Abstract:
A decompression valve assembly is normally open thereby allowing thermal pressure build-up in an auxiliary circuit to be dissipated via a bleed path. During operation, the bleed path is sealed by a check valve, whereby high pressure flow can be fully directed to the work tool powered by the auxiliary circuit, for high system efficiency. In addition, a velocity fuse feature limits the rate of flow to the bleed path, thereby to allow for controlled release of pressure from the auxiliary circuit, as is desirable to protect against a rapidly falling load.

Description:
RELATED APPLICATION  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/568,200 filed May 5, 2004, which is hereby incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to fluidic systems and more particularly to a quick-disconnect coupler manifold including a decompression valve assembly for relieving pressure from pressure lines for facilitating coupling of, for example, auxiliary hydraulic system components.  
       BACKGROUND OF THE INVENTION  
       [0003]     A trend in the construction industry has been to utilize smaller, more versatile machinery on the job-site. For example, mini-excavators and skid-steer loaders are often used to perform a variety of tasks. In many cases, a skid-steer loader or mini-excavator is equipped with an attachment for performing a particular task. Such attachments are typically powered by an auxiliary hydraulic circuit on the skid-steer loader or mini-excavator. Numerous attachments exist for performing a variety of tasks. For example, attachments exist for allowing a skid-steer loader to be used as a backhoe, an earth auger, an angle broom, a drop hammer, a snowplow, a brush saw, etc. These attachments typically are designed to be quickly connected and disconnected from the skid-steer loader or other machine by an operator on the job-site. The ability to quickly change attachments on the job-site makes these smaller machines more versatile than larger machines.  
         [0004]     Quick-disconnect couplers are often used to allow quick and convenient connection and disconnection of hydraulic lines of an attachment to the auxiliary hydraulic circuit of the machinery. These types of couplers also are often used on construction equipment or agricultural tractors for connecting auxiliary circuits that power work tools or pull behind implements. The couplers are frequently housed in valve stacks or banks on the machinery in a position that is easily accessible to the operator when connecting an attachment. As such, the couplers are generally in close proximity of each other.  
         [0005]     In general, an operator manually connects the hydraulic lines of an attachment to the auxiliary hydraulic circuit of the machine. To form the connection, a plug-like coupler part and a socket like coupler part are customarily used to couple the supply/return lines. In many instances, the connection is made while internal hydraulic pressure exists in one or both of the lines to be connected. Such internal hydraulic pressure can be residual hydraulic pressure from operating the attachment, or may be due to thermal hydraulic pressure buildup in the hydraulic circuit. Regardless, hydraulic pressure in the circuit can make forming the connection more difficult, especially with standard quick-disconnect couplers.  
         [0006]     The ability of a coupler to connect and disconnect as intended to another coupler or fitting can be highly dependent on the system within which it operates, and specifically, the flow and pressure potential within the coupler. Many couplers have internal valves that are biased closed by internal hydraulic pressure when the coupler is not connected to another coupler or fitting. Once the coupler is connected to another coupler or fitting, the internal valve is opened allowing flow therethrough. For the user, it becomes increasingly difficult to make a connection as internal pressure, and thus hydraulic force, on the valves of the two couplers to be connected increases. In the hydraulic coupling industry, difficulty in making a connection due to hydraulic pressure is known as the “connect under pressure” problem.  
         [0007]     Hydraulic pressure within a coupling is essentially a form of trapped energy. Thus, in order to connect a coupling under pressure, the trapped energy must be dissipated or otherwise managed. In general, this means that the energy within the coupling must be dissipated during the connection, or must be moved or contained in a place where its effects are minimized.  
