Pressure reversing valve for a fluid-actuated, percussive drilling tool

Abstract

A pressure reversing valve for a fluid-actuated percussive drilling tool has a front thrust surface in communication with a rear chamber and a rear thrust surface in communication with a pressurized volume isolated from the flow coming from the source of pressurized fluid. The pressurized volume is in communication with a front chamber and allows the valve to take advantage of the imbalanced profile of the pressures inside the front and rear chambers that naturally occurs for enabling an asymmetric feeding process of the rear chamber that is also less sensitive to the bottom hole pressure.

Claims

1. A percussive drilling tool comprising: a cylindrical outer casing having a rear end and a front end; a rear sub affixed to said rear end of the outer casing for connecting the percussive drilling tool to a source of pressurized fluid; a drill bit mounted to said front end of the outer casing; a piston slidably disposed inside said outer casing and capable of reciprocating due to a change in pressure of the pressurized fluid contained inside of a rear chamber and a front chamber located at opposites sides of the piston; and a valve slidably mounted between a valve carrier and a probe carrier, the valve having a valve front thrust surface in communication with the rear chamber and a rear thrust surface in communication with a pressurized volume formed by surfaces of the probe carrier and the valve; wherein said pressurized volume is isolated from high pressure flow coming from the source of pressurized fluid, and wherein the pressurized volume is in communication with the front chamber through at least one passageway defined cooperatively by a longitudinal passageway in a probe and by a longitudinal bore in the piston extending therethrough, the longitudinal passageway in the probe being open to the pressurized volume in its rear end and the longitudinal bore in the piston being open to the front chamber in its front end.

2. The percussive drilling tool of claim 1, wherein the valve further includes a front support surface for engaging a rear valve support surface on the valve carrier when the valve is in its frontmost position.

3. The percussive drilling tool of claim 1, wherein the valve further includes a rear support surface for engaging a front valve support surface on the probe carrier when the valve is in its rearmost position.

4. The percussive drilling tool of claim 1, wherein the valve further includes a biasing thrust area exposed to the high pressure flow coming from the source of pressurized fluid.

5. A percussive drilling tool comprising: a cylindrical outer casing having a rear end and a front end; a rear sub affixed to said rear end of the outer casing for connecting the percussive drilling tool to a source of pressurized fluid; a drill bit mounted to said front end of the outer casing; a piston slidably disposed inside said outer casing and capable of reciprocating due to a change in pressure of the pressurized fluid contained inside of a rear chamber and a front chamber located at opposites sides of the piston; a cylinder disposed in between the outer casing and the piston; and a valve slidably mounted between a valve carrier and a probe carrier, the valve having a valve front thrust surface in communication with the rear chamber and a rear thrust surface in communication with a pressurized volume formed by surfaces of the probe carrier and the valve; wherein said pressurized volume is isolated from high pressure flow coming from the source of pressurized fluid, and wherein the pressurized volume is in communication with the front chamber through at least one longitudinal passageway in the cylinder, the longitudinal passageway in the cylinder being open to the front chamber in its front end and being open to the pressurized volume in its rear end.

6. The percussive drilling tool of claim 5, wherein the valve further includes a front support surface for engaging a rear valve support surface on the valve carrier when the valve is in its frontmost position.

7. The percussive drilling tool of claim 5, wherein the valve further includes a rear support surface for engaging a front valve support surface on the probe carrier when the valve is in its rearmost position.

8. The percussive drilling tool of claim 5, wherein the valve further includes a biasing thrust area exposed to the high pressure flow coming from the source of pressurized fluid.

9. A percussive drilling tool comprising: a cylindrical outer casing having a rear end and a front end; a rear sub affixed to said rear end of the outer casing for connecting the percussive drilling tool to a source of pressurized fluid; a drill bit mounted to said front end of the outer casing; a piston slidably disposed inside said outer casing and capable of reciprocating due to a change in pressure of the pressurized fluid contained inside of a rear chamber and a front chamber located at opposites sides of the piston; and a valve slidably mounted between a valve carrier and a probe carrier, the valve having a valve front thrust surface in communication with the rear chamber and a rear thrust surface in communication with a pressurized volume formed by surfaces of the probe carrier and the valve; wherein said pressurized volume is isolated from high pressure flow coming from the source of pressurized fluid, and wherein the pressurized volume is in communication with the front chamber through at least one longitudinal passageway in the outer casing, the longitudinal passageway in the outer casing being open to the front chamber in its front end and being open to the pressurized volume in its rear end.

