Compressed air on ships is used for different purposes. High-pressure air of 30 bar is mainly used for the main engine starting.

This high-pressure air is reduced to lower working pressures through pressure reduction valves and is used for other important purposes.

The air at reduced pressures of 7-8 bar is used as service air for a number of applications.

Some of these include starting of Auxiliary Engines, Emergency Generators, Charging of freshwater and drinking water hydrophores, blowing the fog horn, spring air for exhaust valves of the Main Engine, dry washing of Main Engine turbochargers, for use in sewage treatment plants for aerobic sewage breakdowns, soot blowing of boilers, pneumatic pumps for oil transfers and many more applications such as service air for the use of cleaning, painting operations, chipping and operation of pneumatic tools such as grinders, chisels etc.

One more important branch of this 7-8 bar compressed air is used as control air. The control air is a filtered branch of the service air which is made free of any moisture and oil carry-over. This controlled air is used for pneumatic controllers and is important for the operation of machinery onboard ships.

This makes the air line on a ship a very important aspect of ship operations. This article throws light on the air line of a Ship in general, its important components and working.

The complete pneumatic air line on a ship includes the Main High-pressure airline, the service air line and the control air line.

Main Air Compressor

The main air compressor is the heart of the air-line onboard. The air compressor compresses air by means of reducing its volume so as to raise its pressure. Air compressors can be of various types. They include

1. Centrifugal Compressors
2. Rotary vane compressor
3. Rotary screw compressors
4. Reciprocating Air compressors

Most modern merchant vessels are employed with multi-stage reciprocating air compressors having intercoolers & aftercoolers with auto-draining and unloading arrangements.

The capacity of the main air compressor is expressed in terms of Free Air Delivery (FAD) and is stated in cubic mtrs /hour.

Free Air Delivery can be defined as the volume of air actually discharged by the compressor in 1 hour, that would occupy if expanded down to atmospheric pressure and cooled to atmospheric temperature.

The discharge of the main air compressor is led into a main air bottle or reservoir which stores this pressurised air at a maximum of 30-32 bar.

A ship may have 2 or 3 main air compressors depending upon many factors such as each air compressor capacity, amount of volume of air needed for starting of the Main Engine, demand of air on that particular ship etc.

The marine boilers and exhaust gas economizers on certain ships are soot blown with air, these ships may be employed with higher capacity air compressors at the design stage depending on ship owners.

As per SOLAS requirements, a ship’s main air compressors should be able to fill its air reservoirs from 0 to maximum pressure (30bar) within 1 hour.

Main Air Reservoir

Each ship is equipped with a set of 2 air reservoirs. They may be of the vertical or horizontal type.

Air reservoirs are hydraulically pressure tested to 1.5 times its working pressure.

As Per Solas Regulations –

The total capacity of air reservoirs must be sufficient to give at least 12 consecutive Main Engine starts for a reversible engine, and at least 6 consecutive starts for a non-reversible engine without refilling of the reservoirs.

There must be 2 identical main air receivers and 1 emergency air bottle for every vessel.

Air Reservoir Mountings

Each air reservoir should be equipped with the following mountings:

1. Fusible Plug

Composition – Bismuth 50%, Tin 30%, Lead 20%
Melting Point: 220deg F (104.4deg cel) Fitted at the reservoir’s bottom or on the reservoir at the ship side when a relief valve (safety valve) is not directly fitted on the reservoir.
It is fitted to release the compressed air in the event of abnormally high compressed air temperature.

2. Atmospheric Relief Valve

It is provided as over-pressure protection and as a back-up of the fusible plug.

In case of an Engine Room fire when CO2 flooding is required, this valve is to be opened before evacuating the engine room.

(The air receiver relief valve opening could either open outside the engine room through the ship’s funnel or inside the engine room itself. In case of the latter, CO2 bottle calculations for fighting a fire in the Engine room is done accordingly and the extra CO2 required is taken into consideration at the ship’s design stage)

3. Spring Loaded Safety Valve

Setting pressure 32 bar (for a 30-bar working pressure) with equal to or greater than 10% rise in accumulation of pressure may be fitted directly or with extension.

4. Compensation Ring

When a hole is cut or machined into a pressure vessel, higher stresses will subject to the material around the hole, and to reduce this, compensation rings are fitted.

It is a flange on which a valve or fitting is usually mounted. A compensation ring provides for structural integrity in the air pressure vessel.

5. Manual Drain valve or Automatic Drain valve

6. Pressure gauges

7. Access doors

8. Main Starting valve, auxiliary starting air valve, fitting valve, service air or whistle air valve

Large cylindrical air bottles usually have one longitudinal welding seam. The longitudinal and circumferential seam is machine welded with full penetration welds.

The welding details are governed by the pressure of air that is to be stored in conjunction with classification society regulations.

All welded air receivers have to be stress relieved or annealed at a temperature of about 600 deg Celsius and the welding is to be radiographed for safety purposes.

Receivers are subjected to statutory survey and inspection, periodically hydraulic tested at 1.5 times the working pressure, is to be applied every 10 years for large receivers.

Air Bottle Inspection

Air receivers are to be inspected as per PMS and checked for any signs for corrosion. Moisture in air receivers can give rise to corrosion and despite the proper operation of compressor cooler drains, a large amount tends to collect, particularly in humid conditions.

It is good practice to check air reservoir drains regularly to assess the quantity of liquid present. In extreme conditions, drains may have to be used 2-3 times daily to remove accumulated emulsion. Mostly corrosion is found near the air receiver drain.

After thorough visual inspection, if required, thickness measurement can be done using an ultra-sonic thickness gauge. If the thickness of the air receiver is compromised, we have to reduce the air pressure to be contained in that particular air bottle.

This, after certain calculations, can be done by changing the cut-in, cut-off settings of the air compressor when that particular receiver is in use and relief valve settings have to be re-adjusted. Also, the air receiver can be isolated completely and kept on stand-by, can be filled manually with caution, whenever required.

All internal welds or small changes in cross-section need to be thoroughly inspected.

If the air bottle is too small to manually enter, then internal inspection can be carried out using a camera with a probe.

Internal Surface Coating

Should be graphite suspension in water, Linseed oil, Copal Vanish or Epoxy coating, having basic properties such as anti-corrosive, anti-toxic and anti-oxidation.

Safety Devices On Main Air Bottle

1. Fusible Plug
2. Pressure relief valve
3. Atmospheric Relief Valve
4. Low-Pressure Alarm
5. Automatic or Remote-control moisture drain valve

The Control Air System

A branched airline through a pressure reducing valve is supplied to the Control Air line.

Pneumatic control equipment is sensitive to contaminants which may be in compressed air. Viscous oil and water emulsions can cause moving parts in control equipment and control valves to stick and produce general deterioration of diaphragms, spools and other parts made of rubber.

Water can cause rust build-up which may also result in parts sticking or being damaged by these rust particles. Metallic wear and other small particles can cause damage by abrasion.

