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Escalator Refurbishment – London Underground Definition and Summary
London Underground (LU) defines escalator refurbishment as follows:
“Replacement of a portion of the mechanical and electrical components of an existing escalator but retaining the significant structural elements (e.g. truss)”.
Within this definition, there are a number of categories of work:
• Full refurbishment (modernisation).
• Partial refurbishment.
• Extension of Life.
For the full and partial refurbishments the expected nominal life post-refurbishment of the escalator is 15~20 years - with the timing of the refurbishment intervention being dependent on the condition and usage of the escalator. The decision between full and partial is made based upon the machine in question and whole life cost considerations. The extension of life works are specific scope items to extend the life of an asset for a specified period (for example, two years extended life so that a full project can take place in line with a wider project at a station) until such time that the machine is totally replaced with a new machine.
Why it felt the escalators need to be refurbished
The escalators are refurbished to ensure safety, performance and reliability - this is invariably linked to machine operability and the management of risk should the machine fail. The risk could be safety risk or operation risk. A typical escalator consists of many mechanical and electrical components - many of these components are consumables or will degrade through time/usage due to wear and tear, therefore the need exists to refurbish and replace certain components before they fail. Escalators have a nominal design life of 40 years. Throughout this life they have a comprehensive intervention plan (including standard maintenance, handrail replacements and so on). A key intervention is the refurbishment usually undertaken at approximately half life to reset the residual life of mechanical and electrical components.
There are more than 427 escalators on the LU network and nearly 30 types of escalator. These escalators are all of varying age and condition and as such London Underground has a continuous work bank of escalator refurbishments. These refurbishments are prioritised based upon a number of factors, including:
• Performance of machine.
• Age of machine.
• Coordination with other works.
These factors lead to a decision on the type of intervention required and an intrusive condition survey is combined with a pre-set assumed scope to decide the full scope of the refurbishment.
Possible Engineering Designs Considered – why this design was chosen
Historically, the above has been the core option. Escalators had a half life refurbishment and were then fully replaced, including all structural elements at the end of their life. The scope of these refurbishments have adjusted over time based on whole life cost considerations and obsolescence. For example, on some machines gearboxes are replaced and some are refurbished depending on how troublesome it is and the availability of spares etc. This scope variation is true of many other components of the escalator.
However, feasibility is currently taking place to consider the option of an “in truss replacement”. This means for old and poor performing machines there is the option to modify the truss and install a modern, modular escalator rather than refurbing the existing machine. This decision will be made going forwards on a business case basis.
In summary, there are three types of escalator refurbishments with regards to engineering options:
• Refurbishment where some or the majority of the mechanical and electrical components are replaced with ‘like for like’ components.
• Refurbishment where some or the majority of the mechanical and electrical components are replaced with modern equivalent components.
• Refurbishment where all the mechanical and electrical components are replaced with modern, modulised components with only the original escalator truss (structure) remaining.
The decision on which of the above is chosen is based on the type of machine, its condition and the cost of refurbishment.
Limitations on escalator refurbishments include:
• Escalator standards - LU escalators need to conform to EN 115 requirements.
• Space and access constraints.
• Closure constraints - an LU escalator undergoing a refurbishment intervention requires typically 16~18 weeks to complete the refurbishment works. During this time the escalator has to be closed off and would not be available for customer use.
Structural constraints do not generally apply to LU escalator refurbishments as the escalator structural truss is generally not affected during escalator refurbishments.
Overall, the strategy for escalator refurbishments is decided based upon ensuring safety and reliability for our customers at the lowest whole life cost.
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