Abstract:
Novel Counterbalance valves, more particularly, to counterbalance valves that provide hold, capture, and motion control benefits of prior art CB valves while improving upon one or more performance characteristics of current CB valves are herein disclosed. The novel counterbalance valves are useful, inter alia, for providing good system stability across a range of load pressures and/or reducing power consumption (improving energy efficiencies) as compared with prior art devices.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims benefit of priority thereto under 35 U.S.C. Section 119(a-d) to U.S. Provisional Application No 62/051,121 filed Sep. 16, 2014, the disclosure of which is hereby incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to the field of counterbalance, load control, motion control and overcenter valves. 
     BACKGROUND 
     Prior Art CounterBalance Valves 
     Counterbalance (CB) valves are applied in various hydraulic circuits and are used to hold, capture, or control the motion of loads. Essentially, CB valves are modulating devices that allow free flow from an inlet valve port to a load port and then block reverse flow until a load pressure, pilot pressure, or combination of load and pilot pressure open the valve. Modern CB valves control loads and minimize instability (e.g., chattering) in machines. As a result, CB valves are frequently incorporated in positioning circuits, load-holding and purging circuits, and regenerative circuits. Examples of machines that utilize CB valves are boom lifts, forklifts, industrial drills, and excavators, among many other machines. 
     The modulation of conventional CB valves is a function of both load pressure and pilot pressure. This characteristic ensures loads must be driven from a fluid power source, even when loads are overrunning.  FIG. 3  graphically depicts how pilot pressure decreases as load pressures increases. In particular, the graph of  FIG. 3  illustrates a prior art CB valve in which pilot pressure I changes as load pressure II rises steadily with time to a predetermined maximum setting III. On the other hand, pilot pressure would rise if load pressure fell steadily over time. 
       FIG. 1  illustrates a prior art, three port, pilot-to-open CB valve  1001  having a valve body  1038 , a load port  1004 , a valve port  1008 , and a pilot port  1012 . In operation, CB valve  1001  serves as a counterbalance and holds a load at load port  1004 . If the load pressure applied at load port  1004  exceeds the spring force created by springs  1020 , then piston  1032  moves axially to compress springs  1020 . Such axial movement of the piston to an open position creates a flow path between load port  1004  and valve port  1008 , or put differently, it provides a relief function. Because having only a relief function is inefficient, a pilot function is also provided. The pilot function allows a user to apply pilot pressure to open a flow path between the load port  1004  and the valve port  1008 . As a result, pressure at either the load port or the pilot port can be used to open a flow path between the load port and the valve port. A combination of pressure at the load port and the pilot port will also open a flow path. 
     Traditional CB valves have a fixed or adjustable setting. Fixed setting valves are typically set by the manufacturer and are not adjustable. Adjustable CB valves feature adjustment screws so the setting can be changed in the field. While settings can be set in the field, settings are not typically changed when the valves are being operated. CB valves with adjustment screws are illustrated in  FIGS. 1 and 2 . Adjusting CB valves generally involves rotating adjusting screw  1024  when the CB valve is not in operation. Rotating adjusting screw  1024  changes the compression of springs  1020 , thus changing the setting of the CB valve. More specifically, when springs  1020  are in an uncompressed position, the CB valve allows piston  1032  to slide to an open position at a low load pressure. In contrast, when the springs are adjusted to a compressed position, a greater load pressure is necessary to move the piston to an open position. 
       FIG. 2  illustrates a prior art, four port, pilot-to-open CB valve  1036 . CB valve  1036  is vented to eliminate the effect back pressure on the valve port has on the operation of the valve. In particular, CB valve  1036  is provided with drain or vent port  1016  that eliminates sensitivity to back pressure. 
     Drawbacks of Prior Art Counterbalance Valves 
     Although CB valves have highly desirable qualities in the hold, capture, and motion control of loads in hydraulic circuits, CB valves also have drawbacks. CB valves must be set for the maximum load that a machine must control. One significant drawback is increased energy consumption in machines that utilize conventional CB valves, when load pressures vary significantly over the operating cycle. Another drawback is increased wear in machines and machine components when high pilot pressures are frequently needed to control light loads. Although energy efficiency and wear and tear have long been important considerations in machine design, the current economic, environmental, and political atmosphere has led to an extraordinary demand for innovations that improve efficiency and longevity of machines, including machines that incorporate CB valves. 
