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Suck it and see

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To be called ‘the world’s most powerful vacuum excavator’ is a big claim, but that is exactly what the new RailVac RA7 is. Built and designed by the Swedish companies Railcare AB and the DISAB Group, the RA7 really does do what these companies say it will, and they have seen it in action for many years on Sweden’s railways.

That said, when can vacuum excavation be used and how does it work? For those familiar with track maintenance and renewal work, it’s easier to start by describing what the RailVac RA7 does not do. Vacuum excavation means there is:

– no need to cut rails or remove sleepers – perhaps keyhole surgery could describe the way vacuum excavation works, because the RA7 excavates between the sleepers to the required depth and width;
– no need to waste time disconnecting switches, tie-rods or crossing components;
– no risk of impacting on any highly valuable infrastructure such as existing pipework, drainage, cabling and electrics, any damage to which only exacerbates the time and cost issues involved.

Damage prevention

In seven years of using the RailVac, the Swedish company that operates it, Railcare AB, has never once had a possession over-run or even broken a cable. Any rail engineer will realise how that can benefit normal railway operations by the lack of disturbance to schedules. So how does vacuum excavation compare with traditional techniques?

Digging by hand, or excavating with mechanical tools, cannot avoid having an impact on track and the trackbed, so a CAT scan is often used in conjunction with these traditional techniques, adding to the time and cost required. By comparison, the impact made by vacuum excavation means is much less so CAT scans aren’t needed. Furthermore, with vacuum excavation, no track has to be taken up – and that’s largely why there are no over-runs with the RailVac.

Possession time is the common factor in any rail maintenance or renewal project, and the RailVac maximises valuable track possession time. With the RailVac wagon in place, excavation can start immediately. Shutdown is just as fast, so all the time is focused on repair and maintenance. Once the RailVac has done its job, and the repair is completed, new ballasting is done immediately while the RailVac takes away all the old ballast it has vacuumed for disposal.

Undercutting is another form of traditional excavation technique. However, while faster than doing things manually, it takes far longer than vacuum excavation and doesn’t cope with compacted material like clay.

Anything goes

On the other hand, the massive suction power of the RailVac will handle any material, as seven years of successful operation has proven. Basically, anything that fits up the RailVac’s hose – goes. The RailVac’s 225mms diameter flexible suction hose has a metallic end pipe which is manoeuvred by a hydraulically-operated excavator arm. Just one operator controls this (think of a PlayStation console!) while standing close enough to see what’s going on at the sharp end.

Typical repairs that demonstrate the benefits of using a RailVac are:
switch and crossing units, which normally need the track to be cut back, taken out and lifted, while 300-400mm of ballast is removed and a new unit is installed and ballasted. Typically, this requires 16 hours and a 12-man gang, with a 24 hour possession and all the subsequent impact and disturbance to normal running schedules. The RailVac doesn’t need to work this way; 300-400mm of spent ballast can be removed with everything else in place and a C, D or E crossing fitted over four 3-4 hour shifts of track possession time during the week, so there is no disruption to normal schedules nor any need to disturb weekend running either.

Other typical repair examples include plain line re-ballasting, drainage installations, level crossing refurbishments, and under track crossing (UTXs). A RailVac can vacuum excavate a double track UTX in 20-30 minutes, up to 1.5 metres below the sleepers and with no disturbance to the sleepers or normal operational schedules.

The number of operatives required on site also underlines the RailVac’s advantages over traditional techniques. A typical track repair usually needs upwards of a dozen men. The RailVac needs fewer – just a controller, two other RailVac operatives and a small gang for jacking and packing. Using a RailVac can be safer for as well.

On a recent trial at Beeston in Nottinghamshire, a Gv crossover was replaced with the RailVac excavating 300mms below the track. The operation took 8 hours in total – just two four hour possessions for each unit, with no interruption to normal daily operational schedules.

UK specific

The RA7 RailVac unit is Railcare AB’s first bespoke air/vacuum excavator, or to give its full name, a Ballast Vacuum Extraction System (BVES), for the UK market. Designed and built in partnership with the most powerful vacuum equipment available from the DISAB Group of Sweden, it conforms with W6A loading gauge standards. In wagon mode the RA7 can be dead hauled in train formation, and when in a track possession situation and working in the self-propelled mode, it is classed as on track machine (OTM).

The RA7’s suction power comes from two Caterpillar C9 diesel engines, two vacuum pumps and two air compressors, creating an impressive 19,000 cubic metres of air flow per hour at around 95% vacuum efficiency. The machine’s flexibility comes from a manipulator arm for excavation and a unique hydrostatic transmission system that is powerful, reliable and precise in its operation. There are about 40 identified RailVac applications suitable for the UK, some of which are already creating benefits for Network Rail.

The braking system on the RA7 is controlled from all driving/operating positions. To reduce the risks of injury to personnel and damage to the infrastructure, a number of emergency safety systems have also been built into the machine.

A Network Rail Engineering Acceptance Certificate (EAC) was issued early in 2012 and the unit can now provide ballast excavation services for infrastructure owners and maintainers all over the UK. Network Rail has already granted Railcare AB a certificate of Full Product Acceptance for the RailVac method of work.

RailVac excavation services in the UK are supplied by Bridgeway Railcare LLP, a collaboration between Bridgeway Consulting Ltd in the UK and Railcare AB of Sweden. As a specialised contractor, Railcare AB is now investing heavily in the UK railway market. Coming from Sweden, where the 7 day railway philosophy is already a reality, Railcare AB’s methods are not only innovative but very well placed to help the UK’s railway operators and owners make a dramatic difference to the traditional techniques, time and costs of track maintenance and renewals.

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  1. great stuff! – now we just need these type of innovations month-in month-out, so that rail can keep up with the other modes of transport, which are also innovating at a furious pace…


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