Patent Publication Number: US-7712552-B2

Title: Water hammer

Description:
TECHNICAL FIELD 
   The present invention relates to a boring machine, and more particularly, to a drive rod of machine which is directly driven using high pressure water and enables a relatively deep hole to be bored in the ground, like a drilling work, and a water hammer using the same. 
   BACKGROUND ART 
   A boring machine for perforating the ground is generally based on a technique of simply circulating a bit (Oscillating method), a technique of not only circulating a bit or a ball cutter but also pressurizing the same (Reverse Circulation Drilling method: ROC), and so on. According to the oscillating method, in a state in which a standard casing having a diameter of 800 to 3000 mm is clamped by a hydraulic chuck, boring is performed by oscillating a cylinder installed rotatably in a left-right direction. According to the ROC method, the ground is bored using a drive rod having a rotary bit or ball cutter installed at its end portion by rotating the bit or ball cutter. The oscillation method can cope with a soft ground condition, that is, a boring work is properly carried out through soft ground such as soil. However, for a hard-boring operation, it is necessary to demolish rocks under the ground by dropping a large-sized hammer, requiring additional equipment such as a pile driver. 
   Meanwhile, in the RCD method, which is an advanced method compared to the oscillation method from the viewpoint of boring capacity, a soil layer is first dug using an oscillator or a rotator, both a soft rock layer and a hard rock layer are dug by rotating drill rod a specially designed bit attached to its end portion, and air-suctioning circulating water and cloven rocks through a drill rod pipe, followed by hoisting the rocks to the surface of the ground. The RCD method is essentially employed in large-diameter cast-in-place and top-down method for a foundation work. 
   Korean Patent Publication No. 10-0372049 discloses a boring machine using a crane. The disclosed boring machine includes a drive rod, a tool housing, a breaker, a bit, a case, and an air pressure excavating means. The drive rod transfers water pressure and air generated from a hydraulic drive unit to a digging position along water pressure and air passages. The tool housing is mounted to an end portion of the drive rod and accommodates various structures. The breaker, which is provided at an upper end of the inside of the tool housing, has a piston to strike by water pressure while elevating. The bit, which is vertically movably attached to a lower end of the tool housing, performs a boring operation such that the breaker strikes the piston. The case is inserted into the tool housing to form a passage ranging from the ground surface to the digging position. The air pressure excavating means is connected to the passages and air holes to allow the tool housing to communicate with the bit such that the air pressure supplied from the outside of the tool housing is discharged through a lower portion of the bit. 
   In the above-described boring machine, the piston of the breaker is driven by a hydraulic drive unit. Thus, as the depth of a bored hole increases, the configuration becomes complicated, and additional equipments for driving the same become bulky. Particularly, since the bit digs soil using air pressure, it is quite difficult to smoothly excavate the soil as the hole becomes deeper. In addition, when air is used as a pneumatic actuator of a piston breaker, a large amount of air is consumed, resulting in a considerable increase in the operation cost. 
   In the above-described boring machine, the hammer is installed in each drive rod and a water pressure line and a high pressure line are separately formed to operate the piston of the hammer and to rotate a digging unit. A gas chamber of a back head is provided at an upper end of the piston operated by a water pressure supplied through the drive rod. A nitrogen gas is injected into the gas chamber of the back head. When the piston is lowered by the injected nitrogen gas, an impact applied to a target is increased. 
   As described above, when the gas chamber of the back head is provided at an upper end of the piston, the gas pressure of the gas chamber should be relatively increased to withstand an earth pressure, which becomes increasingly greater as the depth of the bored hole increases. If the pressure of the back head gas chamber is not high enough, the striking force of the bit is undesirably reduced. 
   DISCLOSURE OF INVENTION 
   To solve the above problems, it is an objective of the present invention to provide a drive rod of a boring machine having a simplified structure by operating a water hammer for directly striking a bit using a water pressure. 
   It is another objective of the present invention to provide a drive rod of a boring machine, which can reduce consumption of a large amount of water used to drive the same by operating a piston using a difference in the pressure applied to an internal surface selectively defined by a valve and can be applied to existing boring equipment without special improvement, and a water hammer connected thereto. 
   It is still another objective of the present invention to provide a drive rod of a boring machine, which enables a relatively deep hole to be bored in the ground, and a water hammer connected thereto. 
   It is yet another objective of the present invention to provide a drive rod of a boring machine, which can increase a striking force of a bit by adding a compressive force to a pneumatic force of a piston for lowering the piston using a water pressure. 
