Learning Objective: Learning Objective: Describe the basic design Describe the basic design features and functions of various marine features and functions of various marine auxiliary machineryauxiliary machinery

Machinery: Air CompressorMachinery: Air Compressor

Specific Objectives:Specific Objectives: • Recognize the various names and locations of auxiliary machinery found on board

• Describe the basic operation of the machinery

• Identify the main parts of the machinery

• Sketch and label the main parts

AIR COMPRESSOR

Introduction

Air compressor is a thermal machine used for repeated compression of gas known as atmospheric air to produce high-pressure air

Air Composition: mainly 23% oxygen and 76% nitrogen by mass (small quantities of other gases such as carbon dioxide, argon, helium, neon and water vapor)

A mixture of them will behave as a perfect gas, following Boyle and Charles law.

When air is compressed, its temperature and pressure increase as its volume is reduced.

Uses of Compressed Air

Air compressors of various designs are widely used in numerous applications including the operation of equipment and portable tools.

Ship board compressed air usage may divided as follows: Starting operationControl & InstrumentationGeneral Service/ Utilities

Compressed air is used onboard ship for a number of purposes and at varying pressures depending on that purpose.

- High-pressure air – 25 to 40 bar – for starting

and reversing of diesel engines (two or three stage-

reciprocating units) - Medium pressure air – 7 bar – for general service air,

deck air pneumatic systems, power positioners, servo mechanisms and air puff soot blowers (single/two stage reciprocating units & rotary units)

- Medium/low pressure air – 4 and 5 bar – Utilities- ‘pneu-press’ and ‘grinell sprinkler’ by single/two stage-reciprocating units or by rotary units.

- Low-pressure air – 2 bar – Control & Instrumentation pneumatic control systems by single stage or rotary units

Starting operation (average 25 to 40 Bar)

Starting the compression ignition diesel engine require normally 30 Bar or related with total capacity of the air bottle

On generators, starting air system is normally connected to emergency air compressor driven by small engine or manually operated

Prior to starting, engine is blown through with air to remove any condensate or residue in cylinder

Control & Instrumentation (1.4 to 7 Bar)

Pneumatically controlled instruments for pressure, temperature, level, speed, flow etc., with working pressure in the range of 1.4 to 7 Bar.

The range of pressure is obtained by using a small reducing valve or solenoid valve to supply air at the correct value

General Service (4 to 7 Bar)

Service air is used for kind of tools (considered as pneumatic tools) which are operated by compressed air (e.g., drilling machine, impact wrenches, hand grinder, lifting gear etc.,)

Used on auxiliary or deck machinery operated by compressed air

(e.g., Wilden pump, lifeboat davit, de-mucking winches etc.,)

Pneumatic wrenches for even tightening of studs Fuel injector testing Water Pressure Test Used for cleaning purposes. Dust cleaning/clearing at

narrow spaces where brush and finger tips cannot reach Cleaning any dust from the electrical machinery e.g.

alternator, motor etc.,

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IN T E R M IT T E N TF L O W

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C O N T IN U O U SF L O W

A IR C O M P R E S S O R

ClassificationCompressors can be classified based on

operational principle of compression as follows: Positive displacement compressorsDynamic compressors

Specially designed compressors used for specific purpose are further defined by:The number of compression stages Method of cooling (air, water, oil) Drive method (motor, engine, steam, other) How they are lubricated (oil, oil-free) Packaged or custom-built

Multi stage compressors

They are used for three reasons:

By cooling between stages: the air is kept in a moderate temperature range, less work is required to compress a given

quantity of air to a required pressure (closer to isothermal)

Lubrication difficulties minimized (low air temperatures)

The capacity of an air compressor is measured by the number of cubic metres of free air discharged per minute (FAD).

Air Receivers (Air Bottles) are provided as

per Regulations. Safety features include Fusible plugs and Relief valves

The Volumetric Efficiency of an air compressor is measured by the number of cubic metres of free air discharged (FAD) per minute compared with the displacement of the LP piston in cubic metres per minute.

Modern air compressors have a Volumetric

Efficiency of 80 to 90%.

Summary

Uses of Compressed Air onboard.Uses of Compressed Air onboard.Compressor TypesCompressor TypesOperation of Single and Multi-stage Air Operation of Single and Multi-stage Air

CompressorCompressorComponents of Air Compressor Components of Air Compressor Safety features an Air Compressor and Safety features an Air Compressor and

Air Reservoir.Air Reservoir.