Marine Air Compressors

Air compressors work by compressing air into a small space, increasing the air pressure. This compressed air is then stored or used directly by various equipment on the ship.

Common applications on board include

• Pneumatic tools: These include tools such as drills, grinders, sanders, impact wrenches and spray guns used by your crew.
• Air operated pumps: Such as fuel transfer pumps and oil pumps.
• Pneumatic control systems: Including power valves, actuators and sensors, can be seen in the control rooms
• Deck machinery: Including windlasses and anchor winches.
• Ship engines: Both main and auxiliary engines.
• Refrigeration system: For Air Conditioning and cold room
• Safety equipment: Such as life rafts, lifeboats, fire extinguishers and foam systems.

There are actually many types of marine air compressors. Here we present four of the most common types, all designed for specific applications.

• Reciprocating compressors

The most common type found on ships, they use pistons driven by a crankshaft to compress air in cylinders. These compressors are often used for high pressure applications due to their efficiency and high pressure output. They are known for their simple structure, compact design and low initial cost. Reciprocating compressors are ideal for applications such as starting a ship’s main engine and powering pneumatic tools.

• Rotary Screw Compressors

Rotary screw compressors use two intermeshing screws to compress air. They provide smooth, continuous operation with stable gas flow and pressure. These compressors are efficient, produce low vibration and minimal pulsation, making them quiet and reliable. With low maintenance costs, they are suitable for long-term use in systems such as HVAC and air control.

• Centrifugal Compressors

Centrifugal compressors use rapidly rotating impellers to add velocity to air and convert this kinetic energy into pressure. Centrifugal compressors are ideal for large volume air production, but are not suitable for high pressure applications. They tend to be more expensive and complex in design. These compressors are often used in large-scale tasks such as hull lubrication and fresh water production.

• Scroll Compressors

Scroll Compressors operate with two spiral-shaped scrolls, one fixed and the other orbiting around it to compress the air. These compressors are known for their quiet operation and oil-free performance, with fewer moving parts, reducing wear and tear. However, they can be more expensive. Scroll compressors are commonly used in air conditioning systems and diving gas systems.

The main difference between water-cooled and air-cooled marine air compressors is how they dissipate the heat generated during the compression process.

If you don’t know which compressor cooling system to choose, I believe this chart will make it clear:

Let’s summarize:

• Water-cooled compressors are more efficient and suited for larger, more demanding applications or environments with readily available water sources, like large vessels or offshore oil rigs.
• Air-cooled compressors are typically smaller, simpler, and less expensive, making them more appropriate for applications where space or water access is limited. They are commonly used on smaller vessels or when environmental conditions don’t require heavy-duty cooling.

1. Oil Level Maintenance
Regularly check the oil level in the compressor to ensure it’s within the recommended range. The oil should be free of leaks, foaming, and excessive wear.

Oil Type: Due to the marine environment’s high humidity and saltwater, use SAE40 / ISO 100 compressor-oil (or other suitable oil).
Oil Change Schedule: For a new compressor, change the oil after 15 hours of operation. Then, replace the oil every 250-500 hours of use.

2. Air Filter Care
Clean or replace the air filter regularly to prevent clogging. Dust and debris can damage internal parts and reduce the compressor’s efficiency.

3. Heat Exchanger Cleaning
Clean the heat exchanger once a year. Seawater cooling systems often accumulate salt deposits, so use an acidic cleaning fluid like CA-100 for effective descaling.

4. Drain Condensate Regularly
Condensate, or water droplets formed from cooling air, should be drained from the compressor regularly. Ensure the condensate drain pipe is functioning correctly to prevent moisture buildup and bacterial growth, which can lead to corrosion and reduced air quality.

5. Monitor Pressure
Regularly monitor the pressure to avoid potential issues.

• Too High Pressure: Can be dangerous.
• Too Low Pressure: Reduces efficiency and wastes energy.

Pressure Relief Valve: Test the valve manually every 3 months. If the cracking pressure deviates by more than ±5% from the set point (e.g., 30 bar for main compressors), recalibrate the valve.

6. Monitor Temperature and Vibration
Temperature: Use temperature sensors to monitor compressor temperature. High temperatures can decrease efficiency and cause damage.
Vibration: Monitor vibration levels to detect mechanical issues such as misalignment or imbalance, which can lead to failures.

7. Other Key Components to Inspect
Bursting Discs: Inspect annually and replace any discs showing signs of pitting or thinning.

Crankcase Volume: According to BV air compressor design requirement, crankcase volume should ≥ 0.6 m³.

Belt Tension: Check monthly for proper belt tension and pulley alignment. Misalignment of >1 mm per 300 mm can cause premature bearing failure.

Loud Noise: If the compressor produces excessive noise, it may be due to misalignment or slippage.