DRILLING APPARATUS

Tools percussive drill and more particularly to a fluid operated tools for applying blows repeated impacting to a drill bit in the drilling of oil and gas well and their equivalents. In particular, the present invention relates to hammer for incorporation into streams drill pipe, axially causing vibrations or oscillations at the same [...] bits that they are rotated for drilling such wellbores. The invention relates particularly to improvements in the valve means percussion engines. In the past a number of designs of engines for drilling boreholes have been suggested. Those which, in practice, have had some success have been constructed for use with a flow of high pressure gas, such as compressed air or natural gas. The percussion motor is mounted to the lower end of the drill string and in turn is connected to a suitable drill bit. The flow of high pressure gas, passing through the drill string, in the percussion motor in the drill bit, causes the oscillation of the percussion bit against the base layer, thereby providing a substantial portion of the drilling effect. The drill string is generally rotated, to J. a times to produce additional drill and to reduce the gaps in the direction of the hole. The compressed gas from the percussion motor normally flows out of openings in the drill bit and up the annular space between the walls of the hole and the drill string carrying the drill cuttings from field and of well fluids to the surface. Although the use of compressed gas is perfectly is revealed advantageous in drilling a plurality of wells, it is many cases where the compressed gas cannot be used as a drilling fluid. Numerous times it is necessary to use liquid (generally water or an oil-based liquid as drilling fluid) to control the flows of fluids from the base layer into the well and for conveying drill cuttings from the layer at the surface. It is well known that the hydraulic pressure imposed by the liquid column in the borehole provides a means to control the flow of fluids from the base layer into the well hole. Percussion The motors that were previously used principally for the gas or compressed air are not functioning well at all when the drilling fluid is a liquid. Even if the drilling fluids rising to the surface usually vibrating sieves pass through and circulate in the clarification areas in the bin for goat, it is substantially impossible to obtain a flow of material to recirculate in the drill string which contains no abrasive solids content. Therefore, it is a particular problem in the design of the percussion drilling motors actuated by. a liquid maintain the operation of the valve and without undue abrasion wear as to result. Therefore, it is a object of the present invention to provide an improvement in the valve system of a percussion motor, and particularly for a percussion motor actuated by liquid, although the improved valve system can be used with engines operated by a gas, if desired. According to the present invention, there is provided a percussion drill tool comprising a housing or casing, a hammer axially hollow, slidably disposed within said housing and snugly, a hollow anvil axially, slidably disposed within said housing and snugly and positioned adjacent to one end of said hammer, and a valve means imparting a reciprocating motion to said hammer between an upper position away from said anvil and a lower position in contact with it valve action of the valve means to a stream of fluid flowing through the hollow axial portion, wherein said valve means includes a valve element, an inner seat annular valve on said hammer, which is positioned such that the lower surface of said annular seat is in contact with an upper surface of the valve member, said element moving slidably between an upper position and a lower position, valve guide means supported from said housing within said hammer and guiding said element, and a valve stop means supported by said valve guide and positioned to stop the upward movement of said valve member so that the valve member, when in its uppermost position, is spaced from said annular valve seat provided on said hammer when said hammer is in its upper position. In to include 1' invention it will be now described with reference to the accompanying drawings, in which: The Figures IA and IB are, respectively, of the lower and upper portions of a cross-section of a percussion motor using the valve device of the present invention; and Figures^-2-6, The including, are schematic representations illustrating different phases during operation of said percussion motor; Figure 7 represents a lower portion, partially sectional, of a change in the percussion motor of IA and Figures Figure 8 is a view, partially sectional, of the upper portion d ' motor having a stepped percussion hammer to different [...] that represents a changing of the pattern of the hammer of stepped Figures IA and IB; Figure 9 represents a special seal for use in the tool. A motor comprises two movable parts normally elements which are a hammer stepped piston type and a set/Se^{r [...]