In a European context favouring a unique rail system, the design and use of trains are becoming increasingly complex. They must comply with a wide range of specifications and regulations while proposing standardisation of the systems. This is known as interoperability.
Interoperability of the rail systems operating in Europe, supported by directive 2016/797, means that the same rolling stock can be used outside the borders of a particular country, with weather constraints caused by extreme temperature variations.
Temperatures down to -40 °C/-50 °C are a reality for the equipment, no matter where it was manufactured. This temperature constraint has an impact on the technology employed for the low-pressure circuits and gives the designer/ operator a new use challenge.
The fluid transfer connection technology is no exception. Very low temperatures must not be allowed to affect the basic connectors principles. These basic principles revolve around the ease of installation, the leak-tightness and pressure performance, the fast maintenance of the circuit and the mechanical strength.
Cold is known to cause structural damage which may threaten a person's safety but also affect the operation of the machines:
Increased rigidity of polymer materials can lead to equipment breakage
Faster corrosion of metallic materials can cause equipment malfunction
Use of products or methods which damage equipment
Designers and operators, therefore, need to review the criteria they use to validate low-pressure circuits to overcome the cold constraint.
The low-pressure components of rolling stock can be classified into two categories, depending on whether they are used inside or outside with temperature variations between -25 °C and -40 °C/-50 °C.
These temperatures place the low-pressure circuits under considerable stress and may lead to loss of performance or premature wear of some train components.
Cold temperatures may limit the performance and operation of the onboard low-pressure systems, causing the trains to slow down or even stop, in order to guarantee the safety of the passengers.
It may, therefore, affect the service rate of rolling stock and the profitability of installations. Rail operators, therefore, need to employ specific methods such as:
When considered right from the beginning design stage, these practices, necessary due to the cold conditions, ensure that the connector is fully compatible. The circuits assembled in this way will guarantee optimum service rate and increased profitability of the installations. More specifically, tests must be conducted to validate the behaviour of a low-pressure connector exposed to cold. For example, standard NF F11806 describes the requirements and mechanical tests applicable to shut-off valves down to -40 °C.
Cold may also aggravate corrosion phenomena. In this case, we speak of structural damage to the materials possibly leading to breakage of the low-pressure circuit. Premature wear is due to:
A build-up of frost forming a continuous contact between water and the parts, and
Use of anti-freeze products which increase the chemical attack of the materials.
Standard ISO 9227 describes the tests and corrosion resistance levels of metallic components, helping designers to make appropriate choices. The corrosion resistance requirement may be very high, possibly demanding exclusive use of stainless steel.
To conclude, it is a truism that rolling stock manufacturers want to ensure that systems can operate at 100 percent service rate to guarantee customer satisfaction. Cold changes the technological deal, and the design and use of the connector systems must be adapted accordingly. Choosing the right connector is an increasingly critical challenge.
Article contributed by Laurent Orcibal, ebusiness manager, Lower Pressure Connector Europe, Parker Hannifin Corporation.
This article is Part 1 of a two-part series. Read the second part at Key Cold Weather Design Factors for Connector Technology in Rail.
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