How a seed drill works.


	The Seed Metering unit is mounted at the base of the seed hopper. The fan (B) is driven from the rear of the power harrow via a pulley and belt (A). The airflow is forced through a venturi at (C) where the seed is dropped into the airflow. The seed /air mixture moves up a tube inside the seed hopper in the direction of the blue arrow.The seed rate is maintained at a rate proportional to ground speed via the shaft drive (D) Adjustment of the rate is made by handle (E) which opens or closes the seed aperture. (F) is a meter which records the area in hectares sown.
	The air and seed moves via the tube (G) to the distribution head (H) located inside the seed hopper where it swirls until it passes into one of the 28 tubes (J) leading to the coulters. Solenoid valves (K) shut off the grain flow when a tramline is required.
	The wheel (M) which drives the metering unit via the shaft (N). The hoses (L) which carry the seed to the coulters (O).
	The seed passes down the tube of the coulter (P). A ceramic tip (which has good wearing properties) cuts a groove in the soil for the seed exiting at (R) to fall into. Pressure on the coulter is adjusted by tensioning the spring (S). (T) is a plastic plug which swings into the seed aperture to prevent blocking if the drill should be reversed whilst in the soil.
	A following harrow assists in covering the seed completely. Some pictures of a drill working may be found here