When driving through farmlands, have you ever wondered what the tall cylindrical building is beside a barn? It’s probably a grain silo. A grain silo is not the only kind of silo in use today. A silo can be used as a:
- Storage silo – to store dry grain, corn, silage (fermented animal feed), woodchips, sawdust, cement and others.
- Missile silo – found in a secure underground military location, cylindrical in shape and used to store and launch intercontinental ballistic missiles or ICBMs
- Believe it or not, there is even a silo by the river in Lewiston, New York that is now a restaurant called Silo Restaurant.
The three basic types of storage silos are:
- Tower – usually cylindrical in structure that can go up to 275 feet; made of concrete, wood or metal; uses gravity to pack and distribute the stored materials.
- Bunker – long cement trenches lined by heavyweight plastic used to store grain and silage; filled using loaders or tractors; inexpensive.
- Bag – heavy-duty plastic tubes (8-12 ft in diameter) of different lengths depending on the amount of material for storage; used when towers or bunkers are full; inexpensive.
A grain silo can be a single structure or a group of silos connected together to form a grain elevator. A grain elevator can also have a grain bin or a grain tank. However, the manner of loading and unloading grain into the different storage structures is basically the same. Before the invention of motorized machines, the farmer loaded silos with grain manually. Now, apart from gravity, bucket elevators, conveyors, chute systems, sweep augers and unloaders are used.
Loading a silo
The grain is first deposited in a pit at the bottom of the silo. Grain travels via a bucket elevator to the top of the silo. This is a vertical conveyor belt with several small buckets attached to it. A distributor at the top of the silo directs the bucket to a gravity chute that is higher than the silo. By means of gravity, the grain travels down into the silo. As more grain is deposited into the silo, the weight of the grain allows the silo to be packed. This results in more grain stored in the silo.
Unloading a silo
Just like in loading a silo, gravity plays a big part in unloading the grain. An unloading door is opened at the bottom of the silo and the grain travels directly onto a conveyor or into the carrier vehicle. The grain is pushed out because of the pressure from its weight. Grains that remain on the bottom of the silo are gathered using a sweep auger. It is a rotating device that has a shank shaped like a screw. As the sweep or grain auger turns, helical flighting occurs that moves the grain to the conveyors and unloading doors. Grain can be moved into trucks, freight cars, barges or storage containers for transport to grain distribution centers or direct buyers.
Silos have come a long way from loading and unloading it by hand during its early days. Now automated mechanical devices do much of the work. Because of this, storage silos will continue to be in use for a long time.