Case Study: Servicing Air-Conditioning on Modern Trains
Air Conditioning Servicing and Maintenance - ThermaCom
Modern train carriages are effectively sealed capsules. Maintaining a comfortable environment is essential and is the principal reason for passenger complaints after late trains.
For the well known Virgin Pendolino’s serving the West Coast Mainline 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 cooling system. This compressor reliably provides an equivalent to around a million track miles service.
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 in Germany. As the carriage is sealed, it maintains the re-circulated & make-up airflow at a comfort temperature around 22oC. However, like any machine with rolling bearings, it has a finite service life, and typically the compressor will provide reliable service for around 7-8 years or 50,000 run-hours.
In this way the train makers have designed a very successful and effective cooling 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 compressors of similar design typically expect to achieve around 25,000 hours in other industrial applications.
Service Life Extension
The common service failure of a 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 inconvenience to the train user is to be avoided.
ThermaCom have been anticipating such a fate for the Pendolino rolling stock since 2005. These trains first entered service around 2002, and by 2009 we were observing an increase in service failures and nature of such failures increasingly showed 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.
Quality & Procedures
The Pendolino Fleet comprises some 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 standard of the Railway, 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 of our fitters, with dedicated overhaul procedure for the specific compressors.
Full Simulation Test Facility
ThermaCom have created a refrigeration based test facility. This is adaptable to force compressor operation in the most arduous Summer operating conditions, with computerised data records of a procedural pass on all compressor.
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 have 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.
Environmental and Cost Benefits
These area are not complicated every compressor is qualified to meet its original design specification those that have failed or beyond economic remanufacture are held and where appropriate the parts are qualified and again held for use or disposed off.
The end results are a pool of compressor going back into services available to cover tens of thousand of hours and 7-8 years available use. Each compressor is static and dynamically tested in a bespoke test equipment. Not just tested for function the feed back on the failure of the original compressor are built into the test to enable a high quality and reliable machine.
The result 500 compressor returned to a full design specification a reduction of 60% on compressor cost the largest saving throughout the total maintenance project and a project given a rotation of materials allowing the flexibility required for the train availability for maintenance. The project team gain valuable knowledge enabling diagnostic and incite to compressor failure given a new prospected of there maintenances program.