The Types, Operations and Maintenance of Air Compressor Plants

1. Maintenance and Operation
of
Air Compressor Plants
Nejat ÖZTEZCAN
Chief Engineer

2. Air Compressors

3. What Is A Compressor?
A Compressor is a machine which compresses the air at
ambient temperature (taken as 15 Deg C) and atmospheric
pressure (1 Bar) to higher pressure such that its density i.e mass
per unit volume increases.

4. What’s the Difference Between a Pump and a Compressor?
Moving hydraulic fluid through a system requires either a pump or
compressor. Both achieve this goal, but through different operating
methods.
Pumps have the ability to move liquids or gases.
Compressors typically only move gas due to its natural ability to be
compressed. Pumps and compressors both have very high pressure
rises.
The primary purpose of an air compressor is to take in air and compress
it to decrease its volume and increase its energetic potential.

5. DIFFERENCES BETWEEN MARINE AND OTHER COMPRESSORS
Marine air compressors are designed to function within the ship
environment.
Often, these machines need to withstand wet conditions, as well as the
presence of salt in the water and air. Not all metals handle the
conditions as well, so using an air compressor that isn’t designed for
these specific conditions can result in device failure or
even safety hazards.
Compressed air can serve multiple functions designed to assist with ship
operations.

6. Compressed air can serve multiple functions designed to assist with
ship operations.
Marine air compressors are normally separated based on the
following uses:
•Starting Diesel engines(Main Engines and Aux. Engines)
•Instrumentation and control systems,
•Various pneumatic tools and cleaning equipments,
•Boiler soot blowing
•Ship’s whistle.

7. MAIN MARINE AIR COMPRESSOR
The main air compressor on a ship provides power for starting primary
and auxiliary engines.
Pressurized air is stored in an appropriate tank, and released to provide
the power necessary to start engine operations. Often, these
compressors are high capacity, as it can require a significant amount of
energy to start the engines.

8. DECK MARINE AIR COMPRESSOR
Marine air compressors have a variety of uses on the deck.
Often, these are smaller systems that maintain a lower capacity.
This helps ensure the systems are more portable.
Air compressors can operate a variety of pneumatic power tools,
allowing for certain ship repairs and other mechanical operations to
be completed while out on the water.
They also have functions related to cleanliness and sanitation.

9. Control Air
There are many uses of control air on board ships.
Control air plays a vital role in propulsion of ship and it is used for
controlling the function of ship engines including
•Ship’s engine speed
•Direction of running
•Starting/stopping/reversing
The pipe lines in engine rooms are fitted with valves. Some of these
valves are manually operated but some valves related to critical
operations also have pneumatic control which refers to the use of
control air for opening and closing of these valves in a remote-
controlled fashion.
Control air is used to provide signals to these boilers during their
operation.

10. EMERGENCY MARINE AIR COMPRESSOR
As the name suggests, emergency air compressors provide a backup
source of potential energy in case of an emergency. Often, they are
designed to provide power to auxiliary engines should the main
compressor fail.
What is emergency air compressor ?
It is a small compressor independently driven by a prime mover having
power supply from emergency switch board. They are also driven by
diesel engines.
It must be fitted to press up the emergency air bottle and to start
auxiliary engine of a dead ship.

11. Compressed Air System
• Normally three systems
– Starting air (30 Bar)
– Service air (7/8 Bar)
– Control air (7/8 Bar)
• Require two main compressors to charge two air
receivers from atmospheric within one hour.
• Capacity of receivers sufficient to produce:
– 12 starts for reversible engines
– 6 starts for non-reversible engines
– 3 starts for auxiliary engines

12. What do you mean by capacity of a compressor and what is
required capacity?
By capacity of compressor we mean that amount of free air
delivered by a compressor in an hour.
• As per Solas , each compressor used onboard must be capable
• enough to fill one air bottle in 60 minutes.
• If two compressors are running simultaneously, must fill one air
• bottle in 30 minutes.
• The Solas requirement for compressed air bottle and both the
Compressors on board is that it should provide sufficient air for 12
Consecutive start for reversible engine and 6 consecutive start for
non-reversible engine.

13. Compressed Air System
• No connections to other machinery between air
compressors and main air receivers
• Emergency air compressor can be diesel driven or power
supplied from emergency generator
• Pressure reduction stations and filters are required to be
duplicates
• Safety relief valves are fitted at receivers and set at 10%
above operating pressure

14. Volumetric efficiency of an air compressor
It is the ratio of the actual volume of air drawn in each suction stroke
to the stoke volume.
Volumetric efficiency = (Actual volume of air drawn in suction
stroke) / (Stroke volume)
Factors affecting volumetric efficiency of an air compressor .
•The bumping clearance (the larger the bumping clearance the less air
is discharged per stroke).
•Sluggish opening and closing of suction and delivery valves.
•Leakage past compressor piston rings.
•L.P inlet air temperature too high.
•L.P inlet filter dirty and choked.
•Inlet cooling water temperature too high.
•Insufficient cooling water owing to fouling of coolers.

15. How do you check compressor efficiency during running ?
•Checked by filling time with the previous record and also check
the first stage discharge pressure.
• If compressor efficiency is lower, compressor will run longer and
compressor temperature will rise.
First stage and second stage pressure gauge must be correct and stable.
•No escape of air from suction filter.
•Intercooler and after cooler outlet air temperature should not be high.
•If open drain valve nothing can be found.
•Low L.O consumption.
•Oily air mixture must not blow out from breather pipe.
•Total no. of Air Compressors must be sufficient to fill the empty Air
Bottle to maximum pressure within 1 hour.

16. 3
2
1
4

17. The Compressed Air system is designed to generate and supply
compressed air for ship systems by:
1.Compressed Starting & Service Air System.
2.Control Air System.
Starting Air System
The Starting Air System produces and supplies compressed air for
starting ME and DEs. All engines are started by means of compressed air
with a nominal pressure of 3 MPa (30 bar).
In automatic operating mode, the Main Start Air Compressors are
switched on by the pressure control at low pressure 28 bar (LEAD)and
26 bar (FOLLOW), respectively switched off at max pressure 30 bar
(FOLLOW) and 30 bar (LEAD).
The compressors can be also operated manually from the LOP.

18. Control Air & Service Air System
The Control Air & Service Air System produces and supplies
compressed air for pneumatic mechanisms (e.g. valves, pumps) and
safety and control devices.
In automatic operating mode, when the pressure in the Air receiver
drops <7.5 bar the compressor automatically starts.
The compressor can be also operated manually from the push button
box.

