Two Frequently asked questions: “What is Air Compressor?” and “How air compressor works?” Air compressor is a mechanical device that compresses air and releases the air at high pressure. The widespread use of air compressor is noticeable from home to industry in different type of cases. To meet the user demand and to make the air more efficient, varied types of air compressor are built. Today we will learn on types of air compressor and how air compressor works including centrifugal compressor.
How Air Compressor Works-The Basic Type
Main Components of Air Compressor:
There are mainly three parts of an air compressor: the electric motor, pump, and the receiver (tank). the receivers may be vertical or horizontal varying in size and capacity.
The main purpose of an electric motor is to power the pump. the motor drives a pully through belts which transfer power from the motor to the pump pistons via a flywheel and crankshaft. The mechanism of flywheel is to cool the compressor pump.
The purpose of the pump is to compress the air and discharge it into the receiver. Two stage air compressors has at least two pump cylinders. By compressing the air twice first in a larger low-pressure cylinder then in a smaller high-pressure cylinder two stage compressor can produce pressure from 145 to 175 PSI.
The receiver tank is stores the compressed air. A check valve at the receiver inlet prevents the compressed air in the receiver from flowing back into the compressor pump.
Read More: Air Compressor Maintenance Guide
Types of Air Compressor:
Fundamentally, air compressor can be classified into 3 types.
- According to the pressure delivered.
- According to the design and operational principle.
- According to air compression ratio.
Basing on the output pressure the air compressor is categorized into 3 types.
- A) Low pressure air compressor: This type of air compressor may discharge pressure up to 150 PSI.
- B) Medium pressure compressor: This type of compressor can deliver 150 PSI to 1000 PSI.
- C) High pressure air compressor: These giant types of compressor always produce pressure above 1000PSI.
If we classify air compressor according to the design principle and its operation, then air compressor can be divided into two types
2.A) Rotary-Screw Compressor
2.B) Turbo Compressor
The third fundamental classification of an air compressor is based on compression ratio. This category can also be classified into two types.
3. A) Positive Displacement air compressor
3. B) Roto-dynamic air compressor.
Last but not the least, positive displacement air compressor can be classified into three types: Piston type, rotary-screw type and Vane type.
How A Piston Type Air Compressor Works?
Both in industry and in the home an air compressor plays a very important role. In a very basic way we will see how an air compressor works. Usually they have a big piece of pipe works called a cylinder with a piston inside driven by a crankshaft and a connecting rod.
A couple of automatic valves complete the items needed for our explanation. Firstly, the compressor system begins to look downwards into the cylinder. This creates a partial vacuum in the atmospheric pressure that opens the inlet valve.
As the piston goes down, the cylinder is filled with atmospheric air this results in an entire cylinder filled with air at ambient pressure. When the crankshaft completes careful revolution, the piston begins to go upwards again. The pressure generated inside the cylinder in addition to a spring mounted on the valve close the inlet valve. Then the increased pressure opens the automatic outlet valve. when the piston reaches its maximum upper position, the outlet valve closes again.
The cycle repeats itself and the pressure becomes higher and higher inside the storage tank. A special sensor mounted on the tank senses the pressure and chucks off the compressor driving motor. Whenever the pressure drops in the tank either due to air usage or leakage the sensor will restart the motor.
The lubrication of the compressor is carried out by means of a certain amount of oil contained in the compressor oil pan and also by lubricating devices placed in the air inlet pipe to maintain a suspension of oil droplets to lubricate the valves in the inside of the cylinder. there is also a transparent filter where most air accumulates to be drained periodically thus preventing is from entering the compression chamber. This is roughly the way a basic compressor
Centrifugal Compressor Working Principle
Let’s examine the centrifugal compressor which uses non-positive displacement vapor compression for compressing large amounts of refrigerant and are typically used in very large capacity cooling systems. A centrifugal compressor has three basic components:
- An impeller
- A diffuser
- A volute casing
Large capacity centrifugal compressors may have two or more impellers or stages in the same casing. Centrifugal compressors are usually driven by hermetic electric motors. However open-drive and centrifugal compressors are also available for applications using steam turbine, gas turbine or engine drives.
The impeller is a rotating circular disc with curved blades that is driven at high speed by the electric motor. As the impeller rotates, it moves refrigerant vapor from the suction opening in its center to the outer edge using centrifugal force. The vapor enters the suction at a relatively low velocity and leaves the outer edge of the impeller at a high velocity; this means that the impeller transfers its rotational energy to the vapor but high velocity does not relate to high static pressure.
To achieve the desired pressure-increase or compression, the vapor must be slowed down converting its velocity pressure to static pressure. That’s where the diffuser comes in. As high velocity vapor moves radially outward through the diffuser, the flow area increases slowing the vapor and increasing the static pressure.
Some centrifugal models have diffusers with vanes or pipes which change flow direction and further slow the vapor. The volute shaped casing collects the slow-moving high-pressure vapor from around the diffuser and conveys it to the discharge connection of the compressor.
Inlet guide vanes control a centrifugal compressors capacity. These moveable vanes are located in the suction opening. With vanes turned fully open the compressor produces its full cooling capacity. As the vanes are closed, they reduce refrigerant flow through the compressor reducing the capacity of the refrigeration cycle.
In addition, capacity control in a centrifugal compressor can also be obtained by changing the rotating speed. this concludes our segment on the mechanical non-positive displacement vapor compression cycle using a centrifugal compressor.