Patent Publication Number: US-2005120693-A1

Title: Brush cutting breakaway system

Description:
Applicant hereby claims priority of provisional patent application No. 60/357,147 filed on Feb. 13, 2002. 
    
    
     BACKGROUND OF THE INVENTION  
      In brush cutting technology it has long been a problem that while cutting brush, when the blades of the mower or cutter head encounter an object that is difficult or impossible to move, the cutter head futilely continues to whack at the object because there is no option for moving the brush cutter head away from the object. If the cutter head continues to hit such an object, there can be damage to the cutter head, engine or other parts of the brush cutting machine. Also, the shock of hitting this type of object is absorbed by the cab of the tractor which is physically difficult for the operator and can damage the frame of the tractor or cutter head frame. This is particularly true in the use of a shoulder or wing type of brush cutting machine, so named because it is adapted to cut the shoulder area of a highway or road, where unknown immovable objects such as rocks or stumps may appear at any time. A shoulder or wing type of brush cutting machine presents a particular problem because the boom in such a brush cutting machine is very short and close to the tractor. It is therefore particularly difficult to fit the mechanics required for a brush cutting breakaway into the smaller space of the boom of the shoulder or wing type of brush cutting machine, requiring improved design to include the necessary mechanics, linkages and pivot points within the space limitations of the shoulder or wing type of brush cutting machine. When the cutter head of a shoulder type brush cutting machine hits an immovable object in the prior art, the brush cutting operator is at the mercy of the situation and after whacking at the object, the tractor of the brush cutting machine would have to be backed up and the immovable object avoided on a second pass. This is time consuming, inconvenient and not fuel efficient for the brush cutting machine. Also, often in the prior art, a directional control valve used as the valve associated with a switch, is a hydraulic-only valve which requires that a lever integral to the valve be manually moved. Thus, it would be necessary to have very hot hydraulic fluid under high pressure within inches of the operator.  
      What is desired then is a simple, convenient and inexpensive way for the brush cutting machine to raise and lower a mower or cutter head, to give the mower or cutter head a forward and aft motion, to respond to the above described situation and for the blades of the mower or cutter head to breakaway from an offending object.  
     SUMMARY OF THE INVENTION  
      In order to overcome problems inherent in the prior art, there has been devised by the present invention multi-part improvements over conventional brush cutting technology and in particular in a shoulder type of brush cutting machine. First, in the present invention the mower or cutter head portion of a brush cutting machine is attached to the boom and a swing tower by a single horizontal pin at each location. This makes it possible to install a vertical pin for the second improvement. In the second improvement of the present invention the boom is attached to the tractor of the brush cutting machine by the single vertical pin. This allows the mower or cutter head portion of the brush cutting machine to have a forward and aft movement, not previously available in the prior art.  
      Third, the present invention includes a swing tower which gives the mower or cutter head portion of a brush cutting machine the ability to swing forward and aft. This is an improvement over the prior art in that prior art brush cutting machines allow the mower or cutter head portion of the brush cutting machine to only be at a ninety-degree angle relative to the tractor portion of the brush cutting machine. The swing tower portion of the present invention allows the mower or cutter head portion of the brush cutting machine to also swing forward and aft, giving the mower or cutter head portion of the brush cutting machine much greater flexibility in moving around a difficult object by moving ahead of or behind the object without having to reposition the brush cutting machine as much as previously required.  
      Fourth, the present invention includes a breakaway cylinder which holds the blades of the mower or cutter head portion of a brush cutting machine at a ninety-degree angle relative to the tractor portion of the brush cutting machine until the cutter head portion comes into contact with an object that is not easily moved. This portion of the multi-part improvements of the present invention is an improvement over the prior art in that in prior art brush cutting machines the mower or cutter head is rigidly positioned at a ninety-degree angle relative to the tractor portion of the brush cutting machine with no other options. The breakaway cylinder of the present invention allows the mower or cutter head to be at an angle other than ninety degrees relative to the tractor portion of the brush cutting machine also providing the brush cutting machine with greater flexibility and maneuvering capabilities.  
      Fifth, the present brush cutting breakaway system of the present invention includes a control, generally in the form of a joystick, used to raise and lower the cutter head of the brush cutting machine within the cab of the brush cutting machine. The joystick controls a fold up cylinder and a lift cylinder. The lift cylinder lifts and lowers the cutter head. This is an improvement over the switches of the prior art, since the single joystick of the present invention replaces as many as four switches in the prior art that would be located in several locations. The joystick is mounted at a position in the cab where all functions are conveniently available at the operator&#39;s finger tips for remotely raising and lowering the cutter head of the brush cutting machine.  
