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Double Acting Compressor – Working Principle, Components, and Applications

The compressors are most widely used in different industries for various applications. There are many types of compressors and a double-acting compressor is one of them. According to the working of the piston, the reciprocating compressors divide into two main types:

  1. Single-acting compressor
  2. Double-acting compressor

In a single-acting air compressor, only one side of the piston works. But the double-acting compressor working principle is a little bit different than a single-acting compressor. In the previous article, we deeply discussed single-acting compressors but in this article, we will mainly discuss double-acting compressors.

What is a Double Acting Compress?

A double-acting compressor is a very famous type of positive displacement compressor from the category of the reciprocating air compressor. A reciprocating air compressor that uses both sides of the piston to suck and compress the air is called a double-acting compressor. In simple words, the piston of a double-acting reciprocating compressor uses its both sides for air or gas suction and compression.

In this type of compressor, one end of the piston uses for sucking the air while the other end uses for compression. In simple words, when the piston moves backward then it sucks the air, while when it moves forward then it compresses air. These types of air compressors reduce air volume during compression.

The inlet and outlet valves operate according to the piston movement and the stroke of the double-acting air compressor.

A single-acting compressor’s work efficiency is 22 to 24 kW / 100 cfm air, and a double-acting compressor’s working efficiency is 15 to 16 kW / 100 cfm air. Thus, these compressors produce cheap electricity compared to the single-acting compressor for the same amount of compressed air.

As the compression heat increases, the double-acting reciprocating compressor is mostly water-cooled. Similarly, a mechanism has been added between the piston and the crankshaft that generally slows down the speed. This compressor has a higher initial price than a single-acting reciprocating air compressor because of its size, water jacket, and additional components. But it has too high efficiency.

Double Acting Air Compressor Working Principle

The double-acting reciprocating compressor working principle is very simple.

So, the double-acting air compressor has four valves (2 outlets and 2 inlet valves), as shown in the above-given diagram.

There is a fan similar to a single-acting air compressor. The crankshaft is driven by a turbine/ engine/ electric motor. With this type of compressor, air compression occurs on the piston’s both sides. As the crank turns, the piston begins to alternate. When the piston moves downward and reaches the BDC, air enters in valve “1” due to the vacuum created by the downward movement.

When the piston moves up, the air begins to compress. As the piston reaches the TDC, the air stroke completes and the compression process also completes. When the air is fully compressed then releases it into the air reservoir via the delivery or outlet valve “2”.

During the upward motion of the piston, a vacuum is created on the opposite side of the piston. Next, the suction or the inlet valve “3” opens, and air enters. When the piston begins to descend, the air that has passed through valve “3” becomes compressed, and the pressurized air discharges into the air reservoir through delivering or outlet valve “4”. After discharging the compressed air, the piston again starts to move downward. This downward motion allows air to enter through valve “1” and repeats the entire process. And this is a complete working cycle of a double-acting compressor.

Double Acting Compressor Components

The Components of a double-acting compressor are given below in detail:

  1. Cylinder
  2. Piston
  3. Connecting Rod
  4. Piston Ring
  5. Suction and Delivery Valve

1) Cylinder

The cylinder includes in the essential double-acting compressor components. On small compressors, the cylinder is made by drilling directly into the compressor body. This part of the double-acting compressor makes of cast iron. In large multi-cylinder compressors, the cylinders are manufactured separately and attached to the compressor body. If the cylinder damages, this compressor allows you to easily replace it with a new liner without replacing the entire compressor.

2) Piston

The piston moves up and down in the cylinder. This movement knows as a reciprocating movement. The piston sucks and compresses the air during its motion. Mostly, the pistons of these compressors make of aluminum or cast iron. During the piston movement within the cylinder, the coolant must not leak through the space between the piston and the cylinder wall. So, this air compressor component covers with the piston ring. A small compressor does not need a piston ring. The space between the cylinder and the piston also covers with lubricating oil to prevent the compressed refrigerant from entering the crankcase.

3) Connecting Rod

The connecting rod includes in the most essential double-acting compressor components. It makes a link between the crankshaft and the piston. One side of the connecting rod connects to the crankshaft via the connecting rod cap. While the rod’s other side connects with the piston via the piston pin. These two connections on the connecting rod make it possible to convert the crankshaft rotational movement into the piston reciprocating movement in the compressor cylinder. Usually, the connecting rods make of the forged carbon steel.

4) Piston Ring

The piston ring circulates around the piston. As the piston reciprocates in the cylinder, the piston ring comes into contact with the cylinder wall. There is a great deal of friction between the piston ring and the cylinder wall that must be replaced with time for the compressor to function correctly. The piston ring extends the life of the piston. It prevents the replacement of the entire piston.

5) Suction and Delivery Valve

The suction valve uses for sucking the air into the compressor cylinder. And the delivery valve uses for discharging the air.

Advantages & Disadvantages of Double Acting Compressor

Advantages:

  1. It produces cheap electricity from compressed air as compared to a single-acting compressor.
  2. The piston works in both directions.
  3. These compressors have high efficiency.
  4. It produces efficient compression.
  5. This compressor doesn’t require much maintenance and just requires routine vise maintenance.
  6. It has a long life.

Disadvantages:

  1. The initial cost of this compressor is high.
  2. It has a large size as compared to the single-acting compressor.
  3. These compressors can’t stay in the middle position.
  4. A Long-stroke cylinder needs to guide the piston rod correctly.
  5. It requires high space for installation.

Applications of Double-acting Compressors

  • It uses in the steering cylinder
  • These compressors use to fill gas cylinders
  • Uses for boom extension
  • These compressors use in hydraulic cylinders
  • These compressors use in pneumatic cylinders

In this article, we deeply study double-acting reciprocating compressor working and some other aspects. So, if you have any questions, then let me know in the comment box. I will try my best to give you a proper answer.

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