Patent Publication Number: US-11661959-B2

Title: Pressure booster

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2020-053573 filed on Mar. 25, 2020, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a pressure booster capable of boosting and outputting a pressurized fluid from a fluid supply source. 
     Description of the Related Art 
     Conventionally, there has been known a pressure booster that boosts air with a primary pressure, supplied from a compressor and outputs the air with a predetermined secondary pressure. 
     As an example of such a pressure booster, Japanese Laid-Open Patent Publication No. 2018-084270 discloses a pressure booster having drive cylinders arranged on both sides of a pressure boosting cylinder. As described in this document, the pressurized fluid output from the pressure booster is usually stored in an external tank and used in a manner that it is supplied from the tank to the fluid pressure device. 
     SUMMARY OF THE INVENTION 
     However, when filling the tank with air from atmospheric pressure, it takes a long time to fill the tank, especially when the pressure booster is small. Further, since part of the pressurized fluid from the fluid supply source is discharged to the outside while the pressure booster operates, the consumed amount of the pressurized fluid increases as the degree of dependence on the pressure booster is greater. 
     The present invention has been devised in view of the above circumstances, it is therefore an object of the present invention to provide a pressure booster having high filling efficiency of the tank and low consumption of pressurized fluid. 
     A pressure booster according to the present invention includes a pressure boosting unit and a bypass unit. The pressure boosting unit includes an input port connected to the side of a fluid supply source and an output port connected to the side of a tank. The pressure boosting unit boosts the pressure of a pressurized fluid supplied to the input port and outputs the pressure-boosted pressurized fluid from the output port. The bypass unit includes a bypass flow path having one end connected to the fluid supply source side and the other end connected to the output port side. The bypass flow path is provided with a bypass check valve configured to block flow of the pressurized fluid from the output port side to the fluid supply source side. 
     According to the pressure booster, the filling efficiency of the tank is improved, and the pressurized fluid consumption is reduced. 
     Since the pressure booster according to the present invention includes a path for directly supplying the pressurized fluid from the fluid supply source to the tank, the tank can be filled in a shorter time. In addition, the consumption of the pressurized fluid can be reduced as much as possible. 
     The above and other objects features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is an external perspective view of a pressure booster according to an embodiment of the present invention; 
         FIG.  2    is a sectional view taken along line II-II of the pressure booster of  FIG.  1   ; 
         FIG.  3    is a diagram showing a state in which the pressure booster of  FIG.  1    is separated into a pressure boosting unit and a bypass unit; 
         FIG.  4    is an overall schematic diagram of the pressure booster of  FIG.  1    using a circuit diagram; 
         FIG.  5    is a side view of the pressure booster of  FIG.  1   ; 
         FIG.  6    is a sectional view of the pressure booster of  FIG.  1    taken along VI-VI line in  FIG.  5   ; 
         FIG.  7    is a sectional view of the pressure booster of  FIG.  1    taken along line VII-VII of  FIG.  5   ; 
         FIG.  8    is a diagram showing a structure of a first pilot valve in the pressure booster of  FIG.  1   ; 
         FIG.  9    is a diagram when the first pilot valve of  FIG.  8    is in a different operating position; and 
         FIG.  10    is a diagram showing the relationship between the pressure of the tank and elapsed time in a case that the tank is charged with air from atmospheric pressure. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, a preferable embodiment of a pressure booster according to the present invention will be described in detail with reference to the accompanying drawings. 
     As shown in  FIGS.  1  and  2   , a pressure booster  10  of the present invention is composed of a pressure boosting unit  12  and a bypass unit  88 , and is arranged between a fluid supply source (compressor) and a tank. The fluid supply source and tank are not illustrated. 
