Turbo compressors are dynamic compressors widely used for compressing air and gas. Compression results from the air gaining kinetic energy as it is thrown outward at high speed by rotation. In turbo compressors, the air is accelerated by centrifugal force (out of the impeller) and accumulates at the impeller outlet, converting its kinetic energy into pressure energy. The compression ratio of a turbo compressor impeller (drawing in and throwing out the air) is typically between 1:1 and 2:1.
These machines build pressure according to the dynamic principle, meaning the pressure increase is achieved (by using the velocity of the air) without any mechanical reduction of volume (displacement), as in positive displacement compressors. In turbo compressors, the high-speed rotating element that compresses the air (gas) is called the impeller or turbo fan. There is no piston or any other type of mechanical displacement or compression element between the air inlet and air outlet of a turbo compressor.
Typically, blades were riveted onto fan hubs and the fan was then balanced. Until the early 1950s, little money was invested in turbo compressor production in Europe. Because of the larger American market, turbo compressors developed further in America were exported to Europe. Early riveted fans could only reach a pressure ratio of 1.2:1. Therefore, 10 or 11 fan stages were required to reach an effective pressure of 7 bar at the turbo compressor outlet. Modern impellers can deliver a pressure ratio of 8:1 in a single stage. However, since the efficiency of a single-stage turbo compressor without intercooling remains lower than that of an intercooled design, multi-stage turbo compressor designs are preferred. Still, this shows that there has been, and will continue to be, further progress in technology, materials and manufacturing methods.