20. Bumping clearance in an air compressor
This is a clearance must be provided between the piston top and
the cylinder head when the piston is top dead centre.
It must be kept as small as possible for achieving the best
compressor efficiency.
Why need bumping clearance in an air compressor ?
•To prevent mechanical damage to the compressor.
•To provide for thermal expansion
•To provide necessary space for valve operation.
How to adjust the bumping clearance ?
It can be adjusted by two ways.
•By altering the head gaskets (cover joint ) thickness.
•By adding and subtracting shims between the connecting rod foot
and bottom and bearing.

21. Main air compressor bumping clearance taking procedure
•Stop the compressor and (lock off) take out fuse.
•Drain the cooling water.
•Remove the cylinder cover.
•Clean the cylinder head face and piston crown.
•Place the lead wire ball on the top face of the piston. That is larger
size than expected by clearance.
•Cylinder cover is placed on the cylinder with correct joint thickness
and tightens the head bolts.
•Turn the compressor slowly by hand over top centre so that lead
wire ball is pressed.
•Then remove cylinder cover again.
•Remove the compressed lead wire ball.
•Take the measurement of lead wire thickness by using micrometer.

22. Air Receivers

23. Auxiliary Air
Receiver

24. Pressure-reducing Station

25. Control Air Dryer (Refrigerant-type)

27. Compressors are classified in many ways out of which the common
one is the classification based on the principle of operation.
Types of Compressors:
1. Positive Displacement and
2. Dynamic Compressors.
Positive displacement compressors can be further divided into;
Reciprocating and rotary compressors.
Under the classification of reciprocating compressors, we have
•In-line compressors,
•“V"-shaped compressors,
•Tandem Piston compressors.
•Single-acting compressors,
•Double-acting compressors,
•Diaphragm compressors.

28. Reciprocating compressor:
It is a piston-liner assembly, piston is attached to the crankshaft via a
connecting-rod.
The shaft is further coupled to motor which drives the assembly.
It is used onboard to fill compressed air into air bottles mainly to
supply starting air to main and auxiliary engine, and for other
subsidiary purposes.

29. Reciprocating In-line Compressors:
These are most commonly used compressors with varying pressure
ranges.
These are simple in design with almost very little automation. The
cylinders of various stages are found in a straight line when seen
from top. These compressors are commonly direct driven by
electric motors or diesel engines. Refer the attached diagram of the
reciprocating in-line compressors.

30. Single acting compressors
They are the reciprocating compressor which has piston working
only in one direction.The other end of the piston is often free or
open from which no work is performed.There is only one side
compression or the upper part of the piston is used to compress the
air.the bottom part is open to crankcase and is not utilized for the
compression of air.

31. Double acting compressors
As from its name it uses its both sides to compress the air. These type
of compressors have two sets of suction/intake and delivery/exhaust
valve on both sides of the piston. As the piston moves up and
down,both sides of the piston is utilized in compressing the air.The
intake and exhaust valve operates corresponding to the movement of
the piston or with the stroke of the compressor. The air is compressed
accordingly and delivered continuously as compared to single-acting
air compressor

32. Single Stage, Double Acting
Reciprocating Compressors

33. V-shaped compressors
They are come under air cooled compressors with concentric
valves mounted on each cylinder head unit which are placed in V-
shaped i.e. at the angle of 90 degrees from each other and may or
may not be connected to same crank pin on the crank shaft.
They are compressors of higher capacity so the cooling is
required.The v-shaped is given to such compressor for achieving
better torque and balancing by displacing different units at some
angle.

34. The rotary compressors are divided into
•Screw compressors,
•Vane type compressors,
•Lobe and scroll compressors and other types.
Under the Roto-dynamic compressors, we have
•Centrifugal compressors, and the
•Axial flow compressors.

35. Vane Type Rotary Compressor
This is an another type of rotary compressor. There is a fixed casing in
Vane type compressor in which a rotary rotor disc is placed which
has slots that are used for holding the sliding plates.
Whenever rotor rotates the disc also rotates thus allowing the sliding
plates to slide as the inner surface of casing is eccentric. Whenever
the plates moves away from the center a huge amount of air get
trapped inside it and with the rotation the sliding plates converge
due to its shape and the trapped air get compressed.This results in
compression of air.

37. Lobe Type Air Compressor
This is one of the simpler compressor type.In this there is no
complicated moving part.There are two lobes attached to the driving
shaft by the prime mover.These lobes are displaced with 90 degrees
to one another.Thus if one of the lobe is in horizontal direction the
other lobes will be exactly positioned at 90 degree i.e in vertical
direction.
The air gets trapped from one end and as the lobes rotates the air
gets compressed as shown in image. The compressed air is then
delivered to delivery line.

38. Dynamic Compressors.
Dynamic compressors operate by imparting velocity and pressure to the
admitted air, through the action of a rapidly spinning impeller or
rotating vanes.
The main types of dynamic compressors are centrifugal (radial) and
axial compressors.

39. Centrifugal compressor:
It consists of a rotary wheel with blades mounted on them, the
wheel and blades when rotated develops a negative pressure, the
inducer guides air into the blades .
Centrifugal force generated due to moving blades increases the
velocity of air. The air is guided to the diffuser which acts as a
divergent nozzle and reduces the velocity and increases the
pressure.
Thus, the density of air i.e mass per unit volume increases.
It is used onboard in turbocharger , for supplying compressed air
for combustion in engine cylinder.

40. Axial Flow compressor
• It consists of a casing fitted with several rows of fixed blades and
rotor attached with several rows of moving blades.
• The fixed and moving blades are placed on alternate rows the
function of the fixed blades is to receive the high velocity air from
the moving blades.
• Axial flow compressor is also a high speed machine and speed
may even vary from 10,000 to 30,000 RPM. Pressure ratio of 10:1
can be achieved.

41. A Centrifugal compressor primarily consists of;
1.Stationary casing
2.Rotating Impeller
3.Diffuser
Centrifugal compressor is also known as Radial Compressor.