     (Configuration of Pressure Boosting Unit  12 ) 
     As shown in  FIG.  3   , the pressure boosting unit  12  has a triple cylinder structure in which a first drive cylinder  16  and a second drive cylinder  18  are joined to a first end side (one end side) and a second end side (the other end side) of the pressure boosting cylinder  14 , respectively. A first cover member  20  is interposed between the first drive cylinder  16  and the pressure boosting cylinder  14 , and a second cover member  22  is interposed between the pressure boosting cylinder  14  and the second drive cylinder  18 . 
     As shown in  FIG.  6   , a pressure boosting chamber  24  is formed inside the pressure boosting cylinder  14  while a first drive chamber  26  and a second drive chamber  28  are formed inside the first drive cylinder  16  and the second drive cylinder  18 , respectively. In this case, the first drive cylinder  16  has a third cover member  30  fixed at the A1-side end thereof and the first cover member  20  arranged at the A2-side thereof, forming the first drive chamber  26 . Further, the second drive cylinder  18  has the second cover member  22  arranged at the A1-side end thereof and a wall  31  arranged at the A2-side for closing, forming the second drive chamber  28 . 
     A piston rod  32  is arranged so as to penetrate the first cover member  20  and the second cover member  22 . The first end (one end) of the piston rod  32  extends to the first drive chamber  26 , and the second end (the other end) of the piston rod  32  extends to the second drive chamber  28 . In the pressure boosting chamber  24 , a pressure boosting piston  34  is coupled at the center of the piston rod  32  so that the pressure boosting chamber  24  is partitioned into a first pressure boosting chamber  24   a  on the A1 direction side and a second pressure boosting chamber  24   b  on the A2 direction side (see  FIG.  4   ). 
     In the first drive chamber  26 , a first drive piston  36  is connected at the first end of the piston rod  32  so that the first drive chamber  26  is partitioned into a pressurizing chamber  26   a  on the A1 direction side and a back pressure chamber  26   b  on the A2 direction side (see  FIG.  4   ). In the second drive chamber  28 , a second drive piston  38  is connected to the second end of the piston rod  32  so that the second drive chamber  28  is partitioned into a pressurizing chamber  28   a  on the A2 direction side and a back pressure chamber  28   b  on the A1 direction side (See  FIG.  4   ). The pressure boosting piston  34 , the first drive piston  36 , and the second drive piston  38  are integrally connected by the piston rod  32 . 
     As shown in  FIG.  3   , the pressure boosting cylinder  14  has an input port  40  to which a pressurized fluid (compressed air) is supplied from the fluid supply source via the bypass unit  88 . The input port  40  is opened in the upper part of the front face of the pressure boosting cylinder  14 . 
     As shown in  FIGS.  4  and  7   , the first cover member  20  and the second cover member  22  have, installed thereinside, a fluid supply mechanism which introduces the pressurized fluid supplied to the pressure boosting unit  12  into the first pressure boosting chamber  24   a  and the second pressure boosting chamber  24   b . This fluid supply mechanism has a first supply flow path  42   a  that connects the input port  40  and the first pressure boosting chamber  24   a , and a second supply flow path  42   b  that connects the input port  40  and the second pressure boosting chamber  24   b.    
     The first supply flow path  42   a  includes a first supply check valve  42   c  that blocks a fluid flow in the direction from the first pressure boosting chamber  24   a  toward the input port  40 . The second supply flow path  42   b  includes a second supply check valve  42   d  that blocks a fluid flow in the direction from the second pressure boosting chamber  24   b  toward the input port  40 . 
     As shown in  FIGS.  2  and  3   , the pressure boosting cylinder  14  is provided with an output port  44  that outputs the pressure-boosted pressurized fluid toward the tank, and a merging port  46  that connects the output port  44  to the bypass unit  88 . The output port  44  is opened on the bottom face of the pressure boosting cylinder  14 , and the merging port  46  is opened in the lower part on the front face of the pressure boosting cylinder  14 . 
