According to the Pressure Systems Safety Regulations 2000 (PSSR) the user of an installed system and the owner of a mobile system shall ensure that the system is properly maintained in good repair, so as to prevent danger. To satisfy this regulation there should be a maintenance programme for the system as a whole. It should take into account the system and equipment age, its uses and the environment.
The regulations do not specify how often a system should have a full check but supplies recommendation usually fall between 2000 and 4000 running hours.
It is widely recognised that compressed air is industry’s fourth utility, alongside gas, water and electricity. While the process of producing compressed air can be costly it is also incredibly wasteful, with the Carbon Trust estimating that as little as eight to ten per cent is converted into useable energy. As a necessity in a wide range of business operations it is therefore imperative that we better understand how it is currently used; highlighting any bad practices, and then implementing some further efficiency measures.
Energy audits
“A compressed air system audit is a great place to start, offering a precise analysis of the existing system with a particular focus on energy consumption,” Mark Stone, product manager at Flexion, part of ERIKS UK, explains. “Any energy audit should be tailored to the compressed air system in question, as each system is different and the application requirements can vary.”
The reason such significant savings can be obtained from a full system audit is due to its holistic view of the system, highlighting the true costs of compressed air and identifying opportunities to improve efficiency and productivity. Generally, a full system audit will analyse the performance of the four key areas of a compressed air system including; power, pressure, flow, and temperature under different operating conditions.
“It is vitally important to measure the amount of energy used to operate a compressed air system, in order for businesses to have an estimate of the annual electricity consumption,” Stone continues. “This includes not only the measurement of the current voltage utilised by the compressor, but also the full-load and no-load input power. This measurement should be taken over a pre-determined period, usually seven days, and the results can give an accurate overview of the money that is spent annually on the production of compressed air.”
By measuring the pressure of a compressed air system, engineers have access to vital feedback for future control adjustments and to identify where potential pressure drops are occurring across equipment. “Unfortunately, compressed air is often generated at the compressor's maximum pressure which can lead to significant inefficiencies,” Stone says. “However, reducing system pressure leads to significant savings, reducing the pressure by one Bar gives a five per cent saving, and considering all systems have leaks, reduced pressure reduces the leakage experienced. Through the careful monitoring of system pressure, users will be able to implement small incremental reductions, resulting in increased energy efficiencies with no effect on operations.”
Implementing flow meters into the analysis of a compressed air system helps to measure the total flow of the system and determine air consumption. This consumption can be a direct measurement of flow in the pipe, or via a calculation based on the inlet vacuum on modulating machines. “This measurement allows engineers to record the approximate air usage, rate of change, and changes in flow associated with wider system events, as well as make the necessary adjustments to maintain the required flow levels,” Stone adds.
Another crucial element to consider is temperature. Measuring the temperature of a compressed air system during peak operation helps to indicate if the equipment is performing within the parameters set out by the manufacturer. Traditional compressed air systems generally operate below 200°F. Any systems that operate at hotter temperatures than specified, will not perform at peak efficiency.
“Unfortunately many organisations only do a detailed analysis of their compressed air system when errors or machine downtime occurs and yet, this hesitancy to invest in regular energy audits, especially when there is little understanding of the true possible savings, can severely affect the long term performance of a compressed air system,” Stone concludes. “An audit will not only highlight the true cost of compressed air but also provide greater transparency of its uses across the business and therefore as a result, opportunities to make savings. Herein lies the opportunity to not only lower energy costs, but enhance the efficiency of their production lines too.”
Putting it down on paper
Compressor manufacturers will outline the specific intervals at which their equipment needs to be serviced, but, alongside this, a document called a Written Scheme of Examination provides guidelines and timescales for legally required inspections.
“Written Schemes of Examination are a legal requirement under the Pressure Systems Safety Regulations 2000, and virtually without exception every compressed air system must have one,” Andy Jones, managing director at Mattei, comments. “It will specify the parts of the system that need to be examined, the nature of the examination required, the preparatory work needed and the maximum interval allowed between examinations.
“Worryingly, many businesses operating compressed air systems either ignore this important responsibility, or are simply not aware of it.
It’s important to have a maintenance plan in place for the whole compressed air system, not just the compressor. This should include checking the pipework for rust, corrosion and, importantly, leaks. “In many systems in excess of 30 per cent of air generated is wasted through leaks – but they are simple and cost-effective to identify and rectify,” Jones adds. “Leak detection surveys should ideally be done on an annual basis, and always before a new compressor is installed.
“As part of a preventative maintenance regime, additional checks should also be carried out on compressor oil levels as well as any intake filters and coolers to ensure they remain free of blockages and to avoid overheating. We’d advise asking the service provider if they are using the original manufacturer’s genuine parts and oil; if not performance and reliability could be affected.
“When a new compressor is being purchased, it’s worth considering the level of maintenance involved, and the impact this will have on life cycle costs.”
Lifecycle cost
When it comes to the lifecycle cost of a compressor system Andy Westwood, service and technical manager at BOGE Compressors, feels that the financial impact of poor maintenance is often understated. “Probably the most important thing for me is the life-cycle costs, because obviously everyone is looking at the total cost of ownership of a piece of kit,” he explains. “A pie chart that gets bandied around a lot shows 75 per cent energy, 15 per cent investment, ten per cent maintenance. Although that’s very accurate and obviously highlights the importance of energy efficiency, and energy-efficient products the maintenance aspect, I believe, is slightly false because it’s showing at ten per cent.
“In actual fact, the maintenance aspect does affect the large energy portion, because bad maintenance and neglecting maintenance will in time cause wear and deterioration in performance. Then you’ve got a deterioration in energy-efficient performance, so you’re actually affecting the 75 per cent as well as the ten per cent of the life-cycle. That to me is really important.
“Don’t get hoodwinked that maintenance only affects ten per cent of the total life-cycle. Then maybe if you include something about you can go to the nth degree of remote monitoring, condition monitoring, and that’s really top-end package where you’ve got peace of mind.
“If you can get the manufacturer to look after the kit and then provide extended warranty package, then you’ve no hidden costs. You then tie in some preventative maintenance, remote monitoring, condition monitoring, so you’re keeping on top and you’re constantly viewing temperature parameters, pressure parameters, control of compressors if it’s a multi-compressor system. Also you’re looking at oil sampling, so if there’s any foreign particles in oil, you’re going to spot it before a major failure occurs. Vibration analysis as well, so if something starts creeping, you’re going to be able to act on it before a major failure occurs again.
“A poorly maintained compressor system is going to fail as well as the energy performance is going to deteriorate, because a compressor performs best when all the components are in tiptop condition.”