Patent Publication Number: US-11028860-B2

Title: Pressure booster

Description:
TECHNICAL FIELD 
     The present invention relates to a pressure booster for increasing the pressure of pressurized fluid and outputting the pressurized fluid. 
     BACKGROUND ART 
     Conventionally, there has been known a pressure booster that consecutively increases the pressure of pressurized fluid using reciprocating motion of a piston and then outputs the pressurized fluid. 
     For example, a pressure booster described in Japanese Laid-Open Patent Publication No. 08-021404 includes a pair of booster cylinders disposed to face each other and an energy collector cylinder disposed between the pair of booster cylinders. The booster cylinders and the energy collector cylinder include their respective pistons directly connected to a piston rod. In the pressure booster, compressed air is supplied to a compression chamber and a working chamber of one of the booster cylinders and to a compression chamber of the other booster cylinder, whereby the air supplied to the compression chamber of the one booster cylinder is boosted in pressure and then output. Switching operation of air-supply between the booster cylinders and of flow channels connected to the collector cylinder is performed by reed switches detecting the positions of the pistons in the booster cylinders to thereby turn on and off solenoids of a switching valve accordingly. 
     SUMMARY OF INVENTION 
     In the pressure booster described in Japanese Laid-Open Patent Publication No. 08-021404, the pair of booster cylinders are provided with the working chambers for driving the pistons and the compression chambers for compressing fluid. This may limit flexibility in design. In addition, since the reed switches and the solenoids are used to perform the switching operation, electrical means including electrical wiring is required. 
     The present invention has the object of providing a pressure booster including cylinders for driving pistons and for compressing pressurized fluid that are arranged separately in an organized manner, and which is capable of performing switching operations without electrical means. 
     A pressure booster according to the present invention, including a booster cylinder and drive cylinders disposed respectively on both sides of the booster cylinder, includes a pair of pilot valves each configured to be actuated when a piston of the corresponding drive cylinder is in abutment with the pilot valve at a moving end of the piston, and a pair of operating valves each configured to switch a state of supply of pressurized fluid from a pressurized fluid supply source, between pressure chambers of the drive cylinders, wherein when each of the pilot valves is actuated, the pressurized fluid is supplied to the pair of operating valves through the corresponding pilot valve to thereby switch the state of supply of the pressurized fluid. 
     Moreover, a pressure booster according to the present invention, including a booster cylinder and drive cylinders disposed respectively on both sides of the booster cylinder, includes a pair of pilot valves each configured to be actuated when a piston of the corresponding drive cylinder is in abutment with the pilot valve at a moving end of the piston, and a pair of operating valves each configured to switch a state of supply of pressurized fluid from a pressurized fluid supply source, between pressure chambers of the drive cylinders, wherein when each of the pilot valves is actuated, pressurized fluid from the booster cylinder is supplied to the pair of operating valves through the corresponding pilot valve to thereby switch the state of supply of the pressurized fluid. 
     According to the above-described pressure booster, it is possible to enhance flexibility in design. For example, it is possible to make the inner diameter of the cylinders for driving the pistons different from the inner diameter of the cylinder for compressing pressurized fluid. Moreover, since the pilot valves and the operating valves can be operated using mechanical means including fluid circuits, the need for electrical means including electrical wiring is eliminated. 
     In the above-described pressure booster, it is preferable that each of the operating valves switch between a state in which the pressurized fluid is supplied to the pressure chamber of the corresponding drive cylinder and pressurized fluid in a back pressure chamber of the corresponding drive cylinder is discharged, and a state in which part of the pressurized fluid in the pressure chamber of the corresponding drive cylinder is collected in the back pressure chamber of the corresponding drive cylinder. This makes it possible to reduce the consumption of pressurized fluid as much as possible. 
     In this case, it is preferable that each of the pilot valves include a push rod configured to protrude to an inside of the back pressure chamber of the corresponding drive cylinder by a biasing force of a spring and that the piston of the corresponding drive cylinder come into abutment with the push rod at the moving end. According to this, the pilot valves are actuated in a stable manner since the pilot valves are disposed in areas in which fluid pressure fluctuation is less likely to occur. In addition, when a silencer is provided in a channel through which the pressurized fluid in each of the back pressure chambers of the drive cylinders, it is possible to reduce exhaust noise generated at the operating valves and to prevent leakage, to the outside, of striking noise generated when the pistons of the drive cylinders come into abutment against the push rods of the pilot valves as much as possible. 
     Moreover, it is preferable that each of the push rods include a piston portion, that a space on a first side of the piston portion be exposed to an atmosphere while a space on a second side of the piston portion is connected to a pilot channel for switching the states of the pair of operating valves, and that the space on the first side and the space on the second side communicate with each other via a hole formed inside the push rod when the piston of each of the drive cylinders is not in abutment with the push rod. According to this, the pilot channel for switching the states of the operating valves can communicate with the atmosphere by using a simple structure. 
     Furthermore, each of the pilot valves may include a valve element with which the corresponding push rod is abuttable, and when the piston of each of the drive cylinders comes into abutment with the push rod and then brings the push rod into abutment with the valve element, the space on the second side may be connected to the pressurized fluid supply source or to a corresponding booster chamber of the booster cylinder and may be sealed from the hole formed inside the push rod. Moreover, each of the push rods may be slidably disposed inside a valve seat and a valve seat retainer, a first end face of the valve seat retainer may face the back pressure chamber of the corresponding drive cylinder while a second end face thereof is in abutment with the valve seat, and the space on the first side may include a groove formed on the second end face of the valve seat retainer. 
