Plant & Works Engineering
Small parts make a big difference
Published:  03 January, 2017

Ken Revell, Business Line Manager Sales & Marketing for Atlas Copco’s Compressor Technique Service Division, looks at how small parts can make a big difference to production equipment performance and reliability.

Few would deny the logic of ensuring the continued performance of production equipment, but recent findings show that not everyone is aware that the quality of spare parts can have a significant effect in terms of costs and efficiency. At a time when capital expenditure and budgets are under increasing pressure it’s vital that manufacturers guarantee continuous production, and to do so they need to ensure their machinery is properly maintained.

In the case of compressor components, it is essential that high quality systems should be maintained and serviced with genuine spare parts to reduce the risk of performance dips, over-usage of energy and reduced lifetime, all of which can have a negative impact on the compressor owner’s capital investment.

The importance of maintaining performance levels is clearly demonstrated by recent testing carried out by TÜV Rheinland that compared two single-stage screw compressor blocks to verify their efficiency in low pressure and low pressure operation mode. The test items were a new Atlas Copco Z2 MkII and a refurbished Z-series compressor block. The results showed that the specific energy requirement (SER) of the refurbished block was, depending upon speed and pressure, between 6.2 to 25.6% higher – an average of +13% – than the original.

But not everyone relies on manufacturer approved engineers for servicing or makes certain that only genuine OEM spares are provided. Industry survey results indicate that over 30% of compressor owners rely upon third party service providers to maintain their equipment. These compressor engineers may be tempted by the availability of relatively cheaper; non-genuine ‘soft’ common spare components such as air/oil filters, separator elements, line filter cartridges and, importantly, compressor lubricants. The same scenario applies further up the scale to the ‘hard parts’− such as electric motors, sensors or safety valves not to mention the big-ticket items such as compressor elements and air ends.

So, what can go wrong?

First, let us take the analogy of maintaining a high quality, high performance car. It is unlikely that a discriminating owner would take it to a back-street garage for servicing or consider having fitted anything other than genuine, manufacturers’ parts. Protecting investment in a premium product dictates the need to match its quality in every aspect of maintenance procedures − and that precludes any substitutes for OEM parts.

Compressors may be suffering in silence: in the long term, non-genuine spare parts, including lubricants, can be creating unseen damage to machinery, surreptitiously diminishing efficiency or, worse still, affecting process air purity which in turn might result in end-product quality issues. The impact may not be immediate, although the effect on total lifecycle costs can be massive. The consequences could not only create an unnecessary cost burden but also potentially do significant damage to a company’s reputation due to production downtime and failure to fulfil orders. To illustrate this, a snapshot survey of compressor owners in 2015 revealed that over 40% had suffered compressor breakdowns during the past year, with some instances of production downtime costs in the region of £20,000.

Here are just some examples of what happens when original spare parts or recommended lubricants are not employed:


The optimal operation of a conventional screw compressor is dependent upon lubricants to reduce wear and to seal, cool and clean. Compressor oils comprise base oils combined with a balanced selection of specific additives relative to the viscosity, solvency, volatility, oxidation resistance and surface activity requirements of the oil circuit design relative to anticipated operational conditions. In much the same way as all other components of a modern compressor, these lubricants are developed, verified and field tested for suitability to specific models or ranges of compressor solutions. Therefore, it is vital that the additive balance is exactly right in every case.

Non-specific substitutes are likely to cause problems. The wrong specification can result in poor lubrication of the compressor screw element which does not seal properly, allowing air to ‘slip’ back and be re-compressed. Each compression cycle reheats the air increasing the operational temperature of the compressor thereby reducing its efficiency and pushing up its SER (Specific Energy Requirement) level. At the same time the increased heat may result in oxidisation of the oil, reducing its efficacy and contributing to sludge blockages in the oil circuit.

Furthermore, incompatibility with rubber or metal parts can create leakages and the chances are that high surface activity will take place within the oil separator. With the wrong lubricant, excessive foam will saturate the separator resulting in higher concentrations of residual oil and a decreased lifetime of the unit.

Although the compressor element sealing requirement is not relevant in an oil-free compressor, correct lubrication of the drive train is paramount. Impacts from non-specified oil include halved lifetime for bearings and oil pumps, deposit build up creating increased internal pressure, and the risk of breakdown for high speed bearings.

Air filters

These are a compressor’s first line of defence for its oil circuits and compression elements against external contamination. When correctly matched to a compressor system, they are capable of a >99.9% separation efficiency and able to extract all particles larger than 3micron in size from the incoming air. But non-genuine units, either of competitive design or actual ‘pirate’ parts, may create problems caused by ingress of unfiltered air. These stem either from dimensional differences, whereby incompatibility of the filter element to its housing increases intake of unfiltered air, or the inferior quality of the filter paper. A chain reaction is created affecting the efficiency of the downstream air/oil filter and the air/oil separator, resulting in significant pressure drops.

In much the same way, non-genuine oil filters too are likely to exhibit lower separation efficiency, inadequate sealing and cracking of the filter paper pleats, all resulting in a damaging unfiltered oil flow. Absence of a bypass valve can also lead to clogging, overheating and breakdown of the compressor element.

The design of alternative oil separators may offer only limited corrosion protection and it may not feature a sufficient filtration area to be effective. In either case, the result is increased pressure drop coupled with a marked increase in energy consumption.

Overall, the impact on compressor performance from fitting non-genuine OEM components of this type is hard to ignore. A pressure drop of 1 bar from the oil separator will increase energy consumption by 7%. In the case of air filters, for every 25 mbar pressure drop, compressor output is decreased by 2%.

Electrical components

Cheaper electrical components are equally tempting but not without risk. A rewind operation for a burned out electric motor may be attractive but a subsequent 10% loss in efficiency may prove less so − replacement with an updated, high-efficiency unit can prove a better proposition. In other areas, system control issues are often found to be the consequence of fitting cheaper but unreliable pressure transducers that are responsible for substantial increases in energy consumption.

Replacement part or replacement compressor?

There is a further consideration on replacement parts related to the age of a compressor. Survey results suggest that in the UK 40% of single compressor installations are between 5 to 10 years old. Likewise, 20% of the compressor population is between 11 and 20 years old. It follows that there has to be a right time to consider a complete replacement for a long-service compressor rather than fitting individual components to keep it going. For example, it can mean the difference between spending £10K on an authentic replacement element or £30K on the latest, state-of-the-art, energy efficient solution. It may be a more expensive move in the short term but it will pay back in the medium to long term in terms of performance, reliability and energy savings. With ready availability of credit, including OEM’s finance packages, the initial costs can be effectively offset.

But well before any compressor reaches worklife retirement age, the simple truth is that only by using original spare parts can its designed performance and efficiency be maintained at the same level as when it was purchased. In that way, investment is not compromised and neither is the compressor’s quality output. What’s clear is that small parts can make a big difference.

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