Compressed air is a source of energy that can be stored in a vessel (tank) and in distribution pipe work. The air compressor draws air from the atmosphere and the compresses this air to between eight and ten times it's normal pressure. During compression the molecules in the air speed up and this creates our energy source, which is then stored in the tank or pipe work ready for use.
Q. What is pressure?
Q. Why are compressors
sometimes fitted to a tank?
Q. How do I know which
size compressor to choose?
Q. What determines the capacity of compressor that is needed?
What is pressure?
Pressure is a measurement of force in this case relative to our normal atmospheric pressure (1 bar or approx 15psi). Most air tools etc operate at a pressure between 2 bar (30psi) and 6 bar (90psi). Spray painting requires lower pressure than some air tools, as too high a pressure will cause the paint or material to over atomise resulting in the material being lost to the atmosphere. Most car tyres are inflated to between 1.5 - 2 .5 bar (22 - 35psi). Most air tools including drills, sanders, nailers and chisels etc will operate at a pressure of 6 bar (90psi) approx.
Why are compressors sometimes fitted to a tank?
The air receiver or tank allows the storage and control of compressed air. A
device on most compressors maintains pressure at a pre-determined pressure range, allowing the compressor to operate automatically as the air is used, switching on and off accordingly. The air receiver will also be fitted with a safety devise to prevent over pressurisation, a means of draining condensate and various outlet sockets. The size of air receiver (usually measured in litres) will normally be proportional to the size or capacity of air compressor fitted. Air compressors are available without an air receiver and these must be switched on/off manually during use.
How do I know which size of air compressor to choose?
The size of compressor to choose can be ascertained by the following criteria.
What power supply is available? Single phase 230v or three phase 400v or maybe none of these.
If single phase power only is available then the largest machine you can operate will be driven by an electric motor of no more than 2.2kw (3hp) usually.
Air compressors running from three phase 400v power are available in larger capacities but are not normally considered portable due to the availability of three phase power.
Where there is no source of electrical power a compressor powered by a diesel or petrol engine may be chosen.
What determines the capacity of compressor that is needed?
The compressor capacity required will be determined by the number of people using air tools at the same time, the frequency of use and the type of tools being used. A simple guide is to take the tools that require the most volume of air and multiply these by the number of people who could be using these tools at the same time. The frequency of use is an important factor, if the tools are to be used continuously then a compressor should be oversized in order to prevent excessive wear on the compressor. In applications where the compressor is used infrequently then the air receiver is a valuable buffer of stored compressed air. By fitting a larger air receiver a slightly smaller compressor can be used in applications where infrequent use is anticipated. The larger air receiver will compromise portability however, and this should also be considered.
All of the air tools or accessories that are used will require both a certain pressure of air as well as a certain volume of air to be supplied. Whilst most compressors will provide ample pressure, what differentiates a small compressor from a large one is the volume of air that is produced measured in litres/min, cu metres/min or cu feet/min (cfm) and the amount of air produced will be determined by the power of the electric motor and the type of compressor fitted.
So in brief the main points to consider when selecting an air compressor are.
||Power supply available
||What level of portability is required?
||What tools or accessories are to be used and how many people will be using them?
||What will be the frequency of use? Intermittent or continuous?
||Plan for future use!