      Sixth, the present invention includes two relief valves, one of which is pre-set to a lower pressure than the other relief valve. The breakaway cylinder operates when there is additional pressure created by the mower or cutter head when the mower or cutter head comes into contact with an object that is not easily moved. The two relief valves are pre-set to bypass under the additional pressure condition created by the mower or cutter head of a brush cutting machine coming into contact with an object that is not easily moved. In this event, as the brush cutting machine carrying the mower or cutter head moves back because of the object, hydraulic pressure is applied to the piston side of the breakaway cylinder whereupon hydraulic fluid is moved from the piston side of the breakaway cylinder to a first of the two relief valves. From the first of the two relief valves, hydraulic fluid moves to the second of the two relief valves and back to the rod side of the breakaway cylinder thereby equalizing pressure in the breakaway cylinder, whereby the breakaway cylinder can operate, moving the cutter head aft to a position of more or less than ninety degrees relative to the tractor portion of the brush cutting machine, avoiding damage to the brush cutter, mower or cutter head, or blades. If the two relief valves were not in the system to equalize hydraulic pressure, the brush cutting machine and mower or cutter head would have no counter balancing pressure and would continue to whack futilely against an offending object, thereby causing damage to the brush cutter engine, mower or cutter head, or blades.  
      Seventh, the present invention includes a control valve, which is a directional control valve that is electrically operated by a switch, generally in the form of a toggle switch, located at the base of the joystick. The toggle switch allows the operator of the brush cutting machine to move the mower or cutter head back to a ninety-degree angle relative to the tractor of the brush cutting machine after the mower or cutter head has been successfully negotiated around a troublesome object. Typically, in the prior art, after the mower or cutter head has cleared the object, the operator would step on a clutch and brake causing the brush cutting machine to stop. Then, the operator would place the transmission in reverse, let off the brake and clutch, moving the tractor back from the troublesome object. Then, the operator would step on the clutch and brake and place the transmission back into the forward position, again letting out the brake and clutch, starting the brush cutting machine forward once again. In using the present invention, however, if all of the breakaway cylinder movement to the aft direction is not used, the operator can move the cutter head further aft, then raise the cutter head, drive forward past the troublesome object, bring the cutter head forward to its original ninety-degree angle relative to the tractor of the brush cutting machine, and then lower the cutter head and continue on, thereby minimizing the need to back up and start again. The breakaway cylinder ordinarily allows the cutter head to swing backward in an arc of around six to eight feet. So, if all of the breakaway cylinder movement is not used in the present invention, the operator can move the cutter head the remaining distance by moving the toggle switch within the tractor. As the operator moves the toggle switch forward causing hydraulic fluid to return to the piston side of the breakaway cylinder, hydraulic fluid is also thereby caused to go back from the rod side of the breakaway cylinder and back into the hydraulic system, which returns the mower or cutter head to its original ninety-degree angle relative to the tractor of the brush cutting machine. This is also an improvement over the prior art in that in the prior art, the mower or cutter head can only stay at a ninety-degree angle relative to the tractor portion of the brush cutter and to clear an object the whole tractor portion of the brush cutting machine must be moved to maneuver around the object. The type of electrically operated valve used in the present invention, an electronic over hydraulic valve, also eliminates the need to have very hot oil under high pressure within inches of the operator, in the cab of the brush cutting machine.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a side environmental view showing the features of the present invention positioned within a brush cutting machine.  
       FIG. 2  is a cross-sectional view taken through lines  2 - 2  of  FIG. 1  showing the arrangement of the parts of the present invention.  
       FIG. 3  is a top view of the present invention showing the brush cutting breakaway in an inactive state.  
       FIG. 4  is a top view of the present invention showing the brush cutting breakaway when it encounters an immovable object and the cutter head is raised from the object.  
       FIG. 5  is a top view of the present invention showing the brush cutting breakaway after the cutter head is being returned to a ninety-degree angle relative to the tractor portion of the brush cutting machine.  
       FIG. 6  is a schematic view showing in general how the two relief valves of the present invention operate.  
       FIG. 7  is a schematic view showing the breakaway cylinder, the two relief valves and the directional control valve as they work together in the present invention.  
