Hydraulic height sensing system with cylinder by-pass

摘要

An agricultural harvesting machine having a plurality of independently supported row crop harvesting units is provided with a hydraulically operated vertical positioning mechanism for adjusting the height of the units in accordance with ground surface variations. Each unit is provided with a ground-engaging feeler mechanically coupled to a control valve which adjustably varies the hydraulic fluid flow to a single acting unit lift cylinder. The cylinder includes fluid bypass capabilities to permit continued hydraulic fluid flow upon full extension of the cylinder piston and thereby avoid a fluid system pressure and consequent temperature increase.