What is Compressed Air Preparation?

This article will explain what compressed air preparation is and how it works.

What is Compressed Air Preparation?

The application of air preparation units in any given compressed air line supports system optimisation and the longevity of the pneumatics components. Whilst the valves and cylinders (actuators) produce the control and linear motion in pneumatically powered automation systems, it is the air preparation that allows these components to operate trouble-free for their stated service life. Unplanned maintenance always costs a business valuable time and money.

Untreated compressed air is wet and dirty

Although modern compressors can produce air of better quality compared to years gone by, there is often legacy pipework and, possibly, temperature differences between compressed air source and end-use, these two things alone are responsible for a range of contaminants and water to be present in the line .For example, the compressor house may be a separate building from the plant; the ring main will pass outside before entering the plant building and be subject to the outside ambient temperature and its changes and as a result condensate will form in the line. Correctly chosen filtration will remove significant amounts of the water and any particulate contamination down to a specified particle size.

Compressed air costs money – don’t waste it

The compressor may produce air at a pressure of, say 10 bar. However, components and tools may have optimum working pressure many bar below this. A pressure regulator, placed upstream of the point of use, can make this adjustment. Over-pressure will not only reduce the life expectancy of components and tools (and may even lead to immediate failure and, worse, personal injury), it will result in air loss and cost money. A false perception is that compressed air is ‘free’ – it is not! The Carbon Trust (2012 paper on Compressed Air) state that the energy used to produce compressed air can be as much as 30% of the total site electricity usage. The British Compressed Air Society (BCAS) advise that every 1 bar of over-pressure represents a 7% increase in compressor energy costs (2018); this relationship is linear for applications between 6 bar and 12 bar which covers the vast majority of industrial applications. The introduction of a pressure relief valve will protect sensitive downstream components and equipment from the possibility of over-pressurisation.

Keep components correctly lubricated

Further to the above particulate and water contamination, there will always be some oil carry over from the compressor and the possibility of residual oil in pipework. In 1927, Carl Norgren recognised the importance of the controlled introduction of lubricant when he invented the automatic airline lubricator. It seems contradictory that we discussed the removal of oil as a contaminant above, but now outline the introduction of oil! However, the important distinction is the word controlled. Below we will introduce the types of lubricator available in the market.

Make maintenance easier and improve plant efficiency

During maintenance cycles, it is not efficient or effective to shut down the whole compressed air system for the overhaul of one component or one sub-system. In these cases, the use of a shut-off valve is recommended to isolate just the component or sub-system for maintenance. Another advantage of a shut-off valve at point of use, is that the process can be isolated from the main air ring when not in use; this will save energy and money. There are many different designs of shut-off valve, ranging from slide type mechanisms to ball type. Feedback showed that Customers (operators) preferred the ball type design as it offers full laminar flow (and zero pressure drop) and minimal manual force to operate compared to other designs.

How does Compressed Air Preparation work?

Detailed descriptions can be found in articles on each of the individual units; here, we will give a general overview:

  • Filters - dependent on application, the filters’ jobs are to remove dirt and water, oil droplets or oil vapour from the compressed air stream. The mesh size of the filter will determine the maximum particle size allowed to be transmitted and for a ‘general purpose filter’ this will typically be 40 microns; a ‘depth filter’ construction will also remove long strands. Filters can be ‘daisy-chained’ for particular applications – a general purpose filter (40 micron) should remove at least 95% of water content at specified temperature (if conforming to Class 8 for water extraction according to ISO8573); putting two together will effectively remove 99.5% of water. A ‘Golden Rule’ is that general purpose filters (40 micron, then 5 micron if required) MUST precede an oil removal filter and both MUST precede an oil vapour removal filter

  • Regulators - the regulator works to reduce downstream pressure to the required operating level, usually by adjusting a spring tension against the supply pressure. For example, a compressor may supply a pressure of 10 bar to the air main, but an application may only require 6 bar for optimum working; over-pressure to a sub-system may reduce the operating life of components and certainly will waste energy and money, as evidenced above.

