Patent Publication Number: US-9416798-B2

Title: Hydraulic circuit, and combination valve used in same hydraulic circuit

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a national stage application of PCT/JP2013/059661 filed Mar. 29, 2013, which claims priority to Japanese Patent Application No. 2013-064386, filed Mar. 26, 2013, and Japanese Patent Application No. 2012-086768, filed Apr. 5, 2012. The priority application is hereby incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     The present invention relates to a hydraulic circuit which makes it possible to perform maintenance, as needed, on valves and/or a hydraulic device such as a hydraulic cylinder and a hydraulic motor coupled to the hydraulic circuit (for a reciprocating hydraulic cylinder used in an apparatus for driving a floodgate or in a factory facility, hydraulic oil merely moves in the circuit but does not circulate through the circuit, whereas for the hydraulic motor, hydraulic oil circulates through the circuit), or to perform various functions such as flushing on a circuit for the hydraulic device and an emergency action, and also relates to a composite valve used in the hydraulic circuit. 
     BACKGROUND ART 
     Examples of the floodgate driven by the hydraulic cylinder include a tilting gate apparatus constructed crossing a river. Such a tilting gate apparatus is used for effective use of water resources of the river by controlling the degree of tilting of the tilting gate provided crossing the river. Further, such an apparatus is used for preventing mixing of seawater with fresh water when provided at an estuary, and used for tide prevention when provided at a shore. Meanwhile, examples of the factory facility include various hydraulic devices used in a machining center. 
     In the tilting gate apparatus for effective use of water resources, piers are provided on both sides of the tilting gate provided crossing the river, and in each of the piers, there are provided a shaft secured to the tilting gate, and a cam secured to the shaft and rotated by the hydraulic cylinder. The degree of tilting of the gate is controlled through the shaft coupled to the cam provided in each pier and rotated by the hydraulic cylinder. Meanwhile, examples of the machining center include a hydraulic clamper for clamping a workpiece. 
     A circuit for driving the reciprocating hydraulic cylinder used for operating the tilting gate is divided by the hydraulic cylinder, and merely the amount of hydraulic oil needed for operating the hydraulic cylinder (the amount corresponding to the capacity of the hydraulic cylinder) travels back and forth in the circuit. Therefore, the hydraulic oil in the circuit and in the hydraulic cylinder does not circulate. Accordingly, longtime use may cause contamination of the hydraulic oil with a contaminant such as a piece of a sealing member broken by a diesel explosion caused by adiabatic compression, in the hydraulic cylinder, of a dust having entered into the circuit or the hydraulic cylinder, or of air having entered from a sealed portion of the hydraulic cylinder. As well, the hydraulic motor of the factory facility has a problem that a contamination of hydraulic oil caused by damage to a sealing member or by metal powder produced by friction between a rotating portion of the hydraulic motor and a body of the motor causes a malfunction in a control device such as a control valve and a speed adjustment valve. 
     The control device in which a malfunction occurs due to the contaminated hydraulic oil needs to be disassembled and cleaned to eliminate the cause of the malfunction, in order to properly control the hydraulic cylinder. Generally, before a malfunction occurs, such a control device needs maintenance and inspection to prevent the malfunction. Further, if a malfunction occurs in the hydraulic device such as the hydraulic cylinder and the hydraulic motor due to the above-described contamination, the malfunction has to be resolved, and to prevent the malfunction, maintenance and inspection are needed. Conventionally, for a hydraulic circuit, a configuration shown in  FIG. 9  has been widely known as a circuit for repair, inspection, maintenance, disassembly and cleaning, or regular checking on such a control device. 
     The hydraulic circuit of Non Patent Literature 1 shown in  FIG. 9  is the circuit for the hydraulic cylinder; however, the circuit may be used for a hydraulic motor. Therefore, in the following description, the hydraulic cylinder represents the hydraulic devices. In the hydraulic circuit shown in  FIG. 9 , a pile-up type stack valve  80  constituted by a lower stack valve  87  and an upper stack valve  88  is coupled to a hydraulic power supplier  10  and a hydraulic cylinder  61 . The lower stack valve  87  includes a maintenance valve unit  81  and a maintenance valve unit  86 , while the upper stack valve  88  includes a speed adjustment valve unit  82 , a load check valve unit  84 , and a solenoid switching valve unit  85 . 
     Hydraulic pressure oil discharged from a hydraulic pump  11  of the hydraulic power supplier  10  in the above circuit passes through a manifold  89 , the maintenance valve unit  86  of the lower stack valve  87 , stop valves  81   a  and  81   b  of the maintenance valve  81 , and the speed adjustment valve unit  82  of the upper stack valve  88 , and then reaches a solenoid switching valve  85   a  of the solenoid switching valve unit  85 . The direction of the flow of the hydraulic oil to/from a hydraulic device  60  is switched using the solenoid switching valve  85   a . The hydraulic oil is supplied to/discharged from the hydraulic cylinder  61  of the hydraulic device  60  through speed adjustment valves  82   a  and  82   b  of the speed adjustment valve unit  82  and stop valves  86   a  and  86   b  of the maintenance valve unit  86 . 
     In the above structure, the hydraulic oil from the hydraulic power supplier  10  is supplied/discharged so that a rod  65  of the hydraulic cylinder  61  moves from one position toward the other position, through operation on the solenoid switching valve  85   a  of the solenoid switching valve unit  85 . 
     In the conventional art having the above structure and functions, when trouble occurs in any of the valves included in the upper stack valve  88  where delicate control devices of the pile-up type stack valve  80  are collectively disposed, or when inspection and maintenance are needed, the stop valves  81   a  and  81   b  of the maintenance valve  81  and the stop valves  86   a  and  86   b  of the maintenance valve  86  are closed thereby to close the communication between the hydraulic power supplier  10  and the hydraulic device  60 ; and then the upper stack valve  88  of the pile-up type stack valve  80  is detached, to perform repair, inspection, and/or maintenance. 
