What do you need to put in a locomotive to make it work? They need either water and coal or diesel or electricity, oh! and sand. Most engine sheds had storage for coal, water and oil, they also had facilities to provide dry sand.
Sand drying facility
Extreme example of damage to railway tracks after wheelslip
Sanding process
Steam sanding
The development of steam sanding was influential on locomotive design. As the sand could now be blown horizontally and directly under the wheels, it was no longer blown away by cross-winds before it could be effective. This prompted a resurgence of interest in some older single-driver locomotive designs, that had previously been limited by their adhesion performance.
The development of Holt's steam sanding gear on the Midland Railway in 1886 prompted Johnson to design his successful 'Spinners' of 1887, twenty-one years after the last singles, and which would remain in production for a further sixteen years.
On diesel and electric locomotives and railcars, sandboxes were, and still are, fitted close to the wheels so as to achieve the shortest possible length of delivery pipe.
A means was needed to improve the grip of the wheels on the track and a simple solution was found in applying sand betweent the driving wheels and the rails. This became part of the firemans duties and they would climb down from the engine and apply sand directly to the rails. This was a slow process, the engine then only able to go at the speed of the fireman applying sand to each side of the locomotive for the length of the affected section. Very quickly this was automated so a driver could drop sand directly in front of the wheels via pipes from sandboxes mounted above the wheels. Gravity fed, the process depended on a supply of dry sand to pass freely through the pipes. Any sign of dampness and the sand would stick together and clog the pipes.
Gravity sanding had other problems too. Although tubes were angled towards the driving wheels, gravity was often not enough to shoot the sand under the wheels of a stationary locomotive. Any wind was also enough to deflect the flow of sand. The sand was also applied to the rails at the wrong point for a static engine trying to reverse.
"Leaves on the line"
One of the most frustrating things as a passenger on a wet and windy autumn day was when the announcement came over the tannoy that the trains were delayed because of leaves on the line. You looked at this monster locomotive in front of you and were in total disbelief that something as tiny as a leaf could stop it, just another British Rail excuse!
Remembering those science lessons you partly slept through at school however would have pointed you to the world of friction. Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other.
Ice on steel has a low coefficient of friction, while rubber on a pavement has a high coefficient of friction, so you don't slip over. One of our problems is that steel on steel has a low coefficient of friction too. This is overcome by the sheer weight of the engines, both steam, diesel and electric, which enables the engines to grip onto the track so they can pull loads of 1000 tons or more.
The friction is so low however that it can be lost when too much force is applied to the driving wheels. In cars you hear the screech on hard acceleration where the wheels spin, in locomotives the same thing can happen and it is called wheelslip. Friction can be overcome by lubricants however and wet leaves provide just enough lubrication to cause problems.
There is a well documented incident of wheelslip that occured to the Blue Peter locomotive. Multiple problems resulted in the driving wheels loosing traction and accelerating to a theoretical speed of 140 mph before the cylinders and connecting rods failed.
60009 Union of South Africa using steam blown sanders
Sand oven and dry sand storage at Barrow Hill
The provision of dry sand became an important function of all locomotive sheds and Barrow Hill was no exception. Our coal trains often contended with branch lines which were used infrequently and thus a build up of debris was common. Slippery gradients with a load of full coal trucks were a special problem.
The sand drying oven and its chimney have all but disappeared from Barrow Hill. It was located in the corner of the shed now adjacent to our platform. The wagons containing the damp sand, from the quarries at Leyton Buzzard, were pulled alongside the high level access and the sand was thrown in to the top of the oven. In simple terms, as the sand dried it fell away at the bottom to be collected, riddled to remove any stones, and taken in sand buckeds to fill the individual locomotive sand boxes.. The oven was fueled by coal or scrap wood. When the area became a smokeless zone in the 1960's this system could not be used and two internal drying stoves were used. The original oven chamber had a floor put in to accomodate these stoves but this system also only lasted a few years.
In later years the drying of sand at Barrow Hill ceased completely and the sand was brought in ready dried from Mansfield Sand Company, initially in bulk but later in bags.
And today?
Diesel and electric locomotive still suffer from the same problems of loosing traction. Indeed with the vastly increased power that these locomotives can produce it is just as important that this power can be used effectively by the driving wheels.
In front of each wheel is a nozzle that uses compressed air to spray sand, which is stored in tanks on the locomotives. The sand dramatically increases the traction of the drive wheels. Modern engines have an electronic traction-control system that automatically starts the sand sprayers when the wheels slip or when the engineer makes an emergency stop. The system can also reduce the power of any traction motor whose wheels are slipping.
Sand drying equipment has also moved on away from its coal fired origin. Types of drying equipment are now plentiful, compact and varied in design. Here is an example, both outside and in, of a rotary sand dryer. Although small this can dry a vast amount of sand very quickly.
The blue tower, local nicknames either "the octopus" or "the spider", was a container for the dry sand in the diesel era. No longer did fireman have to carry bucket loads of coal from the sand oven to the individual engines. The locomotive would drive under the tower and the sand would be fed by gravity into the sand boxes.
This was not particularly successful as condensation inside the storage container dampened the sand and inhibited the gravity feed.
Location of the original sand drying oven, now closed and turned into a general store room. The original roof was designed in a similar way to the roof of the workshop
Dave ascending the ladder to the second floor where the two replacement stoves were positioned. Little can now be seen of this facility apart from the holes in the roof for the two chimneys.
In the UK, it was standard practice to fit the sandboxes near the running plate, sometimes attached to the wheel splashers. In America the practice was to add a sand dome to the top of the boiler, in an attempt to use the boiler heat to keep the sand dry.