     In accordance with the pressure booster according to the present invention, flexibility in designing the cylinders for driving the pistons and the cylinder for compressing pressurized fluid can be increased, and the need for electrical means including electrical wiring for the pilot valves and the operating valves is eliminated. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic perspective view of a pressure booster according to a first embodiment of the present invention; 
         FIG. 2  is a side view of the pressure booster in FIG.  1 ; 
         FIG. 3  is a cross-sectional view taken along line III-III in  FIG. 2 ; 
         FIG. 4  is a cross-sectional view taken along line IV-IV in  FIG. 2 ; 
         FIG. 5  is a cross-sectional view taken along line V-V in  FIG. 2 ; 
         FIG. 6  is an overall schematic view of the pressure booster in  FIG. 1  using a circuit diagram; 
         FIG. 7  is an enlarged view of part B in  FIG. 5 ; 
         FIG. 8  is an enlarged view of the part B in  FIG. 5  when a pilot valve is actuated; 
         FIG. 9  is a view, corresponding to  FIG. 6 , illustrating a state of the pressure booster after transition from the state illustrated in  FIG. 6  to another state; 
         FIG. 10  is a view, corresponding to  FIG. 6 , illustrating another state of the pressure booster after transition from the state illustrated in  FIG. 9  to still another state; 
         FIG. 11  is an overall schematic view of a pressure booster according to a second embodiment of the present invention using a circuit diagram; and 
         FIG. 12  is a view, corresponding to  FIG. 11 , illustrating a state of the pressure booster after transition from the state illustrated in  FIG. 11  to another state. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Preferred embodiments of a pressure booster according to the present invention will be described in detail below with reference to the accompanying drawings. 
     First Embodiment 
     A pressure booster  10  according to a first embodiment of the present invention will now be described with reference to  FIGS. 1 to 10 . The pressure booster  10  is disposed between a pressurized fluid supply source (compressor; not illustrated) and an actuator (not illustrated) actuated by pressurized fluid whose pressure is boosted. 
     As illustrated in  FIGS. 1 and 3 , the pressure booster  10  has a triple cylinder structure including a booster cylinder  12 , a first drive cylinder  14  disposed at a first end of the booster cylinder  12  (an end on an A1 direction side), and a second drive cylinder  16  disposed at a second end of the booster cylinder  12  (an end on an A2 direction side), which are connected in a row. That is, in the pressure booster  10 , the first drive cylinder  14 , the booster cylinder  12 , and the second drive cylinder  16  are arranged in this order from the A1 direction to the A2 direction. 
     A first cover member  18  in the form of a block is interposed between the first drive cylinder  14  and the booster cylinder  12 , and a second cover member  20  in the form of a block is interposed between the booster cylinder  12  and the second drive cylinder  16 . 
     The booster cylinder  12  includes a booster chamber  22  formed thereinside. The first drive cylinder  14  and the second drive cylinder  16  respectively include a first drive chamber  24  and a second drive chamber  26  formed thereinside. In this case, the first drive chamber  24  is formed by securing a third cover member  28  to an end portion of the first drive cylinder  14  on the A1 direction side and arranging the first cover member  18  at another end portion on the A2 direction side. The second drive chamber  26  is formed by arranging the second cover member  20  at an end portion of the second drive cylinder  16  on the A1 direction side and closing another end portion on the A2 direction side with a wall portion  30 . 
     As illustrated in  FIG. 3 , a piston rod  32  is arranged to pass through the first cover member  18 , the booster cylinder  12 , and the second cover member  20 . The piston rod  32  includes two shaft members connected in series. A first end portion of the piston rod  32  extends into the first drive chamber  24 , and a second end portion of the piston rod  32  extends into the second drive chamber  26 . 
     In the booster chamber  22 , a booster piston  34  is connected to the midsection of the piston rod  32 . Thus, the booster chamber  22  is partitioned into a first booster chamber  22   a  on the A1 direction side and a second booster chamber  22   b  on the A2 direction side (see  FIG. 6 ). In the first drive chamber  24 , a first drive piston  36  is connected to the first end portion of the piston rod  32 . Thus, the first drive chamber  24  is partitioned into a pressure chamber  24   a  on the A1 direction side and a back pressure chamber  24   b  on the A2 direction side (see  FIG. 6 ). Moreover, in the second drive chamber  26 , a second drive piston  38  is connected to the second end portion of the piston rod  32 . Thus, the second drive chamber  26  is partitioned into a pressure chamber  26   a  on the A2 direction side and a back pressure chamber  26   b  on the A1 direction side (see  FIG. 6 ). The booster piston  34 , the first drive piston  36 , and the second drive piston  38  are connected to each other in an integrated manner via the piston rod  32 . 
     As illustrated in  FIG. 1 , a supply port  40 , to which pressurized fluid is supplied from the pressurized fluid supply source (not illustrated), is formed in an upper portion of the front surface of the booster cylinder  12 . As illustrated in  FIGS. 4 and 6 , a fluid supply mechanism is provided inside the booster cylinder  12 , the first cover member  18 , and the second cover member  20 . The fluid supply mechanism communicates with the supply port  40  and delivers supplied pressurized fluid to the first booster chamber  22   a  and the second booster chamber  22   b . The fluid supply mechanism includes a first supply channel  42   a  connecting the supply port  40  to the first booster chamber  22   a  and a second supply channel  42   b  connecting the supply port  40  to the second booster chamber  22   b.    