     CITATION LIST 
     Non Patent Literature 
     
         
         Non Patent Literature 1: A brochure of a maintenance valve published on the website of Hirose Valve Industry Co., Ltd. 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     To perform repair, inspection, and/or maintenance on the upper stack valve  88 , the circuit for the hydraulic cylinder mentioned in the above Non Patent Literature 1 and another hydraulic circuit including the pile-up type stack valve  80  used in this circuit are closed by the maintenance valve  81  and the maintenance valve  86 . Therefore, there is a problem that a trial run of the hydraulic cylinder  61  and/or flushing of the circuit cannot be performed during the repair, inspection, and/or maintenance (mending) of the upper stack valve  88 . In other words, the hydraulic power supplier has to be stopped during repair, inspection, and/or maintenance (mending) of the stack valve. 
     The present invention provides a hydraulic circuit which makes it possible to perform repair, inspection, and/or maintenance on a stack valve of the hydraulic circuit and/or on a hydraulic device to/from which hydraulic oil is supplied/discharged through the circuit while driving a hydraulic power supplier, and to perform flushing of the circuit in parallel with repair, inspection, and/or maintenance on the stack valve and/or on the hydraulic device. 
     Solution to Problem 
     A hydraulic circuit of an aspect of the present invention includes: a hydraulic power supplier including a tank configured to store hydraulic oil, and a hydraulic pump coupled to the tank and configured to feed hydraulic pressure oil; a stack valve coupled to the hydraulic power supplier, the stack valve including a direction switching valve configured to control supply/discharge of the hydraulic pressure oil from the hydraulic power supplier to a hydraulic device; a multifunction valve provided in the vicinity of the hydraulic device, the multifunction valve including (i) a first stop valve and a second stop valve which respectively open/close a first supply/discharge circuit and a second supply/discharge circuit for the hydraulic device, and (ii) a bypass circuit positioned closer to the stack valve than the first stop valve and the second stop valve, the bypass circuit including a third stop valve; and a composite valve coupled to the hydraulic power supplier, the stack valve, and the multifunction valve. The composite valve includes: a multifunction valve-side first passage including a multifunction valve-side first stop valve configured to open/close communication between the multifunction valve and the stack valve; a multifunction valve-side second passage including a multifunction valve-side second stop valve configured to open/close communication between the multifunction valve and the stack valve; a pump-side passage including a pump-side stop valve configured to open/close communication between the hydraulic pump and the stack valve; a tank-side passage including a tank-side stop valve configured to open/close communication between the tank and the stack valve; a pump-side bypass circuit branching off from the pump-side passage at a position closer to the pump than the pump-side stop valve, the pump-side bypass circuit including a pump-side bypass stop valve configured to open/close communication with the multifunction valve-side first passage; and a tank-side bypass circuit branching off from the tank-side passage at a position closer to the tank than the tank-side stop valve, the tank-side bypass circuit including a tank-side stop valve configured to open/close communication with the multifunction valve-side second passage. 
     A hydraulic circuit of another aspect of the present invention includes: a hydraulic power supplier including a tank configured to store hydraulic oil, and a hydraulic pump coupled to the tank and configured to feed hydraulic pressure oil; a stack valve coupled to the hydraulic power supplier, the stack valve including a direction switching valve configured to control supply/discharge of the hydraulic pressure oil from the hydraulic power supplier to a hydraulic device; a multifunction valve provided in the vicinity of the hydraulic device, the multifunction valve including (i) a first stop valve and a second stop valve which respectively open/close a first supply/discharge circuit and a second supply/discharge circuit for the hydraulic device, and (ii) a bypass circuit positioned closer to the stack valve than the first stop valve and the second stop valve, the bypass circuit including a third stop valve; and a composite valve coupled to the hydraulic power supplier, the stack valve, and the multifunction valve. The composite valve includes: a multifunction valve-side first passage including a multifunction valve-side first stop valve configured to open/close communication between the multifunction valve and the stack valve; a multifunction valve-side second passage including a multifunction valve-side second stop valve configured to open/close communication between the multifunction valve and the stack valve; a pump-side passage including a pump-side stop valve configured to open/close communication between the hydraulic pump and the stack valve; a tank-side passage including a tank-side stop valve configured to open/close communication between the tank and the stack valve; a pump-side bypass circuit branching off from the pump-side passage at a position closer to the pump than the pump-side stop valve, the pump-side bypass circuit including a pump-side bypass stop valve configured to open/close communication with the multifunction valve-side second passage; and a tank-side bypass circuit branching off from the tank-side passage at a position closer to the tank than the tank-side stop valve, the tank-side bypass circuit including a tank-side stop valve configured to open/close communication with the multifunction valve-side first passage. 
     A hydraulic circuit of still another aspect includes: a hydraulic power supplier including a tank configured to store hydraulic oil, and a hydraulic pump coupled to the tank and configured to feed hydraulic pressure oil; a stack valve coupled to the hydraulic power supplier, the stack valve including a direction switching valve configured to control supply/discharge of the hydraulic pressure oil from the hydraulic power supplier to a hydraulic device; a multifunction valve provided in the vicinity of the hydraulic device, the multifunction valve including (i) a first stop valve and a second stop valve which respectively open/close a first supply/discharge circuit and a second supply/discharge circuit for the hydraulic device, and (ii) a bypass circuit positioned closer to the stack valve than the first stop valve and the second stop valve, the bypass circuit including a third stop valve; and a composite valve coupled to the hydraulic power supplier, the stack valve, and the multifunction valve. The composite valve includes: a multifunction valve-side first passage including a multifunction valve-side first stop valve configured to open/close communication between the multifunction valve and the stack valve; a multifunction valve-side second passage including a multifunction valve-side second stop valve configured to open/close communication between the multifunction valve and the stack valve; a pump-side passage including a pump-side stop valve configured to open/close communication between the hydraulic pump and the stack valve; a tank-side passage including a tank-side stop valve configured to open/close communication between the tank and the stack valve; and a direction switching valve configured to change a manner of communication of the pump-side passage and the tank-side passage with the multifunction valve-side first passage and the multifunction valve-side second passage. 
