Introduction to Scroll Compressors
To understand the different types and technologies of compressors, we need to first understand two basic principles of compressed air: dynamic compression and positive displacement compression. In this article, we will introduce scroll compressors. This is a type of positive displacement compressor widely used in air conditioning and refrigeration systems, heat pumps, and automobiles.
What is a Scroll Compressor?
A scroll compressor (also known as a screw compressor or scroll pump) is a positive displacement compressor that works by internally compressing air or gas. Scroll compressors include oil-lubricated and oil-free models, the latter being ideal for applications requiring clean, dry air quality and free from oil contamination in the compression chamber.
How Scroll Compressors Work
These machines consist of two helical scroll main units, bolted together. This includes a stationary scroll and a driven scroll, which is driven by an electric motor. The scrolls continuously move relative to each other without any metal-to-metal contact, while air is compressed into increasingly smaller volumes within crescent-shaped cavities.
Let's delve deeper into the positive displacement compression mechanism of scroll air compressors. The drive scroll is driven by a short-stroke crankshaft and rotates eccentrically around the center of a fixed scroll. The movement of the drive scroll generates suction, drawing air in from the inlet, located at the top of the main unit housing.
Air or gas collected in a cavitation chamber between the two scrolls is gradually compressed while moving towards the center of the housing. The outlet and check valve are located here. The compressed, pressurized gas exits from the outlet at the center of the assembly. The check valve or refrigerant check valve prevents backflow of gas or refrigerant.
A 180° rotation, or phase shift, provides radial stability to the scroll compressor. As air or gas is compressed, the compression chamber becomes increasingly smaller; this is often referred to as internal compression. Leakage is minimized during this process because the pressure difference in the cavitation chamber is lower than the pressure difference between the inlet and outlet.
Efficiency:
Similar to internal compression in screw compressors, the amount of internal compression is determined by the exhaust port. Due to a special design of the exhaust port, scroll air compressors can compress more air or gas while using less power.
These machines have very high volumetric efficiency compared to other compressors. This is because there is no piston for compressing the gas.
Noise:
Scroll air compressors emit significantly less noise than other compressors. The entire compression cycle requires 2.5 revolutions, including intake, compression, and exhaust rotation phases. These phases occur simultaneously, providing a constant, pulsation-free airflow throughout.
Scroll air compressors feature a scroll motor, providing smooth, vibration-free operation. Compared to reciprocating compressors, it exhibits virtually no torque variation. The scroll air compressor's simple design contains only one moving part. This makes it more reliable and quieter than equivalent reciprocating and screw compressors.