         [0008]     The majority of couplers capable of connecting under pressure do so by dissipating the internal hydraulic energy by allowing the hydraulic fluid (e.g. oil) to expand prior to connection. Some couplers have internal bleed valves that let the oil expand to a low-pressure line within the hydraulic system. Other couplers are designed with an internal bleed valve that lets the oil expand into and through the mating coupler. Still other couplers incorporate a mechanism for providing a mechanical advantage to generate enough force to overcome the hydraulic forces acting on the valves. And still other couplers have an external bleed valve that lets the hydraulic fluid expand external to the system, i.e., into the environment.  
         [0009]     Many prior art coupler designs providing connect under pressure functionality have specialized internal valving that provides the connect under pressure functionality. Such couplers are more complex and cost more than a standard coupler (i.e., couplers without internal valving) due to the internal valving. Further, many prior art coupler designs utilize elastomeric seals that are required to throttle flow during connect under pressure. It is well known that throttling flow over elastomeric seals increases the potential for seal damage and often results in such. Many prior art coupler designs also involve the need for operator training as the operation of the couplers is not intuitive.  
       SUMMARY OF THE INVENTION  
       [0010]     The present invention provides a quick coupling system with a novel decompression valve assembly that, when actuated, allows internal hydraulic pressure in the couplers and/or the hydraulic circuit to be released in a uniquely controlled manner. Unlike prior art decompression valves used in coupler manifolds for quick coupling systems, the decompression valve assembly of the present invention is configured to automatically close under certain conditions, such as in the event of a sudden surge flow.  
         [0011]     More particularly, the decompression valve assembly is normally open thereby allowing thermal pressure build-up in an auxiliary circuit to be dissipated via a bleed path. During operation, the bleed path is sealed by a check valve, whereby high pressure flow can be fully directed to the work tool powered by the auxiliary circuit, for high system efficiency. In addition, a velocity fuse feature limits the rate of flow to the bleed path, thereby to allow for controlled release of pressure from the auxiliary circuit, as is desirable to protect against a rapidly falling load.  
         [0012]     Consequently, principles of the present invention can be applied to avoid one or more drawbacks associated with prior art quick coupling systems, including the elimination of the need for connect under pressure couplers that contain specialized internal valving, thereby allowing the use of standard couplers; the elimination or reduction of thermal pressure buildup in the auxiliary circuits; the elimination of the need for elastomeric seals previously required in some systems to throttle flow, and others.  
         [0013]     Accordingly, the present invention provides a quick coupling system comprising a fluid circuit including a quick coupling, and a decompression valve assembly that, when actuated, allows internal hydraulic pressure in the fluid circuit to be released to a bleed path, wherein the decompression valve assembly is normally open thereby allowing thermal pressure build-up in the fluid circuit to be dissipated to the bleed path, the decompression valve assembly is closed by high pressure flow in the fluid circuit, and the decompression valve assembly includes a velocity fuse that limits the rate of flow to the bleed path, thereby to provide for controlled decompression of the auxiliary circuit.  
         [0014]     According to another aspect of the invention, a coupling system comprises at least one high pressure flow passage; a bleed passage; a check valve that when open and closed respectively permits and blocks flow of fluid from the high pressure flow passage through the bleed passage; and an actuator normally biased to a valve open position at which the actuator prevents the check valve from closing, and the actuator being movable to a valve closed position allowing the check valve to close when pressure in the bleed passage exceeds a valve close level.  
         [0015]     In a preferred embodiment, the actuator is manually operable, as by means of a push button, to open the check valve when held closed by pressure in the high pressure flow passage. A flow restrictor, such as an orifice, may be provided in the bleed passage downstream of the check valve for restricting flow through the bleed passage and for generating back pressure upstream of the flow restrictor, which back pressure acts on the actuator to move it valve closed position in response to the back pressure exceeding the valve close level.  
