Marine Air Compressor

 

1. What is a Marine Air Compressor?

A marine air compressor is a machine used on ships to compress air and store it in air bottles under high pressure. This compressed air is used for several ship operations, such as:

  • Starting the main engine and auxiliary engines
  • Operating pneumatic tools and control systems
  • Automatic control valves and instruments
  • Deck air for cleaning and maintenance

 2. Types of Marine Air Compressors

🔹 1. Starting Air Compressor

  • Used to supply high-pressure air (usually 30 bar) to start engines.

🔹 2. Working Air Compressor (Service Air)

  • Supplies air at lower pressure (usually 7–10 bar) for general ship use.

🔹 3. Control Air Compressor

  • Supplies clean, dry, and stable air (6–7 bar) for automation and control systems.

 3. Principle of Operation

A marine air compressor works on the principle of increasing air pressure by reducing its volume using piston movement (in reciprocating compressors) or rotors (in screw compressors).

 4. Types Based on Design

🔹 A. Reciprocating Air Compressor

  • Uses pistons and cylinders
  • Air is compressed in two or three stages
  • Commonly used on ships

🔹 B. Screw Air Compressor

  • Uses two rotating screws (rotors)
  • Continuous compression
  • Quieter and less maintenance

 5. Stages of Compression

📌 Single-Stage Compressor

  • Compresses air in one cylinder
  • Used for low-pressure applications

📌 Two-Stage Compressor

  • First stage compresses air → goes to intercooler
  • Second stage compresses again to higher pressure
  • Used for starting air (30 bar)

 6. Main Parts of a Reciprocating Marine Air Compressor

1.  Air Filter – Cleans air before compression

2.  Suction Valve – Allows air into cylinder

3.  Piston and Cylinder – Compress air

4.  Discharge Valve – Sends air to receiver

5.  Intercooler – Cools air between stages

6.  Aftercooler – Cools air before entering the bottle

7.  Crankshaft and Connecting Rod – Transmit motor power

8.  Motor (Electric) – Drives the compressor

9.  Lubrication System – Reduces wear on moving parts

10. Safety Valves – Prevent overpressure

11. Unloader Valve – Eases startup by unloading air pressure

 7. Air Bottle (Air Receiver)

  • Stores compressed air
  • Rated up to 30 bar or more
  • Has relief valve, pressure gauge, drain valve, and non-return valve

8. Uses of Compressed Air on Ships

           Use

  Type of Air

 

 

Starting main and aux engines

Starting Air (30 bar)

Control systems and automation

Control Air (6–7 bar)

Cleaning and maintenance

Working Air (7–10 bar)

Whistle, fog horn

Control or Service Air

 

 

 

 

 

 

 

 

9. Safety Devices

  • Relief Valve – Prevents overpressure
  • Temperature Cut-out – Stops compressor if too hot
  • Pressure Switch – Controls start and stop of compressor
  • Oil Pressure Alarm – Stops machine if oil pressure is too low
  • Water Separator – Removes moisture

 

10. Common Faults and Troubleshooting

Problem

Cause

Solution

High temperature

Dirty intercooler or blocked valves

Clean intercooler and valves

Excessive noise or vibration

Loose parts or worn bearings

Tighten and replace parts

Oil carry-over in air

Worn piston rings or oil overfill

Replace rings, check oil level

Low pressure

Valve leakage or piston problem

Check valves and pistons

Motor overload

Air line blockage or overpressure

Check lines and pressure switch

 

11. Maintenance of Marine Air Compressor

  • Check and change lubricating oil
  • Clean or replace air filters
  • Drain water from intercooler and air bottle
  • Check all valves, belts, and connections
  • Inspect piston rings, bearings, and crankshaft
  • Test safety valves and cut-out switches

 12. Safety Precautions

  • Never open compressor when running
  • Always release pressure before opening
  • Use correct PPE (gloves, goggles, etc.)
  • Follow lock-out/tag-out procedure
  • Keep records of running hours and maintenance

 

12. Important Operating Parameters

Parameter

Value (Approx.)

Starting Air Pressure

30 bar

Working Air Pressure

7–10 bar

Control Air Pressure

6–7 bar

Oil Temperature

< 90°C

Air Discharge Temp.

< 160°C

 

1. What is a marine air compressor?

Answer:
A marine air compressor is a machine used on ships to compress air and store it at high pressure. The compressed air is used for starting engines, operating pneumatic tools, automation systems, and for general service use.

2. What are the types of air compressors used on ships?

Answer:

  • Starting Air Compressor (30 bar) – For starting main and auxiliary engines
  • Working/Service Air Compressor (7–10 bar) – For deck air and tools
  • Control Air Compressor (6–7 bar) – For automation and control systems

 3. What is the working principle of a marine air compressor?

Answer:
It works on the principle of increasing air pressure by reducing its volume using piston (reciprocating) or rotors (screw type).

 4. What are the main parts of a reciprocating air compressor?

Answer:

  • Air filter
  • Suction and discharge valves
  • Piston and cylinder
  • Intercooler and aftercooler
  • Crankshaft and connecting rod
  • Motor
  • Safety valve
  • Oil pump and filters

 5. What is an intercooler?

Answer:
An intercooler is a heat exchanger that cools compressed air between compression stages to reduce temperature and improve efficiency.

 6. Why are marine compressors multi-stage?

Answer:
Multi-stage compressors reduce air temperature between stages (using intercoolers), increase efficiency, and achieve higher pressures safely.

