A two-stage air compressor is often preferred over a single-stage air compressor, particularly for large-scale operations with high energy requirements.
In this post, we will go into what makes 2 stage air compressor better, how does a 2 stage air compressor work, the benefits, and much more.
How Two-Stage Air Compressors Work
The most common types of air compressors are the reciprocating (piston) type, and the rotary type, both of which are positive displacement compressors.
2-Stage Reciprocating Air Compressor
The two stages in reciprocating air compressor involve two cylinders, a low-pressure cylinder, and a high-pressure cylinder. The second cylinder is smaller than the previous one in terms of size to facilitate further compression.
Between the inlet filter and storage tank, these cylinders allow the trapped air to go through compression in two stages.
1st Stage of Compression
At the first stage, the ambient air is drawn into the low-pressure cylinder through an air suction system with an inlet filter. Here the air is compressed with a piston, typically ranging from 40 to 70 psi.
Note that because of the bigger cylinder, the volume of air is high, but the pressure is low.
As you know, compression causes the air to heat up. Before going to the second stage of compression, the heated air is cooled down to a much lower temperature. This is done to reduce the stress on the compressor and make the operation more efficient.
2nd Stage of compression
Now, the compressed, cooled air moves to the high-pressure cylinder with shorter piston for further compression. So, here the volume of air is low, but the pressure is high. At this stage, the final pressure of the air may reach 175 psi to 200 psi.
Right after this process, the pressurized air is cooled and then moves onward to a storage tank. This tank works as a reservoir of compressed air that can be used for various applications, e.g., auto assembly and maintenance, beverage manufacturing, aerospace operation, etc.
Two-stage Rotary Air Compressor
Two-stage rotary compressors are considered to be more energy-efficient, more reliable, and quieter than the equivalent reciprocating air compressors.
Rotary air compressors can be of four types, such as screw type, scroll type, vane type, and lobe type.
Two-Stage Rotary Screw Type Compressor
This type of compressor uses a similar working procedure as the reciprocating compressors. The main difference is that they have two helical rotor screws instead of a piston.
As the space cavity between the rotors becomes progressively smaller, the air compresses.
They usually use an integral coolant flow to prevent overheating during the two successive stages of compression.
Two-stage rotary scroll compressor
This compressor compresses gas through internal compression using two inter-fitting scrolls, where it operates at two levels. With the unique incorporation of opening and closing ports, its design allows air to bypass a portion of the scroll.
As a result, the capacity at the two stages can be modulated. The output of the compressor is thus adjusted, while the shifts between full-load and partial-load capacity are instantaneous.
This kind of two-stage compressor provides you better control over humidity and temperature. Two-stage versions of rotary vane compressor and rotary lobe type compressors are not as common as their single-stage version.
Multistage rotary vane compressors (60-150 psi) are sometimes used for moving bulk materials, such as concrete. Here flow-through lubricants are used for smooth operation.
Nonetheless, research is going on to develop new designs of a two-stage sliding vane rotary compressor to improve the pressure ratio.
Why Get 2 Stage Air Compressor
The reason becomes clear if we compare the operating pressure of the two-stage air compressor to the single-stage one. When the pressure in a single stage compressor is 120 psi, the two-stage compressor can provide you up to 200 psi!
Now the question comes how a two-stage air compressor works to generate almost double the pressure. In this article, I am going to discuss the basic working procedure of a two-stage air compressor.
A two-stage air compressor compresses the air twice. Hence, the compressed air will have much higher pressure with better efficiency and power.
In between the two stages, typically an intercooler system is involved. As a result, the amount of work required, as well as risks associated with overheating, significantly reduce.
Now that you know the basic principle of a two-stage air compressor, let’s dig deeper to understand how different kinds of two-stage air compressors work.
Benefits of two-stage air compressor
Compression is thermodynamically more efficient at lower temperatures. As the two-stage compressor can mostly run at the lower level, it uses less energy to generate high pressure.
This makes the two-stage compressor more energy efficient, making the operating cost much lower.
Moreover, two-stage compressors can deliver higher CFM (cubic feet per minute), i.e., their operating capacity is suitable for the bulky pneumatic tools in industrial applications.
Due to the inter-stage cooling, the two-stage air compressor prevents from overheating.
Consequently, the chances of mechanical damage, as well as the need for maintenance, is quite low. That’s why the compressor can provide you with higher productivity and reliability.
Less Buildup of Moisture
Moisture in compressed air can result in premature wear or equipment failure. As two-stage compressors operate on cooled air, the moisture content is low, hence fewer problem with buildup.
I hope you had an overall idea about the working procedure and applicability of a two-stage compressor from the above discussion.
When should we use a 2-stage air compressor?
Most assembly plants of manufacturing facilities require air pressure of more than 100 psi to run their operations.
So, in the case of a factory or industrial application, where continuous or large-scale operation is a requirement, you should use a 2-stage compressor.
Is a 2-stage air compressor worth the cost?
When you consider the applicability of a 2-stage compressor and its long-term reliability, it is definitely worth the initial cost.