COMPRESSOR TYPES

Q. WHAT ARE THE TYPES OF AIR COMPRESSOR ANDD IT'S WORKING PRINCIPLE?

ANS:- In an air compressor, air is compressed by pulling in atmospheric air, reducing its volume and increasing its pressure. 

There are two types of air compressor:-

1. reciprocating type,
2. rotary type

An air compressor is a versatile device used for supplying compressed at required pressure.

Eg. - for starting main engine of the ship, compressed air is required at 30 bar

-workshop purposes for removing dust

-spray paint

1. Reciprocating Air Compressor:-

• A reciprocating air compressor makes use of piston(s) to compress air and store it in a storage tank(or reservoir) .

• Based on the number of compression stages, reciprocating compressor can be a single-stage or double-stage configuration.

• In the single-stage unit, only one piston is used to compress air, whereas there are two pistons for air compression in the double-stage air compressor.

• Double - stage compressor are used to compress air at higher pressure. As in double stage the air which is compressed in primary stage is input for the secondary stage.

• For marine purpose multistage compressor is used along with inter-coolers at every stage of compression and after-cooler (for maintaining the final temperature)

Since, it compresses air at much higher pressure so it is required to fit safety devices like:-

1. Bursting discs are fitted on the cooler shells (At water side).
2. Relief valves are fitted to discharge side for every stages.
3. Moisture drain valve (unloader) are fitted at each cooler side
4. Cooling water failure alarm.
5. Low L. O pressure alarm.
6. Delivery air high temperature alarm on after cooler outlet (Max 93°C)

2. Rotary Air Compressor

These are either vane or screw type.

• Each stage pressure rise is limited to 7 bar only.
• It requires a high speed drive.

(a) screw type

• Over here, two spinning helical screws or rotors are involved for compressing air (instead of using pistons), hence the name.

• As the screws mesh towards each other, air is compressed and pushed inside a storage tank.

(b)  vane type

• A centrifugal air compressor is also called a dynamic compressor.

• It is applicable when the demand for compressed air is high.

• In this unit, a high-speed rotating impeller increases velocity of air, which is directed towards a diffuser that converts the velocity of air into pressure.

• A centrifugal air compressor requires more energy to operate than the other two air compressors.

Air Compressor: Working Mechanism

• In an air compressor, there are two major parts - a compressing system and a power source.

• The compressing mechanism can be a piston, rotating impeller, or vane depending upon which type of compressor you are referring to.

• As for the power, it is supplied by an electric motor or other energy sources.

• The compressing mechanism, as the name suggests, helps in compressing atmospheric air by using energy from the power source.

• The basic working principle of an air compressor is to compress atmospheric air, which is then used as per the requirements. In the process, atmospheric air is drawn in through an intake valve; more and more air is pulled inside a limited space mechanically by means of piston, impeller, or vane. Since the amount of pulled atmospheric air is increased in the receiver or storage tank, volume is reduced and pressure is raised automatically. In simpler terms, free or atmospheric air is compressed after reducing its volume and at the same time, increasing its pressure.