42. The compressors are also classified based on other aspects like
•Number of stages (single-stage, 2-stage and multi-stage),
•Cooling method and medium (Air cooled, water cooled and oil-
cooled),
•Drive types ( Engine driven, Motor driven, Turbine driven, Belt,
chain, gear or direct coupling drives),
•Lubrication method (Splash lubricated or forced lubrication or
oil-free compressors).
•Service Pressure (Low, Medium, High)

45. İki kademeli ara soğutmalı Kompresör

46. Üç Kademeli Kompresör

48. Why multistage compressors are mostly used than single stage
compressor ?
•More stages are needed to increase the required final pressure.
•Easier to control the air temperature.
•Reducing in air compressor size.
•Lubrication problem does not exit.
•Reduced the thermal stress.
•Lower work done to compressing air.
•Improve compressor efficiency

49. What is multi-staging in compressor and why is it done?
Multi-staging is conducting the process of compression in more
than one stagesi. Air is compressed by two or more pistons before
delivery. Generally, two stage reciprocating compressors are used
on board. The purpose of multi-statging is :
1. If we increase the pressure of air up to 30 bar (pressure of air
at 2nd stage) in one stage, the Lub.oil will start burning due to
rise in temperature.
As per the thermodynamic equation for a polytropic process,
T2 / T1 = ( p2 / p1 ) (n-1)/n where n=1.35 for air.
p2/p1= 30/1 T1=27 deg-celcius. T2= 450 deg-celcius.
at this temperature l.o will burn as flash point of Lub.Oil is 200
deg. celcius. So we keep the pressure ratio limited to 5:1.

50. 2. To reduce the work done by compressor in the whole process.
The compression of air to higher pressure and lesser volume is a
reversible adiabatic process.
Change in temperature takes place, if change in temperature is kept
minimum or zero , the work done by compressor will be minimum.

51. What are the normal parameters of air compressor ?
•LP discharge pressure: 4/5 bars
•HP discharge pressure: 30 bars.
•Intercooler inlet air temperature: 130 ° C
•Intercooler outlet air temperature: 35 ° C
•After cooler inlet air temperature: 130 ° C
After cooler outlet air temperature: 35 ° C
Why need minimum lubrication for air compressors ?
•To prevent carbonizing of the valves
•To avoid loss of compressor efficiency due to sluggish action of valve
•To avoid loss of cooler efficiency due to deposition of oil on the cooling
surface
•To prevent air line explosion, to prevent air bottle corrosion

52. AUXILIARY EQUIPMENT
Air Intake Filters: Filters prevent the admission of atmospheric dust to
the air compressor.
Silencers: Silencers reduce objectionable compressor suction noise.
Separators: Separators remove and collect entrained water and oil
precipitated from the air.
Traps: Traps drain condensed moisture and oil from separators,
intercoolers, aftercoolers, receivers, and distribution piping.
Air Receivers: Air receivers are tanks wherein compressed air is
discharged and stored. They help to reduce pulsations in the discharge
line and provide storage capacity to meet peak demands exceeding the
capacity of the compressor.

53. INTAKE FILTERS
Air filters are provided on air compressor intakes to prevent
atmospheric dust from entering the compressor and causing scoring
and excessive wear. There are two types of air filters, the dry type and
the oil-wetted type.
Dry type filters must be cleaned and replaced more often than oil-
wetted types.
Oil-wetted types are often used where there are heavy dust
concentrations present in the atmosphere.

54. 54Wet Filter Air Intake System
ToEngine

55. SEPARATORS
Separators are used on compressor installations to remove
entrained water and oil from the compressed air.
Centrifugal action forces the moisture particles against the wall of the
separator where they drain to the bottom.
In the baffle type separator the air is subjected to a series of sudden
changes in direction. The heavier moisture particles strike the baffles
and walls of the separator and drain to the bottom of the unit.

57. TRAPS
Traps drain condensed moisture from intercoolers, aftercoolers,
receivers, and distribution piping. The most common traps are the ball
float trap, bucket trap, and inverted bucket trap.
Daily Inspection: Check the operation of drain traps daily. Make sure
the trap is draining properly and not blowing air.

58. AIR RECEIVERS
Air receivers serve as reservoirs for the storage of compressed air so
that air is available to meet peak demands in excess of the compressor
capacity. They also function as pulsation dampers on reciprocating
compressor installations. Receivers are furnished with a relief valve,
pressure gauge,drain valve, and inspection openings.
NORMAL OPERATION: Drain receivers of accumulated condensate at
least once each shift if an automatic drainer is not provided.
Periodic Inspection:
Proceed as follows at intervals prescribed by the manufacturer's
maintenance schedule.
(a) Check operation of safety valve.
(b) Examine receiver for corrosion and peeling paint.
(c) Inspect the receiver internally for corrosion and dirt accumulation.

59. Safety devices on main air bottle ?
•Safety valve.
•Fusible plug.(if safety valve is not directly fitted on the bottle)
•Pressure gauge.
•Low air pressure alarm.
•High air pressure alarm
•.
•Moisture drains valve.

60. DRYERS
Compressed air dryers remove moisture that might otherwise
condense in air lines, air tools, and pneumatic instruments.
This condensate can cause damage to equipment from corrosion,
freezing, and water hammer, and can cause malfunctioning of
instruments and controls.
Air dryers remove moisture that might condense in air lines,
air tools, or pneumatic instruments

61. What Is a Compressed Air Dryer?
A compressed air dryer is a machine that sucks in and significantly
reduces the moisture content of ambient air.
Depending on the moisture levels of a given environment, the use
of a compressed air system can make all the difference between
whether or not a production is even achievable. Compressed air
dryers can be split into the following categories:
•Refrigerated drying units:
•Desiccant drying units:
•Heated — internal or external
The main difference between each dryer type is the agent placed
inside the machine to dry the incoming air.

62. .
Intercoolers and Aftercoolers:
Intercoolers are used between consecutive stages of multistage
compressors to remove the heat of compression.
Aftercoolers are installed on the compressor discharge lines to remove
the heat of compression after compression is completed.
Both are effective in removing moisture and oil from the compressed air.

63. There are two types of heat exchangers used on air compressors.
•Air-Cooled Heat Exchanger: Air-cooled heat exchangers are most often
used on small compressors. The air-cooled heat exchanger is a finned,
tubular radiator.
•Water-Cooled Heat Exchanger: The most common design of water-
cooled heat exchangers, shell and tube type, consists of a single bundle
of tubes enclosed inside a cylindrical shell . The air to be cooled passes
through the tubes while the water passes over the tubes. Baffles are
often provided in the tube bundle to direct the waterflow across the
heat exchanger tubes in the most efficient manner.

64. The intercooler is located between the discharge of one cylinder
and the intake of the next cylinder of multistage compressors. The
intercooler reduces the temperature and the volume of the
compressed air for delivery to the next compression stage.
The aftercooler is located at the discharge of the last cylinder to
cool the air, reduce its volume, and to liquify any condensable
vapors.

65. Advantages of after cooler in air compressor ?
•To reduce final discharge air temperature thus air bottle size can be
reduced.
•To reduce air volume after it has been compressed to the final
pressure.
•So greater amount of air could be stored in air bottle.
•Increase volumetric efficiency

66. Section view of a water cooled intercooler

67. Why Intercooler is fitted in air compressors?
•Reduce air temperature and volume, and increase air density for
next stage.
•Increase Compressor Capacity and Volumetric Efficiency.
•Better lubrication for cylinder and rings.
•Water and excess oil can be drained out, preventing fouling of
Intercooler and pipes, Air Bottle corrosion, and starting airline
explosion.
•Metal stresses reduced, due to control of temperature.

