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Turntables, Traversers Points and Slips
Turntable points and slips are devices that connect two tracks together so that stock could move from one line to another. In the very early days of the railways points were prefabricated in a factory and supplied in kit form to be assembled on-site, by hand. Making points was pushing the limits of the technology, they were expensive to make and maintain and a fault would result in a derailment. They did allow an entire train to be drawn from one line to another but this required a gentle curve to connect the tracks. To avoid the use of points and save a lot of space the early railways made great
use of small hand operated turn-tables to transfer rolling stock and
even locomotives from one track to another. On a standard gauge line
these would be circular and perhaps twelve feet in diameter, usually
with two sets of tracks across then in the form of an X.
Turntables
One point to note is that the tracks
leading from the wagon turn-table need not be at right angles, in
some locations several tracks converged and actually overlapped
slightly where they met the turn-table.
The early railways often took a single siding into a goods yard, where a turntable then fed a series of sidings radiating out from it. In the mid
1830's the Liverpool and Manchester railway had over sixty such wagon
turn-tables at it's Manchester goods depot, which by this time
extended over more than four acres. Goods yards were generally re-laid with points from the later 19th century, but this required more space and occasional surviving turntables were seen in goods yards into the 1960s. One notable example being the station at Llanfairpwllgwyngyllgogerychwrndrobwllantsiliogogogoh on Anglesey, opened in 1848 and known locally as Llanfair P G, where a cramped site meant the single wagon turntable feeding several sidings in the goods yard remained in use up to the end of goods traffic in the 1960s.
The typical small wagon turn-tables could handle wagons of
up to about a maximum of twelve foot wheel base, anything longer
represented a problem. By later nineteenth century the century
several companies were using much longer wagons which were too big
for the existing turn-tables. Large wagons mounted on bogies could
however be handled on wagon turn-tables using the technique
illustrated in the sketch below. First you position the wagon with
the leading bogie on the turn-table (1), rotate this to line it up on
the new track (2) and pull the wagon along, usually using ropes and
either powered capstans or horses, until the rear bogie reached the
turn-table (3), then turn this (4) so the wagon could be pulled off
the turn-table (5).
Fig___ Wagon
Turn-tables & Bogie Stock
Using turntables wagons could be transferred between tracks that crossed at right angles, which had several advantages in a factory or railway goods yard but by the 1850's it became apparent
that the turn-tables were becoming a bottle-neck. With wear and tear
they were not as reliable as had been hoped and they could only
transfer a single wagon at a time, requiring a man or horse to move
it. It was at about this time that the technology for bending rail
using portable equipment such as hydraulic jacks became available, so
that points could be readily made on-site and making them cheaper
than turn tables. Thereafter points and other complex track
formations started to appear in greater quantity, allowing
locomotives to be used for shunting.
Turntables remained in use in many industrial locations into the
1950's and 1960's and the railways continued to use them in some large goods yards and in their own works. Probably the last turntables in regular use were
on the dockside lines feeding coal tipping apparatus. They were
required as wagons with an end-door at one end only had to be turned
round to face the right way and they lasted until the end of
the coal hoists in the mid 1980's.
In some locations the turn-table was located at the entry
point to the factory (this arrangement appears to have been quite
common at wagon works) however this did mean that locomotives could
not be used to move the wagons as they were too big and heavy for the
turntables. The British favoured fairly small four wheeled railway
goods vehicles so individual wagons could be pushed about using man
power but in busy locations such as town goods yards it was common to
use horses or ropes run to 'capstans'. This saved running a locomotive and even after the turntables had been replaced the shunting horse and 'capstans' remained very common in British yards. A capstan is a revolving drum,
generally with a `pinched' middle section, set on end and in railway
yards they were usually powered by electricity. Some capstans were
controlled by a lever operated clutch but others simply ran all the
time, the rope was dropped over in a couple of turns and friction
hauled the wagon into place. A skilled man could throw the rope over
the drum and clear it very quickly, however accidents did occur. The
last British railway installation equipped with capstans was
completed in the 1950's.
One thing to note is that not all
capstans were motorised, some were simply bollards placed so the rope
from the shunting horse or from a powered capstan could be looped
round them. These were provided where the track ran up against a wall
or other obstruction to enable a horse (or a separate powered capstan) to pull the wagons right to
the end of the siding.