   It is a further objective of the present invention to provide a drive rod of a boring machine, which can prevent a piston from malfunctioning due to intermingling of water and air by isolating the air from the water as a pneumatic actuator of a hammer, and can increase a striking force of the hammer using a simplified structure. 
   According to an aspect of the present invention, there is provided a water hammer of a boring machine comprising: a tubular main body having a hollow portion; a socket coupled to an upper end of the main body and having a water pressure supply passage; a cylindrical piston housing connected to the main body; a piston slidably installed in the piston housing, for striking a bit of a bit unit installed at a lower portion of the main body, having a hollow portion through which water is discharged, an annular pressurizing portion protruding on its outer circumferential surface, and a first communication hole connected to the hollow portion; a sliding member fitted into the main body to be coupled to the piston housing, defining a valve installation space, and creating a space portion in which the piston is received when the piston is elevated; a valve member defining the valve installation space into first and second space portions along the length of the piston, the first and second space portions having different cross-sectional areas from each other, and valve member forming a second space portion between the first and third space portions connected to the hollow portion of the piston and connected to the first space portion when the piston is elevated; and a water pressure supply unit for supplying high pressure water delivered to the water pressure supply passage of the socket to the first and second space portions. 
   According to another aspect of the present invention, there is provided a water hammer comprising: a tubular main body having a hollow portion; a socket coupled to an upper end of the main body and having a water pressure supply passage; a cylindrical piston housing connected to the main body; a piston slidably installed in the piston housing, having a hollow portion through which water is discharged, an annular pressurizing portion protruding on its outer circumferential surface, and a first communication hole connected to the hollow portion; a sliding member fitted into the main body to be coupled to the piston housing, defining a valve installation space, and creating a space portion in which the piston is received when the piston is elevated; a valve member slidably installed in the valve installation space and defining the same into a first space portion and a second space portion, the cross-sectional area of the first space portion along the length of the piston being larger than that of the second space portion along the length of the first space portion, and the valve member defining a third space portion between the first and second space portions, connected to the hollow portion of the piston; and a water pressure supply unit for supplying pressure water to the first and second space portions to firstly elevate the valve member using a difference between the cross-sectional area of the first space portion and the cross-sectional area of the second space portion to secondly elevate the piston, causing the water used to elevate the housing to be discharged to the hollow portion of the piston in such a manner that the first and second space portions are connected to each other when the piston elevates, and supplying water pressure to the third space portion to cause the valve member to be lowered. 
   In the present invention, the valve member includes a first shield portion installed between the outer circumferential surface of the pressurizing portion and the internal surface of the cylinder member, an extending portion extending from the first shield portion and forming a passage through which the first and second space portions are connected to each other when the first shield portion and the pressurizing portion are separated from each other, and a second shield portion extending from the extending portion to be slidably coupled to an end portion of the sliding member to form the third space portion. In addition, the water pressure supply unit includes a pump for supplying water having a predetermined pressure to the water pressure supply passage of the socket, a first water pressure passage is formed on at least one of the outer circumferential surface of the sliding member and the main body, a second communication hole connected to the third space portion is formed in the sliding member, a second water pressure passage is formed on at least one of the outer surface of the sliding member and the inner circumferential surface of the main body so as to be connected to the second water pressure passage, and a third communication hole is formed to connect the second water pressure passage with the first space portion. 
   The drive rod according to the present invention comprises: a tubular main body having a hollow portion; a first connection member installed at an upper portion of the main body and having an inlet; a second connection member installed at a lower portion of the main body and having an outlet; and an internal pipe having an upper end fixed to be connected with the inlet of the first connection member, extending toward the second connection member to partition the hollow portion of the main body lengthwise to form an air storage portion, and having at least one discharge hole for discharging water in a radial direction to isolate water from air, the discharge hole formed at an end portion of the internal pipe. 
   The end portion of the internal pipe is connected to the outlet of the second connection member, a shield plate is installed at a side of the internal pipe proximal to the second connection member to cause water induced through the internal pipe to be discharged through the discharge hole, and at least one entrance hole for causing water discharged through the discharge hole to be induced to the outlet is installed at the internal pipe disposed at the lower portion of the shield plate. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic side view of a boring machine according to the present invention; 
       FIG. 2  is a partial perspective view of a water hammer according to the present invention; 
       FIG. 3  is a cross-sectional view illustrating a state in which a drive rod and a water hammer are mounted; 
       FIG. 4  is a partial perspective view of a drive rod according to an embodiment of the present invention; 
       FIG. 5  is a cross-sectional view of the drive rod; 
       FIG. 6  is a partial perspective view of a drive rod according to another embodiment of the present invention; and 
       FIGS. 7 through 12  are cross-sectional views illustrating an operation state of the water hammer according to the present invention. 