} cylindrical. Although the invention relates to a device to improved valve, this improvement includes elementary these two movable parts since the two cooperate to produce 1' ^ [...] desired effect. An explanation will be given engine as a whole, and particularly as total operation enhanced to provide a prolonged duration of the tool. In addition of the hammer assembly and piston type valve, a percussion motor has a housing or casing to close the control fluid and an anvil slidably mounted within the casing under the hammer; however, the anvil is arranged to have limited axial displacement. The housing can transmit force usual downwardly from the bottom rods through the anvil to the drill bit. The anvil is disposed so that its top face receives impacts of a lower face of the hammer during its reciprocating motion. The lower end of the anvil is connected to the drill bit. The anvil, further, is provided with [...] of projections corresponding to splines and like projections formed in the inner lower part of the housing such that the torque applied to the drill string by the housing rotate the drill bit while continues percussive drilling. mounted at the lower portion of a drill string. The drill string is rotated from the surface and a high pressure fluid is directed downward through it. The fluid acts effectively through the percussion motor and escapes through an exhaust passage in the drill bit. The drilling fluid considerable suffers a drop in pressure as it passes through the drill bit in the drill bit and; the fluid pressure in the annular space between the tool and the borehole being normally of 7 kg/cm ^ to 42 kg/cm ^ ^ or 56 kg/cm, or more, lower than the pressure of the fluid in the drill string. This difference IB; cooperates with the other parts to perform During operation, the percussion motor is in pressure is used with advantage to impart to the hammer a reciprocating motion. The core assembly [...] between an upper position and a lower position, which causes, alternately, the application of a force to the upper part and the lower part of the slidable hammer, causing it to oscillate axially or vertically. After each upward stroke of the hammer, is drawn downwardly to strike the anvil, thereby causing the anvil, in turn, applying a series of shots impacting on the drill bit into contact with the base layer. Since it will be shown, the valve means is arranged to reduce wear, especially erosion of valve members. On the drawing, the tubular housing 10 is fixed from below to the lower end 50 d ' a conventional drill pipe (not shown). The tubular housing 10 includes an upper portion 12 of smaller diameter smaller than that of the bottom portion 14. A radial port 18 passes through the wall of the housing 10 below but near the junction 16 of the upper and lower portions. A hammer stepped cylindrical hollow 20 is mounted for axial movement within the housing 10. The diameter upper exterior of the hammer 20 is machined so as to fit tightly into the upper part 12 of the housing 10. Also, the lower outer diameter of the hammer 20 conforms more closely to the adjacent lower portion 14 of the housing 10. Seals 22 and 24 are preferably provided between the hammer and the housing in the upper and lower parts thereof. The tool comprises a hollow hole 26 at its upper end and which is in fluid communication directly with the drill string during operation. The tool is arranged such that there is essentially no leakage of fluid from the hollow hole 26 to the port 18. A seal particularly effective is represented in Figure 9. The gaskets are adapted to be positioned in a groove 24A of Figure 7, for example. The gaskets are ring-shaped and is in cross-section, non-constrained, take the form shown in Figure 9. The left vertical line 150 represents the surface of the hammer and the right vertical line 152 represents the position of the lower side surface of the groove 24A of the housing 10. When introduced into a tool are forced between the lines 150 and 152. The seal has a lip 154 which is a pocket 156. the pocket is subjected to the high pressure that may exist in the distance between the hammer 20 of the housing 10. The standard size of the cross section of the seal of Figure 4 in its unconstrained shape where the line 152 of the seal has a radius d * about 165.10 ram 158 include an angle between the plane of the lip 154 and a right angle with the base 160 of