         [0016]     More particularly, the check valve may have a valve seat and a valve sealing member for sealing against the valve seat, and the actuator may include an axially movable plunger resiliently biased from a valve closed position allowing the valve sealing member to seal against the valve seat to a valve open position displacing the valve sealing member away from the valve seat thereby to allow flow of fluid through the check valve. The plunger may be resiliently biased by a first biasing force from its valve closed position to its valve open position, and the valve sealing member may be resiliently biased by a second, lower, biasing force towards the valve seat, whereupon the check valve is normally open. Preferably, the high pressure flow passage, bleed passage, check valve, actuator and flow restrictor are located in a manifold block to which quick-disconnect couplers can be attached for enabling connection to respective coupler halves of auxiliary equipment.  
         [0017]     According to a further aspect of the invention, a coupling system comprises first and second coupler halves configured to connect with respective mating coupler halves; a chamber connecting at least one of the first and second coupler halves to a drain line coupler; and a decompression valve assembly configured to control flow from the chamber to the drain line coupler. The decompression valve assembly includes a check valve that when open and closed respectively permits and blocks flow of fluid from the respective coupler half to the drain line coupler, an orifice downstream of the check valve for metering flow from the chamber to the drain line coupler, and an open biased plunger configured to force open the check valve when in a valve open position, and to automatically shift to a valve closed position when pressure in the chamber exceeds a predetermined level.  
         [0018]     In a preferred embodiment the check valve is a hard seat check valve, and the plunger is manually movable, as by means of a push button, from its valve closed position to its valve open position.  
         [0019]     According to a still further aspect of the invention, a quick coupling system for enabling quick connect/disconnect of auxiliary equipment to high pressure supply/return lines, comprises first and second high pressure flow lines and respective quick-disconnect coupler halves configured for quick connect/disconnect with mating coupler halves associated with the auxiliary equipment; a low pressure flow passage; a chamber connecting at least one of the high pressure flow lines to the low pressure flow passage; and a decompression valve assembly having open and closed states respectively permitting and blocking fluid flow from the chamber to the low pressure flow passage, the decompression valve assembly including a velocity fuse for closing the decompression valve assembly when flow through the decompression valve assembly exceeds a predetermined level.  
         [0020]     In a preferred embodiment, the velocity fuse includes a flow restrictor for throttling fluid flow from the chamber to the low pressure flow passage. As before, decompression valve may include a valve seat, a valve sealing member for sealing against the valve seat, and a plunger resiliently biased from a valve closed position allowing the valve sealing member to seal against the valve seat to a valve open position displacing the valve sealing member away from the valve seat thereby to allow flow of fluid through the decompression valve assembly, with the plunger being responsive to back pressure upstream of the orifice for movement of the plunger against the biasing force to its valve open position when the back pressure is high enough to overcome the biasing force acting on the plunger. Again, the decompression valve assembly may include a device for manually moving the plunger from its valve closed position to its valve open position, and the chamber may connect both of the high pressure flow passages to the low pressure flow passage via the decompression valve assembly.  
         [0021]     The foregoing and other features of the invention are more particularly described in the following detailed description when considered in conjunction with the drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]      FIG. 1  is a schematic diagram illustrating an auxiliary hydraulic circuit including a coupler manifold having a decompression valve assembly in accordance with the present invention.  
         [0023]      FIG. 2  is a perspective view of a coupler manifold including a decompression valve assembly according to the present invention.  
         [0024]      FIG. 3  is a front view of the coupler manifold of  FIG. 2  according to the present invention.  
         [0025]      FIG. 4  is a side view of the coupler manifold of  FIG. 2  according to the present invention.  
         [0026]      FIG. 5  is a cross-sectional view of the coupler manifold of  FIG. 3  taken along the line A-A.  
         [0027]      FIG. 6 , is a cross-sectional view of the coupler manifold of  FIG. 4  taken along the line B-B.  
         [0028]      FIG. 7  is a cross-sectional view of the coupler manifold of  FIG. 4  taken along the line TOP-TOP.  
         [0029]      FIG. 8  is a cross-sectional view of the decompression valve assembly in the open position according to the present invention.  