10. The percussive drilling tool of claim 9, wherein the valve further includes a front support surface for engaging a rear valve support surface on the valve carrier when the valve is in its frontmost position.

11. The percussive drilling tool of claim 9, wherein the valve further includes a rear support surface for engaging a front valve support surface on the probe carrier when the valve is in its rearmost position.

12. The percussive drilling tool of claim 9, wherein the valve further includes a biasing thrust area exposed to the high pressure flow coming from the source of pressurized fluid.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) In the drawings:

(2) FIG. 1 shows three plots labeled A, B and C. These plots represent the typical behavior for a hammer where the porting depends solely on the relative position of the piston and other auxiliary parts, like the cylinder in the Type F Flow Systems, during the alternating movement of the piston. These hammers are known as valveless hammers. In plot 1A are represented the absolute pressures inside the front and rear chambers (Y-axis) against time (X-axis) with segmented and continuous lines respectively. Points A and B represent the points during a single piston cycle where the pressures inside both chambers are equal. In plot 1B is represented the piston position (Y-axis) against time (X-axis). Piston position is measured from the impact position where its value is cero and positive rearward. Points A and B are also represented. In plot 1C are represented the absolute pressures inside the front and rear chambers (Y-axis) against the piston position (X-axis) with segmented and continuous lines respectively. Points A and B are also represented. Arrows are used to show the direction of the pressure cycles: clockwise for the front chamber and counterclockwise for the rear chamber.

(3) In all these plots, square marks have been used to point out timing limits for the front chamber and triangular marks have been used to point out timing limits for the rear chamber.

(4) Numbers have also been used to point out timing limits. Numbers one (1) indicate the impact position for both chambers and numbers four (4) indicate the maximum stroke position (a small shift has been used when these points overlap). Meanwhile, numbers two, three, five and six (2, 3, 5 and 6) have been used to point out the chambers' timing limits (cycle phases limits) described formerly in the section “operation of the hammer”: a—supply of pressurized fluid, wherein the fluid coming from the source of pressurized fluid is free to flow into the chamber. Process through points 6-1-2 for the front chamber and process through points 3-4-5 for the rear chamber. b—expansion or compression, depending on the direction of the piston's movement, wherein the chamber is tightly sealed and the volume it encloses increases or decreases. Processes through points 5-6 (compression) and 2-3 (expansion) for the front chamber, and processes through points 5-6 (expansion) and 2-3 (compression) for the rear chamber. c—discharge of pressurized fluid, wherein the fluid coming from the chamber is free to flow towards the bottom of the hole. Process through points 3-4-5 for the front chamber and process through points 6-1-2 for the rear chamber.

(5) FIG. 2 depicts a longitudinal cross section view of a DTH hammer with a Type F flow system, specifically showing its main components: rear sub (20), outer casing (1), driver sub (110), drill bit (90), piston (60) and cylinder (40). The rear chamber (230) and the front chamber (240) are also identified. The piston is shown in the impact position.

(6) FIG. 3 depicts a longitudinal cross section view of a DTH hammer with a Type F Flow System and a first preferred embodiment of the valve system of the invention, specifically showing the valve in its close position.

(7) FIG. 4 depicts a longitudinal cross section view of a DTH hammer with a Type F Flow System and the first preferred embodiment of the valve system of the invention, specifically showing the valve in its open position.

(8) FIG. 5 depicts a longitudinal cross section view of a DTH hammer with a Type F Flow System and a second preferred embodiment of the valve system of the invention, specifically showing the valve in its close position.

(9) FIG. 6 depicts the valve of the first preferred embodiment of the valve system of the invention.

(10) FIG. 7 depicts the valve of the second preferred embodiment of the valve system of the invention.

(11) FIG. 8 depicts a longitudinal cross section view of a DTH hammer with a Type F Flow System and the first preferred embodiment of the valve system of the invention, specifically showing the valve in its close position, where the valve has a biasing thrust area.

(12) FIG. 9 depicts the valve of the first preferred embodiment of the valve system of the invention, where the valve has a biasing thrust area.

(13) FIG. 10 depicts the valve of the second preferred embodiment of the valve system of the invention, where the valve has a biasing thrust area.