about 4°. The angle 162 of the face 164 is even about 4°. The total vertical thickness of the cross-section is generally of about 15.24 mm, the section 166 is about 3,175 ram and the length about 120.65 168 of ram. The length 170 has about 7,315 mm and the length about 7,924 mm 172. When the seal is inserted into the tool, it is compressed between the lines 150 and 152. The high pressure fluid from the chamber 156 force the lip 154 in the direction of the line 152 and the face 164 to bear firmly against the hammer, represented by the line 150. The wear surface is the surface 164. When the surface wears, the pressure in the cavity 156 to force the face outwardly to compensate for such wear. The anvil 28 is slidably mounted for limited axial displacement in the bottom end of the casing 10. At its lower end, the anvil 28 is provided with [...] transmit torque of the housing 10 to a drill bit (not shown) that can be fixed at its lower end in a conventional manner, for example by means of threads 30. Different variations can be used for the torque transfer device. A shape IA is shown in Figure wherein the lowermost portion of the housing has several edges [...] between each pair which has splines or grooves. These [...] -tee 32 come on splines or the equivalent grooves cut in the outer periphery of the lower part of the anvil 28. 28A The lower part of the anvil 28 is enlarged to the same diameter approximately that that of the housing 10. The upper surface 102 of the anvil portion 28A is for receiving the lower end 100 of the housing 10 so that a portion of the weight of the drill string above can be applied to the drill bit, this improving the efficiency in the wellbore. The flutes, in both the anvil 28 and in the housing 10.sont longer than the corresponding edges of such that until the bit touches the bottom, there is a vertical distance which the anvil 28 is movable between the position shown in Figure IA and a lower position in which the channels and the adjoining edges are in contact from above. Means not shown are provided to limit this movement typically vertically downwards about 25.4 to about 76.2 mm. Since it will be shown, this extension makes the hammer inoperative. The anvil 28 is provided with a central hole 34. The upper surface 36 of the anvil 28 corresponds to the lower surface 38 of the hammer 20. The surface 36 is provided with a plurality of grooves 40. A plurality of ducts 42 are also provided in the anvil 28 from the surface 36 to the inside of the hole 34. Grooves 40 are intersected by the conduits 42 or otherwise brought with them in fluid communication. The grooves 40-may extend into the well cylindrical [...] 77. The grooves and the conduits, either alone or in combination, permit the discharge of liquid quickly between the hammer and the anvil so as not to damp the impact between the two. The conduit 42 also serves to allow the tool to turn on under certain conditions or the otherwise it does not. Consider to present the tool in the [...] of Figure 2. If the seal 24 is effectively disposed between the anvil 28 and the housing 10 under certain conditions fluid could be trapped within the annular space 89 if there were not the conduit 42. When this happens the hammer 20 cannot step down to it so that the fluid in the chamber 89 is moved. This is because the valve 58 door in the annular seat 78 of the anvil 28 and the inner valve ring 82 forms a valve means with the element 86 of the valve guide 46. Escape of the fluid from the chamber 89, when the tool is in this position, is effected downwards through the conduit 42. A central valve or guide tube 46 is mounted in the filter housing 10 which is threadably coupled to the lower part 50. A ball joint 48 is attached to the upper end of the guide tube 46 corresponds to a socket and ball joint 47 which is mounted in the recess 51 of the lower part 50. The spacer 49 and the spring spacer 49A hold the ball joint and its [...]. Near the lower end of the guide tube, means-type guide [...] 53 supported within the hammer is arranged to center the tube within the hollow portion of the hammer. Have been estimated that this way of mounting the tube 46 provides centering more accurate than when the tube is rigidly fixed to the lower part 50 by means of a thread. As has been illustrated in the drawing, the lower part 50 also provides the means be connected to the drill string. The tube central valve 46 is provided for use in [...] the movement of the valve assembly. The tube 46 is preferably a thin-walled pipe of uniform diameter, concentrically mounted in the housing 10. The upper end of the valve tube 46 is in direct fluid communication with the fluid channel 26. The upper end of the valve guide tube 46 is with several openings 