   

   BEST MODE FOR CARRYING OUT THE INVENTION 
   As shown in  FIG. 1 , a water hammer  10  according to the present invention is configured to strike a bit  21  guided by the lead  2  and installed at an end portion of a drive rod  100  allowed to be lowered and rotate by means of a driving means in a state in which a lead  2  stands upright perpendicularly with respect to a machine body  1 . 
     FIGS. 2 and 3  illustrate the water hammer  10  according to an embodiment of the present invention. 
   Referring to the drawings, the water hammer  10  includes a tubular main body  11  having a hollow portion  11   a , a socket  12  coupled to an end of the main body  11 , having a water pressure supply passage  12   a , and connected to the drive rod  100  for supplying high pressure water, a bit unit  20  installed at a lower portion of the main body  11  and having a bit  21  slidably moving lengthwise by a predetermined length to bore holes through rock and soil layers, and a water hammer unit  30  installed in the main body  11  between the socket  12  and the bit unit  20 . 
   The aforementioned water hammer  10  will now be described in more detail by constituent. 
   The main body  11  is tubular shaped, and preferably has the same diameter with that of the drive rod  100 . The socket  12  is engaged with the main body  11  by screw- or pin-engagement, and has a tapered engagement portion  12   b  provided at its upper portion to be engaged with the drive rod  100 , and a water pressure supply passage  12   a  formed lengthwise. The socket  12  further includes a check valve unit  13  for preventing backflow of water through the water pressure supply passage  12   a.    
   The check valve unit  13  includes a sheet portion  13   a  integrally formed with the socket  12  such that an outlet of the water pressure supply passage  12   a  is spreadly opened, a check valve member  13   b  contacting with and connected with the sheet portion  13   a , and an elastic member  13   e  coupled to the socket  12 , supported to a support member  13   d  having a plurality of throughholes  13   c , and elastically biasing the check valve member  13   b  toward the sheet portion  13   a . The check valve unit  13  is not limited to that described in the illustrative embodiment and any structure capable of preventing backflow of water supplied through the water pressure supply passage  12   a  can be used as the check valve unit  13 . 
   Meanwhile, the drive rod  100  connected to the socket  12  includes a plurality of interconnected drive rod  100 . As shown in  FIGS. 3 through 6 , each of the drive rod units  110  includes an accumulator means for increasing a striking force of the piston of the water hammer  10 , which will now be described in more detail. 
   The drive rod unit  110  includes a tubular main body  112  having a hollow portion  111  formed lengthwise, a first connection member  113  fixedly installed at an upper portion of the main body  112  and having an inlet  113   a , a second connection member  114  installed at a lower portion of the main body  112  and having an outlet  114   a , and an internal pipe  130  having an upper end fixed to be connected with first connection member  113  and partitioning an internal hollow portion of the main body  12  lengthwise to form an air storage portion  120  and a water supply passage. 
   The first connection member  113  is connected to an upper end of the tubular main body  112  to be engaged with another unit rod drive rod, and includes a first base  113   b  fixedly coupled to the main body  112 , and a tapered engagement portion  113   c  extending from the first base  113   b . The tapered engagement portion  113   c  has several screws formed on its outer surface for screw engagement. 
   The second connection member  114  is connected to a lower end of the tubular main body  112 , and includes a second base  114   b  coupled to a lower end of the main body  112 , and an outlet  114   a  formed at its center. 
   The first and second connection members  113  and  114  are not limited to the above examples, and they may take any forms that are installed at opposite sides of the main body  112  to be connected with adjacent drive rod units for interconnecting the drive rod units. 
