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Rotor
A rotor is the rotating part of any machine. It spins in a stationary component called a stator. Its fundamental job is to transfer energy by adding energy to a fluid in a pump or a compressor. How a rotor works depends entirely on its design and the type of air compressor system it’s in.
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Here are the most frequently asked questions about rotors:
FAQs
A rotor’s purpose on any piece of rotating equipment is to transfer energy. It is the spinning “middleman” between a machine’s mechanical parts and working fluids like air, gas or liquid. The rotor’s specific design determines how it transfers that energy, which can happen in two ways:
- Adding energy to a fluid: Pump and compressor rotors are driven with a motor. Rotors for these applications take the rotational energy from the motor and transfer it to the fluid, increasing its pressure and/or velocity.
- Extracting energy from a fluid: Turbine rotors are built to have a moving fluid, like a stream, wind or jet exhaust, push on the motor. A rotor extracts energy from the moving fluid to do work, such as generating electricity.
Rotors are the key components that compress air in some models of air compressor systems. The two main types include:
- Helical screw rotors: This type of rotor consists of a matched pair or two large, spiral-shaped screws. There is a male rotor with rounded lobes and a female rotor with corresponding grooves or valleys. Helical screw rotors work by trapping and directly squeezing fluids.
- Impellers: This type of rotor resembles a complex fan, featuring a precision-balance disc with angled blades or vanes. Impellers work by accelerating air to a high speed and converting that speed into pressure.
Helical screw rotors trap and move a substance as they turn. The matched set of precisely machined rotors follows a four-step process:
- Intake: The screws begin to spin, creating a large cavity near the intake port. Air is drawn in and completely fills the opening space in the grooves of the female rotor.
- Trapping: While the rotors continue turning, the union between the rotors moves past the intake port. This traps a specific pocket of air, sealing it off from the inlet.
- Compression: In this stage, the rotors continue to spin, closing the distance between them. This action reduces the volume of the trapped pocket of air, significantly increasing its pressure.
- Discharge: The trapped pocket of air reaches the end of the rotors at its smallest volume and highest pressure, then flows through the discharge port and into the air tank or piping system.
Impellers use a powerful outward force to generate pressure within a centrifugal compressor. This rotor is a precisely balanced disk with angled blades that spins at high speeds, creating a powerful vacuum at its center. This sucks a continuous stream of air into an opening and slings it outward toward the edge of the impeller.
Once the air is accelerated to a very high velocity, it flies off the tip of the impeller and enters a stationary diffuser that forces the air to slow down. This converts the energy of its speed into pressure.