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
      Referring now to the drawings in general and to  FIG. 1  in particular, there is shown a side environmental view showing the features of the present invention positioned within a brush cutting machine. The brush cutting machine as seen in  FIG. 1  is shown generally by the number  10  and the brush cutting breakaway of the present invention is shown generally by the number  12 . The brush cutting machine  10  as seen in  FIG. 1  has a flail cutter  14  as the cutter head  16 , the flail cutter  14  being seen from the side in  FIG. 1 , with parts of the present invention shown in dashed lines within. The flail cutter  14  as seen in  FIG. 1  is shown by way of example only, and it is to be understood that the use of any kind of cutter head  16  is within the spirit and scope of the invention. The type of boom  18  shown in  FIG. 1  is a shoulder or wing type boom as used more usually with the present invention, however, it is also within the spirit and scope of the invention to use the present invention with other types of booms, such as a swing boom. The brush cutting machine  10  has two front tires  20  and  22 , as seen most clearly in  FIGS. 3, 4 , and  5 , with only one front tire  20  visible in the side view of  FIG. 1 . The brush cutting machine  10  has two rear tires  24  and  25 , also as seen most clearly in  FIGS. 3, 4 , and  5 , with only one rear tire  24  being visible in the side view of  FIG. 1  as well. Positioned between the showing front tire  20  and the showing rear tire  24  is positioned the boom  18 , which carries some sort of cutter head  16  attached to a first end  26  of the boom  18  closest to the ground  27 , as seen most clearly in  FIG. 2 . The boom  18  is a lift-type boom, which allows the cutter head  16  to be moved up and down by means of the lift cylinder  28  attached to the boom  18 . Within the cab  29  of the tractor portion  30  of the brush cutting machine  10  are the usual steering parts  31  of the tractor, some are not shown in  FIG. 1 , and a switch  32 , generally in the form of a toggle switch  33 , and a control  34 , generally in the form of a joystick  35 . One of the purposes of the toggle switch  33 , is to allow the operator of the brush cutting machine  10  the ability to move the cutter head  16  to an angle of ninety degrees relative to the brush cutting machine  10 . One of the purposes of the joystick  35  is to operate the lift cylinder  28  to thereby lift and lower the cutter head  16 . The single joystick  35  of the present invention replaces as many as four switches in the prior art that would be located in various locations. The joystick  35  is mounted at a position in the cab  29  where all functions are conveniently available for remotely raising and lowering the cutter head  16  of the brush cutting machine  10 . The toggle switch  33  is in the same general location as the joystick  35 , generally at a convenient location to the operator. The toggle switch  33  is usually positioned at the base  36  of the joystick  35 , but another convenient location would also be within the spirit and scope of the invention.  
      Referring now to  FIG. 2  of the drawings, there is shown a cross-sectional view taken through line  2 - 2  of  FIG. 1  showing the arrangement of the parts of the present invention. The multi-part improvements of the present invention include first horizontal pins  37  and  38 , the first horizontal pin  37  attaches the cutter head  16  to the boom  18 , and the second horizontal pin  38  attaches the cutter head  16  to a swing tower  39 , a third vertical pin  40 , which is a forward and aft pivot  41 , that attaches the boom  18  to the tractor portion  30 , and the swing tower  39 , as seen most clearly in  FIG. 2 . The swing tower  39  is attached to the boom  18  at the end  42  of the boom  18  opposite to the first end  26  of the boom  18  that has the cutter head  16  attached. The lift cylinder  28  hinges on the upper end  42  of the boom  18  and raises the cutter head  16  up and down. The boom  18  is connected to the tractor portion  30  of the brush cutting machine  10  by means of an upper mounting plate  43  and a lower mounting plate  44  positioned also around the forward and aft pivot  41 . The swing tower  39  of the present invention allows the cutter head  16  of the brush cutting machine  10  to swing forward and aft giving the brush cutting machine  10  greater flexibility and maneuvering capabilities. The swing tower  39  includes the forward and aft pivot  41  connected at its first end  45  to a position near the bottom  46  of the swing tower  39 , and connected at its second end  47  to the tractor portion  30  of the brush cutting machine  10 . The swing tower  39  does not allow the cutter head  16  to go in the aft direction far enough that would allow the cutter head  16  to come into contact with the rear tire  24  of the brush cutting machine  10 . Positioned near the top  48  of the swing tower  39  is a fold up cylinder  49 . The fold up cylinder  49  has the function of allowing the cutter head  16  to be moved up and down, or to be stood up straight. The fold up cylinder  49  hinges on the first horizontal pin  37  and lifts and lowers the cutter head  16 .  