     As shown in  FIGS.  4  and  7   , the first cover member  20  and the second cover member  22  contain therein a fluid output mechanism which outputs the fluid that has been pressure-boosted in the first pressure boosting chamber  24   a  or the second pressure boosting chamber  24   b , from the output port  44 . This fluid output mechanism has a first output flow path  47   a  that connects the first pressure boosting chamber  24   a  and the output port  44 , and a second output flow path  47   b  that connects the second pressure boosting chamber  24   b  and the output port  44 . 
     The first output flow path  47   a  is provided with a first output check valve  47   c  that blocks a fluid flow in the direction from the output port  44  toward the first pressure boosting chamber  24   a . The second output flow path  47   b  is provided with a second output check valve  47   d  that blocks a fluid flow from the output port  44  toward the second pressure boosting chamber  24   b.    
     As shown in  FIG.  3   , a first housing  50  provided with a first operating valve  48  is disposed on the top of the first drive cylinder  16 , and a second housing  54  provided with a second operating valve  52  is disposed on the top of the second drive cylinder  18 . 
     As shown in  FIG.  4   , the first operating valve  48  has a first port  56 A, a second port  56 B, a third port  56 C, a fourth port  56 D, and a fifth port  56 E, and is configured to switch between a first position for driving the first drive piston  36  and a second position for allowing the first drive piston  36  to be driven by movement of the second drive piston  38 . 
     The first port  56 A is connected to the pressurizing chamber  26   a  of the first drive cylinder  16  by a flow path  58   a . The second port  56 B is connected to the back pressure chamber  26   b  of the first drive cylinder  16  by a flow path  58   b . The third port  56 C is connected to the first supply flow path  42   a  by a flow path  58   c . The fourth port  56 D is connected to a first silencer  62  having an exhaust port by a flow path  58   d . The fifth port  56 E is connected to a midway point of the flow path  58   a  by a flow path  58   e . A first fixed orifice  60  is interposed in the flow path  58   d.    
     When the first operating valve  48  is in the first position, the first port  56 A and the third port  56 C communicate with each other, and the second port  56 B and the fourth port  56 D communicate with each other. As a result, the pressurized fluid from the input port  40  is supplied to the pressurizing chamber  26   a  through the flow path  58   c  and the flow path  58   a , and the fluid in the back pressure chamber  26   b  flows through the flow path  58   b  and the flow path  58   d  and is then discharged via the first fixed orifice  60  and the first silencer  62 . 
     When the first operating valve  48  is in the second position, the first port  56 A and the fourth port  56 D communicate with each other, and the second port  56 B and the fifth port  56 E communicate with each other. As a result, part of the fluid in the pressurizing chamber  26   a  is collected into the back pressure chamber  26   b  through the flow path  58   a , the flow path  58   e  and the flow path  58   b , and the remaining part flows through the flow path  58   d  and is then discharged via the first fixed orifice  60  and the first silencer  62 . 
     The first operating valve  48  further includes a pilot port  56 F for introducing a pilot pressure from a second pilot valve  74 , which will be described later. The first operating valve  48  is in the first position when the pressurized fluid is supplied to the pilot port  56 F, and it is in the second position when the pressurized fluid is not supplied to the pilot port  56 F. 
     The second operating valve  52  has first to fifth ports  64 A to  64 E, and is configured to be able to switch between a first position for driving the second drive piston  38  and a second position for allowing the second drive piston  38  to be driven by movement of the first drive piston  36 . 
     The first port  64 A is connected to the pressurizing chamber  28   a  of the second drive cylinder  18  by a flow path  66   a . The second port  64 B is connected to the back pressure chamber  28   b  of the second drive cylinder  18  by a flow path  66   b . The third port  64 C is connected to the second supply flow path  42   b  by a flow path  66   c . The fourth port  64 D is connected to a second silencer  70  having an exhaust port by a flow path  66   d . The fifth port  64 E is connected to a midway point of the flow path  66   a  by a flow path  66   e . A second fixed orifice  68  is interposed in the flow path  66   d.    
