Understanding the Hermetic Compressor: An Overview and In-Depth Analysis

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Understanding the Hermetic Compressor: An Overview and In-Depth Analysis

When it comes to refrigeration and air conditioning systems, the hermetic compressor plays a vital role. This compact and sealed unit is responsible for compressing refrigerant gas, maintaining proper pressure levels, and ensuring efficient heat exchange within the system. In this comprehensive blog post, we’ll explore the workings of a hermetic compressor, its components, advantages, disadvantages, and its applications in various industries.

Table of Contents

What is a Hermetic Compressor?

A hermetic compressor is a type of rotary compressor widely used in refrigeration and air conditioning systems. Unlike its counterpart, the open-type compressor, a hermetic compressor is enclosed within a welded steel shell, creating a sealed unit. This design eliminates the need for external shaft seals, allowing the compressor to operate without leakage. The hermetic compressor is also known as a sealed or reciprocating compressor due to its construction and reciprocating motion.

Hermetic compressors are commonly found in residential air conditioning units, refrigerators, freezers, and small-scale industrial applications. Their compact size and efficiency make them particularly suited for systems with limited space and low to medium cooling capacity requirements.

Working Principle of the Hermetic Compressor

The operating principle of a hermetic compressor involves the compression of gaseous refrigerant to increase its pressure and temperature. It utilizes a piston-cylinder arrangement to achieve compression through a reciprocating motion. Here’s a step-by-step breakdown of the working principle:

  1. The suction valve opens to allow low-pressure refrigerant vapor to enter the compressor cylinder.
  2. The piston, driven by an electric motor, moves downward, reducing the volume in the cylinder and compressing the refrigerant.
  3. The suction valve closes, trapping the refrigerant gas in the cylinder.
  4. The piston moves back upward, further compressing the refrigerant and increasing its pressure.
  5. The discharge valve opens, allowing the high-pressure refrigerant to exit the compressor cylinder and enter the condenser.

Components of a Hermetic Compressor

A hermetic compressor consists of several key components that work together to achieve efficient compression and heat exchange. Let’s explore each component’s function:

1. Housing

The housing of a hermetic compressor provides the outer casing, protecting the internal components from external factors and preventing refrigerant leakage. It is typically made of welded steel or cast iron, ensuring a robust and durable enclosure.

2. Motor

The motor is an integral part of the hermetic compressor, driving the piston’s reciprocating motion. It converts electrical energy into mechanical energy, allowing the piston to compress the refrigerant. The motor is sealed within the compressor housing, ensuring it remains isolated from the refrigerant and other external contaminants.

3. Piston and Cylinder

The piston and cylinder form the heart of a hermetic compressor. The piston moves up and down within the cylinder, creating compression and expansion spaces. As the piston moves downward, the expansion space increases, drawing in the low-pressure refrigerant. On the upward stroke, the compression space decreases, compressing the refrigerant and raising its pressure.

4. Suction and Discharge Valves

The suction and discharge valves are responsible for controlling the flow of refrigerant in and out of the compressor. The suction valve opens during the suction stroke to allow the low-pressure refrigerant vapor to enter the cylinder. Meanwhile, the discharge valve opens during the compression stroke, enabling the high-pressure refrigerant to exit the cylinder and flow towards the condenser.

5. Crankshaft and Connecting Rod

The crankshaft and connecting rod work in tandem to convert the rotary motion of the motor into the reciprocating motion of the piston. The crankshaft converts the rotary motion into linear motion, while the connecting rod transfers the motion from the crankshaft to the piston.

Advantages of Hermetic Compressors

Hermetic compressors offer several advantages over other types of compressors, making them widely used in various applications. Here are some key advantages:

  • Compact Size: The hermetic compressor’s compact design allows for easy installation in space-constrained applications.
  • Cost-Effective: Due to their simplicity and mass production, hermetic compressors tend to have lower production costs compared to other compressor types, resulting in cost-effective solutions.
  • Reduced Leakage: The hermetic construction eliminates the need for external shaft seals, minimizing refrigerant leakage and ensuring system efficiency.
  • Lower Noise Levels: The hermetic design encapsulates the compressor, significantly reducing noise levels compared to open-type compressors.
  • Higher Efficiency: Hermetic compressors are optimized for specific applications, resulting in high efficiency and reduced energy consumption.

Disadvantages of Hermetic Compressors

While hermetic compressors offer various advantages, they do have a few limitations. It is essential to consider these disadvantages when selecting a compressor for specific applications. Here are some disadvantages associated with hermetic compressors:

  • Non-Serviceable: Most hermetic compressors are factory-sealed units, making it difficult or impossible to service or repair individual components. If a failure occurs, the entire compressor unit often needs replacement.
  • Lower Cooling Capacity: Hermetic compressors are generally suitable for applications with low to medium cooling capacity requirements. For large-scale or industrial applications, other compressor types may be more suitable.
  • Limited Cooling Capacity Control: Hermetic compressors may have limited capacity control options compared to other types, which can impact efficiency in applications with varying cooling demands.

Applications of Hermetic Compressors

Hermetic compressors find extensive applications across various industries, thanks to their compact design and reliability. Here are some common applications:

1. Residential Air Conditioning Systems

Hermetic compressors are the key components in many residential air conditioning systems. They provide efficient cooling and maintain comfortable indoor temperatures.

2. Refrigerators and Freezers

Almost all household refrigerators and freezers utilize hermetic compressors. These compressors ensure optimal cooling performance, keeping food and perishable items fresh.

3. Commercial Cooling Systems

In commercial cooling applications, such as convenience stores, restaurants, and small-scale commercial buildings, hermetic compressors are often used. They provide reliable cooling while requiring minimal maintenance.

4. Industrial Cooling

While hermetic compressors are not typically used in large-scale industrial cooling applications, they find utility in smaller industrial systems, including climate-controlled storage units, refrigerated transportation, and machinery requiring localized cooling.

5. Automotive Air Conditioning

Many automotive air conditioning systems incorporate hermetic compressors to provide efficient cooling and climate control within vehicles.

The versatile nature of hermetic compressors makes them suitable for various cooling and refrigeration needs, from residential to specialized industrial applications.


In summary, the hermetic compressor is an integral component of refrigeration and air conditioning systems. Its compact and sealed design provides numerous advantages, including cost-effectiveness, reduced leakage, and higher efficiency. However, it is important to consider the limitations associated with hermetic compressors, such as limited serviceability and cooling capacity control. By understanding the working principle, components, advantages, and disadvantages of hermetic compressors, you can make informed decisions when selecting the most suitable compressor for your cooling needs.


  1. https://www.achrnews.com/articles/131576-know-your-compressors-hermetic
  2. https://www.engineeringtoolbox.com/refrigerant-compressors-d_167.html
  3. https://www.carel.com/the-secret-garden-of-the-compressor

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Understanding the Hermetic Compressor: An Overview and In-Depth Analysis