      The multi-part improvements of the present invention further includes a breakaway cylinder  50 , as seen most clearly in  FIGS. 2, 3 ,  4 , and  5 , which is attached to the second end  47  of the forward and aft pivot  41 . The breakaway cylinder  50  holds the mower or cutter head portion  51  of the brush cutting machine  10  at a ninety degree angle relative to the tractor portion  30  of the brush cutting machine  10  until the cutter head portion  51  comes into contact with an object  52 , as seen in  FIGS. 4 and 5 , that is not easily or is impossible to be moved. When the cutter head portion  51  hits the object  52 , the breakaway cylinder  50  trips causing unequal hydraulic pressure within the brush cutting breakaway  12 , and as the hydraulic pressure equalizes within the present invention, it allows for the cutter head  16  to move at an angle other than ninety degrees relative to the brush cutting machine  10 .  
      Another aspect of the present invention includes the two relief valves  54  and  55 , as seen most clearly in  FIGS. 4, 5 , and  6 , and as explained with reference to  FIG. 6 , that has the first relief valve  54  pre-set at a pressure lower than the second relief valve  55  so that it bypasses when there is the higher than normal hydraulic pressure created in the breakaway cylinder  50  when the cutter head  16  hits an immovable object  52 , as seen in  FIGS. 4 and 5 . At this time, hydraulic pressure increases at the inlet sides  56  and  57  of the two relief valves  54  and  55 , as seen most clearly in  FIG. 6 . When the pressure reaches the pressure set point of the first relief valve  54  of the two relief valves  54  and  55 , hydraulic fluid circulates from the piston side  58  of the breakaway cylinder  50  to the rod side  59  of the breakaway cylinder  50 , as seen in  FIGS. 4 and 7 , allowing the cutter head  16  to move to an angle other than ninety degrees relative to the brush cutting machine  10 , as seen in  FIGS. 2 and 4 . Since the piston side  58  of the breakaway cylinder  50  holds a larger volume of hydraulic fluid than the rod side  59  of the breakaway cylinder  50 , the relief valve  55  of the two relief valves  54  and  55  is connected to a line  60  that allows the excess hydraulic fluid from the piston side  58  of the breakaway cylinder  50  to return to the hydraulic reservoir  61 , as seen in  FIG. 7 . This transfer of hydraulic fluid within the breakaway cylinder  50  allows the breakaway cylinder  50  to operate. This allows the cutter head  16  to move to an angle other than ninety degrees relative to the tractor portion  30  of the brush cutting machine  10  and then the operator can return the cutter head  16  to an angle of ninety degrees relative to the tractor portion  30  of the brush-cutting machine  10 . This aspect of the present invention is most clearly shown in  FIGS. 6 and 7 .  
      A further aspect of the present invention includes the switch  32 , generally in the form of a toggle switch  33 , which operates a control valve  62 , generally in the form of a directional control valve  63 , as seen most clearly in  FIG. 4 . When the operator in the interior  64  of the cab  29  of the tractor portion  30  of the brush cutting machine  10 , as seen most clearly in  FIG. 1 , moves the switch  32  forward, the directional control valve  63 , as seen most clearly in  FIGS. 4, 5 , and  7 , directs hydraulic flow to the piston side  58  of the breakaway cylinder  50  and allows hydraulic fluid to go back from the rod side  59  of the breakaway cylinder  50  and back into the hydraulic reservoir  61 , as seen most clearly in  FIG. 5 . The cutter head  16  is thereby returned to a ninety-degree angle relative to the tractor portion  30  of the brush cutter  10 . The type of directional control valve  63  used in this aspect of the present invention is an electronic over hydraulic valve used with electronic switches. The electric current supplied by the switch  32  activates a solenoid  66  or  68 , as seen in  FIG. 7 , that opens or closes as the electrical current is applied by moving the switch  32  forward or backward, as seen most clearly in  FIGS. 4 and 5 . When the control  32  is in the neutral position, there is no electrical current directed to the first side  70  of the directional control valve  63 , thus it is closed. This aspect of the present invention is best shown in  FIG. 7 . This particular type of directional control valve  63  is used in this invention because when there is an electronic over hydraulic valve used, it is not required that an operator manually use a lever to activate it, thereby eliminating the necessity of having very hot hydraulic fluid under high pressure within inches of the operator, in the cab  29  of the brush cutting machine  10 . It would however, be within the spirit and scope of this invention to use a manually controlled lever instead of an electronic over hydraulic valve.  
       FIG. 3  is a top view of the present invention showing the brush cutting breakaway in an inactive state.  
