Granular materials include grain, seeds and various minerals, the food stuffs were mainly shipped in sacks up to the 1960s although imported grain has been moved in bulk since the later nineteenth century.
To move grain from place to place, such as from a railway hopper wagon to a storage silo, a simple archemedian screw type device is often used. This screw device is commonly known as an auger or screw conveyor, and consist of a long spiral screw mounted in a tube, usually with an electric motor mounted toward one end. Augers have been used since ancient times and have many uses in industry. By having two screws interlaced in a trough the material being moved along also get thoroughly mixed (one application for this is the movement of wet slurry to the kilns in cement works).
The sketch below is based on a photograph of a maltings circa 1937 and illustrates the three main methods for handling bulk grain. The grain is unloaded from the railway wagons (A) into a pit from where a bucket-chain (B) lifts it to the top of the tower. The grain is stored in the hoppers (C) and when required it is moved to the end of the building by the auger (D). From the auger discharge pit either a second inclined auger (as shown at E) or a vacuum system using a fixed nine inch diameter pipe draws the grain into the maltings.
Fig ___ Bulk grain storage & handling
There is a good photograph of a large fixed auger based system used for loading BR era grain wagons in East Anglia in the book British Railways Goods Wagons in Colour by Robert Hendry (see Bibliography). The picture shows the detail of the gantry with its twin discharge pipes but not the facilities for the farmers lorry depositing the grain.
More recently mobile or portable augers have been used to transfer grain from railway hopper wagons to road lorries at railway sidings, the top of one of these is seen in the background of the above mentioned picture.
Fig___ Auger used for Grainflow
These materials can be transported in hopper type wagons and stored conveniently in silo's as they tend to stay loose and do not usually compact down to a solid mass. In the 1930s new handling methods were developed which allowed the use of simple buildings with the material simply piled up on the floor. Since the 1930's the cylindrical silo has migrated from the docks into wider use in industry, for a model railway one option is to use the top of a washing up liquid bottle in the true tradition of Blue Peter.
I made a modern grain depot in N for a friend, based on a photograph, using two of these as the main storage silo's. I used fairly small washing up liquid bottles (just over two inches in diameter I believe) and I only had two but the silos were still large enough when built and it looked the part when completed. I added a length of strip wood across the top with a strip of 1mm scribed card and handrails (OO gauge signal ladders) running along the top of that. The 'tower' at one end was made up from something in my bits box (possibly parts of the Airfix signal gantry). There was a large building in the background, presumably where the grain is sorted and dried. Mine was made using a flattish strip of wood about two inches high, the upper ribbed cladding represented using a strip of card cut from a folder, wound with monofilament fishing line and coated in dilute PVA before painting light grey. The 'roof' was a strip of triangular strip wood (purchased for reinforcing card buildings) with a plain card 'roof' added to the top. The building was presumably connected to the tower by the silos via an underground auger or vacuum pipe. In the photographs there were smaller elevated silos acting as a buffer store but I didn't have any suitably small 'squeezy' bottles to make these with, so to transfer the grain from the silo to the railway wagons I added a small over track building. This had a tower at one end (strip wood covered in brick paper) with a horizontal section made from more strip wood with the sides covered with more fishing line wrapped card and the far end supported by Plastruct H section posts set into holes cut into the end of the wood. The whole job took less than an evening and looked moderately like the photograph (at least he and I thought so).
Fig___ Post 1960's grain loading depot
Similar shaped but lower circular silos are also used for other materials, one associated type used for powdery or granular chemicals is a rectangular building with low walls (perhaps five feet high) and a tall apex roof with a trunking running along the top.
Imported grain has been shipped in bulk since the 1920s at least, handling the imported grain is discussed in the section on docks.
Where grain or other lightweight materials such as small coal has to be lifted to a considerable height one option is to use a vacuum system which involves a heavy hose mounted on a swinging arm. Vacuum unloading of grain from ships holds and coal from canal barges at power stations has been used since the 1930s.
Powdery materials such as flour, cement, salt and slate powder are more difficult to handle, under vibration these materials will compact into a solid mass which will refuse to empty from normal hopper wagons. The LMS built some steep sided cement hoppers in the 1930's but I understand that unloading these often involved much banging on the sides with bits of timber to get the stuff out. As a result up to the 1950s it was normal to ship these materials in sacks, carried in open wagons or closed vans. In the 1940s and 1950s a new system was evolved, called air-fluidisation, which uses containers fitted with air pipes. The pipes have many small holes in them and the air is blasted through to break up the material into something which then behaves like a liquid. The 'fluidised' material can be pumped or (more commonly) the air flow can be arranged to carry it through pipes to storage silos. The silos are similarly equipped for discharging the material. Cement was an obvious candidate for this approach and the first railway wagons to employ this technique were the Presflo hoppers (as available from Graham Farish) introduced in 1954. Privately owned cement tankers soon followed whilst British Railways experimented with the technology in other ways, a BR air-fluidised bulk flour container is sketched in Volume 1 Fig ___.