How a Tamper works
Thanks to Lerpass Mapter for this information
Tamping machines are used to restore or improve the track geometry. The three areas of track geometry are CANT (cross level/transverse level) TOP (longitudinal/vertical level) and LINING (horizontal alignment). Poor track alignment can cause poor ride quality or at worst derailment.
Lifting
The tamping machine measures the track geometry using 3 sets of measuring trolleys/wheels that are lowered onto the track. The measuring trolleys have feeler rods sat on the trolleys (approx. 8ft long). Between the front and rear feeler rods a wire is pulled taught and is used as a datum point for the measuring transducer on the middle feeler rod to measure the track longitudinally, any "dips" in the track are detected by the transducer and the track is lifted by the machine accordingly. This arrangement of feeler rods and transducer are fitted to the left and right of the machine allowing both rails to be measured and lifted independently also allowing track cant to be measured and corrected.
Lining
There are two methods of lining, 3 point and 4 point. The diagram shows 4 point lining. In 4 point lining there are 4 measuring trolleys, 2 of which are shared with the lift system. In a similar way to the lift system-minus the feeler rods, a wire is pulled taught between the front and rear trolleys providing a datum for the 2 measuring trolleys, detecting any error in horizontal alignment by the lining transducer allowing the machine to slew the track left or right to the correct alignment. The measuring transducer is for measuring curves of unknown radius.
Tamping
When the track is being lifted a void will appear under the sleeper, this void must be filled to support the track to its desired position. This is achieved by tamping where by the tamping banks are lowered, causing the tamping tools or tines to penetrate the ballast each side of the sleeper and then squeezing to lift the ballast upwards to support the sleeper. The whole process of lifting lining and tamping takes only around 3 seconds.
There are 3 types of tampers, 16 tool (capable of tamping one sleeper at a time). 32 tool (capable of tamping two sleepers at a time), and 48 tool (capable of tamping three sleepers at a time). The 48 tool machine is of a new design and was introduced into the UK in late 2000.