     Both increased energy consumption and wear of machines operating with traditional CB valves are owed, at least in part, to CB setting and pilot ratio. First, for control and safety purposes, to maintain control of maximum anticipated loads, CB valves are typically set above the maximum load pressure that could be generated. In many machines, however, maximum loads may be encountered infrequently. That is, the majority of time during which a CB valve is in operation, the load pressure is some amount less than the CB setting. During that time, an increase in pilot pressure is necessary to compensate for the difference between the valve setting and the load pressure. Second, and of significant importance, up to half of the working cycle of many CB valves is dedicated to the control of nominal loads, where machines are unloaded. This means that for up to half of its working cycle, and sometimes more, a CB valve may require use of full or high pilot pressure. 
     By way of example, a forklift may be used to raise a full pallet, where it is unloaded and then lowered completely empty. Lowering the empty fork typically requires high pilot pressure. Generating high pilot pressure, of course, necessitates the use of high horsepower and energy. In a forklift, significant pilot pressure, and energy, may be required when lowering any load less than a full load. 
     CB valve adjustments to improve stability of load circuit typically adversely affect energy efficiencies of the machine. Conversely, adjustments to improve energy efficiencies raise the likelihood that increased instabilities in the circuit will occur, especially at elevated external load pressures. 
     For example, when the directional or proportional valve is opened to move the cylinder, the inlet pressure opens the counterbalance valve on the outlet of the cylinder. At high load pressures, the counterbalance valve setting may fall too far, setting off an oscillation in the circuit (“chirping”). The typical remedy to this circuit behavior is to employ valves with a lower pilot ratio. However, the disadvantage of the lower pilot ratio is that an increased pilot pressure is required to move the cylinder. Routinely running at higher pressures means higher energy consumption. Any attempts to increase pilot ratio will raise the potential for instability at higher load. Thus, the selection of counterbalance valves represents a compromise between stability (low pilot ratio) and efficiency (lower required pilot pressure, high pilot ratio). 
     More recent counterbalance valves, such as those reported in US Patent Application Publication No. 2013/0233409, are provided with load-sensing, hydromechanically setting features. The valve relief setting changes dynamically based on the load pressure at the load port of the counterbalance valve. US Patent Application Publication No. 2013/0233409 is hereby incorporated herein by reference in its entirety. 
     As a result, there is a real need for devices that provide the hold, capture, and motion control benefits of current CB valves while improving upon one or more performance characteristics of current CB valves. There is also a need for devices that provide good system stability across a range of load pressures while reducing power consumption (improving energy efficiencies) as compared with prior art devices. The invention is directed to these and other important ends. 
     BRIEF SUMMARY 
     One or more of the preceding drawbacks of currently available CB valves are improved, and an advance is made in the art by a novel counterbalance valve. According to one aspect of the present invention, a CB valve is provided that reduces the likelihood of oscillation instabilities in the hydraulic circuit under high load conditions while reducing overall energy consumption at lower loads. 
     According to another aspect of the present invention, a counterbalance valve is provided that operates with a low gradient when load pressure is high and pilot pressure is low. 
     According to another aspect of the present invention, a counterbalance valve is provided that operates with a high gradient when load pressure is low and pilot pressure is high. 
     According to another aspect of the present invention, a counterbalance valve is provided that operates with a low gradient when load pressure is high and pilot pressure is low and operates with a high gradient when load pressure is low and pilot pressure is high. 
     According to yet another aspect of the present invention, the CB valve preload is adjustable over a range of load conditions. 
     According to yet another aspect of the present invention, the CB valve has an inner spring and an outer spring, wherein preload on both springs is adjustable. 
     According to another aspect of the invention, the counterbalance valve includes a pilot sleeve that assists the main piston spacer in compressing the inner spring when pilot pressure exceeds outer spring preload. 
     According to another aspect of the invention, the counterbalance valve has a further reduced setting of the valve by a fixed pressure when pilot pressures are very low without movement of the load. 
