Before the advent of mechanized railroad tampers the work of getting ballast beneath the ties as well as aligning the track was all done by hand and a good eye. The job involved a track gang of men who would push the ballast beneath the ties one at a time and track jacks were used to properly align the rails. As you can imagine it was slow, very labor intensive work all of which has been greatly improved with the mechanized railroad tamper. Railroad tampers almost always work as some kind of mechanized gang, usually as part of a tie or rail gang (which today normally consists of an army of machines, not men).
Today's tie and rail gangs include such machines as spike or rail anchor pullers (which pull the spikes/anchors clear of the tie), tie cranes (which remove the railroad ties once they are free of the rails), tie extractors/inserters (different from a tie crane these machines work vertically to remove or replace the railroad tie from underneath the rail),
and spike inserters (as you might have guessed these machines use
hydraulics to quickly drive spikes down in the tie plate and tie
itself). If very heavy work is being done other large equipment will be used such
as a mechanized tie relaying machine (which is essentially a type of
railroad tie inserter) and/or even a rail train if new rail is to be laid.
As it is, tie and rail gangs may look like machines simply heading off to work
in an elephant line. However, they are actually very coordinated work
details with each machine and accompanying operator assigned a very
specific task to get the work done as quickly as possible. The reason
for speed and hastiness in finishing a maintenance job is simply, to
keep the trains and goods moving. Delays are quite costly and avoided at
all costs because if the freight isn't delivered the railroad's don't
get paid! Standard railroad tampers work by using sets of heavy-grade steel jacks, which are hydraulically controlled, and feature a small paddle-like design on the very end of the tool.
These jacks are then lowered into the ballast at a certain depth, depending on the thickness of the ties and oscillate at thousands of revolutions per minute. This back and forth motion, along with "pushing" the ballast downward, allows the stone to become very free flowing and causes it to work beneath the ties, giving the track structure maximum support. Tamping also helps to level out the ballast a bit, although final sculpting and angling of the stone is left to ballast regulators. Perhaps, though, the most efficient type of railroad tamper is the production tamper. Looking as if it is a type of auto carrier a production tamper is capable of lifting the entire track structure where it is working (the reason for the extra support beams built into the machine).
The purpose of this is so the machine can not only more efficiently situate the ballast beneath and around the ties but also to properly align the track as well. Using what is known as the Delta System developed in the 1950s production tampers are able to remove the bumps and dips in the rail by aligning the track to a perfectly "flat" traveling surface (excluding superelevated curved track) using triangulation. One other type of railroad tamper is the switch tamper, which is able to swivel its equipment and jacks to work the intricate spaces between railroad switches and diamonds. To learn more about railroad tampers please visit Harsco Rail's website, which provides exact specifications and information concerning their latest models. There you can also check out other types of maintenance machines the company produces such as spike inserters/pullers, undercutters, and blowers.
Lastly, for more reading about tampers you may want to consider the book Railway Maintenance Equipment: The Men and Machines That Keep the Railroads Running
from noted author Brian Solomon. Throughout the book's 128 pages
Solomon covers all types of maintenance equipment from tampers and
undercutters to Jordan Spreaders and rotary snow plows. I own this book
myself and have used it as reference material for this site many times.
It's a great read on an often little understood area of railroading. If you're interested in perhaps purchasing this book please visit the link below which will take you to ordering information through Amazon.com.