     When the second operating valve  52  is in the first position, the first port  64 A and the third port  64 C communicate with each other, and the second port  64 B and the fourth port  64 D communicate with each other. As a result, the pressurized fluid from the input port  40  is supplied to the pressurizing chamber  28   a  through the flow path  66   c  and the flow path  66   a , and the fluid in the back pressure chamber  28   b  flows through the flow path  66   b  and the flow path  66   d  and is then discharged via the second fixed orifice  68  and the second silencer  70 . 
     When the second operating valve  52  is in the second position, the first port  64 A and the fourth port  64 D communicate with each other, and the second port  64 B and the fifth port  64 E communicate with each other. As a result, part of the fluid in the pressurizing chamber  28   a  is collected into the back pressure chamber  28   b  through the flow path  66   a , the flow path  66   e  and the flow path  66   b , and the remaining part flows through the flow path  66   d  and is then discharged via the second fixed orifice  68  and the second silencer  70 . 
     The second operating valve  52  further includes a pilot port  64 F for introducing a pilot pressure from a first pilot valve  72 , which will be described later. The second operating valve  52  is in the first position when the pressurized fluid is supplied to the pilot port  64 F, and it is in the second position when the pressurized fluid is not supplied to the pilot port  64 F. 
     The first pilot valve  72  is disposed inside the first cover member  20 , and the second pilot valve  74  is disposed inside the second cover member  22 . The first pilot valve  72  has first to fourth ports  76 A to  76 D, and is configured to be able to switch between a first position for generating a pilot pressure for the second operating valve  52  and a second position for eliminating the pilot pressure. 
     The first port  76 A is connected to the pilot port  64 F of the second operating valve  52  by a first pilot flow path  78   b . The second port  76 B is connected to the first supply flow path  42   a  by a flow path  78   a . The third port  76 C forms an exhaust port. The fourth port  76 D is connected to an after-mentioned first port  80 A of the second pilot valve  74  by a branch flow path  82   c  and a second pilot flow path  82   b , which will be described later. Further, a branch flow path  78   c  connecting to a fourth port  80 D of the second pilot valve  74 , which will be described later, is provided so as to branch off from the first pilot flow path  78   b.    
     When the first pilot valve  72  is in the first position, the first port  76 A and the second port  76 B communicate with each other. As a result, the pressurized fluid from the input port  40  is supplied to the pilot port  64 F of the second operating valve  52  through the flow path  78   a  and the first pilot flow path  78   b , and is also supplied to the fourth port  80 D of the second pilot valve  74 , which will be described later, through the branch flow path  78   c  branching from the first pilot flow path  78   b.    
     When the first pilot valve  72  is in the second position, the first port  76 A and the third port  76 C communicate with each other. As a result, the pressurized fluid that has been supplied to the pilot port  64 F of the second operating valve  52  is discharged through the first pilot flow path  78   b , and the pressurized fluid that has been supplied to the fourth port  80 D of the second pilot valve  74  is discharged through the branch flow path  78   c  and the first pilot flow path  78   b.    
     The second pilot valve  74  has first to fourth ports  80 A to  80 D, and is configured to be able to switch between a first position for generating a pilot pressure for the first operating valve  48  and a second position for eliminating the pilot pressure. 
     The first port  80 A is connected to the pilot port  56 F of the first operating valve  48  by the second pilot flow path  82   b . The second port  80 B is connected to the second supply flow path  42   b  by a flow path  82   a . The third port  80 C forms an exhaust port. The fourth port  80 D is connected to the first port  76 A of the first pilot valve  72  by the branch flow path  78   c  and the first pilot flow path  78   b . Further, a branch flow path  82   c  connecting to the fourth port  76 D of the first pilot valve  72  is provided so as to branch off from the second pilot flow path  82   b.    