 7. What safety devices are fitted on a marine air compressor?

Answer:

  • Relief valve
  • High-temperature cut-out
  • Low oil pressure alarm
  • Pressure switch
  • Non-return valve
  • Water drain valve

 8. What is the purpose of the unloader valve?

Answer:
The unloader valve removes load from the compressor during starting to prevent motor overload and allows the compressor to build up speed.

 9. What are common problems in a marine air compressor?

Answer:

  • Overheating
  • Oil carry-over
  • Excessive noise or vibration
  • Low pressure
  • High moisture in air

 10. What maintenance is required for a marine air compressor?

Answer:

  • Change lubricating oil
  • Clean filters and coolers
  • Inspect valves, pistons, rings
  • Check motor, belts, and bearings
  • Drain air bottle and intercooler water

 11. What pressure is used in starting air systems?

Answer:
30 bar is the typical pressure used for starting main engines and generators.

 12. What precautions should be taken while operating an air compressor?

Answer:

  • Do not open the compressor while running
  • Drain water regularly from air bottles
  • Check safety devices
  • Ensure proper lubrication
  • Wear PPE during maintenance

1. Compressor Not Starting

Possible Causes:

  • Power supply failure or low voltage
  • Faulty pressure switch or control relay
  • Emergency stop is pressed
  • Overload trip or fuse blown
  • Motor fault

Action:

  • Check power supply and fuses
  • Reset emergency stop
  • Inspect motor, relays, and switches
  • Reset overload relay

 2. Compressor Not Building Pressure

Possible Causes:

  • Suction or discharge valve leaking
  • Piston rings worn out
  • Safety valve leaking
  • Intercooler or aftercooler leaks
  • Air receiver leak

Action:

  • Check valve plates
  • Inspect and replace piston rings
  • Test safety valve and tighten/replace if leaking
  • Pressure test intercoolers/receivers

 3. High Air Temperature

Possible Causes:

  • Cooling water flow low or blocked
  • Air filter dirty
  • Intercooler fouled
  • Ambient temperature too high

Action:

  • Clean sea/central cooling water lines
  • Clean/replace air filters
  • Clean intercooler tubes
  • Improve ventilation

 4. Excessive Oil Carryover

Possible Causes:

  • Oil separator/filter damaged
  • Oil level too high
  • Wrong grade of oil
  • Worn piston rings

Action:

  • Check and replace oil separator
  • Maintain correct oil level
  • Use recommended oil
  • Replace piston rings

5. Abnormal Noise or Vibration

Possible Causes:

  • Loose mounting bolts
  • Bearing failure
  • Misalignment
  • Broken valve plate or connecting rod

Action:

  • Tighten bolts
  • Check and replace bearings
  • Realign compressor
  • Open and inspect internals

 6. Motor Overheating

Possible Causes:

  • Overload due to high pressure
  • Blocked suction filter
  • Bad ventilation
  • Motor bearing problems

Action:

  • Check suction/discharge pressure
  • Clean filters
  • Inspect cooling fan/motor bearing

 7. Oil Leakage

Possible Causes:

  • Damaged gaskets/seals
  • Overfilled oil
  • Cracked crankcase

Action:

  • Tighten or replace gaskets
  • Drain excess oil
  • Inspect and weld/replace crankcase

🔧 Important Maintenance Tips:

  • Daily: Check oil level, temperature, pressure, and unusual sounds
  • Weekly: Drain moisture from air receiver and intercooler drain traps
  • Monthly: Clean air filters, check safety valves, and inspect for leaks
  • Annually: Overhaul valves, piston rings, check crankshaft alignment

 

SOLAS Regulations for Marine Air Compressor

Marine air compressors are critical systems under SOLAS Chapter II-1, which deals with Construction – Subdivision and Machinery. Though SOLAS doesn't directly say "air compressor," it includes mandatory requirements for starting arrangements, compressed air systems, and safety features.

✅ Relevant SOLAS Chapter: Chapter II-1

🔧 Key SOLAS Requirements for Air Compressors (Main Engine Starting)

1. 🔋 Compressed Air Storage Capacity

Regulation: SOLAS Chapter II-1, Reg. 26.3.2

  • For ships fitted with internal combustion engines for main propulsion:
    • Must have sufficient air receivers to start the engine at least 12 times (6 times for reversible engines).
    • If the air is also used for auxiliary engines or other equipment, additional capacity must be provided.

📌 Example:

  • A 2-stroke reversible engine must be able to do 12 starts with full air bottles.

2. ⚙️ Number of Compressors

Regulation: SOLAS Chapter II-1, Reg. 26.3.1

  • At least two starting air compressors must be provided.
  • One compressor should be able to recharge the air bottles to full pressure within 1 hour.

3. 🧯 Safety Devices Required

Covered under SOLAS + Class Rules

All compressors must be fitted with:

  • Pressure relief valves
  • Non-return valves (between compressor and air bottle)
  • Automatic drain valves or manual drain valves (for water condensation)
  • High-temperature cut-outs
  • Lubricating oil pressure cut-out switches

4. 🔥 Fire Safety Consideration

SOLAS Chapter II-2, Reg. 4.2.2.5

  • Air compressor discharge lines must not pass through accommodation areas unless properly protected.
  • Air bottles and compressors must be in well-ventilated spaces with fire detection if required.

5. 🔌 Emergency Operation

SOLAS Reg. 26.3.4

  • If the emergency generator is air-started, its air bottle must be independent of the main/auxiliary system.
  • Ensures starting capability during blackout.

📄 Certificates and Logs Required

  • Starting air compressor maintenance log
  • Air bottle pressure log
  • Relief valve test certificate
  • Class survey records for receiver hydraulic test (every 5 years)

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