Compressed air distribution

According to an EU study (“Compressed Air Systems in the European Union”), in 80% of all enterprises the compressed air distribution systems are the weakest link in compressed air technology. This means that each year thousands of euros are literally blown out of the window for energy costs.

Compressed air distribution has the job of transporting the energy carrier compressed air with as little impact as possible on the

air quality (owing to rust, water, welding scale etc.),
flow pressure (owing to uneconomical pressure losses) and
quantity (owing to unnecessarily large leaks).

Pressure drops cost a lot of money

Each compressed air consumer in the network requires a specific optimal operating pressure. If the operating pressure is too low, e.g. caused by too narrow tube cross sections, the performance of the consumer is disproportionately reduced. By contrast, if pressure is too high it not only pushes energy costs up unnecessarily, it also shortens the service life of the consumers.

Pipeline dimensioning

It goes without saying that the correct dimensioning of the compressed air network has a direct impact on the performance of the compressors, the consumers and hence on the costs of compressed air production.
The most important design criteria for the compressed air network are:

The volumetric flow rate
The operating pressure
The length of the piping
The drop in pressure

If these criteria are taken into account it is possible to ascertain the correct diameter for the compressed air lines. The pipeline diameter is dimensioned either

By using standard layout diagrams (monograms) (c.f. Illusory. 1),
By using standard tables from which the diameters can be read directly (c.f. Illustr. 2) or
By calculating applying an approximate formula:

The first line, A (pipe length) is connected to line B (intake quantity) and extended to axis 1. Then line E (system pressure) is connected to line G (targeted pressure loss). Finally, the resulting intersections on axes 1 and 2 are connected by a straight line. This straight line cuts across line D; the required internal diameter can be read from this.

Illustr. 1: Nomogram for ascertaining the nominal width of compressed air pipes

Illustr. 2: Table for dimensioning nominal widths for compressed air pipes

As a rule the nominal width of the compressed air line should be big. Some of the greatest losses of pressure occur owing to compressed air lines that are dimensioned too small or rather too narrow. Experience shows that in the case of an originally correctly-dimensioned compressed air network over the course of time an increasing number of consumers is attached to the existing pipeline network with the network having been redimensioned to accommodate new requirements. It is not unusual for just the compressor output to be raised to cover the increased consumption.

The economically acceptable drop in pressure (c.f. Illustr. 3)

With an optimally designed compressed air network the drop in pressure between generation and consumer is subdivided as follows:

< 0.03 bars for the main pipe (between compressor room/receiver and the main consumer centre)
< 0.03 bars for the loopline / distributor line (part of pipe that distributed the air within a consumer centre)
< 0.04 bars for the connection line/branch line (connection between distributor line and consumer)

The pressure loss in the individual components of the compressed air treatment system can be represented as follows:

Illustr. 4: Graphic representation of the pressure loss Ap in a compressed air distribution system (from generator to consumer).

The amount of the overall pressure loss depends on:

Degree of contamination and number of treatment components
Type and number of fittings
Nominal width of the compressed air piping system

The less auspiciously a compressed air pipe is conceived, the higher the performance of a compressor must be in order to build up the required pressure and maintain it. This means: 1 bar loss in the compressed air system = 1 bar more output on the compressor = approx. 10% higher power consumption.

The influence of piping elements

Illustr. 5: Impact of pipeline elements on the pressure development (Source: VDMA) The resistances of the individual pipeline elements are represented in metres of straight pipe (equivalent length).

Each element in a compressed air pipe system, irrespective of whether it concerns treatment elements or pipeline fixtures, cause a pressure loss owing to flow resistances.
Taking pressure loss due to fittings into account, in this connection a straight pipeline would be ideal. However, owing to constructional circumstances, as a rule pipelines cannot be laid from the producer to the consumer without fittings.

Changes of direction, for example when circumnavigating supporting pillars, can be avoided by laying the compressed air line next to the obstacle. 90° angles can easily be replaced by large-dimensioned 90° bends (s. Illustr. 5). This makes it possible to reduce the pressure loss to a fraction of the original pressure loss.

In addition to these influences, materials adapted to the various applications must also be used. Factors influencing the use of correct materials include the following:

Compressed air quality
Pipe dimensions
Pressure
Ambient influences
Cost of assembly
Cost of materials

Extending a compressed air line

Another good way of extending the “overrun” compressed air lines is to install a parallel line, which you connect to the existing distributor line. The piping system can hence be extended at no great cost to form a ”loopline system”.

You can find further information on the following topics:

Heat utilisation,
Leak reduction
Speed control

also under the header “Saving money".

Is your interest aroused?
Do you want to know more?
Or do you now think that your compressed air network requires a new roof over it?

Please contact us directly and we will advise you.

Contact ALMiG here.
More information on the topic of "Saving energy".

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