Pneumatic Seed Drill

Overview

A pneumatic seed drill sows cereals, oilseeds, grasses and pulses by metering seed from one central hopper and conveying it on an airstream to many coulter row units. Unlike a mechanical drill that needs a metering device above every row, the pneumatic layout meters once at a single Central Metering Unit and lets air carry the seed out to the rows. That makes wide working widths practical: machines run from a 3 m mounted unit up to a 12 m trailed unit with 18 to 48 rows.

The drill mounts on a tractor three-point hitch or tows on a drawbar. A Seed Hopper Assembly holds 1500 to 3000 L of bulk seed. Below it the metering unit doses seed at the set rate, the Pneumatic Distribution System distributes it, and the Coulter Row Unit place it in the soil. Working speed is typically 8 to 15 km/h, giving daily output well above what a comparable mechanical drill manages.

Main subsystems

Eight subsystems make up the drill. The Seed Hopper Assembly stores seed and feeds it down with an agitator that prevents bridging. The Central Metering Unit sets the dose. The Pneumatic Distribution System conveys and splits the seed. Each Coulter Row Unit opens a slot, places seed and closes it. The Following Harrow and Press levels and firms the surface. The Frame and Folding carries everything and folds for transport. The Hydraulic System powers the fan and folding. The Seed-Rate Controller and ISOBUS ties metering to ground speed over ISOBUS.

How pneumatic metering and distribution work

Seed leaves the tank through the Metering Housing onto the Fluted Metering Roller, a fluted roller whose flute volume and rotation speed set the discharge. An operator swaps the Metering Insert Set to match seed size, from fine grass seed at 1 kg/ha up to beans at 400 kg/ha. The Metering Drive Motor turns the roller, and a Metering Shaft Encoder reports its speed so the controller holds the rate as the tractor speeds up or slows.

Metered seed drops into the Venturi Seed Injector, where the airstream from the Centrifugal Fan picks it up. The fan runs at 3000 to 4500 rpm, driven by the Fan Hydraulic Motor off the hydraulic supply. Air and seed travel up to the Air Plenum Manifold and into the Distribution Tower towers, where a baffle divides the flow equally among the outlets. From each outlet a Seed Delivery Hose runs to one row. A Seed Blockage Sensor watches each line and a Plenum Pressure Sensor confirms the plenum holds enough pressure to feed every row.

Materials and construction

The tank is rotomolded polyethylene, UV stabilized for field storage. The Main Toolbar Frame and Folding Wing Section sections are welded box-section steel. The Double-Disc Coulter discs are boron steel for wear life in abrasive soil, riding on sealed Coulter Hub bearings. The Seed Boot is a hard wear-resistant polymer. Delivery hoses are corrugated PVC or polyurethane that resists kinking on the folding wings.

Variants

Mounted drills hang on a category 2 or 3 three-point hitch at 3 to 6 m widths with 18 to 36 rows, suited to smaller tractors and rigid frames. Trailed drills tow on a Drawbar, reach 6 to 12 m, carry larger tanks, and fold on hydraulic wings for road transport. Row spacing of 12.5 to 16.7 cm suits cereals; wider spacing serves row crops. Some drills add a second tank and metering unit so fertilizer is placed with the seed.

Operation and calibration

Before drilling, the operator sets the rate on the ISOBUS Terminal, fits the right metering insert, and runs a static calibration. The Calibration Flap diverts a measured number of metering turns into the Calibration Tray; the weight collected lets the Implement Job Computer correct the roller speed. In the field a Ground Speed Radar measures true ground speed so the rate holds without wheel slip error. Coulter depth is set on the Depth Gauge Wheel and down-pressure on the Coil Spring of each row unit, typically 80 to 200 kg per coulter depending on soil firmness and residue. The Agitator Shaft keeps the tank feeding evenly, and the Seed Level Sensor warns the operator before the tank empties so refilling can be planned at a headland. On wide trailed machines the operator unfolds the Folding Wing Section sections with the Wing Fold Cylinder rams, lowers the row units, and brings the fan up to speed before the first pass so seed conveying is stable from the start. Section control through the Implement Job Computer shuts off groups of rows on headlands and point rows to avoid double sowing.

Maintenance

Grease the Wing Pivot Bushing and Coulter Hub points on schedule. Check Ball Bearing play in the press and gauge wheels and replace worn Double-Disc Coulter discs and Press Wheel tyres each season. Clean the Tank Filter Screen and empty the tank through the Tank Outlet Slide before storage. Inspect the Seed Delivery Hose runs for cracks and the Centrifugal Fan impeller for seed-dust buildup that unbalances it. Verify the Seed Blockage Sensor heads read clean after washing.