       FIG. 4  is a top view of the present invention showing the brush cutting breakaway  12  when it encounters an immovable object  52  and the cutter head  16  is raised from the object  52 . It can be seen in  FIG. 4  that as the cutter head  16  encounters an immovable object  52 , the forward and aft pivot  41  which is attached to the swing tower  39  and held at a ninety degree position relative to the tractor portion  30  by the breakaway cylinder  50 , causes the cutter head  16  to be moved in the aft direction as the tractor portion  30  moves by the object  52 . This motion by the forward and aft pivot  41  causes the breakaway cylinder  50  to collapse, whereby the additional hydraulic pressure thus created moves through the first relief valve  54  as previously described thereby equalizing hydraulic pressure in the brush cutting breakaway  12 . The collapse of the breakaway cylinder  50  is controlled by the two relief valves  54  and  55  because the two relief valves  54  and  55  can be pre-set at any desired pressure that would allow the piston  72  of the breakaway cylinder  50  to move.  
       FIG. 5  is a top view of the present invention showing the brush cutting breakaway  12  after the cutter head  16  is being returned to a ninety-degree angle relative to the tractor portion  30 . In  FIG. 5  it can be seen that after the cutter head  16  has moved away from the immovable object  52 , the reverse of what happens in  FIG. 4  happens in  FIG. 5 . Thus, the forward and aft pivot  41  attached to the swing tower  39  allows the cutter head  16  to be returned to the ninety-degree angle position relative to the tractor portion  30  of the brush cutting machine  10  that it was in prior to encountering the object  52 . When the operator in the interior  64  of the cab  29 , as seen in  FIG. 1 , of the tractor portion  30  of the brush cutting machine  10  moves the toggle switch  33  forward, hydraulic fluid is thus put back on the piston side  58  of the breakway cylinder  50  forcing hydraulic fluid from the rod side  59  of the breakaway cylinder  50 , which moves the piston  72  of the breakaway cylinder  50  toward the rod side  59  of the breakaway cylinder  50 . The hydraulic fluid then moves from the rod side  59  of the breakaway cylinder  50  through the inlet side  57  of the second relief valve  55  and back into the hydraulic reservoir  61 , as seen in  FIGS. 6 and 7 . This process can also be seen in  FIG. 7 . In operation then, as the operator moves the toggle switch  33  in the direction that is desired in order to move the cutter head  16 , a measured amount of voltage is sent to the directional control valve  63  on the first side  70  of the directional control valve  63 , flowing through to the second side  74  of the directional control valve  63 . The directional control valve  63  is opened a measured distance in relation to the measured voltage received from the first side  70  of the directional control valve  63 . So, the directional control valve  63  works like a rheostat in that the greater distance the toggle switch  33  is moved, the greater distance the directional control valve  63  is opened. When moving the toggle switch  33  in the direction that will open the directional control valve  63 , hydraulic fluid is allowed to flow from the directional control valve  63  through the two relief valves  54  and  55  and into the breakaway cylinder  50 , thereby moving the cutter head  16  to the desired cutting position. When the distal end  76  of the cutter head  16  comes against an immovable object  52 , pressure builds on the piston side  58  of the breakaway cylinder  50  causing the hydraulic fluid on the piston side  58  of the breakaway cylinder  50  to move to the rod side  59  of the breakaway cylinder  50 . When this occurs, the distal end  76  of the cutter head  16  has moved rearward. To return the cutter head  16  back to the position of ninety degrees relative to the tractor portion  30  of the brush cutting machine  10 , the toggle switch  33  is moved in the appropriate direction to correspond to the direction that is desired to move the cutter head  16 .  
