There are several different types of air compressors available to buy on the market these days, and each different type can be used for different purposes. Here we will focus on one specific type, Rotary Screw Compressors, and the different variations available.
Rotary Screw compressors are gas compressors which deploy a rotary type, positive displacement mechanism to generate the air required to power a specific tool or machine. This type of compressor can commonly be found where a large amount of power is required, so they are regularly found in industrial settings, or where high powered tools, such as jackhammers need that extra power.
Internally, there are 2 helical screws (rotors), which mesh together in order to compress the gas. How these screws work is dependent on if the compressor is dry running or oil based. In dry running compressors, timing gears are in place to make sure that the male and female rotors are aligned perfectly. In the oil flooded variation, the rotors don’t need to be aligned as tightly, as oil fills the gaps in the rotors, creating a good seal, and also assisting in the transfer of energy between the driven & driving rotor.
There is also a lot of variation between control schemes when it comes to Rotary Screw Compressors. The most common types are:
Start / Stop:
In this kind of set up, the compressor has relays that are actuated to apply and remove power to the airend motor according to demand.
Load / Unload:
In this scheme, the airend is continuously powered, but when there is no demand for air, the inlet valve closes, which unloads the compressor. This in turn reduces the amount of starts and stops for electric motors, reducing the amount of times equipment needs to be serviced.
Modulation:
Modulation schemes differ from the previous 2 insofar as, they adjust the inlet valve open and closed proportionally, according to demand. Although the yield of pressure is discharged consistently over a range of different requirements, this is usually at the expense of extra power consumption.
Variable Displacement:
This method is favoured by some manufacturers, as the compressor has the ability to change the percentage of the screw compressor rotors working to actually compress the air, via variable displacement. This is done by letting air flow to side step portions of the screws. This method can be practical where large amounts of storage are not required.
Variable Speed:
Variable speed compressors tend to have the lowest operating costs out of all the other methods. However, they also tend to be more expensive to purchase initially. They are not suited to certain conditions, such as hot or humid areas, due to the sensitivity of the equipment.
Those are some of the main types of Rotary Screw Compressors you can expect to encounter, if you are looking to purchase a new compressor.
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