   Meanwhile, the internal pipe  130 , disposed in a hollow portion  111  of the main body  112 , has a diameter relatively smaller than that of the hollow portion  111 , and its upper end is connected with an inlet  113   a  of the first connection member  113  to partition the hollow portion  111 , thereby defining the air storage portion  120 . Here, the first connection member  113  and the internal pipe  130  are connected with each other by welding, so that the air stored in the air storage portion  120  may not be exhausted through the inlet  113   a  or a connected portion of the main body  112  and the first connection member  113 , that is, a hermetical seal must be kept. At the lower end portion of the internal pipe  130  is further provided a separation unit  135  for isolating air from the water supplied through the internal pipe  130  to be stored in the air storage portion  120 . As shown in  FIGS. 4 and 5 , the separation unit  135  includes a shield member  136  for shielding the water causing water flowing through the internal pipe  130  at the end portion of the internal pipe  130 , and a discharge hole  137  formed at the upper portion of the internal pipe  130  adjacent with the shield member  136 , for causing the water flowing through the internal pipe  130  to be discharged in a radial direction corresponding to the air storage portion  120 , that is, to be discharged between the outer circumferential surface of the internal pipe  130  and the inner circumferential surface of the main body  112  to be stored in the air storage portion  120 . In this case, the water discharged from the discharge hole  137  of the internal pipe  130  is discharged through the outlet  114   a  of the second connection member  114 . The lower end portion of the internal pipe  130  is supported by a rib  139  installed between the outer circumferential surface of the internal pipe  130  and internal surface of the main body  112 . 
   As shown in  FIG. 6 , the end portion of the internal pipe  130  may also be supported by the outlet  114   a  of the second connection member  114 . In this case, a plurality of entrance holes  138  are formed in the internal pipe  130  under the shield member  136 , allowing the water discharged from the discharge hole  137  to flow through the inlet  114   a  of the first connection member  114 . In this case, the discharge holes  137  and the entrance holes  138  should be sufficiently provided so as not to be interfered by water flow. 
   The water hammer  10  is connected with the drive rod unit  110  having accumulator means for increasing a striking force, and is driven by elevating the piston using water having a predetermined pressure supplied through the water pressure supply passage  12   a  of the socket  12 , which is illustrated in FIGS.  2  and  7 - 12 . 
   Referring to the drawing, the water hammer unit  30  includes a cylindrical piston housing  31  connected to the hollow portion  11   a  of the main body  11 , and a piston  32  slidably installed in the piston housing  31  to strike the bit  21 . The piston  32  includes a guide portion  32   a  guided as it slidably moves in the piston housing  31 , and a stepped portion  32   b  formed to be gradually stepped between the guide portion  32   a  and the internal surface of the piston housing  31  to form a valve installation space portion  60  where a valve member  50  is to be installed. A pressurizing portion  32   c  having a diameter greater than that of the guide portion  32   a  is formed in the stepped portion  32   b  proximal to the guide portion  32   a . A hollow portion  32   d  is formed in the piston  32  lengthwise, and the stepped portion  32   b  has a first communication hole  32   e  connected to the hollow portion  32   d . As shown in  FIG. 7 , the stepped portion  32   b  of the piston  32  is formed such that a diameter D 1  of the guide portion  32   a  is greater than a diameter D 2  of the stepped portion  32   b  in view of the pressurizing portion  32   c , and a diameter of the first communication hole  32   e  is smaller than the diameter D 2 . 
   Meanwhile, the internal surface of the piston housing  31  corresponding to the stepped portion  32   b  of the piston  32  has a relatively large diameter to form the valve installation space portion  60 . The end portion of the piston housing  31  is connected to a sliding member  40  inserted into the main body  11  between the piston housing  31  and the socket  12 . Here, the inner circumferential surface of an end portion  41  of the sliding member  40  connected to the piston housing  31  has a smaller diameter D 4  so that it has a relatively smaller cross-sectional area. The sliding member  40  has a receiving portion  42  for receiving the end portion of the piston  32  when the piston  32  is elevated. 
   The valve member  50 , which is slidably movable into the piston housing  31  and the piston  32 , is installed in the valve installation space portion  60  defined by the piston housing  31 , the piston  32  and the sliding member  40 , thereby elevating the piston  32  by a pressure of water supplied to the valve installation space portion  60 . As shown in  FIGS. 1 and 2 , the valve member  50  includes a first shield portion  51  installed between the outer circumferential surface of the pressurizing portion  32   e  and the inner circumferential surface of the piston housing  31  so as to have a predetermined width to define a first space portion  61 , an extending portion  52  extending from the first shield portion  51  to be connected to the first communication hole  32   e  to form a second space portion  62 , and a second shield portion  53  extending from an end portion of the extending portion  52  to be slidably coupled to an end portion of the piston  32  to form a third space portion  63  in cooperation with the piston  32  and the end portion  41  of the sliding member  40 . 
