Hydraulic Draft Control: The Plough That Rises When the Soil Gets Hard

Harry Ferguson's linkage made a mounted plough follow the steering and press the tractor's rear wheels down. The next step was to make the tractor hold the plough in the ground by itself. US 2,118,180, *Tractor for Agricultural Implements*, filed 27 January 1937 (British priority 5 February 1936) and granted 24 May 1938, lets the draft of the implement work the hydraulic valve. The top link pushes on a heavy spring. When the plough bites into harder ground the draft rises, the spring compresses, and the valve lets oil into the pump, which lifts the implement a little until the draft falls back and the valve returns to its "dead point". When the draft falls, the release port opens and the plough sinks back. The valve works on the pump's suction side so the oil is not churned under pressure all day. This rung simulates draft control against position control, measures a tine's draft against depth in a sand tray, and builds a spring top link that shows the signal.