     The hydraulic circuit of the present invention includes the hydraulic power supplier, the composite valve, the stack valve, and the multifunction valve attached to the hydraulic device. The composite valve has a function of closing communication between the stack valve and the hydraulic power supplier and between the stack valve and the multifunction valve, and a function of opening/closing communication between the hydraulic power supplier (a pump side and a tank side thereof) and the multifunction valve. The multifunction valve has a function of opening/closing the supply/discharge circuits for the hydraulic cylinder and bypassing the hydraulic cylinder. 
     In the hydraulic circuit of each aspect the present invention, the composite valve closes communication between the stack valve and the hydraulic power supplier and between the stack valve and the hydraulic cylinder to separate the stack valve. This makes it possible to perform repair, inspection, and/or maintenance on the stack valve irrespective of the status of the hydraulic cylinder and the hydraulic power supplier. When the composite valve further establishes a circulation circuit by opening communication between the hydraulic pump and the multifunction valve and the multifunction valve closes the supply/discharge circuits for the hydraulic cylinder while opening the bypass circuit, it is possible to perform flushing, in which pressure oil discharged from the hydraulic pump is circulated. Furthermore, when the multifunction valve closes the bypass circuit while opening the supply/discharge circuits for the hydraulic cylinder, the hydraulic power supplier communicates with the hydraulic cylinder through operation on the composite valve, and this allows the hydraulic cylinder to operate irrespective of the stack valve. Moreover, it is possible to separate the hydraulic cylinder from the supply/discharge circuits by closing the supply/discharge circuits through operation on the multifunction valve, to perform upkeep, repair, inspection, and/or maintenance on the hydraulic cylinder. 
     Thus, in the hydraulic circuit including the hydraulic power supplier, the composite valve, the stack valve, and the multifunction valve attached to the hydraulic device, the stack valve is separable from the other components because of the presence of the composite valve, and this reliably prevents entry of foreign matter (contaminant) from the other components during repair, inspection, and/or maintenance. Further, through the operation on the composite valve and the multifunction valve, various operations such as maintenance (upkeep) and a trial run are performed on the hydraulic cylinder and the supply/discharge circuits for the hydraulic cylinder. It is possible to perform repair, inspection, and/or maintenance on the stack valve in parallel with repair, inspection, maintenance on the hydraulic cylinder and the supply/discharge circuits for the hydraulic cylinder. Furthermore, during the above operations such as maintenance (upkeep), foreign matter generated in an operation on one member is advantageously prevented from entering the other members. 
     A composite valve used in the hydraulic circuit of the present invention has a composite valve unit  30   a  which includes: a P-port coupled to a hydraulic pump, a T-port coupled to a tank circuit, an A-port coupled to a first supply/discharge circuit, and a B-port coupled to a second supply/discharge circuit; and a P1-port connected with the P-port, a T1-port connected with the T-port, an A1-port connected with the A-port, and a B1-port connected with the B-port. The composite valve unit  30   a  further includes: a first section including (i) a first left passage structure connecting the P-port with the P1-port, the first left passage structure including a first left U-shape passage including a lower passage provided with a pump-side stop valve, and (ii) a first right passage structure connecting the T-port with the T1-port, the first right passage structure including (a) a first right U-shape passage including a lower passage which is positioned substantially coaxially with an upper passage of the first left U-shape passage and is provided with a tank-side stop valve, and (b) a first T-shape passage which is positioned substantially coaxially with the lower passage of the first left U-shape passage and is provided with a tank-side bypass stop valve; and a second section including (i) a second right passage structure connecting the A-port with the A1-port, the second right passage structure including a second right U-shape passage including a lower passage provided with a multifunction valve-side second stop valve, and (ii) a second left passage structure connecting the B-port with the B-port, the second left passage structure including (a) a second left U-shape passage including a lower passage which is positioned substantially coaxially with an upper passage of the second right U-shape passage and is provided with a multifunction valve-side first stop valve, and (b) a second T-shape passage which is positioned coaxially with the lower passage of the second right U-shape passage and is provided with a pump-side bypass stop valve. The first left passage structure is substantially same as the second right passage structure while the first right passage structure is substantially same as the second left passage structure when either one of the first section and the second section is rotated 180 degrees in a horizontal direction, and a pump-side bypass circuit couples the lower passage of the first left passage structure of the first section with the second T-shape passage of the second section via the pump-side bypass stop valve, while a tank-side bypass circuit couples the lower passage of the second right passage structure of the second section with the first T-shape passage of the first section via the tank-side bypass stop valve. 
     In the composite valve of the above structure, function-intensive circuits are formed in the two sections, and the function-intensive circuits are substantially the same as each other in configuration when either one of the sections is rotated in its longitudinal direction and overlaps the other. Thus, the function-intensive circuits are uniform, leading to a simple structure. This brings about an advantageous effect of better productivity of the composite valve. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram of a hydraulic circuit of a first embodiment of the present invention. 
         FIG. 2  is a side view of a composite valve of the first embodiment. 
         FIG. 3  is a sectional view taken along a line Y-Y in  FIG. 2 . 
         FIG. 4  is a sectional view taken along a line Z-Z in  FIG. 2 . 