   The valve member  50  includes a throughhole  54  extending from the second space portion  62  to the end portion  41  of the sliding member to reduce a cross-sectional area to which a water pressure is applied. Here, a cross-sectional area along the length of the piston  32  formed by the pressurizing portion  32   c  protruding from the outer circumferential surface of the piston  32  and the first shield portion  51  is relatively wider than that formed between the outer circumferential surface of the stepped portion  32   b  and the inner circumferential surface of the end portion  41  of the sliding member  40 . In addition, the first shield portion  51  contacting with the pressurizing portion  32   c  has a length in which a contact state with the pressurizing portion  32   c  is not removed even when the valve member  50  is elevated. As the contact state is removed due to elevation of the piston  32 , the water supplied to the first space portion  61  to elevate the piston  32  is preferably discharged through the second space portion  62 , the first communication hole  32   e  and the hollow portion  32   d  of the piston  32 . Although not shown, the third space portion  63  and the receiving portion  42  of the sliding member  40  may be interconnected. Here, at an initial elevating stage of the piston  32 , that is, at a time when the first stepped portion  51  and the pressurizing portion  32   c  are separated from each other, the first communication hole  32   e  and the second space portion  62  are connected to each other. As the piston  32  is further elevated, a portion of the piston  32  having a diameter D 2  is connected with the extending portion  52  and a contact state between the first communication hole  32   e  and the second space portion  62  can be prevented. 
   In order to elevate the valve member  50  and the piston  32 , a water pressure supply unit  70  for supplying water having a predetermined pressure, that is, a water pressure, is provided in the first space portion  61  and the third space portion  63 . The water pressure supply unit  70  includes a pump (not shown) for supplying water pressure to the water pressure supply passage  12   a  of the socket  12 , a first water pressure passage  71  formed on at least one of the outer circumferential surface of the sliding member  40  and the main body  11 , and a second communication hole  72  formed in the main body  11  to connect the first water pressure passage  71  with the third space portion  63 . In addition, a second water pressure passage  74  is formed on at least one of the outer surface of the sliding member and the inner circumferential surface of the main body so as to be connected to the first water pressure passage  71 , and a third communication hole  75  is formed in the piston housing to connect the second water pressure passage  72  with the third space portion  63 . 
   In the water pressure supply unit, in a case where the second space portion  63  and the receiving portion  42  of the sliding member  40  are connected with each other, it is not necessary to form the second communication hole  72 . 
   The bit unit  20  is installed at the lower end of the main body  11  to perform a boring operation. The bit unit  20  includes a collar member  22  inserted into the main body  11 , a bit  21  having a hooking part  21   a  with an end portion slidably supported by the collar member  21 , a bit locker  23  inserted into the main body  11  and preventing the hooking part  21   a  of the bit  21  from being separated from the main body  11 , and a front locker  24  fixed to the main body  11  and spline-connected to the bit  21 . The bit  21  rotating relative to the main body  11  is fixed by the front locker  24 . The hooking part  21   a  and the bit locker  23  prevent the bit  21  from deviating lengthwise. The bit unit  20  is not limited to that of the above-described embodiment and any type of a bit unit slidably supported lengthwise and fixed in a rotary direction may be employed. 
   The operation of the aforementioned water hammer of the boring machine will now be described with reference to FIGS.  2  and  7 - 12 . 
   First, in order to perform a boring operation, the water hammer  10 , specifically, the tapered engagement portion  12   b  of the socket  12 , is connected to the end portion of the drive rod  100  of the boring machine. In such a state, the drive rod  100  is lowered and high pressure water is supplied to the water pressure supply passage  12   a  using a pump of the drive rod  100 . The water supplied through the water pressure supply passage  12   a  retracts the check valve member  13   b  elastically supported by a spring  13   e  of the check valve unit  13  to then be supplied to the hollow portion  11   a  of the main body  11 . Then, the water is supplied to the first space portion  61  and the third space portion  63  through the water pressure supply unit  70 , specifically, the first water pressure passage  71 , the second water pressure passage  74 , the second communication hole  72 , and the third communication hole  75 . 
   Since the cross-sectional area of the first shield portion  51  is wider than that of the second shield portion  53  along the length of the piston  32 , a difference in the cross-sectional area between the first and second shield portions  51  and  53  generates a difference in the pressure applied to the valve member  50 , thereby elevating the valve member  50 , as shown in  FIG. 9 . Here, the first shield portion  51  is not separated from the pressurizing portion  32   c  of the piston  32 . Thus, the pressure applied to the first space portion  51  is not applied outside. Some of the pressure applied to the first space portion  51  is applied to a lateral surface of the pressurizing portion  32   c , that is, a lengthwise side of the piston  32 , thereby elevating the piston  32 , as shown in  FIG. 10 . 
