Hydraulic floating system for downpressure control of seeding tools

An apparatus for operating a ground engaging implement comprising a first double acting hydraulic cylinder means having opposite ends adapted to be connected to a frame means of said apparatus and to said ground engaging implement, said first hydraulic cylinder means having thrust and draw sides;

• a hydraulic circuit containing oil and comprising a mode selection valve having first and second positions;
• a first three-way directional valve adapted for connection to pump means and to reservoir means, said pump means being adapted to supply oil in said hydraulic circuit, a pressure absorption means, actuating means for said mode selection valve, and detection means;
• said mode selection valve being adapted in said first position thereof to connect said thrust and draw sides of said first cylinder means to said first directional valve, wherein in a first position of said first directional valve oil from the pump means is delivered to said thrust side for extending said first cylinder means and thus lowering said implement in the ground, whereas in a second position thereof oil is delivered to said draw side to cause said implement to raise;
• said mode selection valve being adapted in a second position thereof to connect said thrust and draw sides of said first cylinder means to said pressure absorption means for providing substantially equal and constant pressures in both said thrust and draw sides of said first cylinder means with a substantially constant downward force resulting therefrom in view of a smaller piston area on said draw side, whereby said first cylinder means is allowed to extend and retract to follow a surface profile of the ground while said implement maintains a substantially uniform operating depth;
• said detection means being adapted to detect oil pressure variations in said circuit when said first directional valve is in said first position thereof such as to lower said implement in the ground and to cause said actuating means to shift said mode selection valve from said first position to said second position upon reaching an oil pressure in said thrust side which is dependent of an accumulator pressure of said pressure absorption means, whereby substantial oil pressure variations of said accumulator pressure are prevented when shifting from an implement carrying mode to a ground working mode;
• wherein, for raising said implement, said first direction valve is shifted to said second position thereof, oil pressure from said pump means causing said mode selection valve to shift to said first position thereof thereby allowing oil pressure to act on said draw side.