A pressing engagement

Travel around the UK rail network, and you’re likely to encounter a tamper. You will often see one (during the day at least) stabled in sidings that are otherwise little used. 

Tampers play a key role in the maintenance and improvements carried out on a daily basis. They are highly technical, and expensive, pieces of kit. Wherever there is a major project, there will be a tamper.   

Peterborough, for example, is being re-modelled. Thousands of passengers pass through the station every day, yet few will have noticed the tamper vehicles gathered around the £43 million rebuild. But without them, the station cannot be expanded.

So, what does a tamper actually do? They are used to pack (tamp) ballast under track, to level and line the track, enabling trains to run fast, safe and smooth. 

This used to be a manual time-consuming job, but not any more. Early designs would simply pack the track, but as technology evolved, so did the tampers. Nowadays, they can correct the alignment of the rail as well as perform their original task. They can correct twists, and carry out accurate alignment.

There are several different types of tamper. There are plain line track tamping machines, and points and crossing tamping machines. Some have 12 tools for use on tracks with conductor rails, while others have 16 tools where there is no conductor rail, 32 tools to tamp two sleepers at a time, and even 48 tools to tamp three sleepers at a time. 

At Woking Yard, which is a base for Balfour Beatty Rail’s (BBR) plant business, there is a collection of these machines. 

BBR is three years into a National On Track Machine contract with Network Rail, for the provision of tampers. BBR supplies the vehicles for all tamping work in Anglia, Kent, Sussex and Wessex, as part of the seven-year deal. 

Geoff Brown, engineering development manager at BBR, tells RAIL: “We work for the National Delivery Service . Our machines can be anywhere, and we like them to work locally to strategic bases. The important thing is keeping On Track Plant working.”

The tampers are here to fix track problems caused when the track moves, says Brown. 

“Greater tonnage means it moves. Generally it moves vertically, but it doesn’t settle evenly. The make-up of the land’s geographical conditions can affect it.

“This is where tampers go. They rarely do tunnels, because the temperature generally stays the same through the rocks surrounding the structure, and there is no weather in there to affect the land.

“If you have beautiful track, then it is smooth, but eventually it begins to move. The track form always settles - the problem is it doesn’t settle evenly and you have to bring it back up. It must always lift.”

Brown explains in detail what happens. “Perhaps you need 150mm of lift in one dip, 1mm in another, and 20mm in another. During a typical maintenance shift a tamping machine will maintain around a mile of track - we generally apply a maintenance lift of approximately 25mm throughout the site. This allows the machine to ensure enough ballast is packed under each sleeper, even the ones with only 1mm of error, for a durable finished product.

“There is more that they can do. You cannot, with a conventional train, go from straight track into a curve. At the end of the straight you need to blend the track into the curve - this is called a transition, where the straight progressively bends into the curve. 

“Through curvature the outside rail is raised up to around 150mm, to allow the train to go round the curve faster without passengers being thrown around in the carriages. In this case the tamper progressively and controllably, using computers to control the alterations, adjusts the one rail up above the other.”

Brown says there are no specific rules on tamping. Track in good condition could go three to four years without any work, while poor track could need tamping every three to four months.

All tampers have a measurement system to enable them to understand where faults exist on the track. This measurement requires three trolleys - one at the front of the machine, one in the centre (known as the measuring trolley), and one to the rear. These three trolleys provide the necessary input to the machine’s computer control system, enabling it to manage the faults by measuring the difference in track alignment or vertical profile between the measuring trolley and the front and rear trolleys. 

Brown explains there are principally two methods of making the measurement - a system using a wire, or a system using a light beam. This depends upon the manufacturer of the tamper - those built by Plasser & Theurer use wire, while those built by Matisa use the light beams.

There are three ways in which a tamper works, he says. Simple smoothing is where the tamper adjusts the track as it goes along, using errors measured only between the front and rear trolleys. 

The tamping machine can only see the errors between those two trolleys, therefore the machine can only improve track over that short distance. This can leave long wavelength faults and is generally no longer used in the UK - it is not suitable for high-speed running of trains. 

The second way is the more common method used in the UK. The tamper arrives at ‘Point A’ and measures the entire track length to ‘Point B’ (a distance that may be up to a mile in length). 

A computer notes all the places where the track level is wrong, and computes what work is required to fix the problem. It comes up with the design for work, then implements that design. Tampers measure at up to 10mph, and the computer takes between two and three minutes to generate the design.  

Finally there is the geometry method, where a design is created and input to the computer. The machine understands where the track is, and creates an offset file that is the difference between what the machine has just measured and the final shape. With the differences understood, the tamper sets off to correct the alignment of the track to the design.

“We either do geometry or maintenance tamping,” says Brown. “Maintenance is almost exclusively used for Network Rail local maintenance. We will arrive, the client representative will jump aboard, we will go down to the site, and get on with the work. The client representative will look at the screens for the work needed - he acts as quality control.

“When working for NR on routine track maintenance, the tamping contractor does not hand back the track - that is done by the TQS .” 

When the tamper is on site, NR staff will have already marked the track that needs to be tamped.  

Temperatures can have an effect on the work. During the summer, when temperatures reach more than 30 degrees, NR will not allow tamping to be completed. The same scenario applies when it is -2 degrees. 