     The first supply channel  42   a  is provided with a first supply check valve  42   c  that allows fluid to flow from the supply port  40  to the first booster chamber  22   a  but does not allow fluid to flow from the first booster chamber  22   a  to the supply port  40 . The second supply channel  42   b  is provided with a second supply check valve  42   d  that allows fluid to flow from the supply port  40  to the second booster chamber  22   b  but does not allow fluid to flow from the second booster chamber  22   b  to the supply port  40 . 
     As illustrated in  FIG. 1 , an output port  44  is formed in a lower portion of the front surface of the booster cylinder  12  to output fluid that has been boosted in pressure by pressure boost (described below), to the outside. As illustrated in  FIGS. 4 and 6 , a fluid output mechanism is provided inside the booster cylinder  12 , the first cover member  18 , and the second cover member  20 . The fluid output mechanism communicates with the output port  44  and outputs fluid boosted in pressure in the first booster chamber  22   a  or the second booster chamber  22   b , from the output port  44 . The fluid output mechanism includes a first output channel  46   a  connecting the first booster chamber  22   a  to the output port  44  and a second output channel  46   b  connecting the second booster chamber  22   b  to the output port  44 . 
     The first output channel  46   a  is provided with a first output check valve  46   c  that allows fluid to flow from the first booster chamber  22   a  to the output port  44  but does not allow fluid to flow from the output port  44  to the first booster chamber  22   a . The second output channel  46   b  is provided with a second output check valve  46   d  that allows fluid to flow from the second booster chamber  22   b  to the output port  44  but does not allow fluid to flow from the output port  44  to the second booster chamber  22   b.    
     Next, the configuration of operating valves will be described. As illustrated in  FIG. 1 , a first housing  50  including a first operating valve  48  is disposed on top of the first drive cylinder  14 , and a second housing  54  including a second operating valve  52  is disposed on top of the second drive cylinder  16 . 
     As illustrated in  FIG. 6 , the first operating valve  48  has a first port  56 A to a fifth port  56 E and is configured to switch between a first position where the first drive piston  36  is driven and a second position where the first drive piston  36  follows the movement of the second drive piston  38  as the second drive piston  38  is driven. 
     The first port  56 A is connected to the pressure chamber  24   a  of the first drive cylinder  14  via a channel  58   a . The second port  56 B is connected to the back pressure chamber  24   b  of the first drive cylinder  14  via a channel  58   b . The third port  56 C is connected to the first supply channel  42   a  via a channel  58   c . The fourth port  56 D is connected to a first silencer  62  equipped with an exhaust port, via a channel  58   d . The fifth port  56 E is connected to a midway point of the channel  58   a  via a channel  58   e . A first fixed orifice  60  is disposed on the channel  58   d.    
     When the first operating valve  48  is in the first position, the first port  56 A is connected to the third port  56 C, and the second port  56 B is connected to the fourth port  56 D. As a result, pressurized fluid from the supply port  40  is supplied to the pressure chamber  24   a  through the channel  58   c  and the channel  58   a , and fluid in the back pressure chamber  24   b  is discharged via the first fixed orifice  60  and the first silencer  62  through the channel  58   b  and the channel  58   d . When the first operating valve  48  is in the second position, the first port  56 A is connected to the fourth port  56 D, and the second port  56 B is connected to the fifth port  56 E. As a result, part of the fluid in the pressure chamber  24   a  is collected in the back pressure chamber  24   b  through the channel  58   a , the channel  58   e , and the channel  58   b , and the rest is discharged via the first fixed orifice  60  and the first silencer  62  through the channel  58   d.    
     The first operating valve  48  has a first introduction port  63 A through which pressurized fluid is introduced from a first pilot valve  72  (described below) and a second introduction port  63 B through which pressurized fluid is introduced from a second pilot valve  74  (described below). The first operating valve  48  switches from the first position to the second position when pressurized fluid is supplied to the first introduction port  63 A, and remains in the second position until pressurized fluid is supplied to the second introduction port  63 B subsequently. The first operating valve  48  switches from the second position to the first position when pressurized fluid is supplied to the second introduction port  63 B, and remains in the first position until pressurized fluid is supplied to the first introduction port  63 A subsequently. 
     The second operating valve  52  has a first port  64 A to a fifth port  64 E and is configured to switch between a first position where the second drive piston  38  is driven and a second position where the second drive piston  38  follows the movement of the first drive piston  36  as the first drive piston  36  is driven. 
     The first port  64 A is connected to the pressure chamber  26   a  of the second drive cylinder  16  via a channel  66   a . The second port  64 B is connected to the back pressure chamber  26   b  of the second drive cylinder  16  via a channel  66   b . The third port  64 C is connected to the second supply channel  42   b  via a channel  66   c . The fourth port  64 D is connected to a second silencer  70  equipped with an exhaust port, via a channel  66   d . The fifth port  64 E is connected to a midway point of the channel  66   a  via a channel  66   e . A second fixed orifice  68  is disposed on the channel  66   d.    