68. Different Parts of a Marine Air Compressor Used on a Ship
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.

70. 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.

71. 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.

72. 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) 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.
12) Driving Motor:
An Electrical motor is attached to the compressor for making it
operational and is connected to the compressor through the
flywheel.

73. 1. Compressor Housing
• Main cross head, connecting rod and motor bearings
2. Cylinder Area
• Valves, packing and compression rings
There are 2 areas that require lubrication in a
reciprocating compressor.
Lubrication

74. Splash Lubrication
• Most common in small compressors.
Pressurized Lubrication
• Usually used on very large compressors.
There are 2 different methods of lubrication.
• Use “dippers” on the connecting rod to scoop oil out of the crankcase.
• A gear pump is used to force oil through
orifices in the connecting rods.

75. What is the type of cylinder liner lubrication in compressor
and how is it done?
For 2 stage compressors, which has two different in-line
cylinder arrangement for both stages, splash lubrication of liner
and piston takes place. The l.o from sump is splashed by the
movement of the shaft into the liner walls and is scraped back
by the oil scraper ring.
For two stage tandem type (in which only one cylinder liner is
used and both pistons are connected), for 1st stage lubrication
a separate line is connected to the suction side , as air is drawn
in for compression, an oil mist of l.o and air is also carried to the
1st stage. Thus, a l.o film is generated and boundary lubrication
takes place. 2nd stage lubrication takes place by splash of l.o
by the crankshaft and is scraped down by the oil scraper ring.

76. What are the safety devices on Main Air Compressor:
•Bursting Disc on Intercooler: (At water side)
•Bursting Disc and Fusible Plug (105°C) on Aftercooler
•Relief valves on LP and HP stages. (Set to lift at 10% rise above normal
stage pressure.)
•Automatic Moisture Drain Valve.
•Cooling water supply failure alarm.
•Low LO pressure alarm.
•Relief valve on crankcase LO pump.
•Delivery air HT cut out and alarm on Aftercooler outlet. (Max. 93°C)
LP discharge pressure 4 bars and HP discharge pressure 30 bar
Intercooler inlet air 130°C and intercooler outlet air 35°C
Aftercooler inlet air 130°C and Aftercooler outlet air 35°C:

77. Safety Valves: Safety valves are used in a compressed air or gas
system. They must open rapidly and fully so that excessive pressure
buildup can be relieved immediately to prevent damage or destruction
of the system components.
Although the terms safety valve and relief valve are often used
interchangeably, this is technically incorrect.
A relief valve is used with liquid systems.
Safety valves are found in interstages air receivers, and between a
positive displacement compressor and any shutoff valve.

78. Difference between relief valve, bursting disc and fusible plug ?
Pressure relief valve
•Excess pressure is released by opening the valve.
•It opens at 10% over working pressure.
•Valve lift is proportional to excess pressure build up.
•Valve setting pressure can be altered by spring tension.
Bursting disc
•Pressure is released by bursting the disc.
•It permanently damaged.
•It burst at setting pressure.
•Setting pressure cannot be altered in place.
Fusible plug
•When the air temperature from compressor is high (above 105 ° C)
pressure is released by melting (fusing) the metal.
•It cannot be used next time. ( permanent damage)
•Release all content or pressure to empty.

79. Bursting Disc:
Fitted on the shell of Intercooler at waterside.
Relieves pressure if the tubes burst.
Bursting disc is fitted for totally release and stop
operation circuit.
Release valve opens excess pressure at compressor
running and reset when pressure reduce or when the
compressor is stopped. Thus cooling water can enter to
compressed air space; it can cause water hammer
when the next start of compressor.

81. Where is the fusible plug fitted and its purpose ?
Fusible plug is fitted under side of the pipe between relief valve and
air bottle.
It is fitted to release the compressed air in the event of abnormally
high compressed air temperature.
Fusible plug melt at 105 °C and release all content of air.
It is made by 50% bismut, 30% tin, 20% lead.
A fusible plug is fitted after the second stage cooler to limit the
delivered air temperature and thus protect the compressed air
reservoirs and pipe work.
Fusible plug is fitted at main air bottle, when relief valve is fitted
indirectly to the air bottle.

82. Compound Valves, why used in Air Compressor?
• Give large area of opening and small amount of valve lift.
• Improve Volumetric Efficiency, as valve open and close in minimum
time.
• Reduce bumping clearance.
• Reduce wear and tear.

83. Leaky Valves in Air Compressors
Valves can leak and finally fail. Valves may fail owing to wear and
fatigue, insufficient of over-lubrication, presence of foreign particles, oil
decomposition and excess valve lift.

85. Intake and Discharge Valves
• Work very similar
to check valves
• Can open and close
720,000 time a day
• The number 1 reason
for compressor downtime
is valve failure
• Check the temperature of
the valves regularly

86. TYPE OF THE VALVE PLATE METALS
•Staınless steel
•Carbon steel
•Cast ıron
ASPECTS TO THINK ABOUT PRIOR TO CHOOSING VALVE PLATE METALS
Run-time: The amount of time that the compressor will be running
makes a huge impact on which metal would be the right choice.
Environment: Corrosion is the natural enemy of metal. It occurs through
oxidation, most from the presence of both oxygen and water.
Vibrations: If there is more vibration than what would be considered
normal running conditions, then you should take this in to account .
Heat: If your compressor just generates more heat than what would be
considered normal running conditions, you need to choose a metal that
will handle the extra temperature.
Pressure: If the compressor you are putting the valve plate is large, then
you will need to make sure the metal will withstand any pressure that
the compressor might generate.

87. CONTROLS: Control systems for air compressors vary from the relatively
simple to the extremely sophisticated. The simpler control systems,
through the use of sensors, monitor the performance of the equipment
and, through the use of lights and/or audible signals, alert an operator
that some variable is outside the normal operating range. Most systems
automatically initiate a shutdown procedure under certain conditions
to prevent equipment damage.
COOLING WATER TREATMENT: Cooling water systems are used in
compressed air plants to remove heat from engines, air compressors,
refrigeration condensers, intercoolers, and aftercoolers. These cooling
systems are classified as either once-through or recirculating.
Treatment is more critical in open recirculating systems because
of solids buildup due to evaporation.