52 in size and number are sufficient to that there is only a very low pressure drop between the fluid pressure in the fluid channel 26 and the fluid channel 55 which is the annular space between the outside of the valve tube 46 and the interior of the hammer 20. A main assembly of valve is provided for the lower end of the valve tube 46 and includes a valve stem 54, a valve piston 56, and a valve head 58 having an upper surface and a lower surface 58A 58B. The valve piston 56 fits tightly within the lower end of the tube valve guide 46. A head annular valve 58 is connected to the lower end of the valve stem 54. The valve stem 54 extends slidably and related in the end member 60 of the valve tube 46. In the area directly above the terminal member 60 are more holes 62 made in the wall of the valve tube 46.La relationship of the location of these ports with the remainder of the tool when the anvil 28 [...] its lowered position will be treated below. The valve stem 54 has a sufficient length that when the moving parts of the tool are in the position shown in Figure 1 of the drawing, there is a recess 64 to 1': interior of the valve tube 46 below the valve piston 56. When the piston 56 is above the orifices 62, the cavity 64 has the same pressure P2 than the pressure in the annular space 55 between the valve tube 46 and the hammer 20. This pressure acts against an area which is the horizontal component of the area of the bottom side of the valve piston 56 which is in communication with the cavity 64. Throttling means fluid, illustrated in the drawing as a nozzle or restriction 66, is mounted at 1' interior of the valve tube 46 above the valve piston 56. The nozzle operates such that the pressure inside of the tube 45 valve guide 46 between the piston 56 and the nozzle 66, is always substantially lower than the pressure P_{3 prevailing in} the annular space between the valve tube 46 and the hammer except an exception, which will be indicated later., when the ports 62 are in communication with the interior 45. That is, this arrangement provides reduced pressure to act downwardly against the horizontal component effective Α ^ [...] of the valve piston 56. The nozzle 66 is to be has a sufficient distance above the piston 56 so that the piston of the valve is not of significant erosion effect. A positive stop 68 is provided in the valve guide tube 46 to limit the upward movement of the valve assembly (54, 56, 58) to a predetermined position which will be explained hereinafter. Since it will be shown, the stop and its position are very important for significantly increased of the valve means. The stop 68 is preferably made of hard metal to resist wear. The stop is represented as a stepped annular part and it is held in its position by an anchoring means such as' an annular member 70, which completes the annular stop 68, and which is rigidly fixed to the guide tube [...] valve 46 for example welded, or integral. A damping material 72 is provided between the positive stop 68 and the anchoring means 70. The damping material may be an elastic material such as rubber or a spring. The underside of the stop 68 may also include los grooves 74 which act as a fluid cushion which helps to reduce the fatigue of the plunger [...] to the impact. D * [...] These features are very important and considerably reduces wear and fatigue due to impact of the valve piston 56 and of the stop 68. Figure 7 represents a particularly desirable form means for stopping the upward movement of the valve assembly (54, 56, 58). This can, in effect, be considered a stop damper. The upper end of the valve head 56 is modified to include a ring-shaped cavity 56C. The lower end of the valve guide tube 46 has been modified to have a downwardly facing cavity 47. 4.7 The cavity is of annular shape and size of the cavity 47 is such that it may slidably receive the top end of the valve stem 56 which forms the cavity 56C. Capture of fluid in the chambers 47 and 56C, , when the upper end of the valve head 56 reaches the lower surface of the valve guide 46A, causes a very effective type damper stop upward movement of the valve assembly. Both surfaces, the surface [...] 