What is a scroll compressor?

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 type 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 type 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.