Standards to Measure Compressed Air Quality

Compressed air is used in a wide variety of manufacturing and commercial operations. Air is generated from the ambient atmosphere around the compressor and typically would contain contaminants in the form of dust and water which are two naturally occurring impurities while a third impurity which is oil typically gets added to compressed air due to the compression process. Oil though can be avoided / eliminated by using 100% oil free compressors however the other pollutants namely dust and water, without proper treatment, can reduce the efficiency of your compressed air system, increase your operating expenses and jeopardize product quality. However if compressed air quality is improved through treatment it can become a major contributor to the successful operation of your plant and improved production quality.

Typical contaminants in compressed air:

Different types of water

Dust particles (from ambient air and/or desiccant)
Liquid water and water vapor
Liquid oil and oil vapor (coming from oil-injected compressors)
Hydrocarbon vapor
Rust particles
Pipe scale
Acidic condensates

How to define your air quality: ISO quality air standard (ISO 8573-1:2010)

The quality of compressed air used in industrial processes is specified in the international standard ISO 8573-1. Untreated compressed air typically contains 3 types of contaminants: dirt, water and oil. The Quality Classes specify the maximum allowed limits.

For example, class 2:4:1 means: - Dirt: max 400.000 particles in the range of 0.1-0.5 µm, 6.000 particles of 0.5-1 µm and 100 of 1-5 µm - Water: max 3°C PDP - Oil: max 0,01 mg/m³

A) Risk of dust

As the compressed air is sucked form the atmosphere dust particles which vary in size from 0.1 micron to 3 micron would enter the compressed air stream, this can be harmful for the downstream equipment causing product rejection / contamination and plant downtime due to malfunctioning of actuating valves and operating machinery. For applications like pharmaceutical, food & beverage manufacturing, several critical applications require sterile air to ensue dust and bacteria are eliminated. This can be achieved through adequate filtration.

B) Risk of moisture

Compressed air pipe damaged by moisture

Concentration of water increases with compression and with subsequent cooling, liquid water is released in the downstream pipe work if no treatment is employed. This creates a huge risk of product contamination and damage to the downstream equipment operating on compressed air. Moreover, the wet air creates corrosion and failure of metal pipes and accessories. A tiny 3 mm hole, for example, can cause leakages up to 27,156 kWh, which in terms of energy consumption equals an annual cost of UAE Dirham 12,220.00.

Hole diameter (mm)	1	3	5	10
Leakage (l/s @ 6 bar)	1	10	27	105
Power loss at the compressor (kW)	0.3	3.1	8.3	33
Energy loss @ 24/7 kWh	2,628	27,156	72,708	289,080
*Annual costs (€)**	131	1,358	3,635	14,454

C) Risk of oil

Compressed air temperature

Oil is not a natural contaminant however it is added due to the type of compressor selected. Mainly oil injected compressors create a problem of oil carryover which can be reduced by using coalescing filters. However filtration efficiency is completely dependent on the temperature. Higher ambient temperature results in greater oil carryover from the compressor and creating a cascading impact on the efficiency and lifetime of the filters. The attached graph indicates the filtration efficiency and the impact of temperature. Coalescing line filters can help reduce the oil carryover but cannot eliminate oil contamination completely. Moreover filters need to be maintained routinely 4000 hours for the general purpose and high efficiency filters and 1000 hours for the activated carbon filters. In summary, the best air quality with respect to oil carryover can only be achieved with oil free compressors.