     When the second operating valve  52  is in the first position, the first port  64 A is connected to the third port  64 C, and the second port  64 B is connected to the fourth port  64 D. As a result, pressurized fluid from the supply port  40  is supplied to the pressure chamber  26   a  through the channel  66   c  and the channel  66   a , and fluid in the back pressure chamber  26   b  is discharged via the second fixed orifice  68  and the second silencer  70  through the channel  66   b  and the channel  66   d . When the second operating valve  52  is in the second position, the first port  64 A is connected to the fourth port  64 D, and the second port  64 B is connected to the fifth port  64 E. As a result, part of the fluid in the pressure chamber  26   a  is collected in the back pressure chamber  26   b  through the channel  66   a , the channel  66   e , and the channel  66   b , and the rest is discharged via the second fixed orifice  68  and the second silencer  70  through the channel  66   d.    
     The second operating valve  52  has a first introduction port  71 A through which pressurized fluid is introduced from the first pilot valve  72  (described below) and a second introduction port  71 B through which pressurized fluid is introduced from the second pilot valve  74  (described below). The second operating valve  52  switches from the second position to the first position when pressurized fluid is supplied to the first introduction port  71 A, and remains in the first position until pressurized fluid is supplied to the second introduction port  71 B subsequently. The second operating valve  52  switches from the first position to the second position when pressurized fluid is supplied to the second introduction port  71 B, and remains in the second position until pressurized fluid is supplied to the first introduction port  71 A subsequently. 
     Next, the configuration of the pilot valves will be described. As illustrated in  FIG. 5 , the first pilot valve  72  is disposed inside the first cover member  18 , and the second pilot valve  74  is disposed inside the second cover member  20 . The first pilot valve  72  and the second pilot valve  74  have a common structure. Thus, the structure of the pilot valves will be described first in a collective manner with reference to  FIG. 7 . 
     The first pilot valve  72  and the second pilot valve  74  each include a valve seat  76 , a valve seat retainer  78 , a valve element  80 , and a push rod  82 . The first cover member  18  and the second cover member  20  each has a valve accommodating hole  84  which is closed on a side adjacent to the booster cylinder  12  and opened on the opposite side. 
     The valve seat  76  and the valve seat retainer  78 , both having a cylindrical shape, are fitted into the valve accommodating hole  84 . A first end face of the valve seat retainer  78  in the axial direction faces the back pressure chamber  24   b  of the first drive cylinder  14  or the back pressure chamber  26   b  of the second drive cylinder  16 , and a second end face in the axial direction is in abutment against the valve seat  76 . A snap ring  87  is secured to the opening of the valve accommodating hole  84  via a groove, and the snap ring  87  is in abutment against the valve seat retainer  78 . Thus, the valve seat  76  and the valve seat retainer  78  are positioned and secured in the axial direction. 
     The inner circumference of the valve seat retainer  78  has an increased diameter on the second end side in the axial direction, whereby an annular recess  98  is formed. The valve seat retainer  78  has a plurality of grooves  100  extending radially, which are formed in the second end face in the axial direction. The grooves  100  communicate with the annular recess  98  on the inner circumference and communicate with the atmosphere on the outer circumference via paths (not illustrated). The inner diameter of the valve seat retainer  78  at the annular recess  98  is smaller than the inner diameter of a portion of the valve seat  76  that lies adjacent to the valve seat retainer  78 . That is, the end face of the valve seat retainer  78  in abutment against the valve seat  76  protrudes inward more than the valve seat  76 . 
     An annular flange portion  88  protruding inward is provided on the inner circumference of the valve seat  76 . In addition, an annular protrusion  88   a  protruding toward the bottom of the valve accommodating hole  84  is formed on the end of the annular flange portion  88 . A first annular recess  90  and a second annular recess  92  are formed in the outer circumference of the valve seat  76 . The valve seat  76  has a plurality of first through-holes  94 , extending from the bottom of the first annular recess  90  to the inner circumference of the valve seat  76 , in a region closer to the bottom of the valve accommodating hole  84  than the annular flange portion  88  is. The valve seat  76  has a plurality of second through-holes  96 , extending from the bottom of the second annular recess  92  to the inner circumference of the valve seat  76 , in a region closer to the opening of the valve accommodating hole  84  than the annular flange portion  88  is. 
     The push rod  82  is slidably disposed inside the valve seat  76  and the valve seat retainer  78 . The push rod  82  includes a head portion  82   a  at a first end thereof in the axial direction and a piston portion  82   b  in the middle in the axial direction. The head portion  82   a  is in sliding contact with the inner circumferential surface of the valve seat retainer  78 , and the piston portion  82   b  is in sliding contact with the inner circumferential surface of the valve seat  76 . The push rod  82  includes a reduced-diameter portion  82   d  formed at a second end in the axial direction via a stepped portion  82   c . The end of the reduced-diameter portion  82   d  can be brought into abutment against the valve element  80 . A central hole  82   e  and a plurality of radially-extending holes  82   f  are formed inside the push rod  82 . The central hole  82   e  passes through the reduced-diameter portion  82   d  in the axial direction and further extends in the axial direction to reach the head portion  82   a . The radially-extending holes  82   f  are orthogonal to the central hole  82   e  and are opened in the outer circumferential surface of the head portion  82   a.    
     A first spring  102  is provided between the annular flange portion  88  of the valve seat  76  and the piston portion  82   b  of the push rod  82 . The push rod  82  is biased in a direction away from the booster cylinder  12  by the biasing force of the first spring  102 , and part of the head portion  82   a  protrudes to the inside of the back pressure chamber  24   b  of the first drive cylinder  14  or to the inside of the back pressure chamber  26   b  of the second drive cylinder  16 . The end face of the piston portion  82   b  comes into abutment with the end face of the valve seat retainer  78  to thereby restrict the movement of the push rod  82  in the direction away from the booster cylinder  12 . 
