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The Scroll Compressor

Displacement Compressors Compressor Types Compressors Compressed Air Wiki

In order to understand different types and technologies of compressors, we first need to understand the two basic principles of compressing air: dynamic and displacement compression. In this article, we talk about the scroll compressor, which is a type of displacement compressor with wide applications in air-conditioning and refrigeration systems, heat pumps, and cars.

What are scroll compressors?

the scroll compressor, a graphic of the inside

A scroll compressor, also known as a spiral compressor and a scroll pump, is a type of positive-displacement compressor that works by internal compression of air or gas. Scroll compressors can be oil-lubricated or oil-free, and the latter is best suited for applications where there is a need for clean, dry air quality without any oil contamination in the compression chamber.

 

How does a scroll compressor operate? A scroll compressor consists of two spiral-shaped scroll elements that are bolted together: a stationary scroll and an orbiting scroll driven by a motor. The scrolls oscillate in continuous motion without any metal-to-metal contact while the air is compressed into increasingly smaller volumes in crescent-shaped air pockets. Let’s dive a bit deeper to understand the mechanism of displacement compression in scroll compressors.

 

The orbiting scroll is driven by a short-stroke crankshaft and runs eccentrically around the center of the fixed scroll. The movement of the orbiting scroll creates suction that draws the air in from the inlet opening that is located at the top of the element housing. Air or gas that is captured in the air pockets between the two scrolls is gradually compressed while moving towards the center of the housing where the outlet port and a non-return valve are found. Compressed and pressurized gas is discharged from the outlet port at the center of the assembly. The non-return valve, or simply the check valve, prevents the backflow of gas or refrigerant.

 

The 180° rotation or phase displacement provides the radial stability of the scroll element. Because the compression chamber becomes increasingly smaller while air or gas is compressed within the compressor, this type of compression is usually called internal compression. During this process, leakage is minimized because the pressure difference in the air pockets is lower than the pressure difference between the inlet and the outlet. Similar to internal compression in a screw compressor, the amount of internal compression is determined by the design of the discharge port. Due to the unique design of its discharge port, the scroll compressor can compress more air or gas with a relatively lower consumption of power. Compared to other compressors, the scroll compressor attains the highest efficiency level in volume because there are no pistons to compress the gas.

 

Noise emission of the scroll compressor is also significantly lower than all the existing compressor technology. The complete compression cycle takes 2.5 turns, including suction, compression, and discharge revolution phases, which take place simultaneously and provide constant flow of pulsation-free air. The scroll compressor offers smooth and vibration-free operation thanks to its scroll element, which hardly has any torque variation compared to a piston compressor. The simple design of the scroll compressor with only one moving part (thus friction-free) makes it highly reliable and quieter compared to equivalent piston compressor or the more traditional rotary screw compressor.

Modular vs. digital scroll compressors

Scroll compressors with variable flow technology bring in the benefits and flexibility of a modular system utilizing two to four compressor modules integrated into one canopy. The Elektronikon® continuously monitors the status of each element and starts and stops the compression elements, thereby ensuring that the compressed air output matches the air demand. Moreover, the perfect air quality and user-friendliness of these units guarantee a superior production process.

The digital scroll compressor, on the other hand, has a mechanical design that matches the output of the compressor to the cooling requirements of the complete process. The digital scroll compressor is mainly used in refrigeration and air-conditioning systems to ensure precise temperature control. When temperatures are kept stable during the transportation of food, for example, this results in better food quality.

Why choose a scroll compressor?

Choosing a scroll compressor ultimately depends on the size, flow and quality requirements of your application. Before choosing any type of compressor, it is important to figure out the correct size and technology for your compressed air needs, starting with whether you need an oil-free or lubricated compressor. For higher capacity and flow, it is possible to choose units with two or four scroll compressor elements in one housing. However, it may be more economical in some cases to go for a single large compressor rather than teaming up several scroll compressors to produce sufficient flow. 

 

The scroll compressor has many advantages due to its simplified yet efficient design. With fewer components than reciprocating compressors, it ensures a high level of operational reliability and requires hardly any maintenance. Many leading industrial applications go for the scroll compressor because it meets all the basic requirements of a general-purpose compressor. Whereas oil-injected screw compressors may be more efficient in large industrial applications with larger volume demands, scroll compressors are still widely used in food, refrigeration, air-conditioning, and transportation industries.

Read more on scroll compressors

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