  • Lubricators - a lubricator, as the name suggests, is employed to introduce oil drops or mist into the air stream. As said, it seems a contradiction that filters can be chosen to remove oil, but then a lubricator is used to re-introduce oil. However, oil from the compressor will be ‘dirty’ (contaminated with particles) and with an uncontrolled droplet size; the lubricator design uses the air flow to ‘pick-up’ droplets and maintain an optimum size to ensure best protection for downstream components against wear.

  • Pressure Relief Valve - the relief valve is designed to ensure that pressure does not exceed an adjustable, pre-set value. This is important to ensure that components or applications do not experience over-pressure, against their optimum operating specification, resulting in reduced lifetime. Commonly, the relief valve can be set by adjusting a spring tension against the inlet pressure; when inlet pressure exceeds the pre-set value, the valve lifts and exhausts the excess pressure.

  • Shut-off Valve - shut-off valves provide a block to air flow into a sub-system. They can be 2/2 function, but 3/2 are recommended allowing the downstream pressure, in the isolated sub-system, to exhaust for safe working.

  • Pressure Gauges - often designed using a coiled tube that ‘unfolds’ as pressure increases, a gauge provides a calibrated measure of the pressure in a system. Modern regulator designs incorporate an integrated valve; this protects the gauge (otherwise exposed) from damage.

How do I select Compressed Air Preparation?

There are several considerations in making a correct choice:

  • What is the flow rate required for a process or system? This will determine the port size and, of course, all units will need to be compatible.

  • What level of filtration is required and to what level of dryness? Is oil vapour a problem, for example if food contact is likely with an air blown bottle? In these cases, an oil vapour removal filter is required, taking account of the Golden Rule above.

  • What is the pressure requirement to operate downstream equipment and what is the supply pressure? This will be the task of the pressure regulator. It is important to note that a quantifiable pressure drop will occur through the filter regulator combination.

  • What level and type of lubrication is required? Carl Norgren was the pioneer who invented the oil drop lubricator and we are still one of only a few suppliers that can provide an oil mist lubricator. The oil drop lubricator is suited to heavy duty applications, such as slow moving, large bore cylinders, air motors and air tools; they operate best over short distance in level pipework. Oil mist lubricators are suited to complex pipework systems and multi-valve and cylinder applications; they operate over longer distances and non-level pipework

  • We would always recommend the use of pressure relief valves and shut-off valves, particularly in legs serving applications with different and, possibly, pressure sensitive operations. What is the optimum operating pressure for the application or components?

  • Is your application sensitive to a sudden ramp-up in pressure on start-up? Or, perhaps, you require a quick release of pressure in certain situations? In these cases, a Soft Start Dump Valve could provide a solution – see our specific article “What is a Soft Start Dump Valve” for more detail on these units.

Types of Compressed Air Preparation

For convenience and confidence of assembly, a combination filter regulator and lubricator box set are available. Filters (general purpose, oil removal and oil vapour removal), filter regulators, lubricators, pressure regulators, pressure relief valves, shut-off valves and soft start dump valves can all be sourced separately.

A range of body series and port sizes, generally G1/4 to G3/4 (with NPT as an option) but G1/8 and up to G2 also available, ensure a flow rate suitable for most applications. Accessories, such as tamper resistant kits, porting blocks, silencers and gauges (where required) are available.

Typical applications of Compressed Air Preparation

Simply put, you are likely to find compressed air preparation in any compressed air system. They can be found in the main supply line and in branch lines supplying specific components that may require, for example, different pressure supply or higher-grade filtration.

Do I need anything else to make Compressed Air Preparation work?

Mounting brackets will be required, as will tubing and fittings. Service kits are an important addition to the bill of materials; regular servicing will keep the units working to their specification and protect downstream equipment from the potential damage caused by poorly maintained air preparation units.

Visit our Air Preparation section to find out more.

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