58B and the bottom surface of the valve head 58 function as valves. Attention will first be drawn to the assembly of the seat for the underside of the valve head 58 of the main assembly of alternating valve. Anvil A valve recess 76 is provided in the top end of the anvil 28. This may be a cylindrical recess which, in effect, may be a magnification of the hole 34. The seat 78 is mounted in a valve recess 76. The upper part of the recess 76 above the seat 78 is called a valve pocket 77 formed by the ring member whose diameter 77A ' is only slightly larger than the diameter of the valve head 58. For example, the game may be about 2.54 to about 2.03 mm. The interior of the bag 77 and the cylindrical outer surface of the valve head 58 form, in effect, a sleeve valve which reduces the flow of fluid before the valve 58 No. Airlifting on the ring seat 78. The annular seat 78 provides a seat for the lower surface 58B of the valve head 58. The [...] / [...]' [...] of the head-. valve 58 is greater than the diameter of the plunger 56. This determines appropriate different areas. The upper surface of the annular valve, seat or of the anvil 78, is below the upper surface 36 of the anvil at a sufficient distance for the entire valve head 58 is substantially received within the valve pocket 77. Damping means 80 is mounted beneath the bottom side of the annular valve seat 78, arranged in the lower part of the valve recess 76. The damping material may be similar to the material 72 which is provided with a positive valve stop 68. This helps to reduce the forces for impact in the valve stem 58 and in the annular valve seat 78, both of which are preferably made from hard metal, such as tungsten carbide. The valve head 58 when it is closed against the seat 78 anvil preventing fluid flow from the annular space 55 to the hole 34 within the anvil 28. For a reason for convenience is called P_{2 printing} within the hole 34 and when the valve 58 is closed by bearing against the seat 78, the value of P_{2 is approximately} that of the external pressure of the tool (and also within the tube guide valve 45), since when the tool is closed, the flow of fluid in the drill bit stops (except a small amount flowing through the constriction 66) and the pressure in the hole 34 is approximately the pressure outside of the tool. The valve head 58 includes an upper surface 58A machined with care, as well as a lower surface 58B machined with care. Near the stepped lower portion of the hammer 20, the hole of the hammer is reduced and a valve member 88 is provided to annular sleeve forming a pocket for hammer valve 85, the depth of which is equal or slightly greater than the distance between the seats and 58B 58A. This requirement with respect to the depth is large and clearly shown on Figure IA. A annular valve seat 90 is provided above the annular element 88 58A for the upper surface of the valve head 58. Damping rings 92 are provided as annular valve seats 90. A retainer 93, which can be an extension of a described [...][...] 82, is provided for the dampers and the dampers and serves to prevent the valve 90 upward movement with respect to the hammer 20. It should be noted that when the valve head 58 is in its closed position on the anvil, i.e., the lower surface on the seat 78 58B, 58A that its upper surface is not in contact with the valve seat 90 or in the valve pocket 35 hammer when the hammer 20 is in its bottom position. This allows the high pressure fluid act on the bottom surface of the hammer 20, forcing it upwardly. L " maintaining. attention will be attracted to an annular valve or secondary [...] can also an annular valve. The ei comprises an annular valve 82 mounted on the inside of the lower end of the hammer 20 over the ring damper retainer 93. The annular valve 82 is preferably provided with a refill hard metal 84. The lower portion 86 of the lower member 60 of the valve guide 46 is preferably a hard metal, such as tungsten carbide atomized, it is machined and carefully as is the interior of the refill hard metal 84 of the annular valve 82 so that the hammer 20 moves upward, an annular valve 82 cooperates with the lower part 86 to stop substantially all of 1' downward fluid flow from the annular space 55. It will occur a flow from the annular space 55 to the cavity 64 while the valve assembly (54, 56, 58) moves upward. Having describes the general configuration of the drilling tool, attention will be called to maintaining its operation and in particular to report the interior of the different parts of the valve that it is estimated to be most important. An operating cycle can begin the parts being in the relative positions shown in Figures IA and IB. There the main valve, i.e., the valve head 58, door on the valve seat 78 that anvil and the hammer 20 rests on the anvil 28. Maintaining is taken into account the predominant forces acting on the valve and on the hammer when the pressure is applied of the fluid in the drill string for each of the positions indicated in Figures and 2-5 in Figures IA and IB; Figures 2-6 are drawn to represent primarily the relative positions of the different parts for the various phases of a cycle of operation rather than their respective dimensions. The hammer then start from the position shown in Figure IA because the net force on the hammer is upwardly