A single siding at a
warehouse or factory might have a track running along one wall with a
row of wagon turn-tables, each feeding a different bay. In some cases
the bay would be a small dead-end recess or there might be further
turntables inside a building serving tracks inside. This can be used
to advantage as it makes the building appear more important than
might otherwise be possible, an example of such an arrangement is
shown in Fig___ below.
Fig___
Wagon turn-tables & Capstans
On some narrow-gauge quarry lines the
wagon turntables were often very simple, one consisted of a simple
circular metal table with a raised circular centre the diameter of
which was the same as the gauge of the track. As the wheel
arrangement on the quarry wagons was virtually a square this design
worked well. These simple one-piece turntables are often called
'turnplates'
Fig___ Suggestion for using wagon
turn-tables.
I have not yet seen a working wagon turntable in N (there have been a few in OO and O) however Peco offer a dummy wagon turntable in their 009 range, this can be used with N Gauge wagons but only as a cosmetic item. Some ranges of set-track include a 90 degree crossing, this can be cut down and used as the basis for a wagon turntable and would allow smooth running along the line.
Sector Plates
A variation on the turntable used for locomotives was the 'sector plate', this was a length of track sitting in a quadrant shaped pit and pivoted at one end (effectively a half-turntable). The free end was arranged to line up with (usually) two tracks and this was used on some passenger termini to allow a locomotive to be released and run-round its train. These sector plates were usually fairly small, only able to handle a large tank engine, although they a definite space saver they do require some skill to build.
Traversers
The final alternative to the wagon turntable was the 'traverser', a platform on rails sitting in a shallow brick-lined trough running at right angles to a row of sidings. A wagon was placed on the traverser and could then be moved to any of the other sidings it served. These were fairly common in goods sheds, as wagons were emptied they were moved onto the traverser and thence to a release road, so they could be removed from the shed without moving all the other stock still being worked on in the shed. There were also used in some passenger stations, notably at the end of a 'carriage shoot' where private road vehicles were being handled, this allowed each wagon to be unloaded without things having to travel through or across several other wagons. Larger version were also used in large railway establishments where locomotives and coaches were being built. Again I have not yet seen a working traverser (other than in a fiddle yard) for N Gauge but they are an easier option than a wagon turntable.
It was necessary to indicate to staff where the various controls associated with the hydraulic or electrical machinery were located, the cast iron signs shown below are typical, these were photographed at the Manchester Museum of Science and Industry, part of which is the original 1830 goods warehouse for the Liverpool and Manchester Railway, later part of the LNWR.
Points and Slips
Most points, or turn-outs
as they are often called today, simply allow one line to split from
another, there are however variations; the 'double slip point' is a
complicated arrangement which serves as both point and crossing and
the 'single slip' is a variant which allows line changing in one
direction but not the other. In N Gauge single and double slips as
well as standard points are now available in the Peco range. The
Fleishmann N Gauge ready-ballasted 'profi track' range has no single
slip but it does offer a double slip and also a most useful three-way
point with tracks diverging to both right and left.
In cases where
one track has to cross another a 'diamond crossing' is used, named
after the diamond shape formed where the tracks cross. In Britain
crossings on the level were not common and tracks very seldom crossed
each other at right angles, other than at junctions and in the approaches to stations one or other track would normally pass over or under the other via a bridge, however Jeremy Skelton commented that:
You say you don't know of a right-angled crossing on a running line in the UK - I may be missing something, but doesn't the flat junction just north on Newark on the East Coast Main Line count? The other line is the one from Lincoln to Nottingham. The two double-track lines crossing each other constitutes a serious bottle neck.
Further information can be found at Level junction From Wikipedia, the free encyclopedia I had completely forgotten about the Porthmadog crossing between the Cambrian Coast line and the Welsh Highland, which for added interest is mixed gauge, maybe because I've never been there!.
Points on running lines used by passenger stock were arranged wherever possible in
a trailing direction, that simply means that the train would normally
never encounter a diverging track on a running line. Trains were
normally required to reverse over points on running lines to change
from one line to the other. Where this could not be arranged the
point was fitted with a locking device, this could be a lever operated device connected to the signal box (in which case the point would have a protective bridge in wood or (more commonly) metal over the mechanism). In some cases the point was manually locked for main line running using a padlock. The illustration below shows (left) such a mechanism exposed (photographed inside a passenger station), and (right) what it would look like when covered.
