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Compressor efficiency: Specification matters

20 May 2013

Energy performance, free air delivery, flow rates, cost of ownership…When it comes to specifying and purchasing a new air compressor, there are many factors to be considered and operators should always explore the latest technologies available in order to make a sound investment. Greg Bordiak, technical officer at the British Compressed Air Society (BCAS), says there is another, vital factor to take in to account during the specification process – ease of maintenance

Maintenance can account for a significant proportion of the total cost of ownership of a compressor during its lifetime, so it makes good commercial sense to consider how the machine will be maintained and factor this in to the overall cost equation in order to deliver the performance required.

Here, Bordiak offers some tips on specifying a compressor correctly to ensure maintenance can be carried out simply and effectively.

Design elements

During maintenance, a compressor will be unable to produce any air.  It’s an obvious point to make, but, in cases where there is no compressed air redundancy available, any process or instrument dependant on this air will also be offline until the compressor is running again.  Operators therefore need their compressed air installation to be easy and quick to maintain, to help limit downtime to the minimum.

A well-designed compressor, where as much attention has been paid to the machine’s serviceability as to its performance features, can be of significant benefit. As a result, many manufacturers are now constructing their machines with easy-to-access service points and quick-change consumable parts as well as a range of diagnostic capabilities via integral controllers.

Control and report

Without accurate data, it is difficult for a plant manager to measure the efficiency of the compressed air system, so it is advisable to consider the wide range and variety of control systems now available on the market. A compressor controller can calculate how efficiently compressed air is being produced.  Performance trends can then be analysed, allowing easy identification of underperforming compressors or other problems in the system. 

By using sequence control, installed machines are able to work in groups. Compressor running hours can be equalised across all machines in the same group and the use of the most economic machines can be prioritised. This can lead to fewer service visits and reduced maintenance costs, as all machines can be serviced at the same time. 

A controller can also automatically shut down machines during non-production times such as nights, weekends and holidays, therefore reducing running hours and service costs. In addition, modern controllers can provide alerts when problems are encountered in the compressed air system; for example, if too much or too little air flow is available.

Genuine spares

Components and lubricants will affect compressor performance and efficiency. Performance and benefits can be compromised if the user takes the decision to use non-genuine replacement consumables and parts. BCAS always recommends the selection of genuine replacement components as part of any routine maintenance.  Every compressor has been purpose-designed to incorporate specific parts in order to deliver the performance quoted and therefore, choosing the right spare parts will typically cost users less in the long run. 

For newer machines, the issues can be slightly different as the focus is very much on total operational efficiency, rather than simply reliable functioning.  In this situation, the use of non-genuine parts will inevitably impact on the overall cost equation, and in the long term, will reduce the cost savings achievable with a modern energy-efficient system.  

Reactive, preventative or predictive?

Investing wisely in a compressor that helps to improve routine maintenance is clearly of benefit, but operators also need to consider the type and frequency of any routine servicing. There are typically three approaches to servicing compressors and each can have a role to play, depending on the criticality of each machine:

Reactive maintenance is carried out on an emergency call-out basis when a machine fails and needs immediate repair.  In some instances, this can be a viable option for compressors that are only required as back-up units or to provide redundancy, but remember that as the repair will be classed as an emergency, the cost of the callout time may be considerably higher.

Planned maintenance has emerged as the most common method of maintenance, with many service providers now offering a range of packages tailored to the compressor type, operating hours and impact on productivity.

Some independent surveys have claimed that planned, preventative maintenance can eliminate breakdowns by as much as 75% and certainly, because servicing is carried out at pre-agreed intervals it has many benefits in ensuring compressors operate reliably and with good performance.

Manufacturers are, however, developing more sophisticated preventative maintenance offers, where monitoring takes place 24 hours a day via a remote telemetry system connected to the compressor.

Data collected can then be used to predict when a part may be under stress and could fail or when maintenance is required, enabling the service team to visit the site and rectify any potential problem before downtime occurs.

In conclusion, says Bordiak, whatever the make, model or application, all compressors require regular, routine servicing to deliver the right performance within budget.  Factoring maintenance in to the procurement process is not just a practical, cost consideration but an essential component in ensuring plant productivity is maintained for the maximum service life of the compressor.