directed. This is represented by examining the dominant hydraulic forces. The downward force acting on the hammer 20 is: (1) P_{2 has5 a 7 3 + p}where Ag is the horizontal component of the area of the upper hammer stepped in contact with the fluid having a pressure P_2, which is the pressure of the fluid in the annular space exterior of the tool; A_{? is} the horizontal component of the upper area of the hammer stepped in communication with the main flow of the drilling fluid in the annulus 55 at a pressure P ^. The force upwardly directed [...]' exerted on the hammer 20 is: (2) 3^{has 6} p where Ag is the horizontal component of the surface area of the lower surface of the hammer. Ag Ag more equal Since A_{? ,} it becomes readily apparent that there is an upward force exerted on the hammer 20 due to the pressure difference. The force at the valve assembly while^{! [...]} hammer is rise (and before the annular valve 82 is pressed or close on the seat 86 arranged outside the valve guide member 46) is given below. The downward force is: O)_{3 (Ayjj-Ayg)} P + P_{X (} ~ Ayp) and the upward force is: (4) P_{3 (} ^ Α [...] - [...] )'^{r p i}wherein [...] is a cross-sectional area of the valve head 58; Ay_{S is a cross-sectional area} of the valve stem; and, Α ^ [...] is a cross-sectional area of the valve piston 56._{3 P is the pressure} the largest within the cavity 64 and of the annular space 55. P '^ is the reduced pressure of the fluid within the hole 34, and as n^{, -is} little flow at that time between the hole 34 and the exterior of the tool, with the exception of the amount over the throttle 66, can be considered for this explanation that P' is also the approximate pressure ^ P ^ of the fluid in the outside of the annular space of the tool. The net force acting at that time on the valve assembly is directed to the sump and it [...] : (5) (_3- P P_x) (A ^)-<?_3- P_x) A_vpbecause A ^ is larger that A by construction. The valve head 58 remains closed, i.e., applied in the anvil, until the hammer 20 rises at a position shown in Figure 2 and the secondary valve closes, i.e., the annular valve 82 corresponds with the lower portion 86 of the valve guide 46. When this happens, the cavity 87 below the element 86 and to the outside of the shaft 54 is cut from the main stream of the drilling fluid. Once the annular member 84 is near the lower end 86 of the tube 46 it restricts the flow of fluid in the cavity 87. This reduction of the fluid flow is accompanied by a substantial decrease in the pressure below the hammer 20 since the volume of the chamber 89 20 between the hammer and the anvil 28 is also extended. When the pressure in the chamber 89 will have decreased sufficiently, 1' valve assembly will be forced upwardly. The net force acting on the valve assembly is (6) (_3- P + (1*2.-P '₃₎[...]wherein a positive sign represents a force upwards and a. negative sign represents a force downwardly. P ' 3 P_{2 approach because} the volume of the cavity 87 and 89 of the chamber between the annular valve, i.e., the upper annular valve 84, and the face of anvil expands more rapidly that the fluid can only "leaking" beyond the annular valve. Accordingly the net force upward on the valve is (7) (P_{3 P-1)} + P_{1 [...]} Ayp Since the value P is positive and_{3 is much larger than} P-L and that is only slightly larger than the valve assembly is literally sprung up. Figure 3 is similar to Figure 2 but represents the valve 58 to about-mi path upwardly between the anvil and the seat of the hammer. The valve continues its way upward until it encounters the stop 68 as shown in Figure 4. The stop 68 is positioned such that the valve assembly is stopped before the valve head 58A comes into contact with the annular ring 90. If the valve was stopped by the annular ring 90, then as the hammer and the valve assembly move up, the cavity 85 decrease of volume and pressure of the fluid trapped there is decreased rapidly. This would cause a violent flow of the fluid by the valve surface 58A and the valve seat 90, causing severe erosion. In the present invention, the valve stop 68 is positioned so that when the secondary valve, i.e., the annular valve 82 closes, the cavity 87 cannot taper in a position "enclosed" once the valve head 58 is stopped. The stop 68 is positioned such that the valve head 58 is stopped at a position just below the valve seat 90 when the hammer is in its upper position. The valve stopper 68 is also positioned such that the annular valve 82 is still closed (i.e., in contact with the valve element 86) when the annular ring 90 is in contact with the valve head 58A on the down stroke of the hammer. A way of performing this is to place the stop 68 so that the valve assembly is stopped after the valve head 58, has reached a distance "h", or preferably slightly less than "h", the point 17 on the face 86 wherein "h" is the distance between the valve seat 90 the upper end of the hard coating 84 of the annular valve 82. This ensures that the cavity 87 cannot "narrow" with fluid therein in a "closed" condition. 