     Advantages of herein disclosed valves over existing CB valves may include their adjustability resulting in higher overall efficiency, reduced exposure of seals to load pressure that can result in lower seal failure rates, flatter relief curves, smaller outer diameters for valve housing and/or less expensive parts. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a cross-sectional side view of a prior art, three-port counterbalance valve; 
         FIG. 2  illustrates a cross-sectional side view of a prior art, four-port counterbalance valve at minimum setting; 
         FIG. 3  graphically illustrates the changes in pilot pressure where load pressure rises steadily with time in a prior art CB valve; 
         FIG. 4  illustrates a cross-sectional side view of a prior art, three-port dynamically adjusting counterbalance valve at minimum setting and in a seated or closed condition; 
         FIG. 5  illustrates a cross-sectional side view of a three port, dual pilot counterbalance valve according to an aspect of the present invention, with no load (or minimal load) and no pilot pressure. 
         FIG. 6  illustrates a cross-sectional side view of a three port, dual pilot counterbalance valve according to an aspect of the present invention, where load pressure is sufficient to shift piston  100 , Spacer  60 , and poppet  90  until poppet  90  comes into contact with pin  200  and where there is insufficient pilot pressure to move pilot sleeve  65 ; 
         FIG. 7  illustrates a cross-sectional side view of a three port, dual pilot counterbalance valve according to an aspect of the present invention, where  FIG. 6  valve experiences sufficient pilot pressure to compress outer spring  45  and move pilot sleeve into contact with a shoulder of piston spacer  60 ; 
         FIG. 8  illustrates a cross-sectional side view of a three port, dual pilot counterbalance valve according to an aspect of the present invention, where  FIG. 6  valve experiences sufficient pilot pressure to compress outer spring  45  and assist piston spacer  60  in compressing inner spring  50 ; 
         FIG. 9  illustrates a cross-sectional side view of a three port, dual pilot counterbalance valve installed in a manifold body  7  according to an aspect of the present invention; 
         FIG. 10  illustrates a cross-sectional side view of a triple pilot counterbalance valve according to an aspect of the present invention, at minimum setting and seated or closed condition and pilot ratio is at high setting; 
         FIG. 11  illustrates a cross-sectional side view of a triple pilot counterbalance valve according to an aspect of the present invention, at an intermediate setting, where pilot pressure is sufficient to partially compress intermediate spring, and pilot ratio is at low setting; 
         FIG. 12  illustrates a cross-sectional side view of a triple pilot counterbalance valve according to an aspect of the present invention, at an intermediate setting where pilot pressure is sufficient to fully compress intermediate spring and outer spring is at low pilot ratio-high pilot ratio crossover point; 
         FIG. 13  illustrates a cross-sectional side view of a triple pilot counterbalance valve according to an aspect of the present invention, where pilot pressure is sufficient to assist compression of inner spring intermediate spring and pilot ratio is at high setting; 
         FIG. 14  graphically illustrates a comparison between prior art CBCA counterbalance valves and two settings of dual pilot valves of an aspect of the present invention, demonstrating the improved power efficiencies of dual pilot valves over prior art counterbalance valves; 
         FIG. 15  graphically illustrates the performance of a dual pilot valve of an aspect of the present invention at two different mechanical settings; 
         FIG. 16  graphically illustrates a comparison of efficiencies for standard CBCA valves versus dual and triple pilot valves of aspects of the present invention at three different hydraulic fluid flow rates; 
         FIG. 17  graphically illustrates a plot of load pressure versus pilot pressure for  4  prior art counterbalance valves; 
         FIG. 18  illustrates a cross-sectional side view of a three port, triple pilot counterbalance valve installed in a manifold body  207  according to an aspect of the present invention. 
         FIG. 19  graphically illustrates a plot of load pressure versus pilot pressure for a prior art counterbalance valve at four different constant flows. 
         FIG. 20  graphically illustrates a plot of load pressure versus pilot pressure for an exemplary triple pilot valve of the present invention at the same four constant flows illustrated for the prior art counterbalance valve employed in  FIG. 19 . 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description and the appended drawings describe and illustrate exemplary embodiments of the invention solely for the purpose of enabling one of ordinary skill in the relevant art to make and use the invention. As such, the detailed description and illustration of these embodiments are purely exemplary in nature and are in no way intended to limit the scope of the invention, or its protection, in any manner. It should also be understood that the drawings may not be to scale and in certain instances details have been omitted, which are not necessary for an understanding of the present invention, such as conventional details of fabrication and assembly. 
