Maintenance intervals: the filter challenge

In recent years, rolling stock operators and maintainers have sought to extend maintenance intervals beyond the originally-defined limits. Station One aims to help professionals in selecting the consumables and wear parts affected by this trend, among them HVAC filters.

To get the most value from the assets at their disposal, many transport operators try to act upon the lever of their rolling stock maintenance plans by replacing wear parts after longer service periods. While all of Alstom’s Citadis light rail vehicles since 2012 come with a 25,000 km maintenance plan as standard, owners of older rolling stock (the first Citadis trams date back to 2000) with 15,000 km maintenance intervals are also increasingly wishing to extend the period between two services.

Such a modification of maintenance plans, supported by a FMECA approach (failure mode, effects and criticality analysis) must be assessed and approved by an independent safety adviser body before their adoption by the operator/maintainer. But technology has naturally developed over the past 20 years and with the benefit of returns on experience, this shift is entirely possible, as long as wear parts can deal with these longer intervals.

Cleaner air for longer

The challenge is particularly notable in the area of HVAC filters, since many models cannot cope with a 65% increase in service time between changes. This is where new solutions are required to filter the air entering HVAC units on rolling stock.

Founded in 1963, Kalthoff is a leading force in the design and supply of air filters in many areas. From buildings to cleanrooms, the firm’s expertise has since the end of the 1990’s extended to HVAC filters in railway rolling stock with its first contract on a new ICE train for Deutsche Bahn. Today, the company works with OEMs or maintainers in all the main German cities with urban rail systems such as Berlin, Hamburg, Munich, Frankfurt, Dusseldorf and Cologne… among others. Outside Germany, the company’s references include London, Madrid, Paris, Bordeaux, Casablanca and Sydney.

Pleated technology

The secret to the longevity of Kalthoff’s filter panels lies in its unique V-type pleated filters: a continuous bead of filter material arranged in an undulating format, increasing the surface area of filter medium. The filter becomes less clogged by particles over time and service life is much longer than that of a conventional flat filter. Customer feedback has indicated that Kalthoff filters need changing between twice and four times a year, comfortably exceeding the 25,000 km barrier, whereas conventional flat filters must be changed once a month. Considering the additional labour required, the extra investment for a Kalthoff model is easily recouped over its service life.

Additionally, air bypasses can occur in a flat filter since these are cut manually to size; the Kalthoff filter panel does not leave any gaps through which dust and particles can pass. The result is a cleaner HVAC unit and lower maintenance.

Individually designed and tested

As every light rail vehicle is different, Kalthoff studies each case individually to design a tight-fitting plug-and-play filter to meet precise needs in terms of airflow and running time, but also suited to the operating environment: heavy pollution, pollen, airborne sea salt, etc. The firm then proposes a field test, installing filters on several vehicles and running them for 3 and 6 month periods to validate their performance throughout the required period. Finally, Kalthoff filters bearing the latest EN45545 fire certification in all Hazard Levels 1-3 and they are made of fully synthetic materials, which eradicates all risk of organic and moisture-related contamination.

Find Kalthoff products on StationOne.