Network matters
March 1st 2011

A poorly designed compressed air distribution system will lead to high energy bills, low productivity and poor system performance.

Here Ray Cave of Atlas Copco Compressors discusses how to ensure that you have designed and dimensioned your compressed air network correctly

There are three basic rules to consider when designing a compressed air distribution system: Firstly, maintain a low pressure drop between the compressor and points of consumption; secondly, ensure a minimum of leakage from the distribution piping, and thirdly, efficient condensate separation must be achieved if a compressed air dryer is not installed.

Network design The starting point when designing and dimensioning a compressed air network is an equipment list that details all of the compressed air consumers, and a diagram prepared that indicates their individual locations. Consumers should be grouped in logical units that are supplied by the same distribution pipe. The pipe is, in turn, supplied by risers from the compressor plant.

A large compressed air network can be divided into four parts: risers, distribution pipes (preferably in the form of a 'ring main'), service pipes and compressed air fittings. The risers transport compressed air from the compressor plant to the consumption area.

Distribution pipes split the air across the distribution area and service pipes then route the air from distribution pipes to points of use.

Dimensioning the network Distribution of compressed air generates some pressure losses, primarily as friction losses – although these can be mitigated with smooth bore pipe work. Throttling effects and changes in direction of flow occurring in valves and pipe bends also create losses which are converted to heat and result in pressure drops. These factors must be taken into account when determining pipework dimensions.Mathematical formulae can be applied for the purpose but, once the flow rate, pressure, allowed pressure drop and pipe length has been established, the best method of calculating the most appropriate standard pipe diameter is a nomogram or by electronic calculator, which the compressor manufacturer can supply.

Pressure drop Fixed compressed air distribution networks should be configured so that the pressure drop in the pipes does not exceed 0.1 bar between the compressor and the most remote point of consumption. The pressure drop in connecting flexible hoses, hose couplings and other fittings must be added to this. It is particularly important to properly dimension these components, as the largest pressure drop frequently occurs at such connections.

There are established tables of fittings and pipe components that show their influence on flow resistance losses in pipes of various diameters.When calculating requirements for different parts of the compressed air network, the table below shows values that can be used for the allowed pressure drop.

Air receiver The air receiver forms a buffer storage area for the compressed air, balances pulsations from the compressor, cools the air and collects condensation. Consequently, the air receiver must be fitted with a condensate drainage device. The size of air receiver is a result of the compressor capacity, the regulation system and the end consumer's air requirement pattern.

For compressors with variable speed drives the required air receiver volume is substantially reduced. In contrast, when the demand for compressed air requires large quantities over short periods of time, it may require a separate air receiver to be placed near the point of consumption and dimensioned according to the maximum air output.

Pipework performance Pipework, despite its seeming simplicity, can have an impact on the performance of the system and its overall lifetime cost. Steel pipe is heavy, its threaded joints require careful preparation, and its inner surfaces are not smooth. This restricts flow and promotes pressure drop, which equates to energy loss.

By contrast, AIRnet's lightweight, durable modular network system of corrosionresistant aluminium pipes eliminates the possibility of leaks. Its smooth inner surface contributes less pressure drop and therefore further energy savings.

Size for size, AIRnet pipework weighs five times less than its steel equivalent and fitting takes about one third of the time. There is no time-consuming pipe threading and no need for special tools or lifting equipment. AIRnet pipe can be simply pushed into the polymer fitting, tightened by hand and secured with a spanner.When the aluminium AIRnet pipe is cut to size, there is no risk of corrosion of the exposed metal and so no risk of leakage.

The pipework has a 10-year guarantee.

AIRnet provides pipework with smooth, anodised internal surfaces as standard. This minimises pressure drop penalties and performs a key role in ensuring that the air supply is kept clean to protect downstream equipment and production processes.

By delivering quality air where it is needed, at the right pressure and at the lowest cost, an efficient compressed air distribution pipework system contributes substantially to energy savings, air quality and production efficiency of any compressed air application.

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