     The cylindrical valve element  80  is disposed inside the valve seat  76  in a position closer to the bottom of the valve accommodating hole  84  than the annular flange portion  88  is. A second spring  104  is provided between the bottom of the valve accommodating hole  84  and the valve element  80 . The valve element  80  is biased toward the annular flange portion  88  of the valve seat  76  by the biasing force of the second spring  104 . 
     A first seal member  110   a  and a second seal member  110   b  are provided on the outer circumference of the valve seat  76  via grooves. The first seal member  110   a  and the second seal member  110   b  are in pressure contact with the inner wall of the valve accommodating hole  84 . A third seal member  110   c  is provided on the outer circumference of the valve seat retainer  78  via a groove. The third seal member  110   c  is in pressure contact with the inner wall of the valve accommodating hole  84 . A fourth seal member  110   d  is provided on the inner circumference of the valve seat retainer  78  via a groove. The fourth seal member  110   d  is in sliding contact with the outer circumferential surface of the head portion  82   a  of the push rod  82 . A fifth seal member  110   e  is provided on the piston portion  82   b  of the push rod  82  via a groove. The fifth seal member  110   e  is in sliding contact with the inner circumferential surface of the valve seat  76 . 
     The first pilot valve  72  and the second pilot valve  74  are configured as above. Next, the first pilot valve  72  and the second pilot valve  74  will be described with reference to  FIGS. 6 to 8 , in relation to the surrounding channels. 
     A channel  86   a   1  is formed inside the first cover member  18 . A first end of the channel  86   a   1  communicates with the first annular recess  90  of the valve seat  76  in the first pilot valve  72 , and a second end thereof is connected to the first supply channel  42   a . A pilot channel  86   b   1  is formed inside the first cover member  18  and the first housing  50 . A first end of the pilot channel  86   b   1  communicates with the second annular recess  92  of the valve seat  76  in the first pilot valve  72 , and a second end thereof extends to the first introduction port  63 A of the first operating valve  48 . A pilot channel  86   c   1  is formed inside the first cover member  18 , the booster cylinder  12 , and the second housing  54 . The pilot channel  86   c   1  branches off from the pilot channel  86   b   1  and extends to the first introduction port  71 A of the second operating valve  52 . 
     As illustrated in  FIG. 7 , in the first pilot valve  72 , the space inside the valve seat  76  is hermetically partitioned into a first area  106  communicating with the first through-holes  94  and a second area  108  communicating with the second through-holes  96  when the reduced-diameter portion  82   d  of the push rod  82  is not in abutment with the valve element  80 , i.e., when the valve element  80  is in pressure contact with the annular protrusion  88   a  of the annular flange portion  88  by the biasing force of the second spring  104 . In addition, the second area  108  communicates with the central hole  82   e  of the push rod  82 . The second area  108  communicates with the pilot channel  86   b   1  via the second through-holes  96  and the second annular recess  92  of the valve seat  76 , and the central hole  82   e  of the push rod  82  is exposed to the atmosphere via the radially-extending holes  82   f  and the annular recess  98  and the grooves  100  of the valve seat retainer  78 . Consequently, the pilot channel  86   b   1  is exposed to the atmosphere under normal conditions. 
     On the other hand, as illustrated in  FIG. 8 , in the first pilot valve  72 , the first through-holes  94  and the second through-holes  96  of the valve seat  76  communicate with each other via the space inside the valve seat  76  in a state that the valve element  80  is pushed by the end of the reduced-diameter portion  82   d  of the push rod  82  to be separated from the annular protrusion  88   a  of the annular flange portion  88  (i.e., in a state that the pilot valve is actuated). In addition, when the reduced-diameter portion  82   d  of the push rod  82  is in pressure contact with the end face of the valve element  80 , the central hole  82   e  of the push rod  82  is sealed from the space inside the valve seat  76 . Thus, the pilot channel  86   b   1  communicating with the second through-holes  96  via the second annular recess  92  is connected to the channel  86   a   1  communicating with the first through-holes  94  via the first annular recess  90 . Consequently, in the above-described state, the pilot channel  86   b   1  is connected to the supply port  40  via the channel  86   a   1 . 
     A channel  86   a   2  is formed inside the second cover member  20 . A first end of the channel  86   a   2  communicates with the first annular recess  90  of the valve seat  76  in the second pilot valve  74 , and a second end thereof is connected to the second supply channel  42   b . A pilot channel  86   b   2  is formed inside the second cover member  20  and the second housing  54 . A first end of the pilot channel  86   b   2  communicates with the second annular recess  92  of the valve seat  76  in the second pilot valve  74 , and a second end thereof extends to the second introduction port  71 B of the second operating valve  52 . A pilot channel  86   c   2  is formed inside the second cover member  20 , the booster cylinder  12 , and the first housing  50 . The pilot channel  86   c   2  branches off from the pilot channel  86   b   2  and extends to the second introduction port  63 B of the first operating valve  48 . 
