Tamping machine

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Ballast tamping machine as used in railroad track maintenance
A Plasser & Theurer 09-16 CSM Tamper / Liner

A tamping machine or ballast tamper is a machine used to pack (or tamp) the track ballast under railway tracks to make the tracks more durable. Prior to the introduction of mechanical tampers, this task was done by manual labour with the help of beaters. As well as being faster, more accurate, more efficient and less labour-intensive, tamping machines are essential for the use of concrete sleepers since they are too heavy (usually over 250 kg (551 lb)) to be packed into the ballast by hand.

Early machines only lifted the track and packed the ballast. More modern machines, sometimes known as a tamper-liner or tamping and lining machine, also correct the alignment of the rails to make them parallel and level, in order to achieve a more comfortable ride for passengers and freight and to reduce the mechanical strain applied to the rails by passing trains. This is done by finding places where the sleepers have sunk from the weight of the passing trains or frost action, causing the track to sag. The tamper lifts each sleeper and the rails up, and packs ballast underneath. When the sleeper is laid down again, the sagged rails now sit at the proper level. In cases where frost action has caused adjacent rails to rise higher, ballast tampers can raise rails above their original level to make the line level again. "Lining" rails doesn't involve ballast tamping, it merely ensures the rails are perfectly parallel and straight as possible. Combining tamping and lining into a single machine saves time and money, as only one machine needs to be run over the track to perform both functions.


A Balfour Beatty ballast tamper/track tamper train at Banbury station
  • Packing of ballast under sleepers
  • Correction of cross level
  • Correction of longitudinal level
  • Driving
    • Run drive
    • Work drive
  • Special functions
    • Twist corrections
    • Track settlement
    • Laser lining
    • Automatic data feeding by computer
    • Recording of track parameter


A GTRM Rail tamping machine
An Amey Plc tamping machine

Tamper machines are built in many different varieties depending on their purpose:

  • Straight track tamping machines:
    • Universal tamping machines (UT)
    • Unomatic
    • Duomatic
    • Continuous action tamping machines
    • Tamping Express
  • Points and crossing tamping machines
  • Multi-purpose tamping machines (MPT)

Additionally, there are non-tamping machines as well:

  • DTS (DGS), Dynamic Track Stabilizing Machine
  • Points and crossing relaying machine
  • Track relaying train (TRT)
  • Straight track laying machines

General arrangement[edit]

The majority of track machines are powered by a diesel engine. This provides power to the driving wheels via a cardan shaft, allowing the machine to propel itself to and around a work-site. The engine also drives an hydraulic pump to provide power for the various tools.

Tamping units[edit]

Closeup of a Plasser & Theurer 08-4x4/4S-RT Unimat 08-RT Tamper
Unimat 09-32/4S at work

For each rail there is a tamping unit attached to the main frame by means of vertical guide columns and a lifting and lowering hydraulic cylinder. The tamping unit consists of tamping tools (arms or "tines"), a hydraulic vibration motor, a vibration shaft and an eccentric flywheel. For each sleeper, a tamping unit is provided with eight pairs of tamping arms (in two units of four) which plunge down into the ballast on each side of the sleeper and grasp it: four pairs for each side of the sleeper, i.e., 16 individual tamping arms (or tines) are used for tamping a single sleeper: two pairs to clamp the sleeper inside the left rail, and two more pairs to clamp inside the rail, with four more pairs to do the same for the other rail (because both rails must be lifted to raise a single sleeper), for a total of 16 tines. This can be visualised as eight sets of "tongs" lifting each sleeper: two tongs lifting the sleeper outside of the left rail, two more lifting outside the right rail, and four more sets lifting from between the rails, (a pair on either side and a space in the middle of the sleeper). This distributes the stress equally across the sleeper to prevent damage, as the exerted forces can be significant, as the rail must be bent slightly, especially if was previously sagged due to the sleepers sinking under the weight of the trains. To process several sleepers simultaneously, a tamping unit may have between 32 and 64 arms (for up to four sleepers), leading to the derivation of machine type numbers: "16" indicates 16 tines, enough for a single sleeper, "32" for two sleepers. Machines capable of processing greater amounts of sleepers per movement are now labelled by the Plasser 'X' methodology. 09-2X for two sleepers, 09-3X for three sleepers and 09-4X for four, etc.