Fig___ Point locking mechanism
The use of points and slips and the rules on the
trailing junction and the trap point, are well illustrated in the
track plan shown below, which is based on Hale station, built by the
Cheshire Midland Railway south of Manchester on the old Cheshire
Lines route to Chester. This station is a particular favourite of
mine as the basis for a model railway and it is more fully discussed
in Appendix ___.
Point 'A' serves as the trap point,
protecting the main lines from the goods yard. Points 'B' and the
single-slip point 'C' form 'trailing cross-overs', that is trains
have to reverse to change from one line to another, the two sets form
a loop to enable goods trains to run round the rake whilst shunting.
Note that 'C' is a single slip point, if it were a double slip it
would present a 'facing point' to the lower track of the main line.
Access to the coal yard 'D' would normally face the direction of
travel (as shown by the arrows on the right), so instead it is fed
from a trailing head-shunt 'E'.
Fig___ Typical
double-track station track plan
At junctions the methods varied, with the development of
mechanical point and signal inter-locking systems things became
easier, but in general facing points remained rare. Even on branch
lines it was common practice to use a crossing (or 'diamond') to
carry the line across the facing line on double track lines.
Fig___
Junctions
Fig ___ (1) shows two double tracks forming a junction,
note the trailing cross-over which allows emergency 'wrong line
operation'. Where a single track joined a double track line it was
common practice to split the single line into two, carrying one
across the facing line of the double track via a diamond crossing as
shown in Fig___(2). Note the sand-drag on the branch line feeding
onto the double track line, sand drags were also put in where the
diverging line ascended a gradient to catch run-away wagons. This
track plan also shows how a single slip could be incorporated to
provide a trailing crossing, again to allow 'wrong-line operation' on
the double track line in an emergency. Crossings were even used where
the line being joined became single track immediately after the
junction as shown in Fig___(3). Note the track plans shown are only
based on the quoted examples, they are not complete or to scale.
After an accident in the 1870's involving a passenger train,
where some wagons rolled back out of a goods yard and fouled the
points on the main line, a new regulation was introduced concerning
'trap points'. These resemble about half of a conventional set of
points but they do not connect to another track, their job is to
de-rail wagons rolling from a yard toward a main line. In practice
this tended to damage the errant wagons, and they then needed to be
manoeuvred back onto the rails to clear the line for other traffic,
so quite a few companies used a full point leading onto a length of
track which was banked up with sand to catch the wagons. The banked
sand was called a 'drag'. On some yards where there was no
gradient as such they simply had a short length of track with a set
of buffers on the end as wagons travelling slowly would be stopped by
these and did not require the 'drag'.
A variation
on this idea is the 'catch' point, installed at the foot of an
incline these resemble trap points but the blades are spring loaded.
A train going up the hill will pass through with no problems but
loose wagons rolling back on the wrong line will be de-railed. These
catch points always had a large wooden sign close by, painted white with CATCH
POINT written on it in black, typically the lettering was about a
foot (30cm) high.
British terminology divides the point
into two sections, a number, indicating the length of the switch
rails and a letter indicating the crossing angle of the frog (the bit
where one rail crosses the other). There is little point in having a
table of these units however as on a model railway the rule of thumb
is to use the longest point with the shallowest crossing angle you
can fit in the space available. This is especially important where an
's' curve in involved, such as when a train has to cross from one
line to the other on a section of double track.
The Americans
use a slightly different system, their points are identified by a
number which refers to the angle at which the track diverges. For
example the two diverging tracks from a 'No.6 switch' will separate
by one unit for every six units of length (i.e. six inches from the
frog the tracks will be one inch apart).
In N the Peco set
track point has a nine inch quoted radius and should only be used in
docks or industrial establishments, the Peco medium radius point has
an eighteen inch quoted radius and is suitable for most purposes and
the Peco large radius point has a quoted radius of thirty six inches.
The most common point on British lines has a radius equivalent to
about thirty inches in N and hence the Peco large radius point is
suitable for high speed cross-overs on main lines.