   If the piston  32  is elevated to a predetermined height in the above-described manner, the first shield portion  51  is separated from the outer circumferential surface of the pressurizing portion  32   c , and the water that imparts a pressure to the first space portion  51  is discharged to the second space portion  62  via a gap between the pressurizing portion  32   c  and the first shield portion  51  and to the hollow portion  32  via the first communication hole  32   e  formed in the piston  32  (see  FIG. 10 ) 
   At this time, the first and second space portions  61  and  62  are connected to each other to thus reduce a water pressure. To reduce a relative cross-sectional area difference between the valve member  50  and the second shield portion  53 , the pressure applied to the valve member  50  is applied to the extending portion  52  having throughholes  54 , as shown in  FIG. 8 . Since the cross-sectional area of the second shield portion  53  is greater than that of the valve member  50 , the valve member  50  is lowered. During this process, the first communication hole  32   e  is engaged with the extending portion  52  at a portion of the end portion  32   b  having the diameter D 2  to then be blocked. 
   In such a manner, the first and second space portions  61  and  62  are connected to each other to create a sealed space. In this state, as shown in  FIGS. 11 and 12 , the diameter D 1  of the guide portion  32   a  of the piston  32  is greater than that of the stepped portion  32   b  in view of the pressurizing portion  32   c . Thus, the pressure applied to the pressurizing portion  32   c  of the stepped portion  32   b  becomes relatively greater, thereby lowering the piston  32  and ultimately striking the bit  21 . 
   When the piston  32  is lowered, the outer circumferential surface of the pressurizing portion  32   c  is brought into contact with the first shield portion  51  of the valve member  50  to partition the first space portion  61 . Then, the above-described process is repeated by the pressure applied to a partitioned portion of the first space portion  61 , thereby allowing the piston  32  to continuously strike the bit  21 . 
   In the course of the piston  32  lowering, the air stored in the air storage portion  120  of the drive rod unit  110  is compressed as the water pressure for actuating the hammer unit  30  increases and the depth of a bored hole is increased. Thus, the compressed force is added to an elastic force based on the lowering of the piston  32 , thereby further increasing the striking force of the piston  32 . 
   As the depth of the bored hole is increased, it is necessary to further connect unitary drive rods  110  to the drive rod. In this case, the air stored in the drive rod  100  is induced and lowered together with the water. Then, the air induced to the internal pipe  130  of a drive rod  100  proximate to the water hammer is discharged to a space between the main body  112  and the internal pipe  130  through the discharge hole  137  to create a difference in specific weight, thereby isolating the air from the water. The isolated air is elevated to then be stored in the air storage portion  120 . 
   The thus stored air becomes compressed to a greater extent as the depth of the bored hole is increased and the water pressure is increased. As the compressed extent of the air is increased, the compressed air further increases the pressurizing force of the piston  32  when the piston  32  is lowered to perform a boring operation. 
   Therefore, the striking force of the piston  32  can be further increased by accelerating the piston elevating using a water pressure. 
   As described above, according to the present invention, the water supplied to a drive rod of a boring machine can impart an accelerating driving force to a piston of a hammer actuated by the water, thereby increasing the striking force of a bit. In addition, unlike in the prior art, it is not necessary to provide a separate gas filling unit for supplying a water pressure hammer with a gas such as nitrogen, thereby obviating a necessity of filling pressurized gas as the depth of a bored hole is increased. 
   INDUSTRIAL APPLICABILITY 
   As described above, in the water hammer of a boring machine according to the present invention, a valve unit and a piston can be directly elevated using high pressure water pumped through a drive rod, thereby simplifying the configuration of the water hammer compared to the conventional configuration in which water pressure is controlled by a pilot pressure. 
   In addition, since the pressure is directly applied to the valve member and the piston, there is little probability of malfunctioning, thereby increasing the operational reliability and enabling the boring machine regardless of the depth of a bored hole. Meanwhile, the striking force of a bit can be increased by imparting an accelerating driving force to the piston of the hammer. The piston of the hammer can be actuated by the water and air supplied to the drive rod. In addition, unlike in the prior art, it is not necessary to provide a separate gas filling unit, thereby obviating a necessity of filling pressurized gas as the depth of a bored hole is increased.