Input performance
The amount of air that the compressor is able to process per unit of time; usually stated in liters per minute. Performance, along with pressure (see below), is one of the most important parameters: it is it that primarily determines how compatible the compressor will be with one or another pneumatic tool.
It is worth choosing a model according to this indicator in such a way that it can be guaranteed to “pull out” all the tools that can be connected at the same time. Air consumption is usually directly indicated in the characteristics of each tool, and it is quite simple to calculate the total requirement. However, due to the design features, the compressor must have a certain performance margin; the specific value of this stock depends on a number of nuances.
The main point is that some companies indicate for their units the performance at the outlet (how much air is supplied to the tool), while others indicate at the inlet (how much air the compressor sucks in). Since no compressor is perfect, part of the air is inevitably lost during the compression process, so the amount of air at the outlet will always be less than at the inlet. Accordingly, if the output performance is indicated in the characteristics, a margin of 10-20% is recommended, and if the input is 35-40%.
There are also more complex techniques that allow you to more accurately derive the required performance depending on the characteristics of specific tools; they can be found in...special sources.
Power
The power of the engine installed in the compressor. It is not the main parameter in evaluating the efficiency of the device — here the performance and nominal pressure play a decisive role (see above), and the engine is selected in such a way that its power is sufficient to ensure the claimed characteristics. However, this indicator still has practical significance: in compressors with an electric motor (and there are now most of them; see “Engine type”), the engine power determines the total energy consumption of the device, as well as the requirements for the network where it is planned to connect it (for more details, see “Voltage networks"). In addition, the power of the engine (regardless of its type) must be known in order to calculate the optimal performance value using some special formulas.
For internal combustion engines, power is traditionally expressed in horsepower (hp); you can convert it to watts in this way: 1 hp. = 735 W.
Rotation speed
The speed of rotation of the compressor motor shaft in normal operation. This parameter, usually, does not affect the efficiency of the unit — the main indicators are still the performance and nominal pressure (see above). At the same time, it allows you to evaluate the design features of the compressor and its durability. The fact is that a higher rotation speed allows the use of fairly simple and inexpensive working mechanisms, but it increases the wear of moving parts and reduces the motor resource. Therefore, a model with a lower number of revolutions is likely to cost more than the "high-speed" version, but it will also last longer (ceteris paribus characteristics — performance, pressure, drive type, design; see all above).
Design features
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Frequency converter. This function is used to automatically control the power of the motor in the compressor (see "Motor type"), more precisely, to adjust the speed to the current air consumption and maintain a constant pressure.
In electrical units, in addition to reducing wear and tear and eliminating current surges in the network, such systems provide the most stable air pressure at the outlet, and energy is spent more rationally. At the same time, frequency converters are expensive and take up quite a lot of space; and the advantages mentioned are relevant for heavy professional-grade equipment. Therefore, this function is found mainly among industrial compressors with an operating voltage of 400 V and based on internal combustion engines.
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Dehumidifier. The purpose of such devices is already clear from the name: they are designed to dry the air at the compressor inlet, that is, to remove excess moisture from it. The need for such a procedure is primarily due to the fact that high humidity adversely affects the state of the compressor: it leads to condensate settling, and it, in turn, contributes to corrosion and the formation of various emulsions, due to which the channels become dirty and the wear of the entire unit increases .
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Tandem. Devices created according to the "tandem" scheme are actually two compressors on one receiver, connected
...in parallel. This allows you to turn on both compressors at once, or only one of them — in this way you can adjust the power and performance even in those models where special regulators such as a frequency converter (see the relevant paragraph) are not provided at all.
Among the disadvantages are heavy weight, bulkiness and high cost. In addition, the tandem operation scheme is mainly suitable for powerful performant units — otherwise the individual compressors would have to be made too small, and this does not make sense.
— Wheels for transportation. The presence of special transport wheels in the design of the compressor. Modern compressors can be of considerable weight, which would require the participation of several people when carried; wheels, on the other hand, allow you to move even rather weighty devices without problems by the forces of one, in extreme cases — two people.Noise level
The maximum noise level produced by the compressor during operation. When evaluating it, it must be taken into account that the decibel used to evaluate noise is not an absolute value. In fact, this means that noises, for example, 20 dB and 40 dB differ in level not by a factor of 2, but by 100 — it is this multiplicity that corresponds to a difference of 20 dB; a twofold increase corresponds to a 3 dB increase. Therefore, to assess noise levels, it is worth referring primarily to comparative tables. For values found in modern compressors, this table would look something like this:
70 dB — loud conversations at a distance of about 1 m;
75 dB — scream;
80 dB — motorcycle engine with silencer;
85 dB — loud scream;
90 dB — freight train car at a distance of 5-7 m;
95 dB — noise inside the subway car.
Anyway, the lower the level of noise produced by the unit, the more comfortable its use, the less it will “hit on the ears” and increase the volume of the entire set of working instruments.