     Definitions 
     Chattering: undesirable and uncontrolled opening and closing of a valve resulting in poor valve modulation. 
     Load Pressure (P load ): load applied to the load port. 
     Pilot Pressure (P pilot ): pressure required on the pilot port to open the valve. 
     Pilot Ratio (R): relief area divided by pilot area or ratio that acts as a multiplier to reduce the mechanical setting of a valve. 
     Setting (S): load pressure at which the valve begins to unseat or open. 
     Parts List 
     
         
           1  Load Port  1   
           2  Valve Port 
           3  Pilot Port 
           5  Dual Pilot CB Valve Body 
           7  Manifold 
           10  Guide Cap 
           15  Adjust Screw Lock Nut 
           20  Adjusting Screw 
           25  Adjusting Nut 
           30  Spring Adjust Spacer 
           35  Adjusting Screw Seals 
           40  Cap Seal 
           45  Outer Spring 
           50  Inner Spring 
           55  Pin 
           60  Piston Spacer 
           65  Pilot Sleeve 
           70  Pilot Spring Spacer 
           75  Intermediate Spring 
           80  Retainer 
           85  Wire Retaining Ring 
           90  Poppet 
           95  Check Spring 
           100  Piston 
           105  Sleeve 
           110  Nose O-Ring Seals 
           115  Internal O-Ring Seal A 
           120  Sleeve Retaining Ring 
           125  Internal O-Ring Seal B 
           130  Spring Chamber 
           135  Internal O-Ring Seal C 
           140  Internal Seal 
           145  Outer O-Ring Seal D 
           150  Internal Sleeve Seal 
           155  Wire Stop Ring 
           160  Setting Control Region 
           165  Main Stage Region 
           166  Shoulder of Adjusting Screw 
           167  Shoulder of Piston Spacer 
           168  Shoulder of Pilot Spring Spacer 
           169  Pilot Stage Region 
           170  Internal O-Ring for Spacer B 
           175  Internal O-Ring for Piston 
           180  Internal O-Ring E 
           185  Internal O-Ring F 
           190  External O-Ring for Lock Nut 
           195  Internal O-Ring for Lock Nut 
           200  Spacer B 
           205  Manifold 
           206  Triple Pilot CB Valve Body 
       
    
     In certain embodiments of the present invention, adjustable dual pilot ratio valves are provided that employ a pilot pressure sleeve that assists in valve opening. When pilot pressure exceeds an outer spring preload force, the sleeve is able to assist the main piston spacer in overcoming biasing spring forces and compressing an inner spring in the valve. These dual and triple pilot ratio valves have the advantage of lower required pilot pressure to control loads, resulting in increased energy efficiency. 
     In other embodiments, the invention as disclosed provides dual and triple pilot ratio valves having low pilot ratios in areas where instability of the hydraulic circuit may occur. 
     In still other embodiments, the invention as disclosed provides dual and triple pilot ratio valves having a higher pilot ratio to save energy when the cylinder/motor has a high inlet and a low outlet pressure. 
     In certain embodiments, the invention as disclosed provides a pilot sleeve for higher pilot ratios that can be incorporated in different existing counterbalance valve designs. 
     In other embodiments, the invention provides triple pilot ratio valves that operate similarly to the disclosed dual pilot ratio valves, but give additional savings in energy efficiency as a result of reductions in CB valve setting by a fixed pressure when pilot pressures are very low or when the load is not yet moved. 
     Exemplary Embodiments 
     Referring to the drawings,  FIGS. 5-9  depict an illustrative embodiment of a dual pilot CB valve according to the present invention. CB valve  6  is provided with a valve body  5 , a load port  1 , a valve port  2 , and a pilot port  3 .  FIG. 9  provides an illustration of CB valve  6  installed in a manifold  7 .  FIGS. 10-13  depict a second illustrative embodiment of a triple pilot CB valve according to the present invention. CB valve  206  is provided with a valve body  5 , a load port  1 , a valve port  2 , and a pilot port  3 . In use, CB valves  6  and  206  provide a low pilot ratio in areas where instability of the hydraulic circuit could occur, and a higher pilot ratio to save energy at higher inlet and lower outlet pressures where circuits are typically stable. The triple pilot ratio CB valve further reduces the valve setting by a fixed pressure when pilot pressures are very low, thus leading to additional savings.  FIG. 18  provides an illustration of CB valve  6  installed in a manifold  207 . 