         [0030]      FIG. 9  is a cross-sectional view of the decompression valve assembly in the closed position according to the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0031]     Referring now to the drawings in detail, and initially to  FIG. 1 , an exemplary hydraulic circuit  10  generally comprises a pump  14 , a coupler system  16 , and an attachment  22 . In the illustrated embodiment, which is particularly suited for use in a mini-excavator, skid-steer loader, or similar type of machinery, there is a directional control valve  26  that directs pressurized fluid from the pump  14 , which draws fluid from a tank  28 , to either hydraulic line  30   a  or  30   b  depending on the desired direction of operation of the attachment  22 . Hydraulic lines  30   a  and  30   b  are connected to the coupler system  16  which includes a manifold  18 . More particularly, the lines  30   a  and  30   b  are connected to manifold ports  34   a  and  34   b , respectively. Manifold ports  34   a  and  34   b  are connected internally via the manifold  18  to manifold coupler halves  38   a  and  38   b , respectively.  
         [0032]     In the illustrated embodiment, coupler half  38   a  is a male coupler half and coupler half  38   b  is a female coupler half, this being in accordance with conventional practice. Mating attachment coupler halves  42   a  and  42   b  connect hydraulic lines  46   a  and  46   b  of the attachment  22  to the manifold coupler halves  38   a  and  38   b . A motor case drain port  50  in the manifold  18  is connected internally with a motor case drain line coupler half  54 . The motor case drain line coupler half  54  is coupled to a mating motor case drain line coupler half  55  and motor case drain line  56 .  
         [0033]     The motor case drain port  50  is connected to the tank  28  via line  58 . As will be described in further detail herein, the motor case drain port  50  also is connected internally with the coupler manifold ports  34   a  and  34   b  and coupler halves  38   a  and  38   b  for releasing pressure from the system  10 .  
         [0034]     In operation, the pump  14  provides pressurized fluid from the tank  28  to the directional control valve  26 . Depending on the desired direction of operation, the directional control valve  26  directs the pressurized fluid to either hydraulic line  30   a  or  30   b . By directing the fluid to one or the other of the hydraulic lines  30   a  and  30   b  the direction of operation of the attachment  22  can be reversed. Thus, either hydraulic line  30   a  or  30   b  can supply fluid to the attachment  22  while the other hydraulic line not supplying fluid acts as a return line to return the fluid to the tank  28 . The motor case drain is provided for use with auxiliary equipment that require a low pressure return, such as for draining fluid from a motor case in the auxiliary equipment. However, as will become apparent from the following description, the motor case drain port  50  and line  58  serve a further function of providing a low pressure return path to the tank  28  for fluid bled from the high pressure flow lines by means of the herein described decompression valve assembly. Consequently, the port  50  is herein also referred to as a release, bleed or vent port, and although undesired, the port  50  could be open to the atmosphere or otherwise, as long as a path is provided for bleed flow from the manifold  18 .  
         [0035]     As previously mentioned, a common practice is to use a variety of interchangeable attachments  22  with an auxiliary hydraulic system  10  of a skid-steer loader or similar type of machinery. Thus, the manifold  18  of the auxiliary hydraulic system  10 , which functions as a coupling system, provides a convenient interface for changing attachments  22  by providing a single location for connecting and disconnecting the hydraulic lines of the attachment  22  to the auxiliary hydraulic system  10 . Residual pressure, however, often remains in the system  10  after an attachment  22  is operated, and this can make it difficult to disconnect and/or connect the attachment  22 . Further, thermal pressure buildup in the attachment  22  and/or auxiliary hydraulic system  10  can be an impediment to connecting an attachment  22 . As previously noted, pressure relieving couplers can be used to allow connection under pressure, or the pressure might be relieved to the environment. However, pressure-relieving couplers can be costly and may require operator training, and relieving the pressure to the environment is usually not a viable option.  