58A The valve surface should be applied to the seat 90 before the surface 84 of the ring member 82 is lowered sufficiently to provide clearance for the point 17 on the tube valve guide 46. Were constructed a tool having the housing has an outer diameter of 177.8 mm, a hammer for 136.52 mm outer diameter, a valve piston diameter 60.32 mm, a valve stem of 41.27 mm diameter, and a valve portion 86 on the valve guide 46 69.85 mm in outside diameter. A, the upper part of the ring 82 in its highest position is about 1,016 mm by 6.35 mm above the point of the boundary 17. A 1' stop 68 is preferably controlled so that the surface 58A. is stopped at a distance equal to "h" least about 2.54 mm below the point 17. A short examination of the predominant force acting on 1' valve assembly: (regardless of the weight of the assembly itself) will be maintaining indicated when the various parts are in the position shown in Figure 4 in which the piston 56 is against the stop 68, the annular valve 82 still closed and the valve 58 zero carrying hand. The net force on the valve is: (8) <? 3-rp (V + tt-_3- V wherein the more force acts upwardly and the negative force downwardly. Since P ' approach_{[...] Ρ} 3^the net force is then (P_3- P^) which is positive since P_{3 is much larger than} l^* P When the fluid flow is cut or reduced below ag of the surface of the hammer 58 and that the valve is stopped, the net force down on the hammer rapidly exceeds the force upward and the hammer is forced to descend. (On most of the downward stroke the valve unit and the hammer lowered together.) When the hammer starts to come, the cavity 87 increases and substantially no fluid flows between the seat S0 disposed on the hammer and the upper surface of valve 58A of the valve when it closes. That is, after a certain downward movement, the hammer via the valve 90 [...] force the valve to descend therewith. The relative position of the parts is shown in Figure 5. The upward force acting on the valve is greater than the force directed to the has due to the seal between the valve head and 58A the valve seat 90. The net force on the set [...] due to the fluid pressure is: r <_3- m V < V + h \ h-^{p 3} " [...]wherein a positive sign is a force upward and a negative sign indicates that the force is exerted downwardly, and is the area of the valve head 58 in contact with the fluid pressure P_3. By design, A ^ is larger that A ^_{p that is larger than}[...] -^Accordingly the net force acting on the valve assembly is directed upwards. The inside diameter of the tube 46 is by constructing larger than the smallest diameter of the seat 90. When the hammer strikes the anvil, the hammer is stopped; inertia of the valve but the peeled off of the annular seat 54 90 the [...] polyethylene, toward the seat 78 provided in the anvil as the Figure represents the IA. Now the valve has no more net force upward. The valve chamber 85, in which fits tightly against the valve 58, has a role very ' useful because it allows a pressure difference is maintained perpendicular to the valve 58 [...] so that it continues to descend to engage the seat 78. The valve chamber 77 also fits closely to the head 58 which, as well as the valve chamber 85, prevents the valve head 58 to return prematurely to the seat 90 where it could be applied and secure the assembly. Of course, the tool could be unlocked only lifting it off the lower portion while maintaining the pressurized drilling fluid. Furthermore, any tendency of the valve to jump from its seat 78 is reduced by the close fit of the valve head 58 in the valve chamber 77. The hammer 20 strikes the upper face of the anvil 28. It is important that nothing will interfere with the movement of the hammer as it is about to strike the anvil. Therefore, it is desirable, though not essential, to provide radial grooves 40 aforementioned in the upper end of the anvil 28 and conduits 42 so that the liquid remaining between faces of the hammer and of the anvil can be quickly discharged into the discharge passage 34. The resistance to flow offered by the conduits 42 is much greater than that offered by the hole 34. This allows for maximum pulse during the transfer of the pulse of the hammer 20 to the anvil 28. The grooves 40 may be placed in the lower surface of the hammer if desired. Referring that the [...] and the means for limiting its stroke are provided to prevent excessive wear of the valve mechanism. The