     When the second pilot valve  74  is in the first position, the first port  80 A and the second port  80 B communicate with each other. As a result, the pressurized fluid from the input port  40  is supplied to the pilot port  56 F of the first operating valve  48  through the flow path  82   a  and the second pilot flow path  82   b , and is also supplied to the fourth port  76 D of the first pilot valve  72  through the branch flow path  82   c  branching from the second pilot flow path  82   b.    
     When the second pilot valve  74  is in the second position, the first port  80 A and the third port  80 C communicate with each other. As a result, the pressurized fluid that has been supplied to the pilot port  56 F of the first operating valve  48  is discharged through the second pilot flow path  82   b , and the pressurized fluid that has been supplied to the fourth port  76 D of the first pilot valve  72  is discharged through the branch flow path  82   c  and the second pilot flow path  82   b.    
     Next, the specific structure of the first pilot valve  72  will be described with reference to  FIGS.  8  and  9   . The second pilot valve  74  has the same structure. For convenience, a reference numeral  61  is allotted to the knock pin of the first pilot valve  72  while a reference numeral  69  is allotted to the knock pin of the second pilot valve  74  in order to show the two in a distinguishing manner. 
     The first pilot valve  72  includes a valve seat  86 , a valve seat retainer  87 , and a knock pin  61 , accommodated in a valve housing hole  84  formed in the first cover member  20 . The knock pin  61  has a tip portion  61   a  that projects into the back pressure chamber  26   b  of the first drive cylinder  16 , and is configured to be capable of sliding between two positions, i.e., an abutment position where the knock pin abuts against the bottom face of the valve housing hole  84  (see  FIG.  9   ) and another abutment position where the knock pin abuts against the end face of the valve seat retainer  87  (see  FIG.  8   ). When the projecting length of the knock pin  61  is larger, the first port  76 A communicates with the third port  76 C, whereas when the projecting length of the knock pin  61  is smaller, the first port  76 A communicates with the second port  76 B. 
     When the pressurized fluid is supplied to the fourth port  76 D, the knock pin  61  is urged in a direction in which the projecting length increases. This is because the area of the knock pin  61  on which the fluid pressure in the fourth port  76 D acts to increase the projecting length of the knock pin  61  is larger than the area of the knock pin  61  on which the fluid pressure in the second port  76 B acts to decrease the projecting length of the knock pin  61 . 
     On the other hand, when the pressurized fluid is not supplied to the fourth port  76 D, the knock pin  61  is urged in a direction in which the projecting length decreases. This is because the fluid pressure in the fourth port  76 D which acts to increase the projecting length of the knock pin  61  disappears, whereas the fluid pressure in the second port  76 B which acts to decrease the projecting length of the knock pin  61  continues to act thereon. 
     (Configuration of Bypass Unit  88 ) 
     As shown in  FIG.  3   , the rectangular parallelepiped bypass unit  88  is attached to the front face of the pressure boosting cylinder  14  having the openings of the input port  40  and the merging port  46 , by using multiple bolts  90 . As shown in  FIGS.  2  and  4   , a main flow path  92  and a bypass flow path  94  are formed inside the bypass unit  88 . 
     The main flow path  92  is formed in the upper part of the bypass unit  88  so as to penetrate from the front face of the bypass unit  88  to the rear face which is in contact with the pressure boosting cylinder  14 . The main flow path  92  has an inlet-side end portion  92 A (see  FIG.  1   ) that opens in the front face of the bypass unit  88  and which is connected to the fluid supply source via an unillustrated tube. The main flow path  92  also has an outlet-side end portion  92 B that opens in the rear face of the bypass unit  88  and which is connected to the input port  40  of the pressure boosting cylinder  14 . 
     The bypass flow path  94  branches off from a point of the main flow path  92  and extends downward inside the bypass unit  88 , and its outlet-side end portion  94 A opens in the rear face of the bypass unit  88  and is connected to the merging port  46  of the pressure boosting cylinder  14 . The bypass flow path  94  is provided with a bypass check valve  96  that allows the flow of pressurized fluid from the fluid supply source to the merging port  46  and blocks the flow of pressurized fluid from the merging port  46  toward the fluid supply source. 
