ROLLING STOCK AND TRACTION
Maintaining air-conditioning service on modern trains
Modern train carriages are effectively sealed capsules. Maintaining a comfortable environment is essential and is the principal reason for passenger complaints (after late trains), explains David Lipscombe, works manager at ThermaCom.
T
he Virgin Pendolino’s air-conditioning is provided by a module situated atop the carriage, forming part of the roof structure.
At the heart of the module is a screw compressor, providing the driving force for the refrigeration system. This compressor reliably provides around 50,000 run hours, equivalent to around a million track miles.
The expected lifespan of a typical train car is at least 25 years and during this time it will travel many million miles and will accumulate some 150,000 track travel hours.
During this travel period the compressor will be operating almost continuously.
Screw compressor service life
The screw compressor used in the Pendolino AC module is manufactured by Bitzer, Germany. As the carriage is sealed, it maintains the re- circulated & make-up airflow at a comfortable
Service life extension
The common mode of service failure of the screw compressor is primarily due to bearing fatigue. The problem for the maintainer is knowing just when that fatigue life-point is approaching.
Get it right and change these bearings before failure, and the service life is effectively renewed.
However, once the first bearing fails, total failure is not long away, and the time period from initial distress to complete failure is comparatively short – as little as a few days or hours operation – and for machines intended to operate away from direct engineering scrutiny for many months at a time, this presents a major challenge, especially if considerable inconvenience to the train user is to be avoided.
ThermaCom has been anticipating such a fate for the Pendolino rolling stock since 2005.
Quality and procedures
The Pendolino fleet comprises 500 individual carriages, and the whole upgrade project has been timed to conclude over an 18-month period. For ThermaCom this has meant a rigorous training procedure to satisfy the exacting standards of the railway, and streamlining of supply lines for bearings and other parts. To comply with the rigid safety and compliance standards expected, the whole programme is documented and fully traceable.
Operating safety and reliability are key for train operators. At ThermaCom, we provide the highest levels of overhaul reliability: tooling, calibration, welding to EN standards, and – most importantly – a diligent training regime for our fitters, with dedicated overhaul procedure for the specific compressors.
Full simulation test facility
ThermaCom has created a refrigeration- based test facility. This is adaptable to force compressor operation in the most arduous summer operating conditions, with the whole computerised to provide a data record of a procedural pass.
Remediation techniques
temperature of around 22C. However, like any machine with rolling bearings, it has a finite service life and typically the compressor will provide reliable service for around seven or eight years, or 50,000 run-hours.
In this way the train makers have designed a very successful and effective system, but it is clear these compressors will not provide service for the lifespan of the carriage itself: indeed, achieving an estimated 50,000 run hours is astounding.
Comparatively, most compressors of similar design typically expect to achieve around 30,000 hours in other industrial applications.
These trains first entered service around 2002, and by 2009 we were observing an increase in service failures.
The nature of these failures increasingly aligned with our predictions that these compressors could all reach life-point in an alarmingly short period.
This was not good news for the train maintainer, who is required to provide a high level of serviceability to the train operator. Random failures are at best inconvenient, but when they start happening on a weekly then daily basis, then what in the earlier days was an occasional drama truly becomes a crisis.
A significant proportion are found at or approaching final stage failure. Some are beyond repair, with a further volume suffering loosening of the original bearings such that secondary failure faults would wreck the compressor in short order; but crucially ThermaCom has developed remediation techniques to recover these compressors. Observing that around 25% of the volume would fail within months has borne out the decision for the overhaul investment, and has avoided the train maintainers having to process costly AC failures from the trains in service.
At the time of writing, the Pendolino compressor overhaul programme is halfway through, and the benefits of following an established procedure are self-evident. The throughput is ahead of schedule, and proving highly effective for these trains. The remedial procedures for machines that would otherwise have failed has saved the maintainers a huge sum against the alternative for new compressors and reliability is well proven.
FOR MORE INFORMATION
www.thermagroup.com
rail technology magazine Apr/May 13 | 55
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