Brown explains that BBR has 16 tampers contracted to NR - eight compact Plasser & Theurer machines, six Matisa Tampers, and two Plasser Unimats. The Unimats were built in 2000, the Compacts in 2001-2003, and the newest machines (the Matisas) in 2010, costing around £20 million. “We have the most modern fleet in the UK,” he says. 

They are all fitted with the necessary equipment to work on the main line, just like the locomotives and multiple units that run on NR tracks. They are fitted with Automatic Warning System (AWS), GSM-R signalling equipment, Train Protection Warning System (TPWS) and On Train Monitoring Recorders (OTMR). The whole fleet is also fitted with Track Circuit Actuators (TCA).

Either two or three operators work on each tamper, depending on the machine. If it is a plain line tamper, then two members of staff are on the vehicle; for a switches and crossings (S&C) tamper, it is three. 

The asset life, says Brown, is perhaps 15 to 20 years, while the technology also gets superseded. 

BBR has depots at Woking, Colchester and Hither Green, while it also uses Ashford, Romford, Eastleigh, Sandiacre and Three Bridges. 

Brown shows RAIL around two tampers. The first is DR73928, a compact tamper built by Plasser & Theurer. It has a maximum speed of 60mph. 

“This is ten years old and can go for another five years or so,” says Brown. “It will have a high capital cost and depreciation.”

When heading out on a job, this vehicle will leave its Woking base next to the South West Main Line at around midnight, and be back at around 0500. This five-hour window includes transit to and from the worksite. “If it is a longer trip, then we will go when passenger traffic is still working,” says Brown. 

To measure the track it uses a wire, which receives an electric signal from a box near one of the trolleys. (The trolleys themselves are quite small.) 

There is an operator in each cab and another operating the machine. Surprisingly, considering how complex these machines are, they are controlled by two pedals. 

The control area has a glass screen that allows the operator to watch what is going on. It takes around one month to be trained as an operator, but a year before one of these machines can be driven unsupervised. They have 80 tonnes of lift force.

In the cab, the TQS monitors events via a screen. Every site at which the tamper works, the start and finish time is included on the screen, as is the mileage to be covered. The TQS inputs his requirements, and away the tamper goes. 

Tampers can only tamp in one direction, because of how the equipment is fitted. 

“Invariably we arrive at position A, do our measurements, then move to position B, before going back to position A and then tamping back to position B,” explains Brown. 

“Once work is completed, the recordings are downloaded to a memory stick. This particular machine can ‘ring home’, and through a GPRS system can tell the depot where it is.” 

The TQS normally has five or six years’ experience before taking up this role, and is usually based at the local permanent way depot. 

The tamper tools are suspended 150mm from the rails. When in use they drop to just above sleeper level, and are supported by a lift frame. Once in position they lift and slew the track.

Providing value for money is important for both sides. With the job complete, the track work is signed off by the TQS. 

It is an intense job, but reliability is superb, says Brown. “We record 99.2% reliability. That is industry standard. We are meticulous for hours worked and delays. It is contractual, and you need to know.” 

The second tamper that Brown shows RAIL is a Matisa B41UE. This is a larger machine, and is more advanced than the Compact. 

He explains: “Using the light beam system, there are no moving parts on a Matisa measurement system, which means they are more reliable. The B41UE is primarily a points and crossings machine.

“If I had to rate out of ten… the Compact is a good plain line tamper. It is good for S&C, too, so maybe six out of ten. This is a nine out of ten for S&C, and eight out of ten for plain line tamping. It is quicker than the Compact.” 

The workbook shows that the previous night, this vehicle completed work at around 650 metres per hour.

BBR specialises in third-rail work, and the Matisa tamper banks do a better job than the Compact because better visibility makes it easier for the operator. The difference is that this equipment goes under the cab, so the operator can see the action more clearly. This is not possible with the Compact. The Matisa has 508kW installed power and weighs 100t, against the 304kW and 64t of the Compact. 

The Matisa also has one operator for plain line work, which can be done fully automatically. If the operator wants more control, it goes into semi-automatic mode. Only one pedal is needed to operate the machine. 

Brown explains: “When you arrive at an S&C site, there are normally two operators to work the machine. Only one operator has full control of the working units, but he must make sure the machine is correctly positioned before inserting the tools in the ground. 

“Tamping through S&C is slower, and is a constantly changing shape as the machine moves through the switch. We do the work for both lines from the one line, up to a point where the tracks are about a metre apart. Per switch, it is typically 40 minutes to complete, depending upon the cabling and condition.”

There is also another generation of tamper - the Matisa B66UC (there are two in the UK, both owned by BBR). 

Brown explains that the major difference between the Matisa B66UC and the B41UE is that on the former, the tamping bank is attached to the bogies rather than the body. 

Therefore, while working, the body moves ahead continuously, instead of stopping and starting. Only the tamping banks stop and start for each sleeper insertion, which allows for faster work. “The B66UC can do 1,000 metres per hour,” says Brown. 

Technology, it seems, has moved on again. For those who use these hard-working, very expensive, but largely unknown pieces of railway technology, that is a good thing. And even though they may not be aware of it, for passengers, that is an even better thing.

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