HomeInfrastructureModified MEWPs go underground

Modified MEWPs go underground

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The Four Lines Modernisation (4LM) programme is a major Transport for London (TfL) project to upgrade the four sub-surface lines of London Underground – the Circle, District, Hammersmith & City and Metropolitan lines. This enhancement will bring not only new trains, power supplies and track improvements, but also, and crucially to enable line capacity improvements, a new signalling and control system.

All four lines are now operated by one class of train, Bombardier’s S Stock, and they will soon also have one integrated signalling and control system – a communications-based train control (CBTC) system being provided by Thales. This will bring many benefits in terms of capacity as trains will be able to run faster and much closer together than today, thereby enabling improvements in journey times and train frequency to be realised.

The basis is that the trains and the control centre ‘talk’ to each other so that each train knows where it is at all times and the control centre knows what other trains around it are doing.

The train communicates with the control centre by radio. As radio waves don’t travel well along tunnels, transmission has to be more-or-less by line of sight. Radio antennae will therefore be mounted in the tunnels every 150 metres, on average.

So, installing CBTC in the Underground means installing radio antennas in the tunnels – approximately 450 of them – all linked by cables back to the control centre.

The method originally envisaged for the fixing of the signalling equipment in the tunnel areas was to use mobile scaffold towers. These would obviously have to be continually erected and dismantled, configured for access to the required parts of the tunnel profile at every one of the 450 antennae locations, and all within the very short possession timeframes available.

As this approach introduced some challenges, London Underground and Thales turned to specialist plant supplier Total Rail Solutions (TRS) which proposed to use mobile elevated work platforms (MEWPs). With their ability to easily reach any required part of the tunnel profile, the advantages were immediately apparent. That is, providing suitable MEWPs could be modified for the special constraints of the London Underground and be approved for use on its infrastructure.

Dee McGinn, senior project manager of automatic train control for TfL, emphasised that MEWPs introduce some safety benefits and improve efficiency by allowing teams to achieve more in the limited time available during possessions.

Modified MEWPs

The rail-mounted MEWP selected for this work is the Promax RR14 EVO. This machine had been previously approved and in use on Network Rail. Danny Bliss, 4LM’s health, safety and environmental manager for railway systems delivery, explained to Rail Engineer how he had worked closely with Luke Hersee, head of operations for TRS, and with LU’s plant approval team, to identify the modifications needed to enable the Promax RR14 to operate in the tunnels.

Work on this process commenced in April 2017 and full approval was achieved by 28 June, largely due to the very focussed collaboration between the parties involved. A traditional process would be iterative, whereby modifications needed are first identified by the user, after which designs are produced by the plant supplier and then assessed and either accepted or rejected by the approver. In this case, all three parties worked simultaneously in close partnership to formulate and design the practical modifications needed, achieving their goal in a remarkably short space of time.

Forward vision

Four significant alterations have been made to the standard Promax RR14. These are the design and installation of a blind spot camera system, enhanced fire suppression, an operator crush protection system and the use of EcoPar fuel.

The camera system is essential. When used in an unrestricted situation, the body of the MEWP can swivel through 180º, so it can always be transited with the operator/driver facing the direction of travel. When operating in a tunnel, the machine cannot swivel fully and will have to be reversed either to or from the work site. So without the camera system, the driver would have no visibility in one direction of travel.

The camera is therefore provided on the far end of the machine from the driver and its image is displayed onto a monitor screen at the driver’s position in the operating platform. The camera and screen system was devised and installed by TRS.

Firetrace fire suppression

To operate in London Underground’s tunnels, MEWPs, and other plant, have to be fitted with fire suppression systems. The area to be protected is fitted with patented Firetrace detection tubing and connected to a cylinder containing an extinguishant.

Once the detection tubing is installed, it is pressurised with nitrogen which has the effect of holding the extinguishant safely inside the cylinder. Should a high temperature or fire occur, then the pressurised tubing will burst and the extinguishant will be deployed directly from the burst hole onto the fire.

There is therefore no complicated electrical equipment, such as sensors or valves, involved in the Firetrace system. The fire melts the tube, the extinguishant floods out of the hole directly onto the fire and puts it out. It’s really pleasingly simple.

Crush protection

A special operator crush protection system was designed and installed by the MEWP manufacturer, Promax. Also known as an anti-entrapment system, this is again a modification necessitated by the tunnel environment. It is an additional frame, built onto the operating platform, describing a greater envelope than that of the operator and other persons on the platform and linked to the platform controls.

Should an attempt be made to raise the platform to a height, or traverse it to a side position, where a person could become crushed between the platform and the tunnel wall, the crush protection frame will make contact first and immediately cut the power to the platform, preventing any further movement.

EcoPar fuel

EcoPar is a natural-gas-based low- carbon fuel. It contains no sulphur, no aromatics and no benzene and can be used in conventional diesel engines without the need for any modification. It is especially beneficial if used in areas of poor air ventilation as it almost completely eradicates harmful diesel particulates.

Compared to the use of conventional fuel, it is estimated that carbon monoxide emissions are reduced by up to 76 per cent, carbon dioxide by 30-50 per cent, nitrous oxide by up to 26 per cent and carcinogenic emissions by up to 90 per cent.

The 4LM programme is championing the use of EcoPar by fuelling the MEWPs with it. There is an aspiration within the business to widen the use of this fuel as far as possible, once the benefits of its use in the MEWPs’ engines have been successfully demonstrated.

Credit for the introduction of this major innovation will be justifiably attributable to Total Rail Solutions. Apart from its current contribution to productivity on the 4LM programme, the use of EcoPar fuel may well be a longer-term legacy.

Specifications and progress

Following all these modifications, TfL issued its Certificate of Technical Performance for Rolling Stock, a Plant Approval Certificate and a Use of Plant Safety Plan for the Promax RR14 MEWPs to enable and authorise them to be used on the project. These documents explain clearly all the safety checks, methods of work and maintenance requirements to be followed by all personnel involved in the use of the plant. A reading of the three documents, especially the Use of Plant Safety Plan, gives a good impression of how effective the co-operative approval process was.

The platform can accommodate three people along with tools and materials and has a maximum safe working load of 400kg. The maximum working height from rail level to the underside of the basket is 12.1 metres, if the load in the basket is restricted to 300kg. The working height is less (approximately 9.5 metres) at the full load of 400kg.

The gross weight of the machine is 12.5 tonnes. The MEWP must be brought onto and removed from the track at Road Rail Access Points (RRAPs). These have to be provided at places where track curvature and cant is minimised. Curvature must be less severe than 80 metres and cant must not exceed 120 mm. Also, the track gradient must be less than 1 in 25 at the RRAP. A machine controller must always accompany the machine.

Another requirement specified by TfL is that the MEWPs must always work in pairs at any particular location. This is so that, in the event of a machine breakdown, the second machine is available for recovery of the failed machine.

A total of eight MEWPs have been modified for use on the 4LM programme. The availability of permanent and temporary RRAPs at suitable locations to give more flexibility for access to work sites is also being studied.

With 450 antennas to fit, as well as the many cable runs needed and other associated equipment, in a limited space of time, the new Total Rail Solutions RR14 MEWPs will please a lot of people.

Written by Mark Phillips



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