Back

Compressed Air Preparation

Compressed Air Preparation

Particulates, water, and chemical contamination may have a highly negative effect on compressed air consumers, as well as the compressed air network.

Beyond this, special requirements apply in the food and pharmaceuticals industries. In these cases, no harmful chemical substances may be permitted to come into contact with the respective products via compressed air.

1. Main Criteria for Compressed Air Preparation

The objective of compressed air preparation is to make compressed air with three main characteristics available to consumers:

Quality based upon the following criteria;

• Large media-borne particles, water content, permissible/required oil content.

Pressure with a focus on;

• Minimum/maximum pressure, pressure accuracy.

Quantity in consideration of;

• Minimum and maximum cross-sections as well as tubing shape, connectors, etc., and leakage.

 Compressed Air Quality

Compressed air quality is defined in the DIN ISO 8573 – 1 standard. However, this standard does not apply directly to medical technology. The measuring methods for assignment to quality classes are specified in DIN ISO 7183.

The designation for the air of a given respective quality is made up of three entries:

The quality class for solid contamination:

ClassMax. Particle Size (µm)Max. Particle Density (mg/m³)
10.10.1
211
355
4158
54010

 

The quality class for residual water content:

ClassMax. Pressure Dew Point (°C)Max. Residual water (g/m³)
1-700.003
2-400.117
3-200.88
435.953
577.732
6109.356

 

The quality class for total oil content:

Class

Max. Concentration (mg/m³)

1

0.01

2

0.1

3

1

4

5

5

25

 

The table offers a selection of recommendations for quality classes in several types of application:

ApplicationParticulateWaterOil
Pneumatic cylinder  
Precision pressure regulators		542
General workshop air 
Foundry machines		445
Machine tools
Air motors		435
Packaging machines433
Pneumatic sensor technology333
Air bearings
Gauge air		223
Conveyance of food products221
Sheet material processing111

 

Compressed Air Quantity

Each system/device should be supplied with an optimized quantity of compressed air. It is quite difficult to recognize and achieve an ideal value in actual practice as simple as this may sound. Either too much or too little compressed air has negative effects on the utilized technology and the ergonomics and the operating costs of the respective system.

The following factors must therefore be taken into consideration during layout and selection of the components:

• Compressed air requirements for individual consumers

• The shape of the connectors

• Overall length of the supply line

• The material of which the supply line is made

• Possible leaks

Pressure

Each pneumatic consumer is laid out for its ideal working range. In the event of under pressure, the consumer will function either inadequately or not at all.

The same applies in the case of overpressure. In addition to the destruction of individual components or the entire device, long-term adverse effects may result from over-pressure, such as significantly increased wear at bearings, heat generation, interfering vibration, and unpleasant noise.

For this reason, it's important to adhere as closely as possible to the consumers' ideal working pressure (operating pressure) when laying out and selecting components.

Pressure drop within a system is caused by, for example, the following:

• Long compressed air lines

• Branches and radius in compressed air lines

• Consumers as valves, filters, dryers, etc.

• Leaks

• Rough surface inside of tubing and piping

Pressure increases may result from:

• Exhaust air openings which are laid out too small and

• Clogged/contaminated silencers, filters, etc.


2. Atmospheric Humidity, Dew Point and Condensate

Atmospheric Humidity

Ambient air always contains a certain amount of water vapor. The variable used to describe this content is atmospheric humidity, which is specified in grams per cubic meter.

The diagram indicates the extent to which maximum atmospheric humidity depends upon temperature.

DOWNLOAD PICTURE

Dew Point

The temperature at which vapor begins to condense.

As a rule, the amount of water that is actually contained by ambient air (absolute atmospheric humidity) is less than the maximum possible value.

If the air is cooled down, we gradually arrive at a point at which the water's actual contained amount is the maximum possible amount. Relative atmospheric humidity is then 100 % (absolute humidity = maximum humidity). 

However, compressed air is used in pneumatic applications, in which case the pressure dew point must be taken into consideration.


Condensate

Water is also precipitated as condensate when air is compressed because air can be compressed, but water cannot. After compression, relative atmospheric humidity has a value of 100 %.

Both of these processes for removing water in condensate, i.e., cooling and compression, are used to dry air.
PES Automation © 2024. All Rights Reserved. Privacy Policy Terms & Conditions of Use Terms & Conditions of Sale