unit to move the rail and B point in line with A and C. Tamping units The Tamping units of most Tamping machines will consist of: A set of tines either 8 or 16 per sleeper divided evenly between front and rear of sleeper Mounting or "guide" rods that allow the unit as a whole to move up and down in a linear motion Support frame Squeezing arms Tine mounts, can be either part of the squeezing arm or attached to it via a pin to allow swiveling depending on type of tamping machine To generate the vibration needed for penetration and consolidation there are two leading methods commonly used: Using a hydraulically driven eccentric shaft attached either to the end of the squeezing cylinders or acting as the pivot point for the squeezing arms Using a special squeezing cylinder and valve assembly to oscillate the tines A less common method more often seen on tamping head attachments for excavators is to use a motor driven vibrator assembly that is directly bolted to the support frame. Specialist tamping machines Continuous-action tamping machines A continuous-action tamping machine (CAT) can pack between one and four sleepers at a time, with outputs between 320 m/h and 2600 m/h generally anticipated. Dynamic Tamping Express The 'Tamping Express' is a machine developed by Plasser & Theurer, and in the UK and Europe is referred to as the 09-3X. This machine consists of a conventional CAT-style satellite with tooling for three sleepers in continuous succession, along with a full DTS stabilising unit suspended from the rear most vehicle in the machine. DGS / DTS (dynamic track stabilising) 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