Any solids mixed with oil and water emulsions can conspire to block small orifices. Clean and dry control air is thus essential for the trouble-free operation of control- air systems.

When the source of control and instrument air is the main air compressors and the main air reservoir itself, then special provision is necessary to ensure that air quality is high.

The pressure reducing valve which brings the main air pressure to the 7 or 8 bar required by the control air system, can be affected by emulsion carry over and can require frequent cleaning to stop air contamination.

Automatic drain traps may be fitted in the control air system, but many have traps which require daily draining by the engine crew.

Large amounts of free moisture and oil emulsion carry-over in the air can be removed by special control-air membrane filters installed in the control air line.

Control Air Filter

A typical control air filter arrangement consists of an oil & moisture collecting filter followed by a membrane air dryer filter. The treatment of air through these membrane filters results in the air being filtered and dried in order to remove virtually all traces of oil, moisture and air impurities.

A simple line air filter is provided with a small plastic float and auto drain arrangement.

The filter can also be drained manually if the vessel enters a highly humid environment and frequent draining is required.

The filter dryer unit is made up of a primary filter, secondary filter and membrane hollow fibre elements.

Air Flow Through The Control Air Dryer

The control air enters the dryer chamber through the line filter located in the lower part of the dryer unit. In the dryer unit, the primary filter removes the coarse rust particles, dust and other larger impurities.

The secondary filter acts like a coalescer, separating water droplets and oil mists up to 0.3 microns. A differential pressure gauge indicates the condition of the primary and secondary filters.

A higher differential pressure indicates a dirty membrane filter. The membrane elements are to be renewed as per the ship’s PMS.

Piping

The high-pressure air piping from the air compressor to the receiver should be as smooth as possible without any bends in the pipeline so as to allow air to flow freely to the receiver without restrictions. Bends in the piping can create backpressure in the line in case of accumulated moisture or oil emulsion in the line.

Emergency Air Compressor And Emergency Air Bottle

The emergency air compressor is a small independent air compressor which can be either driven by an independent prime mover like an engine or having a power supply from the emergency switchboard.

It is used to fill up the emergency air bottle which has a sufficient volume of air to start the auxiliary engine of a dead ship.

The control air onboard is also used in the Emergency Shut-Off Valve operating system.

An emergency QCV – Air bottle with 7 bar air pressure is used to operate all Quick Closing valves, fire and funnel dampers on board.

This arrangement consists of a 7 bar Emergency QCV air bottle with QCV- shut off valves that are to be always in a state of readiness.

In case of an uncontrollable fire in the engine room, the Quick closing valves are operated which supply this control air to SHUT specific outlet valves of all Fuel Oil and Lube Oil tanks and ER funnel and Blower dampers thereby cutting off all fuel and air supply.

Control Air Supply is also used on Emergency Shut Down Systems (ESDS) on Gas Tankers.

Disclaimer: The authors’ views expressed in this article do not necessarily reflect the views of Marine Insight. Data and charts, if used, in the article have been sourced from available information and have not been authenticated by any statutory authority. The author and Marine Insight do not claim it to be accurate nor accept any responsibility for the same. The views constitute only the opinions and do not constitute any guidelines or recommendation on any course of action to be followed by the reader.

The article or images cannot be reproduced, copied, shared or used in any form without the permission of the author and Marine Insight.

Compressed Air Line On Ships – A General Overview appeared first on Marine Insight - The Maritime Industry Guide

Marine air compressors are used to start large slow speed and medium-speed marine diesel engines, and therefore are an integral part of engine room on-board.

Generally, there are two compressors onboard a ship ( can be more than two depending upon the requirement of the vessel.)

The two compressors fill up the air receivers, which should have total capacity such that the engine can start 12 times ahead and astern without replenishment of the receivers. This capacity is limited to 6 times if it’s a unidirectional engine.

Each of the air receivers is fitted with a relief valve, which will limit the pressure rise to 10% of the maximum design pressure of the receiver.

Related Reading: Basics of air compressor on ship

Also, the outlet of the relief valves should be outside the engine room so that it doesn’t contribute in case there is a fire near the air receiver.

Usually, air compressors onboard are capable enough to charge both the air receivers from zero to full in one hour.

The air compressors are fitted with several safety devices as well such as relief valves on each stage which limit the pressure rise to 10% of the maximum working pressure.

The delivery side is fitted with a high-temperature switch which cuts off the compressor at a specified temperature or a fusible plug which may melt at 121 degrees centigrade.

Performance of the marine air compressor is taken at the end of every month to ascertain the working capacity of the compressor.

The performance report includes the delivery air temperature, cooling water inlet and outlet temperatures, lube oil pressure and discharge pressures of each stage of the compressor.

Related Reading: Efficiency Of Air Compressor

The compressor is generally started in an unloaded condition so that minimum current is drawn by the motor and the bearings are devoid of oil.

Maintenance jobs carried out on the main air compressor depending on the running hours of the compressor and all these jobs are mentioned in the maintenance manual of the compressor.

• The planned maintenance system devised by the company must be strictly followed else there can be a severe breakdown
• To avoid breakdowns in the main air compressor, the following maintenance must be considered
• Daily morning and evening rounds including checking of lube oil level, discharge pressures of various stages, discharge temperature and running time of the compressor.
• When an engineer takes over, he/she must first take note of all the maintenance jobs that might be due in his/her contract, and take spare part inventory and order the spares, if required with the help of Chief Engineer.
• The engineer must also note the torques required for tightening various bolts, screws and nuts on the main air compressor.
• The testing of air compressor alarms must be carried out as per the PMS, which generally demands the alarms to be tested once every three months.
• One of the most important things in the main air compressor is the bumping clearance of the compressor, which will be discussed later in the compressor maintenance.
• As a basic thumb rule, the main air compressor should run for 3-4 hours every day on an MR tanker. If the running hours exceed this duration, then the required checks must be carried out.

VOLUMETRIC EFFICIENCY OF AN AIR COMPRESSOR

The volumetric efficiency of an air compressor is defined as the ratio of the volume of air discharged by the compressor as free air and the swept volume of the LP piston, whereas free air is defined as the air at atmospheric pressure and 15 degrees centigrade.

Related Reading: Starting and stopping procedure of air compressor

BUSTING THE MYTH ABOUT BUMPING CLEARANCE

Well, you might wonder about Bumping Clearance being marked in bold, here’s the deal:

Bumping clearance is the top clearance in the main air compressor between the top of the piston and the cylinder head when the piston is at TDC.

This clearance is determined by the cylinder head gasket which should be of the correct size and indeed should be a genuine spare.

Related Reading: Top 5 Air Compressor Problems Marine Engineers Must Know

Bumping clearance is important as it relates to the volumetric efficiency of the compressor.

When the bumping clearance of the compressor is large then the clearance volume is big enough to accommodate a large volume of air when the piston is at the end of its stroke.

When the piston moves downwards, then a large amount of suction stroke becomes ineffective as the suction will happen only when the cylinder pressure falls below the atmospheric pressure.

