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Sleeper (1)
Sleepers have two functions: holding the rails at the correct distance apart (GaugeExplain 'Gauge') and transferring the pressures of passing trains from the rails to the ballastExplain 'Ballast'. Usually made of pressure treated hard wood, but softwood is also used and more recently pre-stressed concrete. LNWR experimented with pressed steel sleepers but did not adopt them. Often sleeper density is increased on curved track, where the lateral forces are higher.
Sleeper (2)
A colloquial term for a sleeping carExplain 'Sleeping Car' (or sleeping carriage).
Sleeping Car
A passenger carriageExplain 'Carriage' with facilities for the passengers to sleep, on payment of a supplementary fare, originally only for first classExplain 'Passenger Class' passengers; after the groupingExplain 'Grouping' third class sleeping cars were introduced. LNWR and WCJSExplain 'WCJS – West Coast Joint Stock' sleeping cars, and the LMS carriages of similar design, ran on six-wheel bogiesExplain 'Bogie', and were so solidly built that it was almost impossible to hear, or feel, the rail-beats when running.
Sleeping Composite
A hybrid WCJSExplain 'WCJS – West Coast Joint Stock' vehicle 50ft in length, half ordinary carriage and half sleeping car, provided on trains where demand did not justify a full sleeping car. Curiously, no attempt was made to merge the styles: the sleeping portion looked like part of a sleeping car and the carriage portion like an ordinary passenger carriage.
Sleeping Saloon
The legend on LNWR and WCJS sleeping carsExplain 'Sleeping Car' was “SLEEPING SALOON”; strangely, this appeared not on the waist-band, as in dining carsExplain 'Dining Car', but above the windows.
Slide Bar
A straight piece of metal fixed to the back of the cylinder blockExplain 'Cylinder Block' but parallel to the bore of the cylinder, on which the Cross HeadExplain 'Cross Head' slides. Often two or four were used for each cylinder. Maybe of any shape, but rectangular is most common.
Slide Valve
In its general form, a slide valve resembles an upside-down rectangular pie-dish in the steam chest and moved to and fro by thevalve gearExplain 'Valve Gear'. Pressure of steam in the steam chestExplain 'Steam Chest' holds the valve with its narrow rim against a smooth flat face pierced with three slots (called ports). The outer slots are connected by passages to the ends of the cylinders, the central slot communicates with the blast-pipeExplain 'Blast Pipe'. Movement thus uncovers no more than two slots at a time,allowing expanded steam to be exhausted from each end of thecylinders in turn. Such valves were almost universal in steam engines until super heatingExplain 'Super Heated Steam' demanded something better and the piston valveExplain 'Piston Valve' was adopted.
Slip Coach
A railway carriage which can be uncoupled (slipped) by its guard from the back of a moving train and coast under his control to stop at the next station.
Slip Point
A combination of a diamond crossingExplain 'Diamond Crossing' and either a pair of pointsExplain 'Points', allowing movement from one of the crossing lines to the other (single slip), or two pairs of points, allowing movement from either of the crossing lines to the other (double slip) – also known as a single or double compound.
Slotted Signal Post
In some early signals the signal arm was pivoted in a slot in the post rather than on the side of the post facing an oncoming train. Originally, the arm was concealed in the slot at “off”Explain 'Off (Signal)' (clear), but some slotted posts remained in use after the practice of the arm being lowered to about 45 degrees became general. Slotted post signals had drawbacks: the arm could stick in the post due to ice and show a false ‘off’; arms could blow off or be damaged in severe weather and this also would show a false ‘off’. Such signals were phased out and replaced by normal semaphore signals which showed a positive 'clear' indication.
Slotter
See Frame SlotterExplain 'Frame Slotter'.
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