     Referring to the drawings,  FIGS. 5-9  depict an illustrative embodiment of a dual pilot CB valve according to the present invention. CB valve  6  has a setting control region  160 , a pilot stage region  169  and a main stage  165 . The pre-load setting control region  160  includes an outer valve or hex body  5  and end cap  10  that define a working cavity. Adjusting screw  20  is axially disposed within the working cavity and along the setting control region such that it can rotate within the valve body to advance or retract adjusting nut  25 , to which is it is threadably connected. Adjusting nut  25 , in combination with spacer  30 , can slide axially within the valve body between screw  20  and shoulder  166  to compress or decompress inner spring  50  and outer spring  45  in response to axial rotation of screw  20 . Once the desired pre-load pressure setting is established, it may be set by engaging lock nut  15  with screw  20 , to which it is threadably connected. Pin  55  extends axially from screw  20  and acts as a stop for poppet  90 . Inner spring  50  and outer spring  45  are compressed with the valve body generally between spacer  30  and pilot stage region  169 , in particular, the combination of spacer  60  and pilot sleeve  65 . 
     Piston spacer  60  and spacer  70  are axially disposed relative to each other within pilot stage  169 , and piston spacer  60  slidably engages pilot sleeve  65 . Sleeve  65  can slide axially within the pilot stage, independently of spacer  60  in response to pilot pressure through pilot load port  3 . 
     Main stage  165  includes piston  100 , poppet  90  and spring  95 , each axially, slidably disposed within the valve body  5 . Spring  95  biases poppet  90  to a sealed or seated position against piston  100 . When pressure on load port  1  exceeds the predetermined pre-load setting, piston  100  and poppet  90  together slide longitudinally until poppet  90  contacts spacer  200 . Further upward movement of piston  100  against spacer  60  as well as pilot sleeve  65 , in response to excessive pressure, opens the valve allowing relief through valve port  2 . 
     In more typical operation, dual pilot valves of the present invention have two operating points. The first operating point is a low pilot ratio setting when P 1  (load pressure) is high and P 3  (pilot pressure) is low. The second is a high pilot ratio setting when P 3  is high and P 1  is low, resulting in energy savings through reduced power consumption. 
     The proposed dual pilot ratio valve has a low gradient (low pilot ratio) when P 1  is high and P 3  is low. It has a higher gradient when P 3  is high and P 1  is low. The pilot ratio increases when pilot pressure P 3  is high enough to move a 2 nd  sleeve against the preload of an additional, outer spring. The transition from low to high pilot ratio changes with the setting of the valve since a spacer on the adjust screw of the valve further preloads both the inner and the outer spring when the mechanical setting is changed by turning the adjust screw.  FIG. 15  graphically illustrates the performance of the dual pilot ratio valve for 2 different mechanical settings. The main purpose of this design is to safe power in lowering load with high P 3  and low P 1 . 
       FIG. 16  shows operation points for  4  different load conditions (grey rising straight lines represent a motor at 4 different loads). The dual pilot ratio valve (green) reduces the required power to lower loads from 100 to 79%. The Triple ratio valve needs only 65%. 
     In the example illustrated in  FIG. 16 , the setting of the triple ratio valve is 4000 psi, while the highest load induced pressure is 3000 psi. Reducing the setting of the valve from 4000 to 3400 psi does not cause a movement of the motor. As a result, the initial high pilot ratio (for pilot pressure below 60 psi) is not critical with respect to stability of the load. But the reduced setting helps saving energy for all higher pilot pressures. 
     Referring to the drawings,  FIGS. 10-13  depict an illustrative embodiment of a triple pilot CB valve according to the present invention. CB valve  206  has a setting control region  160 , a pilot stage region  169  and a main stage  165 . The pre-load setting control region  160  includes an outer valve or hex body  5  and end cap  10  that define a working cavity. Adjusting screw  20  is axially disposed within the working cavity and along the setting control region such that it can rotate within the valve body to advance or retract adjusting nut  25 , to which is it is threadably connected. Adjusting nut  25 , in combination with spacer  30 , can slide axially within the valve body between screw  20  and shoulder  166  to compress or decompress inner spring  50  and outer spring  45  in response to axial rotation of screw  20 . Once the desired pre-load pressure setting is established, it may be set by engaging lock nut  15  with screw  20 , to which it is threadably connected. Pin  55  extends axially from screw  20  and acts as a stop for poppet  90 . Inner spring  50  and outer spring  45  are compressed with the valve body generally between spacer  30  and pilot stage region  170 , in particular, the combination of spacer  60  and pilot sleeve  65 . 