     As illustrated in  FIG. 7 , in the second pilot valve  74 , the space inside the valve seat  76  is hermetically partitioned into the first area  106  communicating with the first through-holes  94  and the second area  108  communicating with the second through-holes  96  when the valve element  80  is in pressure contact with the annular protrusion  88   a  of the annular flange portion  88  by the biasing force of the second spring  104  as the reduced-diameter portion  82   d  of the push rod  82  is not in abutment with the valve element  80 . In addition, the second area  108  communicates with the central hole  82   e  of the push rod  82 . The second area  108  communicates with the pilot channel  86   b   2  via the second through-holes  96  and the second annular recess  92  of the valve seat  76 , and the central hole  82   e  of the push rod  82  is exposed to the atmosphere via the radially-extending holes  82   f  and the annular recess  98  and the grooves  100  of the valve seat retainer  78 . Consequently, the pilot channel  86   b   2  is exposed to the atmosphere under normal conditions. 
     On the other hand, as illustrated in  FIG. 8 , in the second pilot valve  74 , the first through-holes  94  and the second through-holes  96  of the valve seat  76  communicate with each other via the space inside the valve seat  76  in a state that the valve element  80  is pushed by the end of the reduced-diameter portion  82   d  of the push rod  82  to be separated from the annular protrusion  88   a  of the annular flange portion  88  (i.e., in a state that the pilot valve is actuated). In addition, when the reduced-diameter portion  82   d  of the push rod  82  is in pressure contact with the end face of the valve element  80 , the central hole  82   e  of the push rod  82  is sealed from the space inside the valve seat  76 . Thus, the pilot channel  86   b   2  communicating with the second through-holes  96  via the second annular recess  92  is connected to the channel  86   a   2  communicating with the first through-holes  94  via the first annular recess  90 . Consequently, in the above-described state, the pilot channel  86   b   2  is connected to the supply port  40  via the channel  86   a   2 . 
     The pressure booster  10  according to the first embodiment is basically configured as above. Next, the operations and operational effects thereof will be described. A state in which the first operating valve  48  is switched to the second position, the second operating valve  52  is switched to the first position, and the booster piston  34  is located adjacent to the middle of the booster chamber  22  as illustrated in  FIG. 6  is defined as an initial position. 
     In the initial position, when pressurized fluid is supplied from the pressurized fluid supply source to the supply port  40 , the pressurized fluid flows into the first supply channel  42   a  and the second supply channel  42   b . The pressurized fluid is then introduced to the first booster chamber  22   a  and the second booster chamber  22   b  of the booster cylinder  12  via the first supply check valve  42   c  and the second supply check valve  42   d , respectively. 
     Part of the pressurized fluid supplied from the supply port  40  is supplied to the pressure chamber  26   a  of the second drive cylinder  16  through the channel  66   c , the second operating valve  52  in the first position, and the channel  66   a . The pressurized fluid supplied to the pressure chamber  26   a  drives the second drive piston  38  in the A1 direction. This causes the booster piston  34  connected to the second drive piston  38  in an integrated manner to slide, resulting in an increase in the pressure of the pressurized fluid in the first booster chamber  22   a  of the booster cylinder  12 . The boosted pressurized fluid is guided to and output from the output port  44  through the first output channel  46   a  and the first output check valve  46   c.    
     On the other hand, when the first drive piston  36  connected to the second drive piston  38  in an integrated manner slides, the volume of the pressure chamber  24   a  of the first drive cylinder  14  decreases. Since the first operating valve  48  is in the second position, part of the pressurized fluid in the pressure chamber  24   a  is collected in the back pressure chamber  24   b  through the channel  58   a , the channel  58   e , and the channel  58   b , and the rest is discharged through the channel  58   d.    
     As illustrated in  FIG. 9 , when the booster piston  34  is further displaced in the A1 direction to reach an end position, the second drive piston  38  comes into abutment with the head portion  82   a  of the push rod  82  in the second pilot valve  74  and causes the push rod  82  to be displaced. As a result, pressurized fluid supplied from the supply port  40  is supplied to the second introduction port  71 B of the second operating valve  52  through the channel  86   a   2 , the second pilot valve  74 , and the pilot channel  86   b   2 , and to the second introduction port  63 B of the first operating valve  48  through the pilot channel  86   c   2 . At this time, since the pilot channel  86   b   1  of the first pilot valve  72  is exposed to the atmosphere, the pressurized fluid supplied to the first introduction port  71 A of the second operating valve  52  is discharged to the atmosphere through the pilot channel  86   c   1  and the pilot channel  86   b   1 , and the pressurized fluid supplied to the first introduction port  63 A of the first operating valve  48  is discharged to the atmosphere through the pilot channel  86   b   1 . Consequently, the first operating valve  48  is switched to the first position, and the second operating valve  52  is switched to the second position. 
     Then, part of the pressurized fluid supplied from the supply port  40  is supplied to the pressure chamber  24   a  of the first drive cylinder  14  through the channel  58   c , the first operating valve  48  in the first position, and the channel  58   a . As illustrated in  FIG. 10 , the pressurized fluid supplied to the pressure chamber  24   a  drives the first drive piston  36  in the A2 direction. This causes the booster piston  34  connected to the first drive piston  36  in an integrated manner to slide, resulting in an increase in the pressure of the pressurized fluid in the second booster chamber  22   b  of the booster cylinder  12 . The boosted pressurized fluid is guided to and output from the output port  44  through the second output channel  46   b  and the second output check valve  46   d.    