Tamping units of a Unimat have swivelling tamping arms to pack points and crossings.

Special units are available for use with third-rail electrified track.

Universal tamping machine[edit]

This type of straight-track tamping machine is the oldest of the varieties. It uses a two-chord lining system for alignment of track (for slewing the track to left or right, as-and-when required). This type of lining is controlled mechanically. The machine has four bogies, one at the front, one at the rear, a third in the centre and a fourth in between the centre and the rear. They are called: front-tightening, rear-tightening, lining bogie and measuring bogie, respectively.

The measuring bogie determines the amount of slewing required and measures the subsequent adjustments applied by the lining bogie. The lining bogie also lifts the track to make it level. The tamping bank behind the lining bogie has a vibrating motor and four arms for each rail.

A tamping cycle comprises three operations:

  1. Penetration – The arms are pushed down vertically into the ballast either side of a sleeper.
  2. Squeezing – The arms squeeze the ballast under the sleeper, packing it together.
  3. Moving – The arms are lifted and the machine is moved to the next sleeper to repeat the cycle.

The operations are controlled from the control cabin by an operator using three pedals, while the lining bogie holds the track in its lifted and slewed position.

Specialist tamping machines[edit]

Continuous Action Tamping Machines[edit]

A Continuous Action Tamping Machine (CAT) can pack between one and four sleepers at a time, with outputs between 320m/h and 2600m/h generally anticipated.[1]

Dynamic Tamping Express[edit]

The 'Tamping Express' is a machine developed by Plasser & Theurer, and in the UK & Europe is referred to as the 09-3X. This machine consists of a conventional CAT style satellite with tooling for 3 sleepers in continuous succession, along with a full DTS stabilising unit suspended from the rear most vehicle in the machine.[2]

DGS / DTS (Dynamic Track Stabilising)[edit]

Tamper in Jarvis PLC Fastline livery

Tamping and cleaning operations have the adverse effect of reducing the resistance of the track to lateral movement. The resistance gradually recovers with the passage of trains, but may require a speed restriction imposed for the duration. This 'consolidation' can be achieved faster and in a more controlled manner using mechanised equipment known as the Dynamic Track Stabiliser (DTS).

A DTS will normally be used only after a stretch of track has been tamped and aligned.

D.G.S. has a vibrating unit which holds the track in position and applies a horizontal vibration and vertical load to simulate the passage of trains. The track parameters (or cross levels), before and after stabilising, can be viewed through bogies in the front and rear.

Dynamic Track Stabilising has the following advantages, resulting in enhanced safety:

  • Increases the resistance of the track to lateral movement
  • Creates a homegenous bed of ballast
  • Permits earlier relaxation of speed restrictions
  • Eliminates non-uniform initial differential settlements caused by rail traffic
  • Retains correct track geometry for a longer period than was achievable using tamping machines alone
  • Vibration frequency: 30–35 Hz
  • Working speed: 1–2 km/h
  • Vertical pressure applied: 100 kg/cm²

The stabilisation achieved by one pass of a D.G.S. is equal to that achieved by 100,000 tonnes of traffic, and allows a speed restriction of 20 km/h to be relaxed to 40 km/h

Dynamic stabilisation is usually avoided on bridges or around overhead structures since there is a risk of damage to foundations.

Image gallery[edit]

See also[edit]


  1. ^ "09-4X Dynamic Tamping Express". PlasserAmerican.com. Plasser & Theurer. 2010. Archived from the original on 23 August 2013. Retrieved 16 January 2015. 
  2. ^ "09-3X Dynamic Tamping Express". PlasserAmerican.com. Plasser & Theurer. 2010. Archived from the original on 27 December 2012. Retrieved 16 January 2015. 

Further reading[edit]

  • Indian Railway Track Design, Construction, Maintenance & Modernisation – M.M. Agarwal (former Chief Engineer, Northern Railway, New Delhi) Hony. Adviser, Institution of P.way Engineers (India), Railway Board Office, New Delhi—ISBN 81-900613-1-3
  • Plasser and Theurer Track Geometry Maintenance Durability Seminar, Athens, October 11, 2011, Ing. Rudolf Becker
  • YouTube video of Iarnród Éireann Tamper: http://www.youtube.com/watch?v=pmnX7L_nQBQ

External links[edit]