     Spacer  60  and spacer  70  are axially disposed relative to each other within pilot stage  169  and each slidably engage pilot sleeve  65 . Spring  75 , disposed axially about spacers  60  and  70  between an arm of spacer  60  and an arm of pilot sleeve  65 , biases sleeve  65  to a minimum pilot pressure setting. Sleeve  65  can slide axially within the pilot stage, independently of spacers  60  and  70  between shoulder  167  at one end and shoulder  168  on the other, respectively, in response to pilot pressure through pilot load port  3 . 
     Main Stage  165  includes piston  100 , poppet  90  and spring  95 , each axially, slidably disposed within the valve body  5 . Spring  95  biases poppet  90  to a sealed or seated position against piston  100 . When pressure on load port  1  exceeds the predetermined pre-load setting, piston  100  and poppet  90  together slide upward until poppet  90  contacts pin  55 . Further upward movement of piston  100  against spacers  60  and  70  as well as pilot sleeve  65 , in response to excessive pressure, opens the valve allowing relief through valve port  2 . 
     As earlier disclosed, dual pilot valves of the present invention have two operating points. Triple pilot valves as presented herein have a further operating point. In addition to a low pilot ratio setting when P 1  (load pressure) is high and P 3  (pilot pressure) is low and a high pilot ratio when P 3  is high and P 1  is low, the triple pilot ratio valve as described herein results in additional energy savings when the setting of the counterbalance valve is reduced with a high effective area before the load starts to move. When compared with typical prior art counterbalance valves, certain embodiments of a triple pilot valve of the present invention advantageously have a lower pilot pressure for the same setting and flow as for the standard CB valve. Thus, the triple ratio valve may be used in certain applications where CB valves with a higher pilot ratio valve (10:1) would cause instability. That provides power savings (about 30% for negative or low loads) or results in higher speeds for the same pilot pressure (up to 100% on winches or cylinders without load). When less power is lost across the counterbalance valve, more power is available to move the cylinder or motor. 
     In situations where spring  75  biasing force is greater than pilot pressure, a pilot ratio setting results due to pilot sleeve contact with spacer  70 . (See  FIG. 10 ). For pilot pressure situations where pilot pressure is greater than spring  75  biasing force but less than outer spring  45  biasing force, the pilot sleeve is not in contact with either spacer  60  or spacer  70 , and the valve has a low pilot ratio setting. The operating range in that pilot pressure region controls overrunning loads. (See  FIG. 11 ). For pilot pressures in excess of the outer spring  45  biasing force, the pilot sleeve  65  is in contact with spacer  60 . Increasing pilot pressure above this point (operating ranges with positive loads where stability is not critical), allows sleeve  65  to assist spacer  60 , reducing the valve setting with a high effective pilot ratio. (See  FIGS. 12 and 13 ). 
     In some aspects of the present invention, the dual pilot or triple pilot counterbalance valve is atmospherically vented.  FIG. 6  provides an exemplary embodiment of a vented dual pilot valve of the present invention. Triple pilot valves of the present invention may be similarly vented, as appreciated by those of ordinary skill in the art. As used herein, the term “vented” refers to situations where pressure on port  2  has no effect on the setting of the valve. The valve is insensitive towards pressure on port  2  because the seal  185  separates the pressure on port  2  from the pressure experienced by the inner spring  50 , outer spring  45  and the spring chamber  130  containing the two springs. The seal contacts the piston on a diameter equal to the seat diameter. Therefore the pressure on port  2  sees no effective area on the piston. 
     In view of the present disclosure, a person of ordinary skill in the art will appreciate that the setting profile of a CB valve of the present invention can be altered or adjusted by changing the differential areas and springs of the CB valve. Therefore, one of ordinary skill in the art will appreciate that the CB valve of the present invention can be readily outfitted to provide a desirable CB valve profile for different applications. 