Hence the piston stroke is wasted by expanding a large amount of air that has accommodated in the clearance volume due to a large bumping clearance.

HOW TO CHECK THE BUMPING CLEARANCE? 

Generally, the bumping clearance of the compressor is fixed by the thickness of the cylinder head gasket used by the manufacturer but it could be measured by a lead ball placed between the top of the piston, assembling the compressor with the manufacturer recommended cylinder head gasket and taking the piston back to the top dead centre.

The ball will compress and then can eventually be measured by a micrometre. It is generally in the range of 1.2 mm to 1.8 mm.

FREQUENCY: 3000 RUNNING HOURS OR DEPENDING ON THE PERFORMANCE. 

HOW TO ADJUST THE BUMPING CLEARANCE?

Bumping clearance could be adjusted by changing the thickness of the cylinder head gasket or by adding or removing shims from the foot of the connecting rod and the bottom end bearing of the compressor.

CHECKING BASIC SCREWED CONNECTIONS

All the unions and screwed connections must be checked for tightness and must be re-tightened, if necessary.

This includes all cooler and airlines, unions on pipe and hose lines, cylinder heads, cylinders, electric motors, measuring and switching devices, bearings and other accessories.

FREQUENCY: EVERY 250 RUNNING HOURS.

REPLACING AIR FILTER CARTRIDGE

The air filter must be checked at frequent intervals and approximately at every 250 hours or whenever the air discharge temperature becomes high.

The air filter element must be replaced with a new one and sufficient spares must be available onboard.

An air filter is the first step to keep the compressor healthy.

It must be noted that the air compressors are installed at a place where there is sufficient air supply to ensure the suction is never devoid of air.

ONE MUST MAKE SURE THAT THE OLD CARTRIDGE IS NOT BLOWN WITH AIR AND RE-USED, AS THIS MAY DAMAGE THE AIR FILTER.

Dirty air filters affect the volumetric efficiency of the compressor and so does the temperature of the inlet air to the compressor.

FREQUENCY: EVERY 2000 RUNNING HOURS.
 

CHANGING OIL

It is important that the oil must be changed according to the maintenance frequency as the lubricating oil is not only used for the lubrication of the running parts of the compressor but also to remove the heat generated during the operation of the compressor.

The compressor must be run for some time before the oil is changed as it ensures that all the sludge and particles are in suspension.

The oil should be completely drained by removing the drain plug and flushed with fresh oil before the oil is replenished back again.

The crankcase should be thoroughly cleaned as well with a lint-free cloth and must be checked for bearing wear as well.

TWO DIFFERENT GRADES OF OIL MUST NOT BE USED AND MIXED. 

FREQUENCY: 1000 RUNNING HOURS.

CLEANING OIL STRAINERS

The oil strainer is generally a mesh in a plate which is supposed to be cleaned at defined maintenance intervals. The filter should also be cleaned when the oil is changed.

It should be cleaned by a solvent and blown with air.

FREQUENCY: 1000 RUNNING HOURS.

CHECKING VALVES

This is one of the most important jobs in the maintenance of the compressor. Hence extreme care must be taken while carrying out this job.

WHEN REMOVING AND INSTALLING A VALVE, EXTREME CARE MUST BE TAKEN THAT NO VALVE PARTS ARE DAMAGED. THIS APPLIES TO THE SEALING SURFACES OF THE VALVE.

Different types of compressors have different types of valves and removal methods for different stages

The valves must be removed and should be checked for leakage with diesel oil or water

The valves must never be held on vice but should rather be held on the tool given for the same.

All the parts must be properly cleaned after opening the valve and they must be checked for the carbonization as well. Over carbonization reveals that the oil topped up is more than required. This would lead to the sticking of the valves and eventually they would break.

Sticking of the valves will also reduce the volumetric efficiency of the compressor as the quantity of air discharged would be comparatively lesser.

The valve plate should be checked by pushing the valve plate from the side of the valve seat by a screwdriver. The valve plate will move a distance which is equivalent to a valve lift.

The springs and valve plates should be changed if required.

The plate could be lapped as well if no spares are available.

FREQUENCY: 3000 RUNNING HOURS FOR THE DISASSEMBLING AND CLEANING OF THE VALVE. 3000 HOURS FOR THE REPLACEMENT OF THE VALVE PLATE. 3000 HOURS FOR CHECKING THE FATIGUE OF THE SPRING AS WELL. 

Related Reading: Troubleshooting Air Compressor On Ships

INSTALLING VALVES

All the valves must be re-fit with new gaskets and rings only. Only original spare parts must be used. Installing non-original gaskets may lead to compressor leaks and damage.

VALVES ARE THOSE PARTS OF A RECIPROCATING COMPRESSOR WHICH ARE MOST STRESSED, THUS THEIR MAINTENANCE MUST BE DONE CAREFULLY AND WITH EXTREME PRECISION.

HEAVILY CARBONISED VALVES DEPICT THAT THE LUBRICATING OIL HAS BEEN CARRIED OVER.

REPLACING VALVES

It is generally recommended by the manufacturer that the valves must not be repaired as they have a life and may fail due to fatigue. Thus, they must be replaced and the old ones disposed of.

The valves are supposed to be replaced in the same way as mentioned in the checking of the valves.

STICKING VALVES? WHY AND HOW DO THEY AFFECT THE COMPRESSOR? 

If a valve is sticking, then it might add to the woes of the compressor as a sticky suction valve might lead to a loss in the air delivered because a part of air will be returned back to the suction side (with the valve not seating properly because of the carbon deposit or the spring being defective).

Similarly, if the delivery valve is sticking then a part of delivery air might return back to the cylinder during the suction stroke of the piston.

VALVE LIFT TOO HIGH? HOW DOES IT MATTER?

The valves with too high a lift will take a lot of time to re-seat and hence are liable to break at the piston delivery stroke as the pressure might be high for the valves to sustain.

INTERCOOLERS AND HOW TO CLEAN THEM?

Intercoolers are generally arranged after every stage of the main air compressor to reduce the work done in compressing the air by successfully cooling it down between stages. The intercooler is generally in the form of copper tubes bent in a U form. The air passes through the tubes and water circulates around them. These intercoolers could be a single tube type or straight tube type.

These types of intercoolers are provided with purge-spots to collect and drain water/oil which might find its way to the air coolers.

The intercoolers are generally opened up as per the maintenance frequency and are supposed to be cleaned by a solvent and the integrity of tubes to be checked as well.

They’re provided with a bursting disc in order to relieve the pressure in case a tube bursts.

The single tube type coolers are difficult to clean and the rate of wear is more than the straight tube types.

The straight tube types, on the other hand, could be plugged if they leak.

FREQUENCY: EVERY 3000 RUNNING HOURS.

CYLINDER LINER, COOLING JACKET AND PISTON

The air carries a lot of moisture in the cylinder liner which could wash away the lubricating oil film from the liner, thus causing liner wear which could also result in the scoring of the liner.