         FIG. 5  is a sectional view taken along a line X-X in  FIG. 2 . 
         FIG. 6( a )  is a circuit diagram of the composite valve of the first embodiment. 
         FIG. 6( b )  is a circuit diagram of a composite valve of a variation of the first embodiment. 
         FIG. 7( a )  is a circuit diagram for describing operation in the first embodiment. 
         FIG. 7( b )  is a circuit diagram for describing the operation in the first embodiment. 
         FIG. 8  is a diagram of a hydraulic circuit of a second embodiment of the present invention. 
         FIG. 9  is a diagram of a hydraulic circuit of a conventional art. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     The following describes a first embodiment, which is a preferred embodiment of the present invention, with reference to  FIGS. 1 to 7 . 
     A hydraulic circuit shown in  FIG. 1 , which is an embodiment of the present invention, includes: a hydraulic power supplier  10  including a hydraulic pump  11 , a tank  12 , and a filter  13 ; a hydraulic device  60  including a hydraulic cylinder  61 ; a multifunction valve  40  provided in the vicinity of the hydraulic device  60 ; and a manifold  50  coupled to the hydraulic power supplier  10  and to the multifunction valve  40 . On the manifold  50 , a composite valve  30  and a stack valve  20  are provided. 
     The relation between the multifunction valve  40  and the hydraulic device  60  is as follows: the multifunction valve  40  is directly attached to a cylinder body  62  of the hydraulic cylinder  61  of the hydraulic device  60  as described in Japanese Patent No. 3696850. The multifunction valve  40  has a function of enabling flushing of the circuit and a function of enabling detachment of the hydraulic device  60 , and therefore, the multifunction valve  40  is preferably attached to the body of the hydraulic device. 
     The stack valve  20  is stacked on the composite valve  30  mounted on the manifold  50 . The stack valve  20  includes: a direction switching valve unit  21  including a direction switching valve  22 ; a load check valve unit  23  including two load check valves  23   a  and  23   b ; and a speed control valve unit  24  including speed control valves  24   a  and  24   b  which control the speed of operation of the hydraulic device  60 . 
     The direction switching valve  22  of the direction switching valve unit  21  of the stack valve  20  has a neutral position  22   a , a right position  22   b , and a left position  22   c . In response to a signal applied to a solenoid portion  22   d  or  22   e , the valve is shifted to the right position  22   b  or the left position  22   c . When no signal is applied to the solenoid portions  22   d  and  22   e , the valve is held in the neutral position  22   a  by means of a spring. 
     Composite Valve 
     The composite valve  30  will be described with reference to  FIG. 6( a )  which is the circuit diagram of the composite valve. The composite valve  30  includes: a multifunction valve-side first passage  31   b  including a multifunction valve-side first stop valve  31   a  which opens/closes communication between the multifunction valve  40  and the stack valve  20 ; a multifunction valve-side second passage  32   b  including a multifunction valve-side second stop valve  32   a  which opens/closes communication between the multifunction valve  40  and the stack valve  20 ; a pump-side passage  33   b  including a pump-side stop valve  33   a  which opens/closes communication between the hydraulic pump  11  and the stack valve  20 ; a tank-side passage  34   b  including a tank-side stop valve  34   a  which opens/closes communication between the tank  12  and the stack valve  20 ; a pump-side bypass circuit  36   b  branching off from the pump-side passage  33   b  at a position closer to the hydraulic pump  11  than the pump-side stop valve  33   a , and including a pump-side bypass stop valve  36   a  which opens/closes communication with the multifunction valve-side first passage  31   b ; and a tank-side bypass circuit  35   b , branching off from the tank-side passage  34   b  at a position closer to the tank  12  than the tank-side stop valve  34   a , and including a pump-side bypass stop valve  35   a  which opens/closes communication with the multifunction valve-side second passage  32   a.    
     The multifunction valve-side first passage  31   b  is provided between a B-port  37   b  coupled to a second supply/discharge circuit  38   b  and a B1-port  37   b   1  coupled to a supply/discharge circuit  24   d  extending to the speed control valve  24   b , and the multifunction valve-side first passage  31   b  is configured to be opened/closed by the multifunction valve-side first stop valve  31   a . The multifunction valve-side second passage  32   b  is provided between an A-port  37   a  coupled to a first supply/discharge circuit  38   a  and an A1-port  37   a   1  coupled to a supply/discharge circuit  24   c  extending to the speed control valve  24   a , and the multifunction valve-side second passage  32   b  is configured to be opened/closed by the multifunction valve-side second stop valve  32   a . Thus, when the multifunction valve-side first stop valve  31   a  and the multifunction valve-side second stop valve  32   a  are closed, communication between the multifunction valve  40  and the stack valve  20  is closed. 
     The pump-side passage  33   b  is provided between a P-port  37   p  coupled to a pump circuit  10   a  and a P1-port  37   p   1  coupled to a supply/discharge circuit  39   a , and the pump-side passage  33   b  is configured to be opened/closed by the pump-side stop valve  33   a . The tank-side passage  34   b  is provided between a T-port  37   t  coupled to a tank circuit  12   a  and a T1-port  37   t   1  coupled to a supply/discharge circuit  39   b , and the tank-side passage  34   b  is configured to be opened/closed by the tank-side stop valve  34   a . Thus, when the pump-side stop valve  33   a  and the tank-side stop valve  34   a  are closed, communication between the stack valve  20  and the hydraulic power supplier  10  is closed. 
