Selecting your compressor

Pressure & flow:

The first step to assess which compressor is adequate for a specific application is to determine (1) the minimum working pressure (usually stated either in bar or PSI) and (2) the required air flow (stated either in litre/cubic feet/meter cube per minute). Without this information you can’t accurately determine which compressors will meet your needs.

The manufacturer of the equipment requiring pneumatic power will state the minimum working pressure and the required air flow in their technical documentation. If you are unsure, please contact either the equipment manufacturer or their distributor. This is a critical step in right sizing your equipment.

Free air delivery (FAD) vs. displaced air:

A common mistake made when selecting a compressor is to use the displaced air figure instead of the free air delivery to assess whether a compressor meets the required air flow. Displaced air (also referred as piston displacement) is the theoretical volume of air a compressor pump can move. This is a calculation based on the mechanics of the pump. The free air delivery (FAD) is the actual amount of delivered by the compressor at the outlet for a set pressure and temperature.

The FAD will decrease when the compressor is working at higher pressure. When operating at higher pressures, the air within the compressor cylinder is more compressed making it harder for the compressor to draw in and compress additional air. This reduced intake volume translates into a lower FAD.

Bambi provides FAD based on 5 bar working pressure as a default but you can select a different operating pressure on each of the product page and the FAD will update automatically.

Tank size:

The size of the tank is also an important consideration. Smaller tanks mean the compressor will be on load (time spent compressing air) for a shorter amount of time as there is less volume to fill. However, depending on the usage this could result in the compressor turning on more frequently adding strain on the start capacitor.

For low and infrequent usage, a small tank can be a good option whilst a larger tank will be more appropriate for longer air demands as they will offer more capacity. Larger tanks can also be more appropriate for installations where air leaks are present.

Tanks that are 24 litres or smaller are also exempt by some insurers from having an annual pressure vessel inspection (PVI) which will be a factor in the ongoing maintenance cost of the compressor.

Noise:

Noise level is a key driver of choice especially when the compressor sits close to personnel. Oil lubricated compressors offer the quietest solution relative to oil free compressors as the oil acts as a lubricant and a coolant reducing friction and heat which are major sources of noise in compressors.

Whilst oil lubricated compressors are quieter than oil-free compressors they carry a marginal risk that the oil could accidentally spin into the airline. Whilst this risk is very remote, this is the reason why customers in the healthcare sector for example will tend to opt for oil free compressors.

Pipework & leaks:

Air leaks are not only a costly waste of air and energy but also an important element to factor in selecting a compressor. Air leaks will result in lower air flow delivered at the point of use. Where applicable, air leaks should be fixed as soon as possible. For installations where repairs are not accessible, you should allow for additional capacity when selecting your compressor to compensate.

How can you assess whether there is likely to be a leak in your compressor?

Turn off the isolation valve of your compressor and let the whole system fill up. Then turn on the isolation valve and leave the compressor for at least one hour whilst there is no air demand (i.e. no equipment is being used). When you reopen that valve if the receiver gauge (larger gauge) shows the pressure is dropping this means that there is an air leak.

Dimensions:

The physical size and shape of the compressor and where you plan on installing the compressor can also be a factor to which compressor is best for you. A perfect example of this would be the BB24 compared to the BB24V. both offer the same mechanical performance with the only difference being the different dimensions resulting from the vertical or horizontal tank they are mounted on.