     On the other hand, when the second drive piston  38  connected to the first drive piston  36  in an integrated manner slides, the volume of the pressure chamber  26   a  of the second drive cylinder  16  decreases. Since the second operating valve  52  is in the second position, part of the pressurized fluid in the pressure chamber  26   a  is collected in the back pressure chamber  26   b  through the channel  66   a , the channel  66   e , and the channel  66   b , and the rest is discharged through the channel  66   d.    
     When the piston rod  32  is further displaced in the A2 direction to reach an end position, the first drive piston  36  comes into abutment with the head portion  82   a  of the push rod  82  in the first pilot valve  72  and causes the push rod  82  to be displaced (not illustrated). As a result, pressurized fluid supplied from the supply port  40  is supplied to the first introduction port  63 A of the first operating valve  48  through the channel  86   a   1 , the first pilot valve  72 , and the pilot channel  86   b   1 , and to the first introduction port  71 A of the second operating valve  52  through the pilot channel  86   c   1 . At this time, since the pilot channel  86   b   2  of the second pilot valve  74  is exposed to the atmosphere, the pressurized fluid supplied to the second introduction port  63 B of the first operating valve  48  is discharged to the atmosphere through the pilot channel  86   c   2  and the pilot channel  86   b   2 , and the pressurized fluid supplied to the second introduction port  71 B of the second operating valve  52  is discharged to the atmosphere through the pilot channel  86   b   2 . Consequently, the first operating valve  48  is switched to the second position, and the second operating valve  52  is switched to the first position. The booster piston  34  repeats the reciprocating motion in the above manner to consecutively output boosted pressurized fluid from the output port  44 . 
     The pressure booster  10  according to this embodiment performs switching of the first operating valve  48  and the second operating valve  52  and actuation of the first pilot valve  72  and the second pilot valve  74  using mechanical means including fluid circuits without the need for electrical means. 
     Moreover, part of the pressurized fluid that has been supplied to the pressure chamber  24   a  to drive the first drive piston  36  is collected in the back pressure chamber  24   b  when the first drive piston  36  is driven by the movement of the second drive piston  38  as the second drive piston  38  is driven. This makes it possible to reduce the consumption of pressurized fluid. Similarly, part of the pressurized fluid that has been supplied to the pressure chamber  26   a  to drive the second drive piston  38  is collected in the back pressure chamber  26   b  when the second drive piston  38  is driven by the movement of the first drive piston  36  as the first drive piston  36  is driven. This also makes it possible to reduce the consumption of pressurized fluid. 
     Furthermore, the push rods  82  face the back pressure chamber  24   b  of the first drive cylinder  14  and the back pressure chamber  26   b  of the second drive cylinder  16  respectively. Since fluid pressure fluctuation is less likely to occur in the back pressure chambers, the first pilot valve  72  and the second pilot valve  74  can be operated stably. Alternatively, the first pilot valve  72  and the second pilot valve  74  may be disposed to face respectively the second booster chamber  22   b  and the first booster chamber  22   a  of the booster cylinder  12 . In this case, care must be given so that an increase in the fluid pressure in the first booster chamber  22   a  or the second booster chamber  22   b  may adversely affect the operation of the push rods  82 . 
     Yet moreover, the first silencer  62  is provided in the channel  58   d  through which pressurized fluid in the back pressure chamber  24   b  of the first drive cylinder  14  is discharged. This reduces exhaust noise generated at the first operating valve  48  and prevents leakage of striking noise generated when the first drive piston  36  comes into abutment against the push rod  82  of the first pilot valve  72 , to the outside. Similarly, the second silencer  70  is provided in the channel  66   d  discharging pressurized fluid in the back pressure chamber  26   b  of the second drive cylinder  16 . This reduces exhaust noise generated at the second operating valve  52  and prevents leakage of striking noise generated when the second drive piston  38  comes into abutment against the push rod  82  of the second pilot valve  74 , to the outside. 
     Second Embodiment 
     Next, a pressure booster  120  according to a second embodiment of the present invention will be described with reference to  FIGS. 11 and 12 . The second embodiment differs from the first embodiment in the sources and paths of pressurized fluid supplied to the first annular recesses  90  of the pilot valves. In the pressure booster  120  according to the second embodiment, the same reference numerals and symbols are used for components identical to those in the pressure booster  10  described above, and the detailed descriptions will be omitted. 
     A channel  87   a   1  is formed inside the first cover member  18  and the booster cylinder  12 . A first end of the channel  87   a   1  communicates with the first annular recess  90  of the valve seat  76  in the first pilot valve  72 , and a second end thereof is connected to the second booster chamber  22   b . The pilot channel  86   b   1  is formed inside the first cover member  18  and the first housing  50 . The first end of the pilot channel  86   b   1  communicates with the second annular recess  92  of the valve seat  76  in the first pilot valve  72 , and the second end extends to the first introduction port  63 A of the first operating valve  48 . The pilot channel  86   c   1  is formed inside the first cover member  18 , the booster cylinder  12 , and the second housing  54 . The pilot channel  86   c   1  branches off from the pilot channel  86   b   1  and extends to the first introduction port  71 A of the second operating valve  52 . 
     While the first pilot valve  72  is not actuated (see  FIG. 7 ), the pilot channel  86   b   1  is exposed to the atmosphere. On the other hand, while the first pilot valve  72  is actuated (see  FIG. 8 ), the pilot channel  86   b   1  is connected to the second booster chamber  22   b  via the channel  87   a   1 . 
