HYDRAULISCHE STUURINRICHTING VOOR HET REGELEN VAN DE STAND VAN EEN TREKARM VAN EEN LANDBOUWWERKTUIG

A pull-type mobile harvesting machine includes a header supported on a main frame and an arch-like tongue swingably connected to the main frame and extending forward over the header for pivoting connection to a tractor. A double-acting hydraulic steering cylinder controlled from the tractor is connected between the frame and tongue for swinging the tongue relative to the frame while the machine is advancing so that the machine is displaced laterally selectively between a range of operating positions, offset relative to the tractor, and transport positions, generally immediately behind the tractor. A shut-off valve in one of the hydraulic lines to the cylinder makes it possible to trap oil in one side of the cylinder in any given condition of cylinder extension, thus locking the tongue in a given position relative to the frame and also preventing flow of oil to the cylinder so that inadvertent manipulation of a cylinder control valve at the tractor does not cause accidental swinging of the tongue and lateral displacement of the machine relative to the tractor.