referring to fig1 a conventional disk harrow 10 includes a flexible 3 - part frame 12 with a main section 14 , and right and left wing sections 16 and 18 , respectively . a wing - folding function is provided by wingfold hydraulic cylinders 20 and 22 . referring now to fig2 a hydraulic circuit 30 controls fluid flow to and from the cylinders 20 and 22 . circuit 30 includes a pump 32 , a reservoir 34 and a 4 - way , 4 - position detent - held selective control valve 36 which may be mechanically connected to a manually operated control lever 38 . circuit 30 also includes pressure - reducing / relieving valves 40 and 42 which may be reducing / relieving valve model ppdb made by sun hydraulics . lines 41 and 43 connect valve 36 to valves 40 and 42 . valve 40 controls communication of lines 41 and 43 with the head end of cylinders 20 and 22 via line 44 . valve 42 controls communication of lines 41 and 43 with the rod ends of cylinders 20 and 22 via line 46 . valve 36 includes an extend or unfold position 50 , a shut - off position 52 , a retract or fold position 54 and a float position 55 . valve 40 has opposed pressure - operated pilots 56 and 58 and is spring - biased towards its illustrated position by manually adjustable spring 60 . pilots 56 and 58 are connected to lines 43 and 44 , respectively . valve 42 has opposed pressure - operated pilots 62 and 64 which are connected to lines 41 and 46 , respectively . valve 42 is spring - biased to its illustrated position by manually adjustable spring 66 . when valve 36 is moved to the extend position 50 , then line 41 is connected to pump 32 and line 43 is connected to sump 34 . valve 40 communicates a reduced pressure ( 0 - 700 psi , determined by the adjustment of manually adjustable spring 60 ) via line 44 to the head ends of cylinders 20 and 22 . at the same time , pump pressure is communicated to pilot 62 of valve 42 while sump pressure is communicated to pilot 64 . thus , valve 42 will connect the rod ends of cylinders 20 and 22 to sump 36 and the cylinders will extend . when the wings are unfolded and cylinder motion stops , then the amount of downward wing force can be controlled by adjusting spring 60 of valve 40 , which permits a pressure variation of 0 to 700 psi for the pressure in the head ends of cylinders 20 and 22 . if , after the wings are unfolded , it is desired to reduce the downward wing force by pressurizing the rod ends of cylinders 20 and 22 , then control valve 36 should be shifted to and held in its retract position 54 . this pressurizes line 43 and connects sump 34 to line 41 . with line 43 pressurized , valve 40 is held in the position shown so that the head ends of cylinders 20 and 22 are connected to sump . at the same time , pressure - reducing / relieving valve 42 will pressurize line 46 and the rod ends of cylinders 20 and 22 to the pressure determined by pressure - adjust spring 66 ( 0 - 2500 psi ). to fold the wings or retract the cylinders , the pressure - adjusting spring 66 on valve 42 must be adjusted to maximize the pressure in line 46 . then , the control valve 36 is moved to position 54 , whereupon valve 42 connects pump 32 to the rod ends of the cylinders 20 and 22 while valve 40 connects the head ends to sump 34 . thus , with hydraulic circuit 30 , the wings 16 and 18 may be folded or unfolded and the pressure in both the head and rod ends of cylinders 20 and 22 may be adjusted . referring now to fig3 the hydraulic circuit 170 controls the cylinders 120 and 122 . circuit 170 includes a pump 132 , a reservoir 134 and a 4 - way , 4 - position , detent held selective control valve 136 which may be mechanically connected to a manually - operated control lever 138 . control valve 136 has a stop position 152 , an extend position 150 , a retract position 154 and a float position 156 . the hydraulic circuit 170 includes a pair of pressure - reducing / relieving valves 172 and 174 , such as reducing / relieving valve model ppdb , made by sun hydraulics . valves 172 and 174 are connected to one port of control valve 136 via line 141 . valve 172 is preferably factory adjusted so that the maximum pressure in line 144 and in the head end of cylinders 120 and 122 is 750 psi , whereas valve 174 may be operator - adjusted to achieve a desired rod end pressure . both valves 172 and 174 are connected to another port of control valve 136 via line 143 . line 143 is also connected to port 175 of 3 - position switching valve 176 . valve 176 is spring - loaded to an intermediate position 178 by springs 180 and 182 , and is urged to positions 184 and 186 by pressure - operated pilots 188 and 190 , respectively . valve 176 also has ports 192 and 194 . port 192 is connected to pilot 188 via a restriction 189 and is connected to line 196 . pilot 190 is connected to line 143 via a restriction 191 . port 194 is coupled to line 195 . the circuit 170 also includes a two - position valve 200 with a port 202 connected to line 196 , a port 204 connected to valve 174 via line 206 , and a port 208 which is coupled to the rod ends of cylinders 120 and 122 via line 209 . valve 200 is urged towards a position 210 by pilot 212 and towards position 214 by pilot 216 and spring 218 . pilot 212 is connected to port 194 of switching valve 176 and to line 144 via restriction 220 and check valve 222 . pilot 216 is connected to line 196 via restriction 224 . assuming that the cylinders 120 and 122 are retracted , ( and the wings folded ), they may be extended by shifting valve 136 to position 150 , whereupon fluid flows from pump 132 to the head ends of cylinders 120 and 122 via line 141 , valve 172 and line 144 . the cylinders 120 and 122 extend and fluid flows out of the rod ends to the reservoir 134 via line 209 , valve 200 ( position 214 ), valve 176 ( position 178 ), line 143 and control valve 136 . this creates a pressure differential between ports 192 and 175 of valve 176 which shifts valve 176 to position 184 wherein passage 185 vents line 195 to sump . this maintains low pressure at pilot 212 and keeps valve 200 in position 214 , as illustrated . restriction 220 is made small enough to prevent pressurized fluid from bypassing the cylinders 120 and 122 . thus , the return fluid flow from the rod ends to sump bypasses the pressure - reducing / relieving valve 174 . because of this , pressure - reducing / relieving valve 174 can be set to any desired setting and the resulting pressure in line 206 is blocked by valve 200 so