Ten typical mistakes with compressed air systems

Along with energy and water, compressed air is one of the most ubiquitous inputs into an industrial plant. Why then are we so aware of the need to conserve energy and water, but often so blasé about optimising the efficiency of our compressed air systems? Here, compressed air system innovator John McNab* offers tips for getting the best from new or existing compressed air systems, by identifying 10 common misconceptions about compressed air. 

1. Thinking compressed air is cheap — and going to stay that way

Air compressors powered by electric motors use large amounts of energy, often 24/7. This expense is only going to increase over the years ahead as we all pay the price of fighting global warming. Already the annual power cost to operate a compressor can equal the initial cost of the unit.

These costs are likely to rise with changes to industrial practices being introduced by the Australian Greenhouse Office and the Equipment Energy Efficiency Program E3 , which is a collection of coordinated programs that deliver economic and environmental benefits to the community and which is co-funded by the Australian government, state and territory governments and New Zealand government. The program focuses on initiatives that require a nationally consistent framework to improve energy efficiency and reduce greenhouse emissions from household appliances and equipment, and commercial and industrial equipment.

Operating in parallel with E3 is legislation such as minimum energy performance standards, MEPS, governing products such as electric motors and other equipment sold in Australia and New Zealand.

These will have a profound impact on the way we operate industries. So be very selective about what compressors you choose (and also about placing unnecessary loads on them, as we discuss further on in the article).

2. Air leaks

You can’t see them — you hardly hear them — and they are not even hazardous to health.

But, an extract from 'Saving Energy Through Compressed Air Systems', an advisory booklet published by the Department of Primary Industries & Energy, states the following: “A 1.5 mm orifice in a 750 kPa gauge air system is likely to discharge air to atmosphere at an FAD rate of about 2.75 L/s.

At today’s prices, this single leak is likely to cost $600 per annum for a 2500-operating-hour year. Ten such leaks in a larger plant operating 100 h per week, therefore, will cost directly at least $10,000 per annum .

So be very particular about the type of system you select and how you maintain it.

3. Pressure loss in piping systems

It is important to minimise pressure drops throughout the compressed air system. A US study estimates that every pound of increase or decrease in pressure requires a 0.5 increase or decrease in power. Therefore, a 10 psi (68 kPa) decrease can save you 5% in power costs.

Ensure your system is designed with an efficient ring system, to provide air flows with minimum resistance, avoiding dead ends, turns that are too tight and pipe diameters that are too small.

If your piping is not corrosion-free polymer, check that the system is not being obstructed by corrosion and replace sections that are.

4. Contamination from the piping system

The amount of dirt, rust and liquids carried along with the air stream will increase when air velocity increases (either because pipes were too small in the first place or became clogged as they corroded internally over time).

The best ways to avoid this are to use piping of the correct dimension in the first place, and to replace rusting sections with new material as they require maintenance (preferably with non-corrosive piping systems, such as Calairs’, as they are easy to integrate with existing systems, as well as being simple to install and modify without special tools or specialist labour).

Steel piping systems usually take the air off the top of an air line when running a line from a header to the point of air usage; this will minimise condensation from corroding the pipe. Polymer and copper pipe can take the air directly off the bottom of the header as condensate cannot corrode these materials. Both of these design principles will not prevent condensate being produced in other sections of the compressed air system. Air dryers should be incorporated to eliminate condensate.

5. Poor condensation management

The extreme variations in Australia’s typical industrial operating environment — from very hot during the day to very cold at night — add to the constant threats of condensation in compressed air systems (moisture precipitation being the natural result of increased air pressure).

This harmful moisture can wash lubrication from air tools and production equipment, causing downtime and maintenance. An inconsistent supply of dry air can cause production quality issues.

Rust and scale can cause water to back up into the compressor and wreck machinery, so it is important to maintain dryers to ensure they don’t become overloaded and destroy in-line filters.

The high temperature tolerance of polymers — combined with their natural insulating properties — is also invaluable in applications where the contents are subject to fluctuating temperatures, such as in feeds to plastics moulding and extrusion equipment and to mixers, feeders and containers.

Note: While many insulation problems can be overcome by using non-metal pipelines with superior inherent insulation values, not all plastic pipes are suitable for compressed air, such as PVC, ABS and poly pipe. Some non-specialist pipe materials could easily fail, either through exploding or inability to cope with a compressible medium.

(Calair’s Pro-Pipe II is formulated for good pressure capability characteristics at elevated temperatures).

6. Supplying higher pressure air than needed

Determine the specific pressure required for all the air departments in your plant — not just the highest pressure required for one isolated piece of equipment.

Sometimes users produce high-pressure air for an entire plant just to satisfy the needs of isolated high-pressure equipment. It is much cheaper to install a pressure booster for the high-pressure area.

7. A lack of system training for maintenance staff

Companies that train their people to understand the importance of saving energy reap the biggest rewards.

Inspections for faults in pipelines, compressors, dryers and filters should be routinely scheduled.

Bear in mind also that some systems are easier to maintain than others. Ask your reticulation system provider for details of existing users in similar applications so you can share user feedback.

It may also aid maintenance and simplify training by selecting a system that can be erected, changed and recycled without the need for specialised tools or specialised labour (such as those requiring welding when assembling or disassembling pipeline systems for expanding or changing production needs).

8. Preventative maintenance

This is essential to maximising the service life of a compressor and reticulation system. Make sure the program matches the application.

Good preventative maintenance means monitoring filter and lubricant condition by measuring pressure drop and by using regular oil analysis.

This regular attention to detail will help create a schedule for change intervals that will provide the best compressor and system protection.

9. Lack of troubleshooting information

Where problems do arise from time to time (and no system is exempt from these), temperature and pressure readings can be used to organise your troubleshooting efforts.

Normal condition readings should be logged and used as a reference point to isolate the cause of the problems.

Readings are usually taken at locations before and after air equipment (including compressors, aftercoolers, dryers, receivers, air tools and filters).

10. Don’t forget safety

Make sure workers can tell at a glance which pipes carry compressed air and which carry other gases or other liquids under pressure. (Some of these substances are volatile, some hot and many potentially dangerous.)

One of the last things a hard-pressed maintenance worker wants to worry about is what is in the pipes he’s working on as another production deadline approaches.

Apart from needing to know quickly where to find the conduits to pneumatic, chemical, waste, water and other services, there’s the safety concern involved if the worker opens or cuts into the wrong pipe.

Because many companies use pipelines to carry many different substances, staff should be strongly aware of the 'Content Identification' requirements of AS 1345-1995, which stipulates including aqua for compressed air, beige for gas, green for water, red for fire services, violet for acids and alkalines, brown for oil and black for waste.

Ideally, the entire pipe should be coloured according to its contents (rather than just tagged, because tags can discolour or, in the worst cases, be totally obscured by industrial grime).

*John McNab is managing director of Calair Pipe Systems
www.calair.net.au