     A channel  87   a   2  is formed inside the second cover member  20  and the booster cylinder  12 . A first end of the channel  87   a   2  communicates with the first annular recess  90  of the valve seat  76  in the second pilot valve  74 , and a second end thereof is connected to the first booster chamber  22   a . The pilot channel  86   b   2  is formed inside the second cover member  20  and the second housing  54 . The first end of the pilot channel  86   b   2  communicates with the second annular recess  92  of the valve seat  76  in the second pilot valve  74 , and the second end extends to the second introduction port  71 B of the second operating valve  52 . The pilot channel  86   c   2  is formed inside the second cover member  20 , the booster cylinder  12 , and the first housing  50 . The pilot channel  86   c   2  branches off from the pilot channel  86   b   2  and extends to the second introduction port  63 B of the first operating valve  48 . 
     While the second pilot valve  74  is not actuated (see  FIG. 7 ), the pilot channel  86   b   2  is exposed to the atmosphere. On the other hand, while the second pilot valve  74  is actuated (see  FIG. 8 ), the pilot channel  86   b   2  is connected to the first booster chamber  22   a  via the channel  87   a   2 . 
     Next, the operation of the pressure booster  120  according to the second embodiment will be described, focusing on the operation of the first pilot valve  72  and the second pilot valve  74 . A state in which the first operating valve  48  is switched to the second position, the second operating valve  52  is switched to the first position, and the booster piston  34  is located adjacent to the middle of the booster chamber  22  as illustrated in  FIG. 11  is defined as an initial position. 
     In the initial position, when pressurized fluid is supplied from the pressurized fluid supply source to the supply port  40 , the pressurized fluid is supplied to the pressure chamber  26   a  of the second drive cylinder  16 , and the second drive piston  38  is driven in the A1 direction. This causes the booster piston  34  connected to the second drive piston  38  in an integrated manner to slide, resulting in an increase in the pressure of the pressurized fluid in the first booster chamber  22   a  of the booster cylinder  12 . The boosted pressurized fluid in the first booster chamber  22   a  is guided to and output from the output port  44 . On the other hand, part of the fluid in the pressure chamber  24   a  of the first drive cylinder  14  is collected in the back pressure chamber  24   b , and the rest is discharged. The boosted pressurized fluid in the first booster chamber  22   a  is also introduced to the first annular recess  90  of the second pilot valve  74 . Since the second pilot valve  74  is not actuated at this moment, the pressurized fluid introduced to the first annular recess  90  remains as it is. 
     As illustrated in  FIG. 12 , when the booster piston  34  is further displaced in the A1 direction to reach the end position, the second drive piston  38  comes into abutment with the head portion  82   a  of the push rod  82  in the second pilot valve  74  and causes the push rod  82  to be displaced. As a result, the boosted pressurized fluid in the first booster chamber  22   a  is supplied to the second introduction port  71 B of the second operating valve  52  through the channel  87   a   2 , the second pilot valve  74 , and the pilot channel  86   b   2 , and to the second introduction port  63 B of the first operating valve  48  through the pilot channel  86   c   2 . Consequently, the first operating valve  48  is switched to the first position, and the second operating valve  52  is switched to the second position. 
     Then, pressurized fluid supplied from the supply port  40  is supplied to the pressure chamber  24   a  of the first drive cylinder  14 , and the first drive piston  36  is driven in the A2 direction. This causes the booster piston  34  connected to the first drive piston  36  in an integrated manner to slide, resulting in an increase in the pressure of the pressurized fluid in the second booster chamber  22   b  of the booster cylinder  12 . The boosted pressurized fluid is guided to and output from the output port  44 . On the other hand, part of the fluid in the pressure chamber  26   a  of the second drive cylinder  16  is collected in the back pressure chamber  26   b , and the rest is discharged. The boosted pressurized fluid in the second booster chamber  22   b  is also introduced to the first annular recess  90  of the first pilot valve  72 . Since the first pilot valve  72  is not actuated at this moment, the pressurized fluid introduced to the first annular recess  90  remains as it is. 
     When the piston rod  32  is further displaced in the A2 direction to reach the end position, the first drive piston  36  comes into abutment with the head portion  82   a  of the push rod  82  in the first pilot valve  72  and causes the push rod  82  to be displaced (not illustrated). As a result, the boosted pressurized fluid in the second booster chamber  22   b  is supplied to the first introduction port  63 A of the first operating valve  48  through the channel  87   a   1 , the first pilot valve  72 , and the pilot channel  86   b   1 , and to the first introduction port  71 A of the second operating valve  52  through the pilot channel  86   c   1 . Consequently, the first operating valve  48  is switched to the second position, and the second operating valve  52  is switched to the first position. The booster piston  34  repeats the reciprocating motion in the above manner to consecutively output boosted pressurized fluid from the output port  44 . 
     In accordance with the pressure booster  120  according to this embodiment, pressurized fluid is extracted from the first booster chamber  22   a  or the second booster chamber  22   b  of the booster cylinder  12  and supplied to predetermined ports of the first operating valve  48  and the second operating valve  52  in order to switch the positions of the operating valves. Since the pressure of pressurized fluid increased in the first booster chamber  22   a  or the second booster chamber  22   b  is higher than the pressure of the pressurized fluid supply source, the first operating valve  48  and the second operating valve  52  can be actuated more reliably. 
     The pressure booster according to the present invention is not limited in particular to the embodiments described above, and may have various structures without departing from the scope of the present invention as a matter of course.