DETAILED DESCRIPTION OF THE INVENTION

(14) Referring to FIG. 2, a direct circulation DTH hammer is shown that has a Type F Flow System and comprises the following main components: a cylindrical outer casing (1) having a rear end and a front end; a rear sub (20) mounted to said front rear end of the outer casing (1); a driver sub (110) mounted to said front end of the outer casing (1); a piston (60) slidably and coaxially disposed inside said outer casing (1); a drill bit (90) slidably mounted on the driver sub (110); a cylinder (40) that is coaxially disposed in between the outer casing (1) and the piston (60); a rear chamber (230); and a front chamber (240);

(15) Referring to FIGS. 3, 4 and 6, the first preferred embodiment of the valve system of the invention is shown implemented in a direct circulation DTH hammer that has a Type F Flow System. The preferred embodiment of the valve system of the invention comprises the following main components:

(16) A valve carrier (300) mounted at the front end of the rear sub (20), the valve carrier (300) having a rear valve support surface (301);

(17) A probe carrier (310) mounted on the rear end of the valve carrier (300), the probe carrier (310) having a front valve support surface (311), one or more fluid passageways (312) and an inner sliding surface (313);

(18) A valve (320) mounted in the space between the valve carrier (300) and the probe carrier (310) capable of slide on the sliding surface (313) of the probe carrier (310) for moving between a close position and an open position, the valve (320) having a central bore (321), a front support surface (322), a rear support surface (323), a front thrust surface (324), a rear thrust surface (325) and creating together with the probe carrier (310) a pressurized volume (314);

(19) A longitudinal central bore (69) machined along the entire piston (60) body;

(20) A probe (330) mounted on the rear end of the probe carrier (310), the probe (330) extending along the central bore (321) of the valve (320) and extending in part or totally along the longitudinal central bore (69) of the piston (60). The probe (330) fitting the valve (320) on its external surface and having one or more ports (331) and at least one longitudinal passageway (332) for connecting the pressurized volume (314) with the front chamber (240);

(21) How the Valve Works in the First Preferred Embodiment of the Valve System of the Invention

(22) At any moment of the piston cycle, the pressure acting on the rear thrust surface (325) of the valve (320) is equal to the pressure inside the front chamber (240) because the pressurized volume (314) created between the probe carrier (310) and the valve (320) is in direct communication with the front chamber (240) through the ports (331) and the passageway (332) of the probe (330) and through the central bore (69) of the piston (60) and because no flow of pressurized fluid is stablished through this path. In a similar way, at any moment of the piston cycle, the pressure acting on the front thrust surface (324) of the valve (320) is equal to the pressure inside the rear chamber (230) because the front thrust surface (324) is directly exposed to the fluid inside the rear chamber (230).

(23) Starting from the impact position (see point 1 in the left side of FIG. 1B) and with the valve (320) in its frontmost position (closed position), the piston (60) moves rearward until it reaches point A where the pressures in the rear and front chambers (230,240) equalize. Because the front support surface (322) of the valve (320) is resting on the rear valve support surface (301) of the valve carrier (300) and the rear support surface (323) of the valve (320) is exposed to the pressurized volume (314) a pressure in the rear chamber (230) higher than the pressure in the front chamber (240) is needed to open the valve (320). After point A and depending on the values of the front thrust surface (324), the rear support surface (323) and the rear thrust surface (325), the valve opens. Ideally, areas must be set up in such a way that the valve (320) opens close after point 3 of the rear chamber (230) cycle is surpassed (see rear chamber diagram in FIG. 1C).

(24) When the valve (320) is open, pressurized fluid is allowed to flow inside the rear chamber (230) from the source of pressurized fluid through the central hole (21) in the rear sub (20), through the fluid passageways (312) and in between the front support surface (322) of the valve (320) and the rear valve support surface (301) of the valve carrier (300). This pressurized fluid flow into the rear chamber (230) complements the flow of fluid coming from the source of pressurized fluid that is free to flow into the rear chamber (230) during the process 3-4-5 (see rear chamber diagram in FIG. 1C), where points 3 and 5 are determined by the relative position between the piston (60) and the cylinder (40).

