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Compressors

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Compressed air can be used in a variety of ways. Perhaps the most well-known use of air compressors is in the case of pneumatic tools such as air-powered nail guns, staplers, sanders, spray guns and ratchet wrenches. So, we have to know how we can obtain compressed air. First, we need to know what is compression?

Compression
Compression refers to the process of reducing the volume of gas (air) in order to raise its pressure. The compressed gas is stored in a solid container, which usually has a pressure gauge and the safety of mechanism.

How it works?
When air enters the piston, it is compressed through increasing its pressure and decreasing its volume. As soon as pressure reaches the maximum set by the operator, a switch mechanism prevents any further air intake in compressor. Also, when the pressure reaches a minimum, set by the operator, the switch lets the air in.

The main parts of marine air compressor

1. Cylinder liner

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

2. Piston

There are two types of pistons: light-weight aluminum alloy pistons used for lubricating type graded; and cast iron pistons used with piston rings for sealing and scrapping off excess oil.

3. Big-end-bearing and main bearing

These are used to provide rigidity to the running rotational mechanism. They are made up of copper lead alloy and have long operational life, if proper lube oil and lubrication is provided. To minimize thrust to the bearing surface we use a connecting rod made of forged alloy steel.

4. Crankshaft

A one-piece designed part that uses counter weights for dynamic balancing during high rotation to avoid twisting due to torsion forces. The big-end-bearing and the main bearing are connected to a crankshaft at crank pin and journal pin which are polished to ensure long working life of bearings.

5. Pumps

There are two types of pumps:

• Oil pump: A lubricating oil pump is fitted to supply lube oil to all the bearings, which can be chain or gear driven, through crankshaft. Pressure of oil can be regulated by means of regulating the screw provided in the pump.

• Water pump: Some compressors may have attached water cooling pump driven by crankshaft through chain or gear.

6. Suction and Discharges

• Valves: These are multi-plate valves made up of stainless steel. They are used to stock and 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.

• Filter: It is an 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 enter the compression chamber.

7. Inter-coolers

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

8. Driven motor

An electrical motor  is attached to the compressor to make it operational.

References
www.brighthubengineering.com
www.marineinsight.com

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