     The pump-side bypass circuit  36   b  is provided between the pump-side passage  33   b  and the multifunction valve-side first passage  31   b , and the pump-side bypass circuit  36   b  is configured to be opened/closed by the pump-side bypass stop valve  36   a . Meanwhile, the tank-side bypass circuit  35   b  is provided between the tank-side passage  34   b  and the multifunction valve-side second passage  32   b , and the tank-side bypass circuit  35   b  is configured to be opened/closed by the tank-side bypass stop valve  35   a . The above structure causes hydraulic oil to flow in a counterclockwise direction, as indicated with an arrow A in  FIG. 6( a ) . 
     In the case where the tank circuit  12   a  is coupled to the P-port  37   p  in  FIG. 6( a )  and the pump circuit  10   a  is coupled to the T-port  37   t , the hydraulic oil flows in a clockwise direction, similarly to the flow in a composite valve  70  shown in  FIG. 6 ( b ) . 
     The composite valve  70  shown in  FIG. 6( b )  has the same structure except the connection manner of the pump-side bypass circuit  36   b  and of the tank-side bypass circuit  35   b . Specifically, a pump-side bypass circuit  36   b   1  connects the pump-side passage  33   b  with the multifunction valve-side second passage  32   b  and includes a pump-side bypass stop valve  36   a   1 . Meanwhile, a tank-side bypass circuit  35   b   1  connects the tank-side passage  34   b  with the multifunction valve-side first passage  31   b  and includes a tank-side bypass stop valve  35   a   1 . 
     The above differences in structure cause the following difference in operation: while the hydraulic oil flows in the composite valve  30  in the counterclockwise direction as indicated with the arrow A in  FIG. 6( a ) , the hydraulic oil flows in the composite valve  70  in the clockwise direction as indicated with the arrow B in  FIG. 6( b ) . The composite valves  30  and  70  are different from each other only in the manner of flow of the hydraulic oil, and the valves are substantially same as each other in the other structures. Therefore, the following description will be given for the composite valve  30 , and the composite valve  70  will be described as needed. 
     Specific Structure of Composite Valve  30   
     The specific structure of the composite valve  30  will be described with reference to  FIGS. 2 to 5 . Note that the specific structure of each stop valve included in the composite valve  30  is substantially same as that of the valve disclosed in  FIG. 2( a )  of Japanese Unexamined Patent Publication No. 2011-231924 without multipurpose ports, and each stop valve is a typical poppet stop valve of which valve member is configured to open/close a passage through operation on a handle. Therefore, the detailed description of each stop valve is omitted. 
     The specific structure of the composite valve  30  will be described with reference to three sections specified in  FIG. 2  illustrating the composite valve unit  30   a.    
     The composite valve  30  includes: a first section  30   b  of  FIG. 3 , which is the section taken along the line Y-Y in  FIG. 2 ; a second section  30   c  of  FIG. 4 , which is the section taken along the line Z-Z in  FIG. 2 ; and a third section  30   d  of  FIG. 5 , which is the section taken along the line X-X in  FIG. 2 . The first section  30   b  and the second section  30   c  are parallel to each other, and these two sections cross the third section  30   d . The stop valves are arranged in these sections for easy design of the composite valve. 
     The first section  30   b  shown in  FIG. 3  includes: the P-port  37   p  coupled to the pump circuit  10   a , and the P1-port  37   p   1  configured to communicate with the P-port  37   p  via the pump-side stop valve  33   a  and coupled to the supply/discharge circuit  39   a ; and the T-port  37   t  coupled to the tank circuit  12   a  of the hydraulic power supplier  10 , and the T1-port  37   t   1  configured to communicate with the T-port  37   t  via the tank-side stop valve  34   a  and coupled to the supply/discharge circuit  39   b.    
     The second section  30   c  shown in  FIG. 4  includes: the B-port  37   b  coupled to the second supply/discharge circuit  38   b  coupled to a port  62   b  of the hydraulic cylinder  61 , and the B1-port  37   b   1  configured to communicate with the B-port  37   b  via the multifunction valve-side first stop valve  31   a  and coupled to the supply/discharge circuit  24   d  coupled to the speed control valve  24   b ; and the A-port  37   a  coupled to the first supply/discharge circuit  38   a  coupled to a port  62   a  of the hydraulic cylinder  61 , and the A1-port  37   a   1  configured to communicate with the A-port  37   a  via the multifunction valve-side second stop valve  32   a  and coupled to the supply/discharge circuit  24   c  coupled to the speed control valve  24   a.    
     The third section  30   d  shown in  FIG. 5  is a plane crossing the first section  30   b  and the second section  30   c . The third section  30   d  includes: the pump-side bypass stop valve  36   a  and the pump-side stop valve  33   a ; the tank-side bypass stop valve  35   a  and the multifunction valve-side second stop valve  32   a ; and the passages which are the multifunction valve-side first passage  31   b  and the multifunction valve-side second passage  32   b , and the pump-side bypass circuit  36   b  and the tank-side bypass circuit  35   b.    
     The composite valve  30  has a configuration such that the third section  30   d  crosses the two planes of the first section  30   b  and the second section  30   c , thereby to improve its machinability. 
     The first section  30   b  shown in  FIG. 3  includes: the pump-side passage  33   b  connecting the P-port  37   p  opening to an under surface  46   a  with the P1-port  37   p   1  opening to a top surface  46   b ; and the tank-side passage  34   b  connecting the T-port  37   t  opening to the under surface  46   a  with the T1-port  37   t   1  opening to the top surface  46   b.    
     A first left passage structure  26  formed by the pump-side passage  33   b  includes a first left U-shape passage  26   k  having a lower passage  26   a   1  and an upper passage  26   a   2 , and extending toward a left side surface  46   d . Communication between the lower passage  26   a   1  and the upper passage  26   a   2  is opened/closed by the pump-side stop valve  33   a  provided coaxially with the lower passage  26   a   1 . The lower passage  26   a   1  has an opening to communicate with the pump-side bypass circuit  36   b  at a position closer to the P-port  37   p.    
