The importance of buffer stops
Not only does a buffer stop mark the end of a track / a track closure, it is also a mechanical safety device that protects passengers, other persons, freight, rail vehicles and buildings and last but not least, the track structure itself from possible damage. This is important, because train formations can amount to several hundreds to thousands of tonnes of moving mass.
Buffer stops are substantially located in track systems. These include main lines, branch lines, metros (underground railways, suburban railways), monorails, trams, crane systems (ports), mountain railways, depots, suspension railways and other rail vehicles.
Even with a careful operational management or when shunting a train formation or individual vehicles, it is still possible that rail vehicles can collide with buffer stops as a result of human, electrical or mechanical errors. The purpose of buffer stops is to brake / decelerate an oncoming rail vehicle safely.
Taking fixed buffer stops as an example (fixed buffer stop)
The effect of fixed buffer stops without hydraulic buffers can be compared to an impact on a rigid wall. Fixed buffer stops pass the impact energy (kinetic energy) back to the colliding traction unit. Such buffer stops are normally designed in such a solid way that any impacts can be returned to the colliding traction unit. However, only a small amount of the kinetic energy is absorbed by the design of the buffer stop. Usually the frames of the traction units are designed in such a way that the force of the rebound can be absorbed in the traction unit.
Types of Buffer Stops
Buffer stops are available in various designs. A general differentiation is made between fixed buffer stops and friction buffer stops.
Fixed buffer stops have only a very slight braking effect. Therefore, they are normally to be found in subordinate tracks such as siding tracks as well as tracks which end at access ramps, e.g. car manufacturers or car trains. They can only absorb the impact if its kinetic energy is absorbed by the elasticity of the buffer stop construction and the buffer springs of the traction units.
Friction buffer stops were invented by the company RAWIE in Osnabrück, Germany and are even today the safest way to stop rail vehicles in case of emergency.
Friction buffer stops are able to absorb a much higher amount of kinetic energy than fixed buffer stops. RAWIE friction buffer stops are able to convert kinetic energy into heat extremely efficiently over a pre-calculated braking distance. The operational reliability of RAWIE buffer stops is particularly high, as each of the friction buffer stops is designed, calculated, and manufactured from suitable materials exclusively for its defined purpose.
Design of the Buffer Stop
The correct choice of a friction buffer stop is determined by the amount of kinetic energy, the train mass and the speed at the time of impact. The length of the available braking distance also has to be taken into consideration. A detailed calculation determines the number of friction elements that are used in order to bring the train to a safe standstill. It is also possible to use friction elements that are placed on auxiliary-rails that are positioned on the sleepers or slab-track between the travel rails. Hydraulic dampers can also absorb additional kinetic energy.
Installation of Friction Buffer Stops
Each buffer stop is supplied with an installation manual / installation instruction by both the manufacturer and the operator of the railway infrastructure. A friction buffer stop is an important safety device. Therefore, the installation must be carried out and inspected exactly the way a safe operation of the track section can be ensured. The following is hereby to be considered:
- The condition of the track is to be conform with the specifications of the friction buffer stop manufacturer.
- The different tightening torques of the screws must be carried out according to the installation instructions.
- The calculated braking distance behind the buffer stop is a necessity for proper functioning.
Maintenance and Servicing of Buffer Stops
When maintaining and servicing the buffer stops, it is essential that the specifications of the railway infrastructure operator are met and that the manufacturer recommendations are observed. This includes the regular maintenance of the steel components with anti-rust treatment and lubrication of the jointed components on the additional friction elements. In dark conditions or in case the visibility is restricted, the buffer stop should either be provided with adequate illumination or it should be provided with a reflecting coat of paint or foil so that the driver of a railway vehicle that is entering the station is able to see the end of the track in time.
A ballastless track / slab track (concrete) must be free from disturbing objects along the entire braking distance. This includes building materials, superstructure components, tools, etc.
Should the slideway of the friction buffer stop be covered, the cover slabs or planks must be able to slide on each other automatically in the event of an impact on the buffer stop.
Buffer stops and especially friction buffer stops should be inspected at regular intervals, but at least on an annual basis. All of the components should be in a perfect condition. An inspection at shorter intervals is absolutely necessary for a safety device that has to stop a mass of hundreds or thousands of tonnes in an emergency situation, especially if the piece of track is heavily used. The regulations of the railway infrastructure operator with regard to the maintenance and servicing of the buffer stops are also to be observed in this case.
In friendly cooperation with A. RAWIE GmbH & Co. KG and Mr Olaf Schöley.