Hydraulic cylinders are frequently used to control transport wheel structure position for seeding and tillage equipment machine frames. Typically, the cylinders are at full extension at maximum frame height and at full retraction at minimum frame height. At full and partial retraction, frame mounted tillage or seeding devices are engaged with the soil. Precise and repeatable control of cylinder length is required to maintain desired soil engagement depth. Other agricultural implements and other cylinder operated devices have similar hydraulic cylinder stroke control requirements.
Available structures for setting hydraulic cylinder stroke length include valves that control the amount of hydraulic fluid within the cylinder. Hydraulic valve activation variations or hydraulic seal leakage adversely affects precision and repeatability of such structures.
Mechanical stops placed on the linkages between the hydraulic cylinders and the wheel structure are also used to control frame height. Such a linkage arrangement is shown, for example, in U.S. Pat. No. 5,988,293. The increased loads that must be transmitted through the linkage increase the strength requirements of the linkage.
Other mechanical devices include screw type stops or removable devices of multiple thickness selectively clipped over the cylinder rod are also commonly available. Clip on devices lack preciseness and easy selectability of operating position and can be easily lost or misplaced.