     A first right passage structure  27  formed by tank-side passage  34   b  includes a lower passage  27   a   1 , a middle passage  27   a   2 , and an upper passage  27   a   3 . The upper passage  27   a   3  and the middle passage  27   a   2  form a first right U-shape passage  27   k  extending toward a right side surface  46   c , while the lower passage  27   a   1  forms a part of a T-shape passage  27   t  branching off from the tank-side passage  34   b.    
     The lower passage  27   a   1  is configured to be opened/closed by the tank-side bypass stop valve  35   a , and the lower passage  27   a   1  is formed coaxially with the lower passage  26   a   1  of the first left passage structure  26 . The tank-side bypass stop valve  35   a  has an opening to communicate with the tank-side bypass circuit  35   b . Further, the middle passage  27   a   2  is formed coaxially with the upper passage  26   a   2  of the first left passage structure  26  and is provided with the tank-side stop valve  34   a . The tank-side stop valve  34   a  opens/closes communication between the middle passage  27   a   2  and the upper passage  27   a   3 . 
     The second section  30   c  shown in  FIG. 4  includes: the multifunction valve-side first stop valve  31   a  configured to open communication between the B-port  37   b  opening to the under surface  46   a  and the B1-port  37   b   1  opening to the top surface  46   b ; and the multifunction valve-side second stop valve  32   a  configured to open communication between the A-port  37   a  opening to the under surface  46   a  and the A1-port  37   a   1  opening to the top surface  46   b.    
     A second right passage structure  28  formed by the multifunction valve-side second passage  32   b  includes a second right U-shape passage  28   k  having a lower passage  28   a   1  and an upper passage  28   a   2  and extending toward the right side surface  46   c . Communication between the lower passage  28   a   1  and the upper passage  28   a   2  is opened/closed by the multifunction valve-side second stop valve  32   a  provided coaxially with the lower passage  28   a   1 . The lower passage  28   a   1  has an opening to communicate with the tank-side bypass circuit  35   b  at a position closer to the A-port  37   a.    
     A second left passage structure  29  formed by the multifunction valve-side first passage  31   b  includes a lower passage  29   a   1 , a middle passage  29   a   2 , and an upper passage  29   a   3 . The upper passage  29   a   3  and the middle passage  29   a   2  form a second U-shape passage  29   k  extending toward the left fight side surface  46   d , while the lower passage  29   a   1  forms a part of a second T-shape passage  29   t  branching off from the multifunction valve-side first passage  31   b.    
     The lower passage  29   a   1  is configured to be opened/closed by the pump-side bypass stop valve  36   a , and is formed coaxially with the lower passage  28   a   1  of the second right passage structure  28 . The pump-side bypass stop valve  36   a  has an opening to communicate with the pump-side bypass circuit  36   b . Further, the middle passage  29   a   2  is formed coaxially with the upper passage  28   a   2  of the second right passage structure  28 , and is provided with the multifunction valve-side first stop valve  31   a . The multifunction valve-side first stop valve  31   a  opens/closes communication between the middle passage  29   a   2  and the upper passage  29   a   3 . 
     The third section  30   d  shown in  FIG. 5  includes the tank-side bypass stop valve  35   a  of the first section  30   b  and the pump-side bypass stop valve  36   a  of the second section  30   c , and the third section  30   d  is a horizontal section crossing the second section  30   c  and the first section  30   b . The tank-side bypass circuit  35   b  and the pump-side bypass circuit  36   b  couples the second section  30   c  to the first section  30   b.    
     In the composite valve  30  having the above-described structure, each set of stop valves are disposed coaxially with each other, and the passages for the stop valves are arranged on each of the planes, which are simply coupled by the third plane crossing these planes. This facilitates construction of the composite valve  30 . Further, the composite valve  30  is configured so that, when the first section  30   b  is rotated 180 degrees in its longitudinal direction as indicated with an arrow C in  FIG. 3 , the first left passage structure  26  and the first right passage structure  27  are substantially same as the second right passage structure  28  and the second left passage structure  29 , respectively. 
     Multifunction Valve 
     The multifunction valve  40  is attached in close proximity to the port  62   a  and the port  62   b  of the hydraulic cylinder  61 . The multifunction valve  40  includes: a first stop valve  40   a  which opens/closes communication between the first supply/discharge circuit  38   a  coupled to the manifold  50  and the port  62   a  of the hydraulic cylinder  61 ; and a second stop valve  40   b  which opens/closes communication between the second supply/discharge circuit  38   b  coupled to the manifold  50  and the port  62   b  of the hydraulic cylinder  61 . The multifunction valve  40  further includes a bypass circuit  42   b  having a third stop valve  40   c  which opens/closes communication between the first supply/discharge circuit  38   a  and the second supply/discharge circuit  38   b.    
     The multifunction valve  40  has the following functions of: establishing communication between the first supply/discharge circuit  38   a  and the second supply/discharge circuit  38   b  by using the bypass circuit  42   b  with the first stop valve  40   a  and the second stop valve  40   b  closed and with the third stop valve  40   c  opened; and allowing the hydraulic cylinder  61  to carry out ordinary operation (i.e., reciprocation) when the third stop valve  40   c  is closed and the first stop valve  40   a  and the second stop valve  40   b  are opened. With the first stop valve  40   a  and the second stop valve  40   b  closed, it is possible to detach the hydraulic cylinder  61  to perform maintenance (upkeep), inspection, and/or repair on the hydraulic cylinder  61 . 
