Automatic tamping machines are able to correct the line and level of railway track in one pass.
By comparing an existing track survey with the designed track layout an onboard computer is able to guide the machine to bring rails to the correct position.
When the machine is over a known piece of track a hydraulic arm clamps and lifts the rails. As the tamper lifts, vibrating tines are inserted into the ballast adjacent to each sleeper. These squeeze up to the sleeper's edges removing any voids from the ballast. Once the tamper signals that the correct lift and cross level has been attained the sleeper is released and the tamper moves on.
In April 1996, Railtrack's Railway Group Standard GM/RT 2400 became mandatory on all new on-track machines. Compared to previous British Rail specifications, the Group Standard imposes several new elements.
The existing national fleet of tamping machines consists mainly of 07 plain line tampers which have an average age of 18 years. These fail to meet all the criteria of the Group Standard and operate at present under so called 'grandfather rights'.
In response Plasser & Theurer introduced a new generation of tamping machines for plain line, and switches and crossings (S&C). The latest tranche of Compactors' expenditure - £4.6M in 1998 - is to go on three of these machines. Two are 08 series dual purpose S&C and plain line machines. One is already in service with the second due in May. And one 09 continuous action tamper follows in August.
The improved control systems of the new generation tamping machines mean increased reliability and productivity.
Unimat 08-4x4/4S-RT S&C and Plain Line Machines are equipped with four tamping units. Each carries four individually tilting tamping tools which can be rotated by 8.5, thus allowing them to treat the skewered sleepers found on junctions.
Each of the four units can be lifted and lowered independently and can be extended laterally by up to 930mm, enabling the turnout and the straight track to be tamped in one pass.
They also have fully sound insulated cabins connected by intercom systems, an integrated trailer with a 3000 litre fuel tank and provision for lifting and lowering all measuring and working units from the cabin. The vehicle has a maximum travel speed of 96kmh.
Compactors machine is the first one in England and Wales.
Compactors has also ordered the first 09-32-RT continuous action tamper. This is a plain line unit that is able to tamp two sleepers at the same time without stopping moving.
Two parallel units carrying a total of 32 tamping tools are mounted beneath the tamper on a 'floating' satellite that is synchronised to the speed of the machine. As the tamper moves forward the satellite remains over a fixed point thus allowing the tamping units to treat two sleepers at the same time.
In discussions with railway plant companies, Plasser & Theurer saw a need for tamping machines engaged primarily in work on rural lines. Such machines would not require all the features of the top of the range models.
In response the company introduced its Series 08-16C-RT Compact Tamping Machines. These machines carry a single sleeper tamping unit and comply with the relevant Group Standards.
Compactors claims it will be the first company in the world to introduce the compact tamper.