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New Thinking for Point Operation

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All IRSE Aspect conferences are an opportunity for airing new developments and areas of research in signalling technology. The reliability and maintenance of point operation, whilst much improved down the years, is still a cause for concern and failures when they happen often lead to significant train delays.

From the beginning of railways, points have depended on movable sliding switch rails to control the direction that trains take at diverging or converging junctions. These require periodic lubrication, a method of moving the rails and a means of proving that they are in the exact position before signals are cleared for safe train movement. These three factors are potential sources of unreliability. So what if the movement of the rails can be accomplished differently? Would reliability be improved?

The development of the clamp lock back in the 1980s was a first step in trying to improve performance, but a completely new and novel design of point mechanism has since been progressed by Loughborough University in the UK. Known as ‘Repoint’, the concept was first hinted at in 2013 (issue 101, March 2013) with a fuller description in issue 131 (September 2015) which has led to a modified design known as ‘Repoint Light’ being launched in 2016. Sam Bemment from the university described the proposal at Aspect 2017

The Repoint Light system

Instead of sliding the rails across, why not lift them away from the sleeper base and lower them into a new position? This is the principle behind the new thinking.

In simplistic terms, three modified stretcher bars between the two stock rails (the outer rails) are fitted with two positioning slots (or more depending on the type of point) into which downward facing studs fitted to three actuator bearers that connect the two switch rails are lowered. The fit of the stud to the slot has to be exact, with strict tolerances, so as to achieve a prevention of movement that effectively locks the points into position.

When the point is reversed, motorised cams in the actuator bearers lift the two switch rails out of the slots, drive the rails across to the reverse position and lower them into different slots on the stretchers linking the stock rails. The power needed for this movement is calculated as less than sliding a conventional point.

Clearly the new position has to be proven with point detection mechanisms to ensure the switch rail is tight against the stock rail. Redundancy is achieved by having the three actuator bearers, and indeed there could be more of these used for high -peed points with an extended length.

Development and refinement since 2013 has reached the stage where an operational trial on a real railway can be planned. Following Aspect, Rail Engineer has learnt that the trial will take place on the Great Central heritage railway near to Loughborough, which has lower permitted speeds than the national rail network, at some time in 2018. Many eyes will be watching to see how Repoint performs in everyday service and weather.

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Clive Kessell
Clive Kessellhttp://therailengineer.com
SPECIALIST AREAS Signalling and telecommunications, traffic management, digital railway Clive Kessell joined British Rail as an Engineering Student in 1961 and graduated via a thin sandwich course in Electrical Engineering from City University, London. He has been involved in railway telecommunications and signalling for his whole working life. He made telecommunications his primary expertise and became responsible for the roll out of Cab Secure Radio and the National Radio Network during the 1970s. He became Telecommunications Engineer for the Southern Region in 1979 and for all of BR in 1984. Appointed Director, Engineering of BR Telecommunications in 1990, Clive moved to Racal in 1995 with privatisation and became Director, Engineering Services for Racal Fieldforce in 1999. He left mainstream employment in 2001 but still offers consultancy services to the rail industry through Centuria Comrail Ltd. Clive has also been heavily involved with various railway industry bodies. He was President of the Institution of Railway Signal Engineers (IRSE) in 1999/2000 and Chairman of the Railway Engineers Forum (REF) from 2003 to 2007. He continues as a member of the IRSE International Technical Committee and is also a Liveryman of the Worshipful Company of Information Technologists. A chartered engineer, Clive has presented many technical papers over the past 30 years and his wide experience has allowed him to write on a wide range of topics for Rail Engineer since 2007.


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