88. What is a discharge unloader and describe its operaton?
One of the most important component, an unloader is used for
unloaded starting of compressor and draining at continuous
intervals.
An unloader is fitted at the end of drain line from inter and
aftercooler. It is basically a solenoid operated spring loaded
valve arrangement.
When compressor is shut and delivery air pressure is zero, the
drain opens the unloader valve against spring pressure, thus it
is always open. When started, slowly the delivery pressure
rises and tries to shut the valve, during this time the actuated
solenoid valve overcomes the air pressure and keeps the valve
open.

89. The solenoid valve is operated by a time delay circuit as the
time span of 10-15 sec gets over the solenoid is deactivated
and the unloader valve shuts.
After every 20-30 mins.It is activated again and clears the
drain for 10-15 secs, then deactivates. If the unloader
does'nt function properly, there is a manually operated valve
just before unloader, which should be open before starting
the unloader.
Why is it so important to start the compressor in
unloaded condition?
It must be unloaded because when started the compressor
draws a very high current, if it will be loaded and valve not
open. The motor which is driving the machine may get
overloaded.

90. Inlet Valve Unloader:
There are several methods of unloading the compressor. One
system holds the inlet valves open mechanically during both
the suction and compression strokes, thereby preventing the air
from being compressed.
The unloader is located above the inlet valve so that the yoke
fingers are almost touching the valve. When the air receiver
pressure rises to the preset unloading pressure, a pressure switch
operates a solenoid unloader valve which operates and sends air
receiver pressure to the inlet valve unloader. The pressure from the
air receiver acting on the diaphragm of the inlet valve unloader
forces the yoke fingers against the inlet valve, holding it open.
The intake air is pushed back out of the inlet valve on the
compression stroke so that no compression takes place.

93. Pressure reducing valves
If it is necessary to provide steam or air at a pressure less than that
of the boiler or compressed air reservoir, a reducing valve is fitted.
This will maintain the downstream pressure within defined limits
over a range of flow, despite any changes in supply pressure.
There are systems onboard a ship which are operated by pneumatics
or hydraulics and sometimes even air or electronics.
For this reason, the relief valve by construction and operation should
be such that even in case of failure of the control system, relief valve
must lift to safeguard the system from over pressurized.

96. OPERATIONS, MAINTENANCE
and
TROUBLESHOOTING

97. OPERATION AND MAINTENANCE RESPONSIBILITIES
OPERATION: Operation includes startup, normal operation, emergency
operation, and shutdown of plant equipment. Good operation is safe,
reliable, and economical. Follow these basic rules of good operation.
• All operators should be thoroughly familiar with the equipment and
systems they operate. Carefully study drawings, diagrams, instruction
manuals, special operation procedures, and emergency procedures.
• Perform work assignments in a safe manner in accordance with
approved operating procedures. Use available protective safety clothing
and equipment.
• Operate equipment and systems economically, safely, and reliably.
• Teamwork and cooperation are essential.
• Be alert and concentrate on your work. Errors and forgetfulness can
cause serious personnel injuries and costly damage to equipment.

98. How to start the air compressor manually on ships ?
•Change the switch to manual position on the switch board.
•Check the L.O sump level and condition.
•Open the moisture drain valve.
•Open the compressor discharge valve & charging valve of air bottle.
•Open cooling water system valves.
•Turn the compressor flywheel by hand (one turn).
•Start the motor, after draining the moisture shut the drain valve.
•Check the motor ampere consumed.
•Check the pressure gauge readings.
•Frequently drain the moisture.
•When charging full, open drain valve and stop the compressor

99. What is first start arrangement on ships ?
•Firstly start the emergency air compressor to fill up the air to the
emergency air bottle up to desired pressure obtained.
•Drain out oil and water.
•Open emergency air bottle outlet valve and pressed up desired
pressure.
•Then start the generator with correct procedure.
•Close the breaker and switch on the lighting.
•Start the required machinery ( especially G/E FO booster pump, SW
cooling pump, E/ R blower).
•Start the main air compressor and press up to main air bottle.
•After that, M/E warming by using generator jacket water and start the
L.O pump.

100. Air Compressor 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
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 relief valve
•Increase in bumping clearance
•Wrong setting of compressor auto cut-in and cut-out (too close)

101. 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 separator is not working correctly hence oil is being carried to the
air receiver
•The cylinder lubrication is adjusted at high quantity, leading to
carry over of oil with air
•The auto drain is malfunctioning

102. 3. Excessive Vibration and Noise:
If the compressor is generating too much of 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 worn out

103. 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 compressor is hot
•No forced ventilation for fresh air near compressor
•Damage in the head gasket
•Chocked air suction filter
•Valves of 1st or 2nd stage leaking

104. 5.Milky Oil in the Crankcase
If there is a accumulation of milky colored oil in the crankcase, it can be
because of the following reasons:
•Water leakage from cylinder liner
•Water leakage form jacket
•Oil running hour is over

105. 6. Lube Oil Pressure Low
The following can be the reasons for lube oil pressure low in Air Comp.
•Faulty pressure gauge or 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.

106. 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.
•Pump not working.

107. 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 2nd to 1st stage.
•Discharge valve of first stage is malfunctioning, and remains in closed
position.
•Spring of discharge valve is malfunctioning.

108. 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.

109. Second stage discharge pressure high:
In 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.

110. 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.

111. What are the safeties in a reciprocating compressor?
1. Lubricating oil pressure low cut out: It is provided such that if
lub. oil pressure falls down the parts which are lubricated like liner,
piston, main bearings, bottom end bearings might get worn out.
2. Bursting disc: It is given in intercooler and aftercooler in the
water side so that if any highly pressurized air tube bursts, the
cooler shell will not be pressurized, bursting disc will burst and
liberate all the water, indicating air-tube burst. Generally made of
copper.
3. Non- return valve in delivery line: It is provided, so that the air
once delivered does'nt return back to the compressor in case a low
pressure develops in compressor side.
4. Discharge unloader:

112. 5. Relief valve on intercooler: A relief valve with setting 10% above
the 1st stage pressure is provided to release air if high pressure is
generated ın 1st stage generally due to valve malfunction.
6. Fusible plug: Generally made of tin, antimony and bismuth, is
fitted in inter and aftercooler to release excess air when temperature
rises up to 121 degree celcius due to rise in pressure.
7. High temperature alarm: At around 90 degree celcius, the alarm
sounds denoting the rise in air temperature.

113. SAFETY PRECAUTIONS
Explosive Hazards. Although compressed air at low or medium
pressures is dangerous if carelessly handled, the dangers associated
with high-pressure systems are of much greater consequence. Serious
explosions, complete destruction of facilities, and heavy loss of life
have been attributed to unsafe practices involving high-pressure
compressed air systems. The air temperature in the confined space is
raised to the ignition point of any flammable material that may be
present.
Preventive Measures:
1. Use of Slow-Opening Valves. These valves are used in pocketed
spaces such as lines to gauges and regulators to prevent a sudden
pressure rise.