     Any other undisclosed or incidental details of the construction or composition of the various elements of the disclosed embodiments of the present invention are not believed to be critical to the achievement of the advantages of the present invention, so long as the elements possess the attributes needed for them to perform as disclosed. Certainly, one of ordinary skill in the hydro-mechanical arts would be able to conceive of a wide variety of valve shapes and sizes and successful combinations of the invention disclosed herein. The selection of these and other details of construction are believed to be well within the ability of one of even rudimentary skills in this area, in view of the present disclosure. 
       FIG. 17  graphically illustrates the load pressure versus pilot pressure curve for four different standard prior art counterbalance valves wherein Q (rated flow) is 20 l/min. When the pilot pressure is 0, the valve is at the spring preload mechanical setting. As the pilot pressure is increased, the valve setting is reduced as the valve gradually opens and holds less load pressure. The slope of the curves for each of the valves illustrates the pilot ratio such that the flatter the curve the lower the pilot ratio. 
     While  FIG. 17  illustrates the gradually reduced valve setting as a function of increasing pilot pressure,  FIG. 14  graphically illustrates some of the advantages of a dual pilot ratio valve as compared to a prior art CBCA counterbalance valve.  FIG. 14  illustrates typical performance curves for dual pilot valves of the present invention at two different settings, that for pilot pressures above a certain setting, the valve transitions to a higher pilot ratio when increasing pilot pressures are supplied, which in turn leads to more efficient use of the power source providing the desired pilot pressure, thus demonstrating the improved power efficiencies of dual pilot valves over prior art counterbalance valves. 
       FIG. 19  graphically illustrates the load pressure vs. pilot pressure for a standard CBCA valve at 4 different constant flows. The valve has a setting of 4000 psi.  FIG. 20  graphically illustrates the triple ratio valve with the same setting under the same conditions. The two lines having positive slope in each figure describe the pressures across a motor that sees 3000 psi overrunning load (upper line) and no load (line through origin). A comparison demonstrates that where a standard CB valve requires 500/275/1525 and 1100 psi load pressure, the triple ratio valve requires only 325/200/1150 and 775 psi to move the motor at the same speed and load. The savings are about 30% on average for those 4 operating points. The four operating points describe a cylinder that sees a high overrunning load (upper line) and no load (lower line). The performance curves of the valve were tested at 4 different flows (1, 4, 10 and 15 GPM). The 4 operating points describe a high and a low load, at 1 and 15 GPM each. For the same cylinder speed and force, it would require 275, 500, 1100 and 1575 psi pilot pressure if the standard counterbalance valve was used, and only 200, 325, 775 and 1150 psi if the ‘Triple Pilot’ valve was used. Both valves had the same setting of 280 bar. When the cylinder is moved at high speed with no outer force against the counterbalance valve with 280 bar setting, an inlet pressure of 1575 psi is required. At a flow rate of 15 GPM that is the equivalent of about 10.8 KW horse power. That loss of power may be reduced to about 7.9 KW if the ‘Triple Pilot’ valve is instead employed. The calculation assumed an equal area cylinder or a motor. The savings could be higher or lower with a differential area cylinder. 
     If only an inlet pressure of 1000 psi is available to move a motor without load (lowering a winch with no load on the hook), a standard CBCA with 4000 psi setting would not open. The triple ratio valve with the same setting would allow a flow of 10 GPM. 
     Illustrative embodiments of the present invention have been described in considerable detail for the purpose of disclosing the practical, operative structure whereby the invention may be practiced advantageously. The designs described herein are intended to be exemplary only. The novel characteristics and features of the present invention may be incorporated in other structural forms without departing from the spirit and scope of the present invention. The invention encompasses embodiments both comprising and consisting of the elements described with reference to the illustrative embodiments. The invention illustratively disclosed herein suitably may be practiced in the absence of any element which is not specifically disclosed herein. The invention illustratively disclosed herein suitably may also be practiced in the absence of any element which is not specifically disclosed herein and that does not materially affect the basic and novel characteristics of the claimed invention. 
     Unless otherwise indicated, all ordinary words and terms used herein shall take their customary meaning as defined in  The American Heritage Dictionary , Third Edition. All technical terms shall take on their ordinary and customary meaning as established by the appropriate technical discipline utilized in that particular art.