Cold weather may force designers to reconsider the usual technical choices regarding rolling stock systems.
Combining ergonomics of use, a cost-effective approach and technical performance are the challenges associated with a low-pressure circuit intended for use at cold temperatures.
This blog describes the specific features of the various connector technologies in a low-pressure circuit and provides a professional opinion regarding the choice of the onboard connection.
Fluid transfer low-pressure circuits on rolling stock consist of four main functions:
The connector used to configure the circuit and connect tubes,
The tube to carry the fluid,
The function fitting used to optimise fluid flow, and
The shut-off valve to regulate the circuit supply.
When choosing connectors, manufacturers and operators must consider in particular two main selection criteria which are the technology and the materials
The connector is chosen according to use criteria related to the disconnection frequency, speed of assembly, tube quality implemented and design habits. The four main connector types are as follows:
Push-in fittings: Available in three gripping versions (by the washer, by gripping and by reversed gripping), to quickly create flexible and modular systems. The gripper technology is recommended for low-temperature applications down to -25 °C, while the washer technology can be used to temperatures as low as -50 °C.
Quick couplings: Available in three valve versions and with various standardised end-fittings, they are suitable for frequent connections-disconnections. This technology provides very good resistance down to -40 °C.
Spigot fittings: Easy to implement, they guarantee direct leak-tightness on a flexible tube with no seal and no anchor ring. Their resistance to cold, as low as -40 °C, depends on the tube quality.
Compression and bite type fittings: Available in two versions with a separate ring or built-in ring, they adapt to all types of a tube (metal or plastic). They offer exceptional resistance to cold, down to -60 °C.
These last two connection types are more complex to implement.
Fitting and tube form a pair which, when correctly associated, guarantee optimum operation of the low-pressure circuit over time.
Key factors when designing the low-pressure circuit, the materials play a role in the performance of the system and its resistance to cold through their composition and structure.
The tube material participates in the chemical and mechanical compatibility of the circuit. Being used throughout the circuit, it has a considerable impact on the resistance to cold. A flame-retardant version is available which can withstand temperatures down to -50 °C.
The materials of the fittings and other connection systems guarantee leak tightness, efficiency over time, the ergonomics of the circuit and operating safety. They are available in two versions: metal and polymer.
Metallic materials are preferably implemented outside and can be used down to -60 °C depending on the type of fitting. Brass with nickel chemical protection represents an excellent technico-economic compromise. Stainless steel meets all chemical and mechanical constraints.
Polymer materials are generally used inside with temperatures down to -25 °C. They offer space savings due to their compactness. Lighter, they can be easily integrated into the interior structures and represent an optimum approach in terms of technology and cost-effectiveness.
Other criteria must be taken into account when choosing the connector, for example, pressure/temperature performance, compliance with standards and regulations. Taking into account all these criteria will guarantee that the connector is perfectly compatible with the operating conditions.
To conclude, the range of Parker LPCE low-pressure connector systems focuses on the safety of persons and goods, having provided solutions for all relevant applications in various types of train and rail vehicles for many years. Two quick-reference brochures detail everything you need to know about a selection of connectors and associated products.
Article contributed by Laurent Orcibal, ebusiness manager, Lower Pressure Connector Europe, Parker Hannifin Corporation.
This article is part 2 of a two-part series. Read the first part at Learn How Cold Weather Affects Connector Design for Rail Applications
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