      Referring now to  FIG. 6 , there is shown a schematic view of the two relief valves  54  and  55  of the present invention, showing the two relief valves  54  and  55  in a static state and showing generally how the two relief valves  54  and  55  of the present invention operate. The outer perimeter  78  of the schematic of  FIG. 6  indicates that there are two relief valves  54  and  55  in a single block. As indicated hereinbefore, as pressure builds in the first valve  54 , hydraulic fluid relieves to the other valve  55 , so that higher pressure relieves hydraulic fluid to the lower side. The first relief valve  54  is open all the time until pressure equalizes between the two relief valves  54  and  55 , then both relief valves  54  and  55  close. The dashed lines  80  and  81  in  FIG. 6  represent pilot lines where internal pressure readings are made at the inlet sides  56  and  57  of relief valves  54  and  55  respectively. Pressure against the arrow  82  in the first relief valve  54  works against the spring  84  of the first relief valve  54  and then connects the inlet side  56  of the first relief valve  54  to the outlet side  85  of the first relief valve  54 . Similarly, the pilot line  81  connotes that pressure is applied against the arrow  83  in the second relief valve  55  which works against the spring  86  in the second relief valve  55  to thereby connect the inlet side  57  of the second relief valve  55  to the outlet side  87  of the second relief valve  55 . The purpose of the two relief valves  54  and  55  is to bypass under the additional pressure condition created by the cutter head  16  of a brush cutting machine  10  coming into contact with an object  52  that is not easily moved. It is within the spirit and scope of the invention that any arrangement of parts that will accomplish this objective can be used. The two relief valves  54  and  55  as shown in  FIG. 6  are used by way of example only. In the two relief valves  54  and  55  as shown in  FIG. 6 , it is necessary that the pressure in the first relief valve  54  be set at a lower pressure than the pressure in the second relief valve  55 . The springs  84  and  86  associated with the relief valves  54  and  55  indicate that the pressure setting for each relief valve  54  and  55  is adjustable. As the cutter head  16  of the brush cutting machine  10  comes into contact with an immovable object  52  the cutter head  16  moves back from the object  52 , as seen in  FIG. 5 . In this event, hydraulic fluid that has come into the inlet side  56  of the first relief valve  54  from the piston side  58  of the breakaway cylinder  50 , through the first relief valve  54  and out from the outlet side  85  of the first relief valve  54  circulates to the rod side  59  of the breakaway cylinder  50  until the hydraulic fluid cannot push the piston  72  of the breakaway cylinder  50  any farther, as seen most clearly in  FIG. 7 . Then, overflow hydraulic fluid relieves from the piston side  58  of the breakaway cylinder  50  to the inlet side  57  of the second relief valve  55  and back through the outlet side  87  of the second cylinder  55  and to the system as symbolized by the hydraulic reservoir  61 .  
      Referring now to  FIG. 7  of the drawings, there is shown a schematic view of the two relief valves of  FIG. 6 , the directional control valve, and the breakaway cylinder of the present invention. The purpose of the directional control valve  63  is to respond to movement of a toggle switch  33  within the cab  29  of the tractor portion  30  to move the mower or cutter head  16  back to a ninety-degree angle relative to the tractor portion  30  of the brush cutting machine  10  after the mower or cutter head  16  has been successfully negotiated around a troublesome object  52 , as seen in  FIGS. 4 and 5 . In a manner similar to that stated with regard to the two relief valves  54  and  55 , it is within the spirit and scope of the invention that any arrangement of parts that will accomplish the above objective can be used and the directional control valve  63  as shown in  FIG. 7  is also used by way of example only. In  FIG. 7  the directional control valve  63 , which is an electrically operated valve, is used in combination with the two relief valves  54  and  55  as shown and described with reference to  FIG. 6 . If the brush cutting breakaway  12  of the present invention, as seen in  FIG. 5 , is in neutral, the solenoids  66  and  68  are de-energized and all ports  88 ,  90 ,  92  and  94  are blocked, whereby the directional control valve  63  is in its center position  96 . The A side  98  of the directional control valve  63  is also marked with a P on the input side  100  of the directional control valve  63  to indicate pressure or the source of hydraulic flow. And the B side  102  of the directional control valve  63  is also marked with a T to indicate tank or hydraulic fluid return. Upon activation, as when the toggle switch  33  in the cab  29 , as seen in  FIG. 1 , is moved forward, the A side solenoid  66  in the directional control valve  63  works against the spring  104  on the B side  102  of the directional control valve  63 . Therefore, as the A side solenoid  66  caused movement against the spring  104  on the B side  102 , the directional control valve  63  moved to the A position  106  which is on the A side  98  of the directional control valve  63 , where P is connected to A and B is connected to T, allowing hydraulic fluid flow through the A pipe  108  to the two relief valves  54  and  55  and further flows as described with reference to  FIG. 6 . The opposite is true when the toggle switch  33  in the cab  29 , as seen in  FIG. 1 , is moved rearward. That is, the B side solenoid  68  in the directional control valve  63  works against the spring  110  on the A side  98  of the directional control valve  63 . As the B side solenoid  68  causes movement against the spring  110  on the A side  98 , the directional control valve  63  moves to the B position  112  which is on the B side  102  of the directional control valve  63 , where T is connected to A, and P is connected to B, allowing hydraulic fluid flow through the B pipe  114  to the breakaway cylinder  50 .