         [0036]     In accordance with the present invention and with reference to  FIGS. 2-6 , the manifold  18  further includes decompression valve assembly  62 . In the illustrated embodiment, the decompression valve assembly  62  includes a push-button  64  (or other manually manipulable device) for manually opening the decompression valve assembly  62  to allow any internal hydraulic pressure in the high pressure circuits to be released to the motor case drain port  50  and line  58  for return to the tank  28 . The decompression valve assembly  62  allows standard couplers to be used without the aforementioned difficulties of connecting under pressure with such couplers. Further, once the pressure in the system  10  is released, the decompression valve assembly  62  remains open thereby continually venting the system  10  and preventing pressure buildup. The decompression valve assembly  62  further includes a velocity fuse that automatically closes the decompression valve assembly  62  when flow through the decompression valve assembly  62  exceeds a predetermined level.  
         [0037]     Referring to  FIGS. 2-4 , the illustrated manifold  18  includes a manifold body  66  (or block) that, as shown, may be provided with mounting holes  70  for securing the manifold  18  to machinery, such as a skid-steer loader, mini-excavator, or other equipment. The manifold block  66  has attached thereto the two auxiliary circuit coupler halves  38   a  and  38   b  for coupling to mating coupler halves on the hydraulic lines of the attachment. As desired and conventional, the manifold coupler halves  38   a  and  38   b  can be male and female, although they could be both male or both female. The coupler halves  38   a  and  38   b  can be of any suitable type, such as quick-disconnect couplers.  
         [0038]     The male and female coupler halves  38   a  and  38   b  are connected internally via flow passages in the manifold body  66  to the auxiliary hydraulic system manifold flow ports  34   a  and  34   b  which can be connected to the hydraulic lines of an auxiliary hydraulic system. The motor case drain line coupler half  54  is connected internally via flow passages to the pressure bleed port  50 .  
         [0039]     Although separate decompression valve assemblies  62  could be provided to release pressure separately from each of the high pressure flow lines, as seen in  FIGS. 5 and 6 , pilot pressure ports  74   a  and  74   b  interconnect passages  78   a  and  78   b  with a common chamber  82  facilitating the use of a single decompression valve assembly  62  to release pressure from both high pressure passages  78   a  and  78   b . To prevent cross-flow between the high pressure passages  78   a  and  78   b , the common chamber  82  is sealed from the passages  78   a  and  78   b  by hard seat check valves  86   a  and  86   b  that block flow from the common chamber  82  back into the passages  78   a  and  78   b.    
         [0040]     Turning to  FIG. 7 , the interconnection of the manifold coupler halves  38   a  and  38   b , passages  74   a  and  74   b , and auxiliary circuit manifold ports  34   a  and  34   b  with the common chamber  82  will be described. It will be appreciated that this description is equally applicable to the interconnection of either set of such elements with the common chamber  82 . In  FIG. 7 , the male coupler half  38   a  is shown connected to the manifold body  66 . The male coupler half  38   a  can be provided with threads  98  on an outer circumference thereof and can be screwed into mating threads of the passage  78   a  for attachment thereto. A sealing member  102 , such as an O-ring, can be provided to ensure a proper seal between the male coupler half  38   a  and the manifold body  66 . Pilot pressure port  74   a  extends perpendicularly from the passage  78   a  and connects the passage  78   a  to check valve  86   a . The check valve  86   a  includes a valve chamber  106 , a sealing member  110 , and valve seat  114 . The check valve chamber  106  connects the pilot pressure port  74   a  to the common chamber  82 . As mentioned, the check valve  86   a  blocks flow from the common chamber  82  back into the pilot pressure port  74   a  to prevent excess pressure in the common chamber  82  from entering the passage  78   a . However, the check valve  86   a  allows excess pressure in the passage  78   a  to be released to the common chamber  82  and ultimately to the tank  28  via the motor case drain port  50  and line  58 .  