Thus, proper draining of the compressor is necessary to prevent the excessive liner and piston rings wear.

Cylinder liners could be lubricated by the oil splashed from the crankcase. They could also be lubricated by lubricating oil quills similar to the main engine delivered by an engine-driven lube oil pump.

The piston rings could wear in due time causing blow past and eventually reducing the volumetric efficiency of the compressor.

FREQUENCY: THE CYLINDER LINERS ALONG WITH THE COOLING JACKET ARE TO BE INSPECTED/CLEANED IN EVERY 3000 RUNNING HOURS OF THE COMPRESSOR. PISTON, PISTON RINGS AND OIL SCRAPER RING TO BE CHECKED IN EVERY 6000 RUNNING HOURS.

LUBRICATING OILS

Different manufacturers have different requirements for the use of lubricating oils. The compressors generally do not permit the use of synthetic lubricating oils with 3 stage air-cooled compressors because the good hydrolytic properties of synthetic oils cause moisture to condense in the crankcase thus there is a risk of corrosion and drive damage.

Because of their design, 3 stage air-cooled compressors have low final compression temperatures, rendering the high-temperature stability of synthetic oils useless.

THE JOBS ARE MORE OR LESS SIMILAR FOR ALL THE COMPRESSORS BUT AN INSTRUCTION MANUAL MUST BE STRICTLY FOLLOWED BEFORE CARRYING OUT ANY MAINTENANCE ON A COMPRESSOR.

Related Reading:

• Procedure For Starting Breathing Air Compressor
• What is a Bearing Scraper?

Disclaimer: The authors’ views expressed in this article do not necessarily reflect the views of Marine Insight. Data and charts, if used, in the article have been sourced from available information and have not been authenticated by any statutory authority. The author and Marine Insight do not claim it to be accurate nor accept any responsibility for the same. The views constitute only the opinions and do not constitute any guidelines or recommendation on any course of action to be followed by the reader.

The article or images cannot be reproduced, copied, shared or used in any form without the permission of the author and Marine Insight. 

Marine Air Compressor Maintenance – Things You Must Know About appeared first on Marine Insight - The Maritime Industry Guide

Marine air compressor is an extremely important auxiliary machinery on ships and other ocean going vessels. It is used for producing compressed air, which has a number of applications on board, both in the engine and deck departments.

It’s a duty of a marine engineer to ensure that the ship’s air compressor is running smoothly and efficiently. Moreover, as several other machinery systems in the engine room are dependent on the air compressor for their operation, it is important that the compressor is kept in up-to-date condition all the time.

This ultimate guide to marine air compressors provides all the details which you would require to understand, operate, and maintain a compressor on a ship.

Uses of Compressed air

As mentioned earlier, the air compressed produced by air compressors is used for a variety of purposes on ships, ranging from starting of main engine to cleaning and maintenance purposes. Read this to find out how compressed air is used in daily routine and maintenance jobs of ships.

Basics of air compressor

Learn about the basics of air compressor used on ships, along with a general overview of different types of air compressors used on board and their applications. This is a must read for all those marine engineers who are just starting their careers at the sea. It is also an excellent resource to brush up your air compressor basics.

Different parts of a marine air compressor

Know about different parts of marine air compressor and how they function together to deliver the compressed air. If you want to get a detailed explanation about each part of the air compressor, then this is a must read article for you.

Starting and stopping a marine compressor

Once you have familiarized with the basics and different components of marine compressor, it is time to get your hands on the machine by learning to start and stop the same without any errors.

This is the ultimate checklist for a marine engineer, who wants to start, operate, and stop the marine compressor in the right manner to avoid any damage to the machinery.

Many ships also have a breathing air compressor on board. Find out the procedure to start this compressor here – Procedure for starting breathing air compressor

Safety features and maintenance procedure of marine air compressor

If you are a marine engineer, you would be more interested in the maintenance and repair of marine compressors.

If you are doubtful about the maintenance procedure you should follow, then read this to find out about different safety features that are found on compressors and how maintenance should be done.

Efficiency of air compressor

As you carry out routine maintenance of the air compressors, you would also assess the performance and efficiency of the machine. Find out about the different factors which decide the efficiency of the air compressor and what steps should be taken to ensure efficient running.

Understanding of Clearance Volume (bumping clearance) of air compressors

While carrying out the maintenance of the air compressor, clearance volume is one aspect which is of utmost importance. It is imperative that every marine engineer understands the importance of measuring bumping clearance along with the procedure to do so.

Find out the significance of bumping clearance and how it is checked in here.

Air compressor condition report

A marine engineer has to make report after he has carried out maintenance and repair work on the air compressor. Here’s a free report sample for you in case you are not sure as to how to make it.

 Air bottle (air receiver)

The compressed air produced on ships is stored in an air bottle, from where it is supplied to different systems. Find out more about the construction, working, and importance of air bottle on ships in there.

Do you think we have missed to mention any important aspect of marine air compressor? Let us know and we will include it in here.

The Ultimate Guide to Air Compressors on Ships appeared first on Marine Insight - The Maritime Industry Guide

Clearance volume or bumping clearance is the space between the top of the piston and the cylinder head of an air compressor. This clearance is an important aspect of the compressors and should be as less as practically possible to improve the volumetric efficiency of the compressor. The clearance volume should not be too less or too more. Moreover, it affects the efficiency of the machinery and thus should be checked at regular intervals of time.

Significance and Effects of Bumping Clearance

In an air compressor, when the discharge valve closes in the end of the compression cycle, a small amount of high pressure air is trapped in the clearance volume.

Before again taking suction, the air trapped in the clearance volume must expand below the suction pressure i.e. below the atmospheric pressure.

The expansion of this trapped air in the clearance volume causes effective loss of stroke due to which the volumetric efficiency of compressor drops. Therefore, the clearance volume has a significant effect on the efficiency of the compressor.

Effects Due to Less Clearance

Small clearance volume may result in piston banging or colliding to the cylinder head.
This is dangerous when the compressor when is running in unloaded condition without any resistance to the movement of the piston.

Effects Due to Large Clearance

Large bumping clearance retards the formation of vacuum on the suction stroke and thus less air is drawn inside for compression and accordingly the weight of the air delivered is reduced proportional to the clearance volume.

Compressor has to run for a longer period to provide the necessary compression pressure.

Reasons for Change in Clearance Volume

During overhauls of the air compressor, if the gasket fitted between the cylinder head joints is of the wrong type, then the bumping clearance will increase, resulting in wear down of bottom bearings or wrong bearings are put in place.

How Bumping Clearance is checked?

Bumping clearance is checked by putting a lead ball or plastic gauges over the piston and then turning the compressor one revolution by hand.

By doing this the lead ball will compress and the thickness obtained is the clearance volume.

This thickness is measured with vernier caliper or micrometer and is then compared with the manufacturer’s value. Adjustments are made in case there is an offset in the value.