valve member, being much lighter than the hammer, is forced upwards at a rate greater than that of the hammer. However, in this design, see that the upward movement is stopped by stops specifically designed which, for some reason very important, are provided with damping material and, very important thing, that part of the assembly that constitutes the valve proper is not included in the stop of the upward movement. Referring, further, that the downward movement of the valve is caused by the hydraulic pressure acting on the hammer and the hammer carries the valve assembly downward at the speed of the hammer, and not to the speed at which the valve assembly has been carried upwardly. In this case, also see that the valve seat 90 provided on the hammer is provided with [...] to help protect the upper surface of the valve head 58. When the valve 58 is seated against the anvil 78 valve seat, the seat is also provided with [...] 80. Referring and the valve assembly is provided with features that reduce the wear or damage of the valve assembly, , however, to operate at the speed required. If it is desired the fluid circulation takes place in the tool without reciprocating movement of the hammer, any co that there is a need to raise 1 is' tool. The parts then take relative positions indicated in Figure 6. There the fluid flows primarily of the annular space 55 between the hammer 20 and the valve guide 46 through the openings 62 45 inwardly above the valve piston 56 ; then descends by the large hollow portion 57 of the valve assembly to the hole of the anvil 34. This also force the hammer 20 upwardly so that the annular valve 82 is closed. If it is desired the circulation thereby, there should be a hole in the wall of the guide tube 46 near its lower end as is transferred through the orifice 62A so that the fluid is not trapped below the piston 56 which would inhibit downward movement. May be the hammering of the tool from the position shown in Figure 6 while circulating the fluid by only lowering the tool until the drill bit is engaged by the lower portion of the borehole, forcing the anvil 28 and the valve assembly (54, 56, 58) applied to the anvil 78 seat, upward until the piston 56 moves upward to close the orifices of the valve tube 62. The tool Modifications to improve its operation. For example, the addition of shear pin (represented sheared by the parties 174A and 174B) between the lower section of the housing and of the anvil is well-useful. This prevents movement of the anvil while it is in the hole. If the anvil is held stationary relative to the housing in its position the lower, the fluid can then be recirculated and to¹operations/enlargement and other similar, may be made while lowering the tool, without the hammer tends to perform its reciprocating motion. Without the shear pin, the hammer tends to perform its reciprocating motion, and is lowered, when the drill bit and the anvil reach uneven portions of the borehole wall, the hammer, relatively speaking, falls to its lower position. When this happens, drill cuttings sometimes accumulate in the holes 18 and in the space above the upper end of the hammer stepped which is in fluid communication with the exterior of the tool. If the accumulation of debris is sufficient it can credit the sketchy jamming of the tool. However, by adding a shear pin, the tool cannot be its reciprocating motion, and the hammer is in its upper position until the tool reaches the bottom. The difficulty resulting from the accumulation of debris is thus eliminated. Once the tool reaches the bottom, the drill bit can rest on the bottom of the hole and the weight may be added to the drill string until the shear pin is sheared. In Figure 7 the pin is represented after being sheared. 174A It comprises an outer portion which is in the housing and the inner part 174B which is in the anvil. Once the pin has been sheared, the tool operates in a conventional manner. The embodiment of Figure 8 a hammer ^ forces r inverted staggered. 20A The hammer has an upper section 176 which has a larger inside diameter than the lower section 178. As a result a shoulder 180 facing upwards between the two which is subjected to the high pressure fluid into the channel formed between the hammer and the tube valve guide 46. The upper section 176 has its inner portion sealed by means of seals with a tubular member 182 184s ' extending downwardly which is fixed to the housing. The upper section 176 of the hammer has an upper shoulder 186 which is in fluid communication with the exterior of the tool through the openings 188. While is exposed above that a limited number of examples of the present invention, various modifications may be made without departing from the scope of the invention