When you’re starting or scaling up an industrial operation, it is imperative that you choose the right tools for the job. There are two major considerations for choosing a compressor: the number of stages, and the compression mechanism. Both of these will affect two of the most common specifications used to describe compressor systems- and dictate what machinery they work with. These specifications are flow, or velocity of flow, measured in CFM(cubic feet per minute), and pressure, most often measured in PSI(pounds per square inch).
A compressor’s stages are the times the air is compressed and cooled. For instance, even in piston-based systems, a compressor is only a two stage compressor if the second cylinder is smaller in volume, generating higher pressure. In general, the more stages a compressor has, the more efficient the system is. The heat displacement which occurs between stages allows the compressed air to more easily be compressed even further. This makes for a more efficient system which reaches higher pressures. Multistage compressors do tend to be more expensive, but if you are working with high pressures, the reliability and energy savings tend to be worth the initial investment.
The compression mechanism is where air compressors vary the most. The aforementioned piston-based compressor is one of the most common, typically referred to as a reciprocating compressor. In a reciprocating system, the air is passed into the cylinder when the piston is at its most retracted. The piston moves forward, pressurizing the air, which is then passed into the next chamber. Depending on the number of stages in the device, this could be another, smaller cylinder following a heat exchanger, or it could be passed into the storage tank. It is worth considering that reciprocating compressors do release pressurized air in bursts, and are therefore prone to surges and dips in air pressure.
A very popular model of compressor is the rotary screw compressor, which uses two interlocking screws. Air is trapped between them and compressed as the two screws, forming a seal, push the air down into only a portion of the screw cavity as they squeeze together. Due to the smooth motion of the screws and the constant intake and release of air, there is very little pressure drop or surging with this type of compressor. This makes rotary compressors, especially a two stage rotary compressor, an excellent choice for when constant pressure is a chief concern.
Another type of rotary compressor, more prone to surging but excellent for high-pressure applications, is the rotary vane compressor. These use an eccentrically-orbiting cylinder with two sprung vanes, which contact the sides of the housing. The sprung vanes allow the compressor to scoop up the air and compress it as the interior cylinder approaches the far wall. There are many options when it comes to industrial compressors, and each has a service lifetime, capacity, and other specifications to consider. But knowing how each works under the casing is your best bet for making an informed decision.