114. 2. Pipe Coloring: High-pressure air lines are identified with a painted
light gray band and adjoining light green arrowhead pointing in the
normal flow direction.
3. Location of Equipment: High-pressure air storage and dryer
cylinders are isolated from other facilities as a precaution against
damage that could result from rupture of the cylinders.
4. System Tests: Before putting a high-pressure system into operation,
the required testing must be accomplished by competent personnel
with an engineer responsible for safety.

115. STARTUP
Prestart Inspection: Carefully inspect the compressor installation to
ensure the following prestart requirements are fulfilled.
(a) Verify all installation and repair work has been completed.
(b) Ensure system has been cleaned and tested for leaks.
(c) Ensure interstage and discharge safety valves are operating properly.
(d) Ensure compressor and drive are lubricated in accordance with the
manufacturers' instructions. On units fitted with a forced mechanical
lubricator, pump or crank by hand to see that the oil is getting to all
parts requiring lubrication.

116. Startup Procedure for Motor-Driven Compressors. Proceed as
follows:
(a) Open all shutoff valves between compressor and receiver.
(b) Make sure compressor is unloaded. Consult the manufacturer's
instructions for procedure.
(c) Turn on cooling water, if provided. Thoroughly vent cylinder
jackets and coolers if vents are provided.
(d) Turn compressor over by hand to see that all parts are free.
(e) Start compressor motor. When up to speed, apply load if
machine is running smoothly.

117. Startup Procedure for New or Overhauled Compressors:
When starting a new compressor, or one that has been overhauled,
allow the compressor to run unloaded for 1 or 2 hours to give the
running surfaces a polished finish.
Periodically check for overheating.
Build up load gradually over a period of several hours.
After a few days of operation, shut down compressor and recheck all
cylinder head, valve cover, cylinder flange, shaft cover, and foundation
bolts for tightness.

118. NORMAL OPERATION:
While the system is operating, perform the following tasks.
(a) Watch for irregular compressor performance; excessive vibration;
and overheating of bearings, motors, and packing.
(b) Maintain proper lubricating oil levels.
(c) Drain intercooler and aftercooler separators as necessary.
(d) If automatic drainers are provided, check their operation.
(e) Check temperatures and pressures of cooling water, compressed
air, and lubricating oil regularly.

119. SHUTDOWN:
Proceed as follows:
(a) Unload the compressor before stopping the drive.
(b) Drain separators, steam cylinders, and turbines.
(c) Shut off cooling water supply if an automatic shutoff valve is not
provided.
(d) If the compressor might be subjected to freezing temperatures
while shutdown, thoroughly drain cylinder jackets, coolers, and drain
traps.

120. Extended Shutdown. Any compressor taken out of service for an
extended period will deteriorate rapidly from rust and corrosion if not
properly protected.
(a) Drain and refill the crankcase with a preservative oil.
(b) Operate the machine without pressure for no less than 15 minutes.
This allows thorough distribution of the oil and elimination of any
crankcase condensate.
(c) While the machine is running, spray a fog of preservative oil into
the compressor intake.
(d) Remove piston rod packing and oil wiper rings from the rod or
corrosion of the piston rod may result. Coat the piston rod and oil wiper
rings with grease and wrap them in waterproof paper.
(e) Tape or plug all openings to keep out moisture.
(f) Relieve V-belts of tension.
(g) Drain the receiver and aftercooler.
(h) Drain the aftercooler cooling water, if used.

121. Good Practices for Safe and Efficient Operation of Air Compressors on
Ships
•Check oil level in sump. Do not overfill. Excessive oil consumption or
pressure build up in the crankcase to be observed, investigated and
rectified as soon as possible.
•Drain all air bottles regularly.
•Ensure air to deck, service air is shut when not in use.
•Give attention to any air leakages reported and rectify.
•Daily record running hours and log it.
•Daily check automatic drains and unloader of air compressor for proper
functioning.

122. •Weekly check the operation of the relief valves connected to the LP,
HP stages by operating manually.
•Follow planned maintenance as per manufacturer’s manual.
•Air filter to be renewed every 500 hours.
•Compressor valves to be removed for inspection every 1000 hours.
•Do not reverse valve plates. There is a danger of fatigue cracking.
•Every automatic drain valves to be stripped, cleaned and checked ev.
2000h.
•Every relief valves to be stripped, cleaned and overhauled, set at
correct press.
•Major overhaul to be carried out as per PMS.

123. OPERATIONAL PREVENTIVE MAINTENANCE:
Operational preventive maintenance includes the following tasks.
(a) Keep daily operating logs that record pressures and temperatures of
air and water in the compressor, intercoolers and aftercoolers, and of
compressor lubricating oil.
Deviations from normal values indicate the
corrective action that must be taken to return the system to normal and
to prevent damage to the equipment from insufficient lubrication or
inadequate cooling.
The operating log also helps in detecting valve troubles.
Locate defective valve by feeling the valve cover plates and determining
which is the hottest.

124. (b) Keep compressor clean at all times. Wipe the machine daily with a
cloth. Dirt on the machine will eventually work its way into the
lubricating system.
(c) Clean intake air filter regularly to prevent atmospheric dust from
entering the compressor cylinders.
(d) Keep piston rod packing tight enough to prevent air leakage, but do
not overtighten. Overtightening causes excessive packing wear and
scoring of the piston rod.

125. Quarterly Inspection:
Inspect the compressor every 3 months for the following conditions:
(a) Wear and dirt on, and proper seating of, compressor valves
(b) Operation of all safety valves
(c) Wear of packing and scoring of piston rods
(d) Sludge accumulations in crankcase
(e) Tightness of cylinder head bolts
(f) Tension, wear, and deterioration of belts
(g) Wear of connecting rods and crossheads
(h) Wear of, and dirt in, bearings
(i) Operation of lubricators and oil cups

126. Annual Inspection. Repeat the quarterly inspection outlined above and
inspect for the following conditions:
(a) Wear, scoring, and corrosion of, and dirt in cylinders
(b) Leakage, wear, scoring, and security to the piston rod of pistons;
(c) Damage, wear, and tightness of, and dirt in, piston rings
(d) Wear at packing glands of piston rods and security of piston rods to
crosshead and piston, check head clearances
(e) Wear and proper operation of crankcase and crankshaft bearings
(f) Wear and proper operation of crossheads, crosshead guides,and pins
(g) Security to shaft of flywheel; wear and dirt on flywheel bearings
(h) Alignment of compressor with drive

127. MAINTENANCE:
Lubrication:
Establish a lubrication schedule for air compressors. Normal oil levels
must be maintained at all times.
Use only lubricants recommended by the manufacturer. Frequency
of oil changes is dependent upon severity of service and
atmospheric dust and dirt.
The time for oil changes can best be determined by the physical
condition of the oil.
When changing oil, clean the inside of the crankcase by wiping with
clean, lint-free rags. If this is not possible, use a good grade of
flushing oil to remove any settled particles.