         [0041]     As shown in  FIG. 6 , the decompression valve assembly  62  is located in an upper portion of the common chamber  82 . As discussed further below, the decompression valve assembly  62  has a push button  64  that can be depressed to bleed off pressure from the chamber  82  through a bleed passage  94 . The bleed passage  94  is connected to a passage  96  that connects the motor case drain port  50  to the motor case drain line coupler half  54 .  
         [0042]     Turning now to  FIGS. 8 and 9 , the decompression valve assembly  62  includes a valve body  118  including a valve passage  120 , a check valve  122 , and an actuator, e.g., a plunger  124 , to which the push-button  64  or other manually activated device is attached. In  FIG. 8 , the decompression valve assembly  62  is in an open state with the push-button  64  depressed and the check valve  122  open. In the illustrated embodiment, the decompression valve assembly  62  is configured as an insert that can be threaded into a valve port  130  in the manifold body  18 . O-rings  134  or other suitable sealing members may be provided to seal an outer circumference of the valve body  118  to the valve port  130  of the manifold as shown.  
         [0043]     The check valve  122  is preferably a hard seat check valve. The check valve  122  includes a valve sealing member, such as a ball valve  138 , and a valve seat  142 . The ball valve  138  is biased closed by a spring  146  or other suitable biasing means.  
         [0044]     The valve plunger  124  is supported for axial movement within the valve body  118 . The valve plunger is biased by a spring  154  or other biasing means from a valve closed position ( FIG. 9 ) to a valve open position ( FIG. 8 ). In its valve open position, the inner end of the plunger  124  extends through the valve seat  142  to unseat the ball valve  138 . The force exerted by the spring  154  on the plunger  124  is greater than the force exerted by the spring  146  on the ball valve  138 , whereby the check valve  122  is normally held open in the absence of fluid pressure.  
         [0045]     The inner end face of the valve plunger  124  is exposed to fluid pressure in the valve passage  120 . When fluid pressure in the valve passage  120  exceeds the biasing force acting on the plunger  124 , the plunger  124  will shift to its valve closed position, allowing the valve ball  138  to seal against the valve seat  142 , thereby blocking flow from the chamber  82  to the bleed passage  94 . The valve ball  138  will remain seated as long as the pressure exceeds the spring force. The pressure at which the check valve  122  closes can be varied as desired by changing either one or both of the springs  146  and  154 .  
         [0046]     If either of the high pressure supply/return lines is pressurized, the valve ball  138  will be forced close thereby to route full fluid flow to the attachment. To facilitate connection and disconnection of an attachment, the pressure in the supply/return lines can be bled off by depressing the push-button  64 , thereby moving the plunger  124  to its valve open position, thereby unseating the check valve  122  and allowing fluid to flow into the passage  120  which is connected to the bleed passage  94 .  
         [0047]     The bleed passage  94  preferably is provided with a flow restrictor, such as orifice  162 . The orifice  162  functions to meter or throttle flow through the bleed passage  94  thereby to avoid a rapid discharge of fluid from the high pressure flow passages  78   a  and  78   b.    
         [0048]     The orifice  162  also provides a velocity fuse function. If the flow rate surges or otherwise exceeds a desired level, back pressure generated by the orifice flow acts on the plunger  124  and if sufficiently great will cause the plunger  124  to shift to its valve closed position, thereby allowing the ball valve  138  to close against the seat  142  and stop the flow of fluid from either high pressure passage  78   a  and/or  78   b . The check valve  122  will remain closed by the trapped pressure in the chamber  82  until the plunger button  64  is again depressed. The size of the orifice  162  and the force applied to the valve plunger  124  by the valve plunger spring  154  can be adjusted as desired to set the flow rate at which the check valve  122  will automatically close.  