Adjustment of bumping clearance

Bumping clearance can be adjusted with the help of inserting shims (thin metallic plates) in the bottom bearings. Inserting shims will move the connecting rod and the piston which will change the clearance.

What should be the Bumping Clearance?

Generally bumping clearance depends on the manufacturer but as a thumb rule it should be between 0.5% to 1% of the bore of the cylinder.

If you liked this article, you may also like to read Different parts of Marine air compressor

What is Clearance Volume or Bumping Clearance in Air Compressors? appeared first on Marine Insight - The Maritime Industry Guide

Air compressors on a ship require special attention and care for their smooth running. It is only through routine maintenance and checkups that you can expect smooth and efficient running of the compressors.

However, compressor is a peculiar equipment which tends to get some or the other problem while working. In this article, we will go through each and every problem that can arise in an air compressor and also enumerate ways to troubleshoot that problem.

This is the ultimate guide for troubleshooting air compressors on a ship

Lube Oil Pressure Low

The following can be the reasons for lube oil pressure low in the air compressor:

• Faulty pressure gauge.
• Cock to pressure gauge in closed position.
• Low oil level in the sump.
• Leakage in supply pipe.
• Suction filter is choked.
• Oil grade in the crank case is not compatible.
• Attached Lube oil gear pump is faulty.
• Worn out Bearing, clearance is more.

2)  Abnormal noise during operation

If you get any abnormal noise during operation, the following can be the reasons:

• Loose foundation bolts.
• Worn out bearings, clearance is high.
• Imbalance crankshaft resulting in high-end play.
• Valve plate broken or faulty.
• Relief valve lifting below setting pressure.
• Bumping clearance is less.
• Piston worn-out, broken piston ring.

Vibration in the machinery:

In case of vibrations, the following reasons are to be considered and checked.

• Foundation bolts are loose.
• Discharge pressure high, faulty discharge valve plates.
• Liner and piston worn out.
• Small bumping clearance.

4)Cooling water temperature is high

Cooling water temperature can go high because of the following reasons:

• Inlet or outlet valve for cooling water is closed.
• Inter-cooler is chocked.
• Cooling water in the expansion tank is low.
• Pipe passage becomes narrow due to scale formation.
• Water-pump belt or gear drive broken.
• ump not working.

5)First stage discharge pressure high
In case the first stage discharge pressure is high, it must be because of :

• Pressure gauge is faulty.
• Inter-cooler air passage is chocked.
• Second stage suction valve is not closing properly, allowing air to escape from 2^nd to 1^st stage.
• Discharge valve of first stage is malfunctioning, and remains in closed position.
• Spring of discharge valve is malfunctioning.

6)  First stage discharge pressure low

In case the first stage discharge pressure is low, it must be because of:

• Pressure gauge is faulty.
• Suction filter is choked.
• Unloader of first stage is leaking.
• First stage suction valve is not closing properly, resulting in compressed air leakage.
• First stage suction valve is not opening fully, leading to less intake of air.
• Discharge valve is faulty and remains open permanently.
• Relief valve after first stage is leaking.
• Piston ring of first stage is badly worn out, allowing air to pass.

7) Second stage discharge pressure high:

In the case of high discharge pressure in the second stage, the reasons can be:

• Faulty pressure gauge.
• Discharge valve to air bottle is shut.
• Second stage discharge valve plate worn out, and even the spring worn out.
• Valve is stuck in closed position.
• After cooler air passage choked.
• Air bottle is over pressurized.

8 ) Second stage discharge pressure low:

When second stage discharge pressure is low, it could be because  of:

• Pressure gauge is faulty.
• Suction valve for second stage is malfunctioning, in open position.
• Suction valve for second stage is not opening fully, and thus less intake of air.
• Discharge valve is faulty and remains open during operation.
• Piston rings of second stage are worn out, leaking out compressed air.
• Relief valve of second stage is leaking.
• Un-loader of second stage is leaking.

9) Relief valve of first stage lifting

If relief valve of the first stage is lifting, it can be because of

• Spring of relief valve is malfunctioning, thus lifting at less pressure.
• Discharge valve of first stage is not opening.
• Intercooler air passage is blocked.
• Suction valve of second stage is in stuck position.
• Water inside the compression chamber due to crack in the jacket and water is leaking inside

10) Relief valve of second stage is lifting

If relief valve of the second stage is lifting, look for the following reasons:

• Relief valve is malfunctioning, lifting at lower than setting pressure.
• Main discharge valve to the air bottle is closed.
• Discharge valve plates and spring are worn out, valve in closed position.
• Blockage in the after cooler air passage.
• Water inside the compression chamber due to crack jacket.

The above-mentioned points are just a brief explanation to the problems of the air compressor tackled on board. However, they serve as a guiding light for finding the right fault in the compressor.

You may also like to read – What is a Bearing Scraper?

Troubleshooting Air Compressors on a Ship: The Ultimate Guide appeared first on Marine Insight - The Maritime Industry Guide

Every Air compressor on a ship is fitted with several safety features to avoid abnormal and dangerous operational errors of the equipment. If safety, alarms and trips are not present on the air compressor, abnormal operation may lead to breakdown of the compressor and may also injure a person working on or around it.

Different safety features on an air compressor are

Relief valve:

Fitted after every stage to release excess pressure developed inside it. The setting of the lifting pressure increases after every ascending stage. Normally fitted between 1st stage and intercooler and 2nd stage – aftercooler.

Bursting disc:

A bursting disc is a copper disc provided at the air cooler of the compressor. It is a safety disc which bursts when the pressure exceeds over the pre-determined value due to leaky air tubes of the cooler (intercooler or aftercooler).

Fusible plug:

Generally located on the discharge side of the compressor, it fuses if the air temperature is higher than the operational temperature. The fusible plug is made up of material which melts at high temperature.

Lube Oil low pressure alarm and trip:

If the lube oil pressure goes lower than the normal, the alarm is sounded followed by a cut out trip signal to avoid damage to bearings and crank shaft.

Water high temperature trip:

If the intercoolers are choked or the flow of water is less, then the air compressor will get over heated. To avoid this situation high water temperature trip is activated which cut offs the compressor.

Water no-flow trip:

If the attached pump is not working or the flow of water inside the intercooler is not enough to cool the compressor then moving part inside the compressor will get seized due to overheating. A no flow trip is provided which continuously monitor the flow of water and trips the compressor when there is none.

Motor Overload trip:

If the current taken by motor during running or starting is very high then there is a possibility of damage to the motor. An overload trip is thus fitted to avoid such situation.

Maintenance

A compressor requires a proper planned routine maintenance for safe and efficient operation and to avoid breakdown maintenance. Routine for maintenance depends on the manufacturer’s advice given in the manual. The following are the maintenance checks that should be carried out after the mentioned running hours.

@ 250hrs:

1) Clean air filter.
2) Check un-loader operation.
3) If belt is provided for driving cooling water pump, check its tightness.