     The multifunction valve  40  includes: the first stop valve  40   a  which opens/closes communication between the port  62   a  of the hydraulic cylinder  61  and the first supply/discharge circuit  38   a ; the second stop valve  40   b  which opens/closes communication between the second supply/discharge circuit  38   b  and the port  62   b  of the hydraulic cylinder  61 ; and the bypass circuit  42   b  branching off from the supply/discharge circuits at respective positions closer to the stack valve  20  than the first stop valve  40   a  and the second stop valve  40   b , the bypass circuit  42   b  being opened/closed by the third stop valve  40   c . The detailed structure of the multifunction valve  40  is substantially the same as the multifunction valve described in Japanese Patent No. 3696850, and therefore the detailed description thereof is omitted here. 
     Hydraulic Device 
     The hydraulic cylinder  61  included in the hydraulic device  60  is configured so that: when hydraulic pressure oil is supplied to a rod-side hydraulic chamber  63   a  of the cylinder body  62  via the port  62   a , a rod  65  operates in a contracting direction; and when hydraulic pressure oil is supplied to a head-side pressure chamber  63   b , the rod  65  operates in an extending direction. 
     Operation in First Embodiment 
     Operation in the first embodiment will be described with reference to  FIGS. 7( a ) and 7( b ) . In  FIGS. 7( a ) and 7( b ) , the load check valve unit  23  and the speed control valve unit  24  shown in  FIG. 1  are omitted since these are less likely to be related to the operation in the present invention. 
     Ordinary Operation 
     Referring to  FIG. 7( a ) , for the ordinary operation of the hydraulic cylinder  61  through operation on the direction switching valve  22  of the direction switching valve unit  21 , first, the tank-side bypass stop valve  35   a  of the tank-side bypass circuit  35   b  and the pump-side bypass stop valve  36   a  of the pump-side bypass circuit  36   b  of the composite valve  30  are closed while the other stop valves of the composite valve  30  are opened. In addition, the third stop valve  40   c  of the multifunction valve  40  is closed while the other stop valves of the multifunction valve  40  are opened. 
     After the composite valve  30  and the multifunction valve  40  are set as described above, the direction switching valve  22  of the direction switching valve unit  21  is shifted to the right position  22   b , and then, hydraulic oil from the hydraulic pump  11  is supplied, through the composite valve  30 , the right position  22   b , the load check valve unit  23 , the speed control valve unit  24 , the first supply/discharge circuit  38   a , and the multifunction valve  40 , to the rod-side hydraulic chamber  63   a.    
     The hydraulic oil in the head-side pressure chamber  63   b  of the hydraulic cylinder  61  returns, through the multifunction valve  40 , the second supply/discharge circuit  38   b , the composite valve  30 , the speed control valve unit  24 , the load check valve unit  23 , the right position  22   b , and the composite valve  30 , back to the tank  12 , and therefore, the rod  65  of the hydraulic cylinder  61  operates in the contracting direction. 
     When the direction switching valve  22  is shifted to the left position  22   c  under the condition that the tank-side bypass stop valve  35   a  and the pump-side bypass stop valve  36   a  of the composite valve  30  and the third stop valve  40   c  of the multifunction valve  40  are closed as shown in  FIG. 7( a ) , hydraulic oil is supplied to the head-side pressure chamber  63   b , and the hydraulic oil in the rod-side hydraulic chamber  63   a  returns back to the tank  12 , with the result that the rod  65  of the hydraulic cylinder  61  operates in the extending direction. 
     Thus, when the composite valve  30  and the multifunction valve  40  are held in the above-described condition, ordinary operation of the hydraulic cylinder  61  is performed through the operation on the direction switching valve  22  of the direction switching valve unit  21 . 
     Regarding checking, repair, inspection, and maintenance of the stack valve, a trial run of the hydraulic cylinder, and flushing, description will be given first for repair, inspection, and maintenance of the stack valve  20 , and a trial run of the hydraulic cylinder  61  with reference to  FIG. 7( b ) . 
     For repair, inspection, and maintenance of the stack valve  20 , the multifunction valve-side first stop valve  31   a , the multifunction valve-side second stop valve  32   a , the tank-side stop valve  34   a , and the pump-side stop valve  33   a  of the composite valve  30  are closed as shown in  FIG. 7( b ) . With this, the composite valve  30  closes communication between the stack valve  20  and the hydraulic cylinder  61 , and between the stack valve  20  and the hydraulic power supplier  10 , and this allows the stack valve  20  to be detached from the composite valve  30  to perform repair, inspection, maintenance and/or the like on the stack valve  20 . 
     For a trial run of the hydraulic cylinder  61 , the pump-side bypass stop valve  35   a  and the tank-side bypass stop valve  36   a  are opened under the above-described condition for repair, inspection, and/or maintenance of the stack valve  20 , and further, the first stop valve  40   a  and the second stop valve  40   b  of the multifunction valve  40  are opened. This allows the hydraulic oil from the hydraulic power supplier  10  to be supplied to/discharged from the hydraulic cylinder  61 , and thereby the rod  65  operates in the extending direction. 
     Meanwhile, flushing is performed in the following manner: under the above-described condition for repair, inspection, and/or maintenance of the stack valve  20 , the pump-side bypass stop valve  35   a  and the tank-side bypass stop valve  36   a  are opened, and further, the third stop valve  40   c  of the multifunction valve  40  is opened with the first stop valve  40   a  and the second stop valve  40   b  thereof closed. This opens the bypass circuit  42   b , and thereby allows the hydraulic oil to flow through the first supply/discharge circuit  38   a , the bypass circuit  42   b , the second supply/discharge circuit  38   b , and the composite valve  30 , to return back to the tank  12 . 
     Since the composite valve  30  of the first embodiment shown in  FIGS. 7( a ) and 7( b )  has the circuit configuration shown in  FIG. 6( a ) , a discharging side of the hydraulic pump  11  is coupled to the head-side pressure chamber  63   b  of the hydraulic cylinder  61 , while the tank  12  is coupled to the rod-side hydraulic chamber  63   a  of the hydraulic cylinder  61 . Because of this, a trial run of the hydraulic cylinder  61  is performed only for the extending direction of the rod  65  of the hydraulic cylinder  61 . 
