On the road and on the rail, the principle is the same: water and dirt can diminish wheel-rail adhesion in any season. Without sanding, the impact would be extremely long starting and braking distances on the rails. If the vehicle provides a central compressed-air supply, a reliable sanding system can be set up in a very economical way.
Here in Oerlinghausen, HANNING & KAHL develops and produces hydraulic braking systems for rail vehicles where impact is naturally limited by low wheel-rail adhesion. Braking systems can only decelerate rail vehicles with best possible impact, even in inclement weather, when the individual wheels are sanded. For over 80 years, Germany’s ordinance on the construction and operation of trams (BOStrab) has therefore required all vehicles of road-dependent railways in Germany which drive faster than 30 km/h, to supplement their brakes with sanding systems.
Since 2018, HANNING & KAHL has been offering customers worldwide braking and sanding systems from one source: HANNING & KAHL’s GripMaster® dispenses the braking sand proportionally when the vehicle accelerates and decelerates. Following each dispensation, the system pneumatically cleans the hoses to prevent deposits accumulating. Dynamic adjustment of the sand quantity minimises the operating costs and the emission of fine dust.
A central compressed-air supply network is certainly an economical option particularly when other pneumatic systems are deployed in the rail vehicle. In these cases, several rotary-vane pumps of the sanding system can be replaced by one HANNING & KAHL pneumatic unit which is connected to the supply network on the input side. The unit consists of a switching valve and a regulating valve to compensate pressure fluctuations on the vehicle. As soon as the switching valve is energised, the processed air flows to the pneumatically-connected, sand-dispensing units.
The switching valve is certified for compliance with IEC 61508 and is the right choice especially for deployment in safety-relevant systems. Extensive type tests verify that the GripMaster® pneumatic unit remains functional during shocks and vibrations in a wide temperature range in compliance with DIN EN 61373. In many installation positions, the fire protection requirements of EN 45545-2 are also met.
Analog to the hydraulic purity classes in ISO 4406, the quality of compressed air is classified in ISO 8573. Apart from the maximum quantities of solid particles (number of particles per volume), limit values are also defined for the oil and water content in the pneumatics. The permissible water proportion is cited as pressure dew point [°C] and depends primarily on the project-specific minimum deployment temperature of the system.