@ 500hrs:

1) Change lube oil and clean sump.
2) Clean lube oil filter.
3) Check and renew suction and discharge valves with overhauled one.

@ 1000 hrs:

1) Crankcase inspection, main and big end bearing inspection.
2) Relief valve overhauling.

@ 4000 hrs:
1) Piston and big end bearing overhauling, piston ring renewal.
2) Intercooler cleaning.
3) Motor overhauling.

Running hour may differ from maker to maker. The above description is a rough idea for a general maintenance of marine air compressor.

Without the supply of air, a ship will soon be termed as a dead ship. It is very important for a marine engineer to understand the importance of the compressor; hence it’s the responsibility of the engineer onboard to maintain the compressor, the air receiver and the air pipe line and the overall system in the proper condition.

You may also like to read – Compressed Air Line On Ships – A General Overview

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An air compressor is an important machinery in the ship’s engine room which supports several other systems, including the main engine. However, the compressor is one machine which requires constant monitoring and maintenance in order to ensure it runs smoothly. Though a number of safety devices are provided on the compressor, it is only prudent to take all the necessary precautions that are required for the smooth running of the compressor.

For understanding common problems with air compressors, it is important to know all the different parts of the system. One must also know all important checks that are required to be made before operating the compressor. As a marine engineer working on ships, you should be able to understand and troubleshoot some of the common problems associated with the marine air compressor. Mentioned below are five such common problems.

1. Compressor Capacity is Low:

This is one of the most common problems seen on all types of ships. Often, compressor capacity can go low or reduced if it is running for a long time and eventually it is unable to cope up with the air demand.

Main reasons for this problem are:

• Leakage in discharge and suction valves
• Fault or leakage in the unloader
• Leakage from the relief valve
• Increase in bumping clearance (Read more about bumping clearance here.)
• Wrong setting of compressor auto cut-in and cut-out (too close)

2. Oil Carry Over in Air:

If the compressed air in the system is carrying oil, would be mainly because of the following reasons :

• Oil-water separator is not working correctly hence oil is being carried to the air receiver
• The cylinder lubrication is adjusted at high quantity, leading to carryover of oil with air
• The auto drain is malfunctioning

3. Excessive Vibration and Noise:

If the compressor is generating too much noise and vibration, it can be because of the following reasons:

• Loose pulley, flywheel, belt, belt guard, cooler, clamps or accessories
• Lack of oil in the crankcase
• Piston hitting the valve plate i.e reduced bumping clearance
• Compressor holding down bolts are loose
• Compressor foundation chocks have worn out

4. Overheating of Discharged Air

If the temperature of the discharged compressed air is high, it can be because of overheating caused as a result of the following reasons:

• Chocked or dirty intercooler tube
• Cooling water pump capacity decreased or insufficient
• The atmosphere at air suction of the compressor is hot
• No forced ventilation for fresh air near the compressor
• Damage in the head gasket
• Chocked air suction filter
• Valves of 1st or 2nd stage leaking

5.Milky Oil in the Crankcase

If there is an accumulation of milky coloured oil in the crankcase, it can be because of the following reasons:

• Water leakage from cylinder liner
• Water leakage from the jacket
• Oil running hour is over

These are some of the most common problems that are found in continuously running air compressors onboard ships.

Do you know any other common compressor problems? Let us know in the comments below.

Top 5 Air Compressor Problems Marine Engineers Must Know appeared first on Marine Insight - The Maritime Industry Guide

Certain steps and systematic procedure need to be followed in order to start or stop an air compressor on a ship. In this article, we will learn how to start and stop an air compressor and also find out checks that are need to be made before starting the air compressor and also during its operation.

Checks before Starting the Air Compressor

The following steps are to be followed before starting an air compressor on a ship.

1. Check the lube oil in the crankcase sump by means of dipstick or sight glass.
2. All the valves of compressor discharge must be in normally open condition.
3. If any manual valve is present in un-loader line, it must always be kept open.
4. All alarms and trips- Lube oil low pressure, water high temperature, over load trip etc. must be checked for operation.
5. All valves in cooling water line must be in normally open position.
6. Cocks for all the pressure gauges must be in open position.
7. Air intake filter should be clean.
8. If compressor has not been started from long time than it should be turned on manually with a tommy-bar to check for the free movement of its parts.

Starting and Stopping procedure: What is Unloading the compressor?

Unloading is a normal procedure during the starting and stopping of the compressor. It is carried out due to following reasons:

1. When starting a compressor motor, since the load on the motor is very high the starting current is also high. In order to avoid further loading of the compressor an un-loader arrangement is provided which is normally pneumatic or solenoid control and which releases the pressure during the starting of the compressor. Once the current comes down to the running value, the un-loader closes automatically. Normally a timer function is used for opening and closing of un-loader.
2. Air contains moisture and during the compression process some amount of moisture gets released. Liquid in any form is incompressible and if some amount of oily water mixture is present inside the cylinder then it will damage the compressor. To overcome this problem un-loader is used. During starting un-loader comes in action and releases all the moisture accumulated inside the cylinder.
3. Intermediate operation of un-loader is also selected so that during the process of compression any moisture or oil accumulation cannot take place inside it.
4. During stopping the compressor un-loader is operated so that for the next starting the cylinder will remain moisture free.

Checks during the Operation of Compressor

1. Check if all the pressure gauges are showing correct readings of lube oil pressure, water pressure etc.
2. Check for any abnormal sound like knocking etc.
3. Check for any lube oil or water leakages.
4. If cylinder lubrication is provided, check the supply from sight glass.
5. Check if the discharge pressure for all units is normal.
6. Check air temperature after the final stage is under limit.
7. Check the flow of cooling water from sight glass.
8. If attached cooling water pump is provided check for its free rotation.
9. Check the relief valve of all units for leakage. In some compressor, provision is given to check the relief valve with hand lever, if provided check all units.

You may also like to read – Compressed Air Line On Ships – A General Overview

Air Compressor on a Ship: Checks for Starting and Stopping a Compressor appeared first on Marine Insight - The Maritime Industry Guide

A marine air compressor provides compressed air for various purposes on a ship. An air compressor is one of the most important equipments on a ship which needs special care and routine maintenance. In this article we will know the basics of the marine air compressor by first getting familiarized with the different parts of the same.

The main parts of the marine air compressor are:

1) Cylinder liner:

It is made of graded cast iron and is accompanied with water jacket around it to absorb heat produced during compression process. It is designed so as to give a streamline passage to the pressurized air resulting in minimum pressure drop.

2) Piston:

For a non-lubricating type compressor, light weight aluminum alloy piston are used and for lubricating type graded, cast iron piston are used with piston rings for sealing and scrapping off excess oil.

3) Piston Rod:

In high capacity compressor which is normally big in size, piston is attached to piston rod made up of alloy steel. They are fitted with anti friction packing ring to avoid chances of compressed air leakage.

4) Connecting rod:

Connecting rod plays its role to minimize thrust to the bearing surface. It is made up of forged alloy steel.