128. Cleaning:
Cylinder jackets of water-cooled compressors should be cleaned
annually with water.
Dirt accumulations interfere with water circulation.
Cleaning can be accomplished using a small hose nozzle to play water
into the jackets.
On compressors fitted with mechanical lubricators , cylinders may be
cleaned with a nonflammable cleaning fluid.
Do not use gasoline,kerosene, or other low flashpoint solvents. A
serious explosion may result.

129. Valves:
Replace all defective valve parts as required.
When a valve disk or plate wears to less than one-half its original
thickness, it should be replaced.
Valve seats may be resurfaced by lapping or regrinding. On some valve
designs it is necessary to check the lift after resurfacing. Carbon
deposits should be removed and the valve assembly washed in
nonflammable cleaning fluid.
Before replacing valves, make sure the valve seat and cover plate
gaskets are in good condition. If any defects are found, replace the
gaskets.
Make sure the valve is returned to the same port from which it was
removed.

130. Piston Rings:
When replacing worn piston rings, the new rings must be tried in the
cylinder for fit.
If the cylinder wall is badly scored or out of round, rebore the cylinder,
or if cylinder liners are fitted, replace them.
If necessary to file for end clearance, take care to file the ends parallel.
Clean the ring grooves and remove any carbon deposits before
installing the new rings. To install new rings, place several metal strips
not more than 0.032-inch ( 0,8 mm) thick between the piston and
rings.
Make sure the ring is free by rotating it in its groove.

131. Piston End Clearance: (Bumping Clearance)
Always check piston end clearance after replacing pistons or after
adjustment or replacement of main, crankpin, wristpin, or
crosshead bearings.
To measure piston end clearance, insert a solder into the cylinder
through a valve port and turn the compressor over by hand so that
the piston moves to the end of its stroke.

132. Bearings:
Sleeve type main bearings are adjusted by removing or adding
metal shims between the cap and body of the bearing housing.
The same number of shims should be added or removed from each side
of the bearing.
Make sure caps are tightly secured so they cannot work loose. Do not
overtighten as this causes overheating of the bearing.

133. V-Belt Drives:
Adjust tension or replace V-belts as required.
When one or more belts in a set require replacement, replace the
entire set with matched belts. If this is not done, the new
unstretched belts, being shorter than the old belts, will carry most of
the load and will be subjected to undue strain.
Removed belts that appear to be in a serviceable condition may be
kept for emergency use.

135. General Problems of Air Compressors on Ships
Most of the problems associated with air compressors lead to increase
in running hours. They are:
•Leaking automatic drains. The reason may be deposition of dirt in the
valve seat.
•Leaky relief valves.
•Unloaders not operating correctly.
•Damaged or worn suction and discharge valves.
•Dirty air filter.
•Leaks in the compressed air systems, such as service air to deck, control
air systems, etc.

136. Effect of Oil and Water Carry Over
•Water carry over in the air can lead to general corrosion and pitting.
•The air bottle is internally coated with a varnish to resist this attack.
•Main air starting lines to be regularly examined for corrosion and
wastage.
•Oxidised lubricating oil in the air also cause corrosion.
•Valves in the starting air line system may jam and corrode.
•Corrosion may cause main air starting valve to stick open, which is a
dangerous situation.
•Possibility of starting air line explosion.

137. SUMMARY
AND
EXERCISES

138.  What happens to air when it is compressed?
A. The air is heated
B. The pressure increases
C. A vacuum is created at the inlet port of the compressor
 What two areas require lubrication in a reciprocating piston
compressor?
1. Compressor housing
2. Cylinder Area
 What will happen to a reciprocating compressor if the air
operated unloading valve fails in the shifted (open) position?
Pressure will not build up at the outlet port

139.  A reciprocating compressor with a water intercooler has shut
down due to over temperature. Name three checks you would
make.
1. Check the intake filter
2. Check for restricted water flow through the cooler
3. Check the oil level

140. •Clogging of air filter leads to reduction in volumetric efficiency of the
compressor.
•Wear on main and bottom end bearings increase the bumping
clearance and reduce volumetric efficiency.
•If intercoolers are clogged air passing to the next stage will be less
dense and at a higher temperature. this may cause overheating,
vaporizing lube oil, increased wear down and possible explosion.
•If non return valves on the discharge line of the compressor not seated
properly, running hours of compressor increases.
•Defective automatic drains cause oil and water to get carried to the air
bottle. This leads to corrosion of the air bottle as well as service pipe
lines. Again, oil film may be formed inside the pipe lines which can lead
to disastrous starting air line explosions.

141. •An air compressor is equipped with an intercooler and an after
cooler to increase compressor efficiency and economy.
•To obtain maximum efficiency, two stage air compressors are
usually fitted with intercoolers.
•If the intercooler of a low pressure air compressor becomes fouled
either internally or externally, the volumetric efficiency will be
decreased.
•After coolers are used with air compressors to reduce the
temperature of compressed air.
•The unloading system on an air compressor will allow the motor to
turn the compressor opposed only by friction.

142. •The function of an air compressor intake filter is to protects against
the damaging effects of airborne solid particles.
•Moisture and impurities can be removed from pneumatic systems
by using blow down valves and filters.
•The purpose of an air compressor unloading device is to delay the
compression process until the motor is up to speed.
• An air compressor can be unloaded at start-up by relieving the
intercooler pressure to the atmosphere.
•The difference between a typical relief valve and a typical safety
valve is a relief valve gradually opens as pressure increases above set
point pressure where as a safety valve fully opens at the set point
pressure.

143. •An important point of consideration when replacing a dry type intake
filter on an air compressor is to select the proper size filter so that air
flow is not restricted.
•Separators are installed ahead of air line lubricators for the primary
purpose of removing moisture in the air supply.
•The unloading system on an air compressor will allow the motor to turn
the compressor opposed only by friction.
•Air compressor cylinder unloaders enable the compressor to start and
come up to speed before air compression begins.
•The unloading of an air compressor may be provided by holding the
intake valve off of its seat and/or temporarily relieving the intercooler to
the atmosphere.