         [0049]     As should now be apparent, the manifold/coupling system  18  can be used to release pressure from the high pressure lines of the system  10  to facilitate connection and disconnection of an attachment. In general, connecting and disconnecting of attachments is done with the pump deactivated or otherwise off-line. To release pressure from the hydraulic system  10 , the push-button  64  of the decompression valve assembly  62  is depressed. The check valve  122  is thereby forced open allowing flow from the common chamber  82  to the bleed passage  94 . The directional nature of the check valves  86   a  and  86   b  in the pilot pressure ports  74   a  and  74   b  allow pressure in either of the high pressure lines to be vented to the common chamber  82  and further into the bleed line  58 . Once the pressure in the common chamber  82  drops to a level less than the plunger spring bias load, the plunger spring  154  will maintain the check valve  122  in its open position without assistance from the operator, thereby freeing the operator&#39;s hands to disconnect and/or connect the hydraulic lines. Once the auxiliary circuit is depressurized, the existing attachment&#39;s hydraulic lines can be easily disconnected and a new attachment&#39;s hydraulic lines can be connected.  
         [0050]     As pressure is being vented, the orifice  162  will serve to meter the rate of flow of fluid from the high pressure lines. This can prevent undesirable rapid release of pressure that may cause damage to the attachment  22  and/or system  10 . For example, when the coupling system  16  is used with a top loader attachment and the top loader attachment is in a raised position, the bucket will drop at a controlled rate as pressure in the auxiliary circuit is bled away.  
         [0051]     In addition to providing metered bleed flow, the system  16  also has a velocity fuse feature. If the flow velocity exceeds a predetermined level which could allow the bucket to drop abruptly and cause damage to the attachment and/or surrounding objects, back pressure generated upstream of the orifice  162  will cause the plunger  124  to move to its valve closed position, thereby allowing the check valve  122  to close and shut off bleed flow. This will stop further descent of the bucket until the push-button  64  is again depressed.  
         [0052]     It will also be appreciated that the coupling system  18  can also automatically release pressure from the auxiliary circuit  10 . When the pressure in the chamber  120  drops below a predetermined level, the valve plunger spring  154  forces the valve plunger  124  to its open position thereby opening the check valve  122 . Pressure from the high pressure supply/return passages and lines is thereby automatically released therefrom. The decompression valve assembly  62  will continue to vent the high pressure hydraulic lines to the bleed line, thereby preventing pressure buildup in the auxiliary circuit. Consequently, any pressure increase arising from thermal or other expansion of the fluid in the auxiliary circuit will be dissipated.  
         [0053]     It will be appreciated that the automatic venting feature of the decompression valve assembly  62  can allow an operator to connect and disconnect lines of an attachment without manually operating the decompression valve assembly  62 . For example, in some applications it is possible to configure the decompression valve assembly  62  to automatically open at a pressure corresponding to a particular position of an attachment. In the case of a top loader attachment, the decompression valve  62  can be configured to automatically open at a pressure corresponding to the bucket of the attachment being in a fully lowered position. Thus, an operator can lower the attachment to the fully lowered position whereat the decompression valve assembly  62  automatically releases pressure from the lines and the attachment can be disconnected from the auxiliary circuit.  
         [0054]     After disconnecting an attachment and reconnecting a new attachment, the pump  14  can be activated or otherwise brought online to once again supply high pressure fluid to the high pressure lines. When the auxiliary hydraulic system  10  is re-pressurized, the high pressure flow from the pump  14  surges past the check valves  86   a  and  86   b  in the pilot pressure ports  74   a  and  74   b  and into the common chamber  82  and decompression valve passage  120 . As the fluid flows from the decompression valve passage  120  to the bleed passage  94 , back pressure generated by the orifice  162  will cause the valve plunger  124  to shift away from the ball valve  138  and allow the ball valve to seal against the valve seat  142 . Once the check valve  122  is closed, the bleed passage  94  is isolated from the high pressure supply/return passages, thereby preventing system energy losses.  
         [0055]     Although the invention has been shown and described with respect to a certain preferred embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.