5) Big end bearing and Main bearing:

They are constructed to give rigidity to the running rotational mechanism. They are made up of copper lead alloy and have a long operational life if proper lube oil and lubrication is provided.

6) Crank shaft:

It is a one piece designed part, using counterweights for dynamic balancing during high speed of rotation to avoid twisting due to torsion forces. Connecting rod big end bearing and main bearing are connected to crank shaft at crank pin and journal pin which are polished to ensure long working life of bearings.

7) Frame and crankcase:

Normally they have rectangular shape and accommodate all the moving parts and that’s why are made up of rigid cast iron. Main bearing housing is fitted on a bore in crank case and is made with highest precision to avoid eccentricity or misalignment.

8 ) Oil pump:

A lubricating oil pump is fitted to supply lube oil to all the bearings, which can be chain or gear driven, through crank shaft. Pressure of oil can be regulated by means of regulating screw provided in the pump. A filter in the inlet of the pump is also attached to supply clean and particle free oil to the bearings.

9) Water pump:

Some compressor may have attached water cooling pump driven by crankshaft through chain or gear. Some system does not use attached pump as they use water supply from main or auxiliary system for cooling.

10) Suction and Discharge valve:

These are multi-plate valves made up of stainless steel and are used to suck and to discharge air from one stage to another and to the air bottle. Proper assembling of valves is very important for efficient operation of the compressor.

11) Suction Filter:

It is a air filter made up of copper or soft steel with a paper material to absorb oil and wire mesh to avoid any metal or dust particle to go inside compression chamber.

12) Inter-coolers:

Inter-coolers are normally fitted in between two stages to cool down the air temperature and to increase the volumetric efficiency of compressor. Some compressor have inbuilt attached copper tubes for cooling and some have outside assembly of copper tube inter-coolers.

13) Driving Motor:

An Electrical motor is attached to the compressor for making it operational and is connected to the compressor through the flywheel.

There are the main parts of a marine air compressor. The parts may vary according to the requirement of the system or ship.

Different Parts of a Marine Air Compressor Used on a Ship appeared first on Marine Insight - The Maritime Industry Guide

A breathing air compressor is used to fill up the oxygen bottles used for fire fighting or entering enclosed spaces. The breathing air compressors, as they are known, needs to be operated in a special way. They are smaller than the conventional compressors found on ship.

While operating the breathing air compressor, there are certain points that should be followed in order to ensure smooth starting and operation of the compressor. The article describes the procedure for starting a breathing air compressor on a ship.

Pre- Starting Procedure

Follow the below step-by-step procedure before starting the compressor.

• Fill water in the filling tank to keep the bottles cooled as heat is generated while filling the air.
• Check oil level in compressor-sump through indicator glass fixed on the side of the compressor.
• Check O-ring is placed in DIN-coupling male part and is in good condition and also no O-ring is there in the female-part of the valve on the bottle.
• Place bottle in water tank.
• Connect hose to the bottle and do not tighten too firmly as the pressure will ensure a proper fit.
• Open the valve on the hose by turning counter clockwise.
• Open the valve on the bottle by turning it counter clockwise.

Procedure for starting the compressor

Following steps are to be followed for starting the compressor:

• Even though the unit has automatic condensate draining you should drain the condensate frequently while filling by turning the knob.

• The compressor will stop on reaching 300Bar. If not you must stop it immediately.

• Close the bottle valve (1) by turning clockwise.
• Close the hose valve (2) by turning anticlockwise.
• After filling all bottles open the hose valve carefully to relieve pressure from hose.
• Drain condensate from the compressor and water from the filling tank.

Procedure for Starting Breathing Air Compressor On a Ship appeared first on Marine Insight - The Maritime Industry Guide

The Efficiency of an air compressor on a ship depends on several factors. A compressor provides highly pressurized air which increases the temperature to exceptionally high levels. In order to get quality performance out of air compressors, it is important to check and control the pressure and temperature within optimum range. In this article we will learn as to what it takes for efficient running of an air compressor on a ship.

Efficient working of Air Compressor

An air compressor is to provide air at high pressure. The temperature during the compression process is known as the compression temperature. The compression temperature that is generated is enough to ignite vaporized oil if present in the system. Moreover, in the process, a lot of energy is also wasted in the form of heat.

To avoid the loss of heat and overheating of internal parts, inter-coolers are fitted in the air compressor. With the help of inter-coolers, it is possible to approach the ideal isothermal compression to achieve maximum volumetric efficiency.

Sea water is commonly used for the cooling purpose in air compressor. Sea water is circulated in the system using an attached pump or by using main or auxiliary sea water circulating system. It is to note that sea water causes scale deposits in cooling passages. Sometimes, fresh water from a closed loop system is also used to avoid scale deposit problems.

Graph showing saved work due to inter cooling

Uses of Compressed Air on Ship

Compressed air is used for the following purposes on a ship.

• For starting of main engine, auxiliary engine, emergency generator and emergency fire pump.
• For automation and control air for main and auxiliary engine.
• For different application on the deck side and in engine room such as chipping, drilling, buffing, pressurized water jet cleaning etc. by use of pneumatic tools and machinery.
• For overhauling machinery by use of pneumatic tools and hydraulic jack.
• For pressure testing of different machinery parts, pipeline etc.
• Compressed air is also used for ships whistle and fog horn.
• It is used in life boat for heaving up the later, if air motor is attached as a heaving provision.
• For supplying water to accommodation and various parts of the ship through hydrophore by keeping the later pressurized with air.
• For conducting aerobic breakdowns of the on board sewage in sewage plant.
• For pressurized spray painting.
• Used in soot blowing of boiler and economizer.
• Used in portable pneumatic pumps like Weldon pumps for oil, water and bilge transfer.
• For general cleaning and services.

The above mentioned are the most common purposes for which compressed air is used. The application and uses may differ from ship to ship.

You may also like to read –  Compressed Air Line On Ships – A General Overview

Efficiency of Air Compressor and Uses of Compressed Air on a Ship appeared first on Marine Insight - The Maritime Industry Guide

A compressor is one such device which is used for several purposes on a ship. The main aim of the compressor, as the name suggests, is to compress air or any fluid in order to reduce its volume. A Compressor is a multipurpose device which finds many applications on a ship. Some of the main forms of compressors used on ships are the main air compressor, deck air compressor, AC compressor and refrigeration compressor. In this article, we will learn about air compressors and its types.

Applications Of Air Compressors

Air compressor is a device with vast application in almost all sorts of industries and household requirements. In the maritime industry as well, air compressors are used in essential equipment or the feeder equipment to different systems. They can be employed in a number of processes ranging from small process of cleaning of the filters to the bigger and crucial tasks such as starting main as well as secondary engines.

Air Compressor produces pressurized air by decreasing the volume of air and in turn increasing its pressure. Different types of air compressors are used according to the usage.

In a more technical language, an air compressor can be defined as a mechanical device in which electrical or mechanical energy is transformed into pressure energy in the form of pressurized air.

