4 common air compressor misconceptions

Even experienced engineers are prone to mistakes and sloppy thinking. We did a bit of research, and discovered that these 4 misconceptions about air compressors are very widely held even among many experts.

The PSI rating might not matter as much as you think

Some buyers only want to know about the PSI rating of an air compressor. They know the PSI rating their pneumatic tools require, and assume that if the air compressor can meet that metric, all will be well. PSI is important, but you have to consider the total volume of airflow, as measured by CFM.

Your tools will also have a CFM rating, and your compressor will have to meet both the PSI and CFM if you want to run them continuously. If you have sufficient PSI but not enough CFM, you’ll have to pause to let the tank pressure build up fairly often.

Displaced CFM is nowhere near as relevant as Delivered CFM.

Delivered CFM – sometimes called ‘free air delivery’ – is a much more useful matric. It takes PSI into account and therefore measures the actual amount of air being delivered by the compressor. Displaced CFM is derived by multiplying the compressor’s RPM by its stroke and bore. As this could be at a wide range of pressures, the actual displacement of this air isn’t all that relevant.

Tank size is often less important than pump size.

Tank size is important, especially if you want to use the air without the pump running. However, even a large air tank will run dry fairly quickly. If you have to choose between a large tank with a small Delivered CFM pump and a larger pump with a smaller tank, you’ll generally be able to get a lot more done in the long run with the better pump.

Tools that operate on short bursts of air – staplers, nail guns, etc – rarely need a large tank, and a 5- or 10-gallon model will achieve all that you need while coming up to full pressure much faster. Tools that need a more constant supply of air – spray equipment, sanders, etc – may require a larger tank to get the job dine without stopping to refill, but make sure the pump has the power to fill a larger tank quickly.

A Single-phase air compressor is very different to a single-stage air compressor.

It is easy to confuse these very similar-sounding terms, especially the first time you buy an air compressor. They really are very different, though.

Single-phase refers to the type of electrical power the air compressor runs on. Most homes and small businesses use single-phase power, and only industrial or large commercial facilities use three-phase power. Almost every air compressor you’ll buy for a home workshop will be single-phase.

Single-stage means the air is compressed only once inside the pump. The alternative is two-stage air compression, where a reciprocating pump compresses the air in stages. Generally speaking, two stage compressors will run more efficiently, and deliver higher CFM. 

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