What is a Two Stage Compressor | How does a 2 Stage Air Compressor work?

Compressors have become an important part of all industries. The compressors have multiple types, and a 2 stage air compressor is one of them. A two-stage or double-stage reciprocating compressor is a famous type of air compressor from the category of reciprocating air compressor

The 2-stage compressors have a different working principle and construction than the single-stage compressors. In this article, we will deeply examine the two-stage air compressor.

What is a 2-Stage Air Compressor?

A 2-stage air compressor is a type of compressor that compresses the air in two stages.  In this air compressor, the fluid compresses two times. It has two cylinders, and each cylinder has a piston. This air compressor uses two pistons. It uses one for compressing the air while the second piston uses to transfer the compressed air from one cylinder to the second cylinder. 

The 2-stage compressors are used for high-pressure applications. The main difference between single-stage and 2-stage air compressors is that single-stage compressors complete the compression in only one stage while 2-stage air compressors complete compression in 2 stages.


The cylinders of the single-stage compressor have the same external diameters. While a 2-stage air compressor has a large diameter of the first-stage cylinder than the second-stage cylinder. Similarly, in this air compressor, a charge air cooler pipe is always connected to the compressor to cool the air before starting the second stage of compression.

A double-stage air compressor has many advantages,  but it may not always be a good option for all applications. In general, the single-stage compressors are appropriate for light-duty, discontinuous applications with pressure needs of no more than 100 PSIG. While 2-stage air compressor provides high reliability and pressure for applications like production and auto repair.

A single-stage reciprocating compressor uses a plunger or piston to suck the air into the compression chamber from the outside and compresses it only once in a single cylinder. While the working of the 2-stage air compressor is the same, it repeats the compression process two times. In simple words, it has two cylinders for storing compressed air, and this process repeats two times.

2-Stage Air Compressor Working Principle

the two-stage air compressor has a piston that is attached to the crankshaft via a connecting rod. The crankshaft is connected to an electric motor or engine. It gets power from the motor.

When the crankshaft rotates the piston, the piston moves forward and backward. The crankcase connects to the crankshaft. The inlet valve and outlet valve are connected to a cylindrical head that contains a valve cavity.

2 stage air compressor working

The above P-V diagram shows a two-stage air compressor. A 2-stage air compressor works in the following way:

  • As the prime mover coupled with the crankshaft starts rotating, the crankshaft also rotates. Due to the rotation of the crankshaft, the piston of the first cylinder (L.P cylinder) also starts its reciprocating motion.
  • During this process, the piston sucks air through the suction valve and filter. The piston of the low-pressure (LP) cylinder compresses the air. The air in the L.P cylinder is compressed to an intermediate pressure “P2”.
  • After compressing the air to a specific degree, the piston of the L.P cylinder sends the compressed air into an intermediate pressure (I.P) air cooler where compressed air is cooled (as shown in the below-given diagram) before transferring it into the second (H.P) cylinder. The first stage compression ratio depends on the degree of cooling required.
  • During the H.P cylinder’s air compression process, the piston moves upward and downward and converts the air into high-pressurized air. At last, the high-pressurized air collects through the outlet valve.
2 stage compressor
Fig: 2 Stage Compressor Working

Read also: How does a single-stage compressor work?

Components of Two-stage Air Compressor

The main components of the two-stage compressor are given below.

  1. Inlet Valve
  2. Intercooler
  3. L.P Cylinder
  4. H.P Cylinder
  5. Crankshaft
  6. Piston
  7. Connecting rod
  8. Outlet Valve

components of two stage compressor

1) Inlet Valve 

The inlet valve uses for sucking the air from an external source into the compressor cylinder.

2) Cylinder

The cylinder is the area where the air is compressed. The 2-stage compressors have two cylinders: a low-pressure cylinder and a high-pressure cylinder.

3) Piston

The piston is employed to compress the air into the cylinder. It moves upward and downward into the cylinder. When it moves upward, it sucks the air into the cylinder while when it moves downward, it compresses the air. This piston air compressor has two pistons. Each cylinder has a piston.

Read More: Piston Parts and Construction

4) Connecting Rod

The connecting rod connects the crankshaft and piston. The piston moves due to the movement of the connecting rod.

5) Intercooler

It uses to reduce the temperature of the air before sending it into the H.P cylinder. It cools the air.

6) Outlet Valve

It connects with the H.P. cylinder. An outlet valve uses to discharge the compressed air.

7) Crankshaft

It is connected to an electric motor or engine. It gets power from the electric motor and drives the piston.

Read More: Crankshaft Working and Construction

Advantages and Disadvantages of Double Stage Compressors

The two-stage compressors have the following advantages and disadvantages:

Advantages of 2-stage Air Compressors

  • They produce higher compressed air than single-stage compressors.
  • These compressors operate with natural gas or electricity. They are more common because they are easier to use. In contrast, gas compressors can be used in areas where electricity is difficult to use.
  • They are used to drive pneumatic tools like air nailers, ratchet pawls, and spray guns.
  • It uses in gas stations and various production power plants.
  • These compressors are usually stationary and can be used to power various tools over long periods.
  • It requires low maintenance.
  • These compressors have a small footprint.
  • They have good reliability.
  • Low moisture buildup.
  • It has a low compression ratio at each stage as compared to the single-stage compressor.
  • It is a small and better-balanced machine.

Disadvantages of 2-stage Compressor

  • These compressors require more power.
  • Requires additional cooling
  • Two-stage compressors have more moving parts than single-stage compressors.
  • It has a high cost for installation.
  • These compressors have heavyweight.
  • They are many troubles involved in buying, transporting, and storing gasoline.
  • They produce high noise.
  • If you want to clean the gas tank from time to time, additional maintenance is required.

Applications of Two-stage Compressors

  1. These compressors highly use in textile industries.
  2. These compressors use in petrol pumps.
  3. Uses in plastic industries.
  4. These compressors use in fertilizers and chemical industries.
  5. They are utilized for pneumatic operations.
  6. Two-stage compressors are used in blowing applications.

Read More
  1. What are the different types of Compressors?
  2. How does a Dynamic Compressor work?
  3. How does a Single-Acting Compressor work?
  4. How does a Single-stage Compressor work?
  5. Reciprocating Compressor Working and Types

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