     Routes for outputting the pressurized fluid from the fluid supply source toward the tank include the following two routes. In one route, the pressurized fluid flows through the main flow path  92  of the bypass unit  88  and the bypass flow path  94  with the bypass check valve  96  interposed therein, and then reaches the output port  44  via the merging port  46  of the pressure boosting unit  12  (which will be referred to hereinbelow as “first route”). In the other route, the pressurized fluid flows through the main flow path  92  of the bypass unit  88 , thereafter enters the pressure boosting unit  12  through the input port  40 , thereafter flows through the first supply flow path  42   a  or the second supply flow path  42   b , the first pressure boosting chamber  24   a  or the second pressure boosting chamber  24   b , and the first output flow path  47   a  or the second output flow path  47   b , and then reaches the output port  44  (which will be referred to hereinbelow as “second route”). 
     The configuration of the pressure booster  10  according to the embodiment of the present invention has been described above, and its operation will now be described next. The initial state is assumed such that, as shown in  FIG.  4   , the first operating valve  48  is switched in the second position, the second operating valve  52  is switched in the first position, and the pressure boosting piston  34  is located around the center of the pressure boosting chamber  24 . It is also assumed that, at this time, the pressure in the tank is atmospheric pressure. 
     In this initial state, the pressurized fluid from the fluid supply source is supplied to the inlet-side end portion  92 A of the main flow path  92  in the bypass unit  88 . Since the output port  44  is connected to a tank of a low pressure, the pressure at the merging port  46  is lower than the pressure at the main flow path  92 . Therefore, part of the pressurized fluid from the fluid supply source flows through the first route and is output from the output port  44  toward the tank. Further, the other part of the pressurized fluid from the fluid supply source flows through the second route, is pressure-boosted by the pressure boosting unit  12 , and is output from the output port  44  toward the tank. The pressure boosting action in the pressure boosting unit  12  will be described later. 
     In the above way, when the pressure at the merging port  46  is lower than the pressure at the main flow path  92 , the pressurized fluid from the fluid supply source is not only directly supplied to the tank through the bypass flow path  94  but also supplied to the tank by being pressure-boosted through the pressure boosting unit  12 . Thus, the pressure in the tank can be increased quickly. 
     As the tank proceeds to be charged and the pressure at the merging port  46  exceeds the pressure at the main flow path  92 , the bypass flow path  94  is closed by the action of the bypass check valve  96 . Therefore, only the pressurized fluid that has flowed through the second route and thereby pressure-boosted is output from the output port  44  toward the tank. As a result, the pressure of the tank can be raised to a predetermined pressure higher than the supply pressure from the fluid supply source. 
     (Pressure Boosting Action in Pressure Boosting Unit  12 ) 
     As a pressurized fluid is supplied to the input port  40  of the pressure boosting unit  12 , the pressurized fluid flows into the first supply flow path  42   a  and the second supply flow path  42   b , and enters the first pressure boosting chamber  24   a  and the second pressure boosting chamber  24   b  of the pressure boosting cylinder  14  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 input port  40  flows through the flow path  66   c , the second operating valve  52  placed in the first position, and the flow path  66   a , and is then supplied to the pressurizing chamber  28   a  of the second drive cylinder  18 . As a result, the second drive piston  38  is driven in the A1 direction, and the pressure boosting piston  34  integrally connected to the second drive piston  38  slides, so that the pressure of the pressurized fluid in the first pressure boosting chamber  24   a  of the pressure boosting cylinder  14  is increased. The thus pressure-boosted pressurized fluid is led to the output port  44  through the first output check valve  47   c  and the first output flow path  47   a , and is then output therefrom. 