that this pressure does not reduce the force which extends the cylinders when control valve 136 is initially in position 150 and oil is flowing . the check valve 222 prevents fluid flow from the rod ends back to the head ends if the control valve 136 is moved to position 152 before complete cylinder extension is achieved so that the wings can be stopped in a partly unfolded position . when the wings are unfolded and the motion of cylinders 120 and 122 stops , the flow across valve 176 ends , thus removing the differential pressure between ports 192 and 175 , and valve 176 shifts back to its center position 178 wherein line 195 is blocked . then , the full 750 psi pressure from line 144 is applied to pilot 212 to shift valve 200 to position 210 wherein the rod ends of cylinders 120 and 122 are connected to valve 174 via port 208 , port 204 and line 206 . at this point , the downward or upward force on wings 16 and 18 is automatically adjusted according to the setting of adjusting valve 174 . to retract cylinders 120 and 122 and fold the wings , valve 136 is shifted to position 154 to pressurize line 143 and pilot 190 . this shifts valves 172 and 174 to the positions shown . it also shifts valve 176 to position 186 and valve 200 to position 214 , whereupon fluid flows from pump 132 to the rod ends of cylinders 120 and 122 via valve 136 , line 143 , valve 176 , line 196 , valve 200 and line 209 , thereby bypassing valve 174 so that full pump pressure is available for wing folding . at the same time , fluid from the head ends of cylinders 120 and 122 flows to sump via line 144 , valve 172 , line 141 and valve 136 . thus , the pressure - reducing / relieving valve 174 ( which controls pressurization of the rod ends ) can be preset to any desired pressure . then , during wing fold or unfold , this preset pressure does not reduce the force tending to extend or retract the cylinders , but when the wings are unfolded and cylinder motion stops , this preset pressure is automatically applied to the rod ends to oppose the head end pressure from pressure - reducing / relieving valve 172 , thus automatically achieving the desired wing force or weight balance . in the stop position 152 of valve 136 , both lines 141 and 143 are blocked . valve 200 assumes position 214 communicating line 209 with blocked line 143 . valve 172 assumes the position shown and communicates line 144 with blocked line 141 . as a result , flow is blocked in lines 144 and 209 and the cylinders 120 and 122 are immobilized . this stop mode is needed to halt motion during a folding or unfolding cycle , such as to prevent a wing from striking an obstruction . in the float position 156 of valve 136 , lines 141 and 143 are both connected to reservoir 134 . valves 172 , 176 and 200 assume the same positions which they assume in the stop mode so that lines 144 and 209 are both communicated with each other and with the reservoir . this allows free motion of the cylinders 120 and 122 . this float mode is useful in the case of a system malfunction or in the case where the disk is operated in soil where no weight transfer is needed . in addition to weight balancing , this invention has other applications in the agricultural implement area . one such application would be disk harrow front - to - rear leveling . front - to - rear leveling is used to control the relative disking depth of the front and rear gangs . disk leveling is important to ensure uniform soil cutout and to maintain a level soil surface across the width of the machine . some current level action disks use a mechanical linkage to control front - to - rear leveling . the linkage utilizes the relative position of the hitch to the main frame to control the compression of the leveling spring which , when relaxed , lets the front gangs penetrate deeper and , when compressed , pulls the front gangs out of the soil . the same effect could be realized if the leveling linkage were removed , a hydraulic cylinder installed between the hitch and main frame and the present balancing system installed to control the position of the cylinder . the system could be set to obtain a level disking job and the same front - to - rear disking depth would be maintained , regardless of the relative position of the hitch to the main frame ( disking over small knolls or through low spots .) another application would be for planting unit down force control . current planting units utilize two extension springs to create a down force to help keep the unit in the soil . this force is not constant and decreases as the planting unit flexes down . the present balancing system would be connected to a hydraulic cylinder which would replace the springs to provide a constant force on the unit . such a system would also be adjustable to compensate for varying soil conditions . while the invention has been described in conjuction with a specific embodiment , it is to be understood that many alternatives , modifications and variations will be apparent to those skilled in the art in light of the aforegoing description . accordingly , this invention is intended to embrace all such alternatives , modifications and variations which fall within the spirit and scope of the appended claims .
a weight - balancing system for a farm implement , such as a disk harrow with foldable wings operated by wingfold cylinders , includes a selective control valve for controlling fluid communication to the head and rod ends of the wingfold cylinders . a pair of pressure - reducing / relieving valves permit individual adjustment of the pressures in both the head and rod ends to achieve the desired balance . in a preferred embodiment , a pilot - operated , two - position valve is connected between the rod ends and one of the pressure - responsive valves . the two - position valve is operated by pressure signals generated by a flow - responsive switching valve connected between the two - position valve and the selective control valve . the switching valve and the two - position valve cooperate to block the pressure - controlled outlet of the one pressure - responsive valve and the rod ends and to bypass return fluid flow from the rod ends to sump when the cylinders are being extended . then , when cylinder motion stops and this return flow ends , the switching valve and the two - position valve are connected to the control pressure outlet of the one pressure - responsive valve to the rod ends to achieve the desired balance .