compensation:

• Minor Leaks: Over time, minor leaks can develop in the compressed air system, leading to gradual pressure loss. Starting with a higher pressure helps compensate for these small leaks and maintain adequate pressure at the control equipment.
• Component Wear: Wear and tear in pneumatic components can also affect their performance and require slightly higher pressures to operate effectively.

5. System Flexibility and Future Expansion:

• Additional Equipment: A higher initial pressure provides the flexibility to add more control equipment to the system in the future without compromising the performance of existing devices.

Key Points to Remember:

• Pressure Regulation: While the supply pressure is higher, pressure reducing valves are typically used at individual control equipment to deliver the precise pressure needed for their operation.
• Energy Efficiency: While a higher supply pressure is beneficial for performance and reliability, it’s important to balance it with energy efficiency considerations. Excessive pressure can lead to increased energy consumption and unnecessary wear on the system.
• Safety: Pressure relief valves are essential components in the system to prevent overpressure and ensure safe operation.   1. What are Pressure Relief Valves | THINKTANK – Control Valves cncontrolvalve.com

In summary, the practice of maintaining a higher control air pressure than the minimum required ensures reliable operation of control equipment, compensates for pressure losses and operational variations, and provides flexibility for future system expansion. It’s a balancing act between performance, efficiency, and safety, ultimately contributing to the smooth and effective operation of the vessel’s pneumatic control systems.