Air compressor works on the principles of thermodynamics. According to the ideal gas equation without any temperature difference, with an increase in gaseous pressure, its volume reduces. The air compressor works on the same principle on which it produces compressed air, by reducing the volume of air this reduction in volume results in an increase in air pressure without any temperature difference.

Types of Air Compressors

General Classification:

Air compressor on ships can be classified into two different types namely:

Main air compressor: These air compressors are high-pressure compressors has a minimum pressure value of 30 bars and used to run the main engine.

Service air compressor: It compresses air to the low pressure of only 7 bars and later used in service and control airlines.

Classification of Compressors As Per Design And Working Principle:

There are mainly four types of compressors:

1. Centrifugal compressor
2. Rotary vane compressor
3. Rotary screw compressor
4. Reciprocating air compressor

However, on ship reciprocating air compressor is widely used. A reciprocating air compressor consists of a piston, connecting rod, crankshaft, wrist pin, suction valve and discharge valves.

The piston is connected to the low and high side of the suction line and discharge line. The crankshaft rotates which in turn rotates the piston. The downward moving piston reduces the pressure in the main cylinder, the pressure difference will open the suction valve.

The piston is taken down by the rotating crankshaft and the low-pressure air gets filled in the cylinder. Now the piston reciprocates upward and this upward movement starts building up the pressure and closes the suction valve.

When the air gets pressurized to its specific value discharge valve gets opened and the pressurized air starts moving through the discharge line and gets stored in air bottle.

This pressurized air in air bottle can be used to run the main as well as auxiliary engines later on. There can be single acting and a double-acting reciprocating air compressor on the ship.

Classification On The Basis Of The Usage 

Normally, air compressors onboard ships are:

• main air compressor
• topping up compressor
• deck air compressor
• Emergency air compressor
• Main air compressor

Main air compressor: It is used to supply highly pressurized air to start main and secondary engines. Air compressor has an air storage bottle which stores the pressurized air. There are available different capacity main air compressors, but this capacity should be adequate for starting the main engine. The minimum air pressure required is 30 bars to start the main engine. A pressure valve is provided which reduces pressure and supplies controlled air from the storage air bottle. The control air filter controls the input as well as output air in the air bottle.

Topping up compressor: This type of compressor is used to cater to any sort of leakage in the system. It implies that if there observed any leakage in the system the topping up air compressor covers up the leakage by taking the lead. With leakage in system, the air pressure declines below the requisite level which can be replenished to its specified level by topping up compressor by supplying pressurized air.

Deck air compressor: Deck air compressor is used for deck use and as a service air compressor and might have a separate service air bottle for the same. These are lower capacity pressure compressors as the pressure required for service air is in between the range of 6 to 8 bar.

Emergency air compressor: An emergency air compressor is used for starting the auxiliary engine at the time of an emergency or when the main air compressor has failed for filling up the main air receiver. This type of compressor can be motor driven or engine driven. If the motor is driven, it should be supplied from an emergency source of power.

Efficiency of Air Compressors

The air compressors can work efficiently if installed properly as per the installation guide. All the crew available should be responsive in working with an air compressor in an emergency as these are the basic part of almost all important machinery systems on the ship. Efficiency of the air compressor can be increased by following techniques and installations.

Pressure-Bar: Pressure-bar or pressure gauge should be installed within all the compressors to ensure that the air pressure and discharge the air at the specified pressure. Without this device if air is pressurized below the requisite value it cannot propel or run the system to which it is employed.

Safety Devices: These are the devices used to reduce the loss of energy from the air compressor and increase efficiency. Safety devices automatically shut down the input and output air when adequate compressing is reached and saves the device from overpressure.

Main Components Of Air Compressor

Some of the important components of air compressor which are common to all the available types of compressors are briefed as under:

1. Electricity or power source: This is the key component of any type of compressor and essential for running the compressor. Power source or electric motor is used to run the compressor efficiently and at a constant speed without fluctuations.
2. Cooling Water: Cooling water is used to cool the compressor in between different stages.
3. Lubricating Oil: Lubricating oil is necessary to keep the all mobile parts of the compressor lubricated. This lubrication reduces the friction in parts of the compressor and thus imparts more life to the compressor by reducing wear-tear of components of the compressor.
4. Air: This is the component without which an air compressor can’t be even imagined. The air around us is in low pressure and served as an input to the compressor.
5. Suction Valve: Suction valve is provided with a suction filter it inputs the air, which is to be compressed in the main compartment of the compressor.
6. Discharge Valve: This valve takes the output air to discharge at a requisite location or to the storage tank or storage air bottle.

Working Of Air Compressor  

Air compressor consists of air bottle which can store compressed air at a specified pressure. The compressor compresses air and stores this pressurized air in air bottle. When this pressurized air injected to the engine through air gun or any other equipment, it kicks the propeller and runs the engine. 

Uses of Air Compressor on Ship

Onboard a ship, compressed air is used for several purposes. On the basis of application, different air compressors are kept for a particular usage.

• Air compressor is used to provide the starting air to various machines and main engine.
• Other than the main engine other systems also require compressed air. These systems are Control valves. Throttle controls and other monitoring systems which work on pressurized air.
• This compressed-air controls many operations in the auxiliary engine as well.
• In pneumatic tools like cleaning, devices compressed air is required to keep the devices running and serve the purpose efficiently.
• In whistling operation of ships also compressed air is employed and the fog horns operate on the compressed air.
• Hydraulic jack in the ship also uses compressed air to perform lifting operations.
• Many times boilers; refrigerants and heat exchangers in ship are started using compressed air.
• Sometimes compressed air is used in kicking the propellers of the ship manoeuvring system.

In a nutshell, the compressor is the mechanical device which runs on the principles of thermodynamics that reduce the volume of air and increases the pressure of air.

This highly pressurized air when injected to run either main engine or auxiliary devices such as heat exchanger; boilers; etc.

The most common type of compressor used in the marine industry are double acting reciprocating air compressors. There are multiple compressors provided on a ship to serve different purposes. They can run main and auxiliary engines.

Sometimes propeller of the ship runs on the compressed air which increases the application of air compressor in the marine industry.

Air compressors can never be forgone from the ship as they have wide applications on board from smaller tasks of cleaning the filters to the crucial process of running the engine and even propelling the ship.

You may also like to read – Compressed Air Line On Ships – A General Overview

Disclaimer: The authors’ views expressed in this article do not necessarily reflect the views of Marine Insight. Data and charts, if used, in the article have been sourced from available information and have not been authenticated by any statutory authority. The author and Marine Insight do not claim it to be accurate nor accept any responsibility for the same. The views constitute only the opinions and do not constitute any guidelines or recommendation on any course of action to be followed by the reader.

The article or images cannot be reproduced, copied, shared or used in any form without the permission of the author and Marine Insight. 

The Basics of Air Compressor On a Ship appeared first on Marine Insight - The Maritime Industry Guide