     On the other hand, when the first drive piston  36  integrally connected to the second drive piston  38  slides, the volume of the pressurizing chamber  26   a  of the first drive cylinder  16  becomes smaller. Since the first operating valve  48  is in the second position, part of the pressurized fluid in the pressurizing chamber  26   a  is collected into the back pressure chamber  26   b  through the flow path  58   a , the flow path  58   e  and the flow path  58   b , and the remaining part is discharged through the flow path  58   d.    
     As described above, in the process in which the pressure boosting piston  34  moves from the initial position by a predetermined distance in the A1 direction, the first pilot valve  72  is in the first position, so that the pressurized fluid from the input port  40  flows through the first pilot valve  72  and is supplied to the fourth port  80 D of the second pilot valve  74 . On the other hand, the second pilot valve  74  is in the second position, and thus no pressurized fluid is supplied to the fourth port  76 D of the first pilot valve  72 . Therefore, in the first pilot valve  72 , the knock pin  61  is urged in the direction so as to reduce the projecting length, and the first pilot valve  72  is stably held in the first position. In the second pilot valve  74 , the knock pin  69  is urged in the direction so as to increase the projecting length, and the second pilot valve  74  is stably held in the second position. 
     Then, the second drive piston  38  comes into contact with the knock pin  69  of the second pilot valve  74  as the pressure boosting piston  34  moves in the A1 direction and to the vicinity of the stroke end. The knock pin  69  is pushed and displaced by the second drive piston  38 , leading to communication between the first port  80 A and the second port  80 B of the second pilot valve  74 . Then, the pressurized fluid from the input port  40  is supplied to the pilot port  56 F of the first operating valve  48  through the second pilot flow path  82   b , and is also supplied to the fourth port  76 D of the first pilot valve  72  through the branch flow path  82   c . As a result, the first operating valve  48  is switched to the first position, and the first pilot valve  72  is switched to the second position. 
     When the first pilot valve  72  has been switched to the second position, the pressurized fluid that has been supplied to the pilot port  64 F of the second operating valve  52  flows through the first pilot flow path  78   b  and is discharged from the third port  76 C of the first pilot valve  72 . As a result, the second operating valve  52  is switched to the second position. 
     Additionally, when the first pilot valve  72  has been switched to the second position, the pressurized fluid that has been supplied to the fourth port  80 D of the second pilot valve  74  flows through the branch flow path  78   c  and the first pilot flow path  78   b  and is discharged from the third port  76 C of the first pilot valve  72 . Therefore, in the second pilot valve  74 , the fluid pressure acts in the direction in which the projecting length of the knock pin  69  decreases. In this way, the knock pin  69  is displaced, by the pushing of the second drive piston  38 , to thereby establish communication between the first port  80 A and the second port  80 B of the second pilot valve  74 , and the thus-displaced knock pin  69  further receives the fluid pressure and is held in a position where the knock pin  69  abuts against the bottom face of the valve housing hole  84 . That is, the second pilot valve  74  is stably held in the first position. 
     Next, part of the pressurized fluid supplied from the input port  40  flows through the flow path  58   c , the first operating valve  48  in the first position, and the flow path  58   a , and is then supplied to the pressurizing chamber  26   a  of the first drive cylinder  16 . The pressurized fluid supplied to this pressurizing chamber  26   a  drives the first drive piston  36  in the A2 direction. As a result, the pressure boosting piston  34  integrally connected to the first drive piston  36  slides, so that the pressure of the pressurized fluid in the second pressure boosting chamber  24   b  of the pressure boosting cylinder  14  is increased. The thus pressure-boosted pressurized fluid is led to the output port  44  through the second output flow path  47   b  and the second output check valve  47   d  and then output therefrom. 
     On the other hand, when the second drive piston  38  integrally connected to the first drive piston  36  slides, the volume of the pressurizing chamber  28   a  of the second drive cylinder  18  becomes smaller. Since the second operating valve  52  is in the second position, part of the pressurized fluid in the pressurizing chamber  28   a  is collected into the back pressure chamber  28   b  through the flow path  66   a , the flow path  66   e , and a flow path  66   b , and the remaining part is discharged through the flow path  66   d.    