144. •If an air compressor is used to supply air primarily to the combustion
control system and other pneumatic controllers, the entire system is
known as the control air system.
•If an air compressor is used to supply compressed air to outlets
throughout the engine room and on deck of a vessel, the system is
known as the ship's service air system.
• If one drive belt on an air compressor is found to be worn you
shouldreplace all of the belts.
•If the foundation bolts of a reciprocating air compressor are loose, the
compressor will vibrate.
•Air compressor receivers should be 'blown down' at least daily.
•Condensate must be drained periodically from the air compressor
receivers to prevent faulty operation of pneumatic valves.

145. •The purpose of an air compressor unloading device is to delay the
compression process until the motor is up to speed.
•An air compressor is equipped with an intercooler and an after cooler
to increase compressor efficiency and economy.
•To obtain maximum efficiency, two stage air compressors are usually
fitted with intercoolers .
•After coolers are used with air compressors to reduce the temperature
of compressed air.
•Condensate must be drained from the intercooler and after coolers of
an air compressor because water contamination causes erratic
operation of pneumatic components.
•Safety devices on Main Air Bottle:
1. Fusible plug.
2. Pressure Relief Valve

146. •A dirty intercooler on the ship service air compressor will result in
higher than normal power consumption.
•A leaking suction valve in the second stage of a two stage, high
pressure, air compressor can cause excessively high first stage discharge
pressure.
•A squealing sound generated by a reciprocating air compressor upon
starting may indicate defective unloader.
•A viscous film of oil collected between the valve face and seat of a low
pressure reciprocating air compressor will retard the opening and
closing of the valve.
•Air blowing from the intake air filter of an operating air compressor
indicates broken discharge valves.
Air compressor cylinder unloaders enable the compressor to start and
come up to speed before air compression begins.

147. •Air compressor receivers should be 'blown down' at least quarterly.
•An unloader is installed on an air compressor to remove the
compression load as the compressor comes up to speed during
starting.
•Broken valve strips in an operating low pressure air compressor will
cause a decrease in compressor capacity.
•Carbon deposits forming on the discharge valves of an air compressor
are caused by oil deterioration under high pressure. The first step in
reducing these deposits would be to reduce the discharge
temperatures with intercoolers
•Condensate must be drained from the intercooler and aftercoolers of
an air compressor because the cooling effect of the condensate
reduces the compressor's efficiency.
•Condensate must be drained periodically from the air compressor
receivers to prevent second stage cylinder lockup.

148. What is the safety devices fitted to an air compressor?
•Low L.O.pressure shutdown
•High air temperature shutdown
•First stage relief valve
•Second stage relief valve
•A fusible plug is fitted after the second stage cooler, set at 120 deg C
•If water cooled, a jacket water safety valve is fitted.

149. Explain how would you start an air compressor and stop it (after
overhauling)
1. Check oil level in crankcase.
2. Then ensure all drains are open. intercooler drain and also unloader
3. Check air intake filters is cleaned
4. Ensure oil pressure gauge is open and that air pressure gauges i.e.
first and second stage are partially open to stop gauge fluctuation.
5. Check water-cooled check valves are open and ensure cooling is
supplied
6. Bar machine over by hand to see if its free to turn
7. Start the machine, check there are no unusual noises or vibration and
oil pressure is correct.
8. Then close drains and unloader

150. What are the reason of the HP Relief Valve opening:
Causes:
•HP discharge valve, in closed position.
•After cooler choked.
•Relief valve, jammed by foreign particles, or spring sticking in
open position.
(Relief Valves opening pressure are set at ≯ 10% above stage
pressure.)
What are the reason of the LP Relief Valve opening:
Causes:
HP suction valve in closed position
Intercooler choked.
Relief valve, jammed by foreign particles, in open position.

151. What are the dangers of excessive lubrication in start air compressors?
There is a danger that excessive cylinder lubrication in start air
compressors could lead to explosions in air start lines/manifolds.
Excessive lubrication can lead to carry over with compressed air, being
deposited in the receiver then transferred to the air start manifold,
where a leaking air start valve may allow hot gases from combustion
into the air start manifold, ignite the oil vapour, causing explosion.
What is the maximum compressed air temperature that should leave
the air compressor?
93 deg centigrade

152. What Causes Explosion?
It is very important to keep in mind that an air compressor has all the
things that are required for a perfect explosion.
A fire propagates at a very fast rate when three things are easily
available – fuel, oxygen and heat source.
This is also known as the deadly fire triangle which needs to be
avoided in all cases where there is a possibility of explosion or fire.
A compressor is a rich source of highly compressed air and when it
gets in contact with other two sources, an explosion is bound to take
place.

153. Sources
How does an air compressor get fuel for explosion?
It is to note that most of the ships use oil lubricated compressors and
it is the lubrication system of these compressors that provide the
necessary fuel for a probable explosion.
One more potent source of fuel is the carbon deposits that are
created when the oil heats up at high temperatures.
The last and the most easily producible factor - the heat source, can
be generated due to variety of reasons.
The most common source of heat source is heat generated due to
friction between two surfaces.

154. Lack of proper lubrication is the most common cause for heat generated
in this way. However, lack of lubrication can also be due to degradation
of lubricating oil, faulty lubricating oil pump, chocked oil filter, worn out
parts etc. These are the prime reasons for the developments of hot
spots.
The lack of lubrication will increase the wear and tear of the moving
parts of the compressor, deteriorating the quality and operation of the
compressor. As the components continue to operate poorly, carry over
of the oil to the air passages takes place, increasing the temperature of
that area.
Also, it is very important to remove this heat generated. If proper steps
are not taken to remove the heat, heat build up will take place
increasing the temperature substantially. Inter-coolers play an important
role in this heat removal and thus need to be properly working.

155. Cooling Problems
Lack of cooling can also occur when the heat transfer surfaces are
covered with scales or carbon deposits, thus affecting the cooling
process. Choked passages of the heat exchangers can also be a
reason.
Sometimes the cooling medium itself is hot due to faulty machinery,
thus providing negligible heat transfer.
Non-continuous supply of coolant might also be a reason. This
happens when the cooling pump fails or the valves of the coolant
line are stuck or accidentally closed.

156. An explosion occurs when all the above mentioned factors come
together to make a vicious cycle that ultimately leads to explosion.
Sometimes the oil film in the pipes also turns to deposited carbon,
which is already having a high temperature.
The compressed air inside the pipe along with the oil and deposited
carbon becomes a fatal combination for explosion.
Thus, only a rise in temperature above a certain limit or just a
generation of a spark or hot spot can ignite or blow off the whole
compressor.