Regarding critical speed
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Why does the critical speed exist only for centrifugal compressors, and not for other types of compressors such as screw compressors?
In my personal understanding, the critical speed refers to the speed at which the compressor starts to resonate; at this point the machine vibrates heavily, and it is necessary to exceed this speed as soon as possible. Meanwhile, reciprocating or screw compressors do not reach the conditions for resonance before reaching their rated speed. It might be determined by their inherent structure.
There are also axial-flow types; it is an inherent property of rotating components! For the suppression of criticality, it mainly involves increasing damping.
Screw compressors rarely operate at high speeds; every rotating device has a critical speed, which is an inherent parameter determined by the rotor itself. However, the operating speed of many devices is not as high as this critical speed. Our factory needs a compressor whose operating speed is below the critical speed.
Due to their different working principles, positive-displacement compressors can achieve high pressure at relatively low rotational speeds; for example, reciprocating compressors operate at around 300 revolutions per minute.