Pneumatic Grain Drills

This type of drill is suitable for drilling a wide range of seeds at relatively high forward speeds. Both trailed and mounted versions are made, with working widths of 2.5-8 m in common use.

Although the seed metering mechanism, usually a fluted roller, is land-wheel driven on most drills, on some it is driven by a hydraulic motor. Seed is supplied from the hopper at a controlled rate to a venturi where it enters an air stream from a fan driven by either the power take-off or a hydraulic motor and blown to a distributor head. This distributes an equal amount of seed to the seed tubes, which deliver it to the coulters. Hydraulic rams are used to control sowing depth. (Fig. 23)

Wide pneumatic drills sometimes have two hoppers with separate metering units which supply seed to the air distribution system. Another type of pneumatic grain drill has indi­vidual fluted roller feed mechanisms for each row or pair of rows, depending on model, and the metered seed is introduced to a flow of air from the fan and transported through the seed tubes to the coulters.

Seed rate is altered by adjusting the metering unit with a lever or handle. The air blast fan must run at the recommended speed for effi­cient operation. Some drills have an electronic control box which can vary the seed rate while on the move. This device has applications when using yield maps produced from the combine at harvest time. The control box may also have flashing lights to monitor seed level in the hopper, airflow and drive to the feed mechanisms.

Figure 23. The path of the seed in a pneumatic grain drill.

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