How To Measure Compressed Air Quality?

Post By: Tom Rowse On: 21-06-2022 Read Time: 5 minutes - Guides - Pneumatics

You’ll find pneumatic systems, of which compressed air is an indispensable element, in most automated industrial plants. Compressed air doesn’t come cheap, since you require a lot of electricity to compress it, about 90% of which is wasted in excess heat production. It’s important, therefore, to ensure that the air you do get for your pneumatic systems is as pure as it can be. Measuring compressed air quality is a necessary part of monitoring your system, and there’s a relevant industry standard you can use as a guideline.

ISO 8573

This international multi-part standard lists the possible contaminants you can find in compressed air and sets out various classes of purity for each of them. It also defines approved methods of measuring compressed air quality and contamination levels. The most common contaminants are oil, water and particulates. ISO 8573-1 lists these and their purity classes, while subsequent parts of the standard, 8573-2 to -9 describe methods of measurement for other contaminants such as gases, humidity and microbiological content.

Compliance with ISO 8573 isn’t mandatory, but it’s a useful checklist on which to base your measurement procedures. There may be additional industry-specific standards, but in general, the quality of your compressed air depends on what processes are involved and where they’re situated. Delivering exceptionally pure air is a costly business, and you only need to do it where absolutely demanded by the application.

How To Measure Compressed Air

Filter-Regulator-Lubricators (FRL)

Compressors take in ambient air for processing, and this always has some water vapour in it. When the air is compressed, it gets hot under the increased pressure, and can hold even more water vapour. This will get condensed out when the compressed air is cooled down again and can cause significant problems in your pneumatic system. You might get bacteria growing in it, or corroded components, which in turn could cause component failures or unresponsive controls. Most pneumatic systems solve this problem with an integral after-cooler, which reduces the temperature and gets rid of any surplus water. The FRL unit in a compressed air system should also take care of most contaminants.

FRL units themselves are often now equipped with the means for measuring compressed air quality. These include various types of sensors for measuring airflow and pressure, contaminant content and dew point. Installing such an FRL unit allows you to monitor machine performance more closely, so you can identify any faults and make necessary adjustments before they cause a problem. A connected device of this type produces analysable datasets of performance parameters which you can then compare against manufacturers’ specs. In this way, you can discover what factors could be affecting your pneumatic system’s performance – and what you can do about them.

Air Dryers

You can also use air dryers to make sure the compressed air is entirely free of water, the most common type being a refrigerant air dryer. But these also need to be monitored for performance, especially if they’re installed in a multiple parallel array. It’s not uncommon for these arrays to be situated in a compressor room, and for compressed air quality to be measured at the outlet of that room, rather than on the air dryer itself. The air dryer display doesn’t show an actual dew point, but indicates its own internal temperature. There are other things that can affect how dry the air is besides its temperature, such as a condensate drain failure, and this won’t show up on a compressor room sensor.

If your sensor is mounted outside the compressor room, the reading of – say – the dew point will be an average of all the units inside the room. This may be insufficient to pick up individual faults. The monitor may only register a slightly higher reading when one of the units is faulty or has even stopped working altogether. If air quality is critical to the proper function of your pneumatic system, then you’ll need a much more accurate and continuous record of the compressor room’s air quality. In the case of multiple air dryers, you should also monitor each individual unit for changes in the dew point and other parameters.

How To Measure Compressed Air Quality

Some of the ISO test methods require samples to be sent for laboratory analysis, but in most cases, ISO 8573 can be implemented by an instrument or connected application for measuring compressed air quality. Such a device can monitor the levels of contaminants like oil and water, as well as airflow and pressure, temperature, dew point and the size and volume of particulates. Connected devices can be monitored remotely, with a signal alarm for necessary maintenance on your filters or air dryers. Constant monitoring helps to reduce the risk of contamination being passed through to pneumatic applications or other end products. This in turn increases the lifespan and process reliability of pneumatic components.

The most common method of measuring compressed air quality is by counting its particles. You can do this with a laser particle counter, with sensors connected to the compressed air system via a quick coupler or ball valve. The air should be continuously analysed, so that readings take account of changes in the environment. Accuracy is influenced by the flow rate through the instrument and the size of the optics and laser diode. The greater the amount of air passing through the counter at any particular time, therefore, the greater will be the accuracy of the measurement.

Modern Monitoring Of Compressed Air Quality

Many modern instruments have been developed for measuring compressed air quality which are highly accurate and can be remotely monitored. You can keep your eye on all the critical factors, preset the parameters according to the particular requirements of your application, and be alerted to any problems. There may be different risk levels for different areas of your manufacturing plant, with different types of potential contaminants, but these can all be taken into account. You can incorporate ISO purity class limits into your instrument settings, and initiate testing procedures in compliance with that standard.