     Then, the first drive piston  36  comes into contact with the knock pin  61  of the first pilot valve  72  as the pressure boosting piston  34  moves in the A2 direction and to the vicinity of the stroke end. The knock pin  61  is pressed and displaced by the first drive piston  36 , leading to communication between the first port  76 A and the second port  76 B of the first pilot valve  72 . Then, the pressurized fluid from the input port  40  is supplied to the pilot port  64 F of the second operating valve  52  through the first pilot flow path  78   b , and is also supplied to the fourth port  80 D of the second pilot valve  74  through the branch flow path  78   c . As a result, the second operating valve  52  is switched to the first position, and the second pilot valve  74  is switched to the second position. 
     When the second pilot valve  74  has been switched to the second position, the pressurized fluid that has been supplied to the pilot port  56 F of the first operating valve  48  flows through the second pilot flow path  82   b  and is discharged from the third port  80 C of the second pilot valve  74 . As a result, the first operating valve  48  is switched to the second position. 
     Additionally, when the second pilot valve  74  has been switched to the second position, the pressurized fluid that has been supplied to the fourth port  76 D of the first pilot valve  72  flows through the branch flow path  82   c  and the second pilot flow path  82   b  and is discharged from the third port  80 C of the second pilot valve  74 . Therefore, in the first pilot valve  72 , the fluid pressure acts in the direction so as to reduce the projecting length of the knock pin  61 . In this way, the knock pin  61  is displaced, by the pushing of the first drive piston  36 , to thereby establish communication between the first port  76 A and the second port  76 B of the first pilot valve  72 , and the thus-displaced knock pin  61  further receives the fluid pressure and is held in a position where the knock pin  61  abuts on the bottom face of the valve housing hole  84 . That is, the first pilot valve  72  is stably held in the first position. Thereafter, the pressure boosting piston  34  repeats the same reciprocating motion, so that the pressure-boosted pressurized fluid is continuously output from the output port  44 . 
       FIG.  10    is a diagram showing the relationship between the elapsed time from the start of filling and the pressure of the tank (pressure at the output port  44 ), when the tank is charged from atmospheric pressure. The solid line shows a case where the bypass unit  88  is installed as in the pressure booster  10  of the present embodiment, and the dotted line shows a case where the bypass unit  88  is not installed. P0, P1 and P2 represent the atmospheric pressure, the pressure of the fluid supplied from the pressurized fluid supply source, and the target pressure of the tank, respectively. As can be understood from the figure, provision of the bypass unit  88  makes it possible to shorten the time required to raise the pressure of the tank to P1. 
     According to the pressure booster  10  according to the present embodiment, since the first route for directly supplying the pressurized fluid from the fluid supply source to the tank is included, the filling time of the tank can be shortened as much as possible, and the consumption of pressurized fluid can be reduced as much as possible. 
     Further, since the input port  40  is connected to the fluid supply source via the main flow path  92  provided in the bypass unit  88  and the bypass flow path  94  branches from the main flow path  92 , the connection between the pressure boosting unit  12  and the fluid supply source and the connection between the bypass unit  88  and the fluid supply source can be completed with a single tube, thus simplifying the routing of tubing or piping. 
     Further, since the bypass flow path  94  is connected to the output port  44  via the merging port  46  provided in the pressure boosting unit  12 , the connection between the pressure boosting unit  12  and the tank and the connection between the bypass unit  88  and the tank can be completed with a single tube, thus simplifying routing of tubing or piping. 
     Further, since the bypass unit  88  is attached to the front face of the pressure boosting cylinder  14  in which the input port  40  and the merging port  46  are opened, the entire device can be made compact. 
     It goes without saying that the pressure booster according to the present invention is not limited to the above-described embodiment, and may take various configurations without departing from the essence and gist of the present invention.