Seals, bellows, and flexible connections keep weather, dust and noise out of a rail vehicle and take up relative movement across its interfaces, without carrying structural load.
They appear at every joint where movement, weather, noise, or pressure must be managed: between cars, around doors and windows, inside axle boxes, and along pneumatic pipe runs.
Gangway and inter-car bellows
The gangway bellow is the flexible inter-car passage assembly that allows passengers to walk between vehicles while sealing the inter-car gap against weather, noise, and draught — one of the least visible rolling stock components, but a constant maintenance item.
Bellows are constructed from multi-layer rubber or PVC fabric composites reinforced with textile cords, taking up the full range of angular, lateral, and longitudinal movement between adjacent carbodies — including curve negotiation at minimum radius and coupler extension under emergency braking. The bellow’s full technical and fire requirements are covered under gangways and inter-car connections.
Replacement intervals depend on route profile and vehicle speed; high-speed bellows face greater aerodynamic pressure loading per kilometre, while regional and metro stock sees more movement cycles from curves and braking but lower pressure differentials.
Sealing functions across the vehicle
Door seals are EPDM rubber lip profiles that compress against the door frame when closed, providing acoustic attenuation, weather exclusion, and draught reduction, and hold sealing force across the door-gap tolerance that accumulates over the maintenance cycle.
Window seals keep out weather. In flush-glazed designs, a separate structural adhesive bead — typically polyurethane — bonds the glazing to the carbody, with the seal handling weather exclusion alongside it.
Axle box labyrinth seals shut out contaminants from the bearing cavity while retaining grease, operating without contact by relying on tortuous path geometry rather than friction. Grease ageing and geometry wear still limit service life, and the seal is inspected on the bearing’s own interval.
Brake and heating, ventilation and air conditioning (HVAC) supply hoses are built to EN 15807/UIC leaflet 830-1 as elastomer-lined, textile-reinforced flexible pipe; PTFE-lined hose and corrugated stainless steel bellows are used only in high-temperature or chemically demanding locations.
Material and fire requirements
Polymer-based sealing and bellow components inside the vehicle passenger zone must satisfy EN 45545-2, which classifies materials by smoke density, toxicity, and heat release under three hazard levels (HL), defined in EN 45545-1 as a combination of operation category (OC1–OC4) and design category (N, A, D or S).
HL2 is the baseline for most passenger vehicles; HL3 applies where evacuation time is extended, including long tunnels, and also under design category S — sleeping and couchette stock, OC3 — relevant for interior seals specifically. The standard tests some materials against a small flame and others against a fully developed fire, depending on the ignition scenario.
Silicone rubber is reported to be replacing PVC in interior sealing applications for its fire performance, though the extent is not independently quantified. EPDM and nitrile rubber remain common for exterior and underframe duties where fire risk is lower.
Environmental ratings
EN 50125-1 defines temperature classes for outdoor rail vehicle equipment: T1 (−25°C to +40°C), T2 (−40°C to +35°C), T3 (−25°C to +45°C) and TX (−40°C to +50°C). Rolling stock in northern and central Europe is typically specified to T2 or TX.
High-pressure washing in depots is a significant ingress risk: axle box, underframe, and door system seals must achieve IPx6 or IPx9K under IEC 60529 — the ratings for directed water jets — rather than the lower IPx5.
UV resistance is required for any elastomer component exposed on vehicle exteriors.