     Meanwhile, when the composite valve  30  of the first embodiment shown in  FIGS. 7( a ) and 7( b )  is modified so as to have the circuit configuration of the composite valve  70  shown in  FIG. 6( b ) , the discharging side of the hydraulic pump  11  is coupled to the rod-side hydraulic chamber  63   a  of the hydraulic cylinder  61 , while the tank  12  is coupled to the head-side pressure chamber  63   b  of the hydraulic cylinder  61 . Because of this, a trial run of the hydraulic cylinder  61  is performed only for the contracting direction of the rod  65  of the hydraulic cylinder  61 . 
     Second Embodiment 
       FIG. 8  illustrates a circuit diagram of a second embodiment. When the tank-side bypass stop valve  35   a  and the pump-side bypass stop valve  36   a  of the composite valve  30  are replaced to a direction switching valve  45  as shown in  FIG. 8 , a trial run of the hydraulic cylinder  61  is performed for the extending and contracting directions, through operation on the direction switching valve  45 . Note that, the direction switching valve  45  has the three positions of: a neutral position  45   a ; a first position  45   b ; and a second position  45   c ; however, the direction switching valve may be a two-position type direction switching valve having the neutral position and either one of the first and second positions. 
     When the direction switching valve  45  is shifted to the neutral position  45   a  as shown in the figure, the tank-side bypass circuit  35   b  and the pump-side bypass circuit  36   b  are closed, and therefore the hydraulic cylinder  61  remains stopped. 
     When the direction switching valve  45  is shifted to the first position  45   b , the tank-side bypass circuit  35   b  and the pump-side bypass circuit  36   b  are opened, and thereby the head-side pressure chamber  63   b  communicates with the hydraulic pump  11 , and the tank  12  communicates with the rod-side pressure chamber  63   a , so that the rod  65  operates in the extending direction. 
     Meanwhile, when the direction switching valve  45  is shifted to the second position  45   c , the tank-side bypass circuit  35   b  establishes communication between the tank-side passage  34   b  and the multifunction valve-side first passage  31   b , and the pump-side bypass circuit  36   b  establishes communication between the pump-side passage  33   b  and the multifunction valve-side second passage  32   b . As a result, the rod-side hydraulic chamber  63   a  communicates with the hydraulic pump  11 , and the tank  12  communicates with the head-side hydraulic chamber  63   b , and therefore the rod  65  operates in the contracting direction. 
     Furthermore, when the third stop valve  40   c  of the multifunction valve  40  is opened with the other valves (the first stop valve  40   a  and the second stop valve  40   b ) closed, the supply/discharge of the hydraulic oil to/from the hydraulic cylinder  61  is stopped. However, the bypass circuit  42   b  of the multifunction valve  40  allows the first supply/discharge circuit  38   a  to communicate with the second supply/discharge circuit  38   b , and this makes it possible to perform flushing on the first supply/discharge circuit  38   a  and the second supply/discharge circuit  38   b.    
     In the above flushing operation, shifting the direction switching valve  45  to the first position  45   b  causes the oil to flow in the clockwise direction, whereas shifting the direction switching valve  45  to the second position  45   c  causes the oil to flow in the counterclockwise direction. Thus, by changing the direction of the flow in flushing, hard-to-remove contamination can be flushed. 
     When the third stop valve  40   c  of the multifunction valve  40  is opened with its remaining stop valves closed, it is possible to completely separate the hydraulic device  60  including the hydraulic cylinder  61  from the stack valve  20  and from the hydraulic power supplier  10 , to perform repair, inspection, and/or maintenance on the hydraulic cylinder  61 . 
     The above-described operation of repair, inspection, and/or maintenance on the stack valve  20  and the hydraulic cylinder  61  is performed after the stack valve  20  and the hydraulic cylinder  61  are completely separable because of the composite valve  30  and the multifunction valve  40 , and this eliminates the possibility of entry of a contaminant. In addition, during repair, inspection, and/or maintenance, there is no need to stop the hydraulic power supplier  10 , and it is possible to structure a circuit for flushing. Therefore, flushing is performable in parallel with repair, inspection, and/or maintenance. Furthermore, it is possible to perform a trial run and/or operation for a slight movement of the hydraulic cylinder  61  after repair, inspection, and/or maintenance of the hydraulic cylinder  61  is/are completed and the hydraulic cylinder  61  is reattached to the multifunction valve  40 . 
     REFERENCE SIGNS LIST 
     
         
           10  hydraulic power supplier 
           11  hydraulic pump 
           12  tank 
           20  stack valve 
           21  direction switching valve unit 
           22  direction switching valve unit 
           23  load check valve unit 
           24  speed control valve unit 
           26  first left passage structure 
           26   k  first left U-shape passage 
           27  first right passage structure 
           27   t  first T-shape passage 
           28  second right passage structure 
           28   k  second right U-shape passage 
           29  second left passage structure 
           29   k  second left U-shape passage 
           29   t  second T-shape passage 
           30  composite valve 
           31   a  multifunction valve-side first stop valve 
           31   b  multifunction valve-side first passage 
           32   a  multifunction valve-side second stop valve 
           33   a  pump-side stop valve 
           33   b  pump-side passage 
           34   a  tank-side stop valve 
           34   b  tank-side passage 
           35   a  tank-side bypass stop valve 
           35   b  tank-side bypass circuit 
           36   a  pump-side bypass stop valve 
           36   b  pump-side bypass circuit 
           40  multifunction valve 
           45  direction switching valve 
           60  hydraulic device 
           61  hydraulic cylinder