(25) After the piston (60) reaches its maximum stroke (points 4 in FIGS. 1A, 1B and 1C) it starts its frontward stroke. After point 4, the rear chamber (230) continues its filling process through the valve (320) and through the geometrically determined filling fluid path, the last remaining open until the piston (60) closes it at point 5 (see rear chamber diagram in FIG. 1C). Nevertheless, after point 5 the filling process of the rear chamber (230) through the valve (320) continues.

(26) After point 6 in the rear chamber (230), the piston (60) will open the discharge of the rear chamber (230) to the bottom of the hole and the pressure inside the rear chamber (230) will drops rapidly causing that the pressures in the rear and front chambers (230,240) equalize again past point B.

(27) Because the rear support surface (323) of the valve (320) is resting on the front valve support surface (311) of the probe carrier (310) and the front support surface (322) of the valve (320) is exposed to the pressure of the flow through the valve, which accelerates due to the pressure drop, a pressure in the front chamber (240) slightly higher than the pressure in the rear chamber (230) is needed to close the valve (320). After point B and depending on the values of the front thrust surface (324), the front support surface (322) and the rear thrust surface (325), the valve closes. Ideally, areas must be set up in such a way that the valve (320) closes close after point B (see rear chamber diagram in FIG. 1C). Once point 1 is reached, the cycle starts again.

(28) The less resistance offered to the fluid flow coming from the source of pressurized fluid by the open (to the bottom of the hole) rear chamber (230) in comparison with the resistance offered by the front chamber (240) when its geometrically determined filling fluid path is open in the frontward stroke (subprocess 6-1 in FIG. 1C) also allows a slower filling of the front chamber (240) avoiding in this way the piston deceleration during the frontward stroke, close to the impact position.

(29) How the Valve Works in the Second Preferred Embodiment of the Valve System of the Invention

(30) Referring to FIGS. 5 and 7, a second preferred embodiment of the valve system of the invention is shown implemented in a direct circulation DTH hammer that has a Type F Flow System. The second preferred valve system follows the same operation principles and comprises the following main components:

(31) A valve carrier (300) mounted at the front end of the rear sub (20), the valve carrier (300) having a rear valve support surface (301);

(32) A probe carrier (310) mounted on the rear end of the valve carrier (300), the probe carrier (310) having a front valve support surface (311), one or more fluid passageways (312), an inner sliding surface (313) and one or more secondary fluid passageways (315);

(33) The rear sub (20) having one or more secondary fluid passageways (29);

(34) A valve (320) mounted in the space between the valve carrier (300) and the probe carrier (310), the valve (320) having a front support surface (322), a rear support surface (323), a front thrust surface (324), a rear thrust surface (325) and creating together with the probe carrier (310) a pressurized volume (314);

(35) The cylinder (40) having at least one longitudinal passageway (333), and rear ports (48) and front ports (49) in the rear and front ends of the longitudinal passageways (333) for connecting the front chamber (240) with the pressurized volume (314) through the secondary fluid passageways (315) in the probe carrier (310) and through the secondary fluid passageways (29) in the rear sub (20);

(36) This valve system follows the same operation principles it does in the first preferred embodiment of the valve system of the invention. The only difference is how the purpose of that, at any moment of the piston cycle, the pressure acting on the rear thrust surface (325) of the valve (320) be equal to the pressure inside the front chamber (240) is achieved. In the second preferred embodiment of the valve system of the invention, the pressurized volume (314) created between the probe carrier (310) and the valve (320) is in direct communication with the front chamber (240) through the secondary fluid passageways (315) in the probe carrier (310), through the secondary fluid passageways (29) in the rear sub (20), and through the rear ports (48), the longitudinal passageways (333) and the front ports (49) in the cylinder (40).

(37) Design Considerations

(38) The first preferred embodiment and the second preferred embodiment of the valve system described previously are only two of many variations of the valve system of the invention that can be envisioned, including for example longitudinal passageways equivalent to passageways (333) but on the inner surface or even in the wall of the outer casing (1).

(39) It will be appreciated by those skilled in the art that other changes, besides the ones mentioned above, could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention. One of those changes can be to completely remove the rear set of recesses that allows the geometrically determined supply of pressurized fluid to the rear chamber in hammers that use, for example, the Type F Flow System, letting in this way the valve be the only mean for feeding that chamber allowing the simplification of the base Flow System or make some parts sturdier. In a similar fashion, the probe carrier (310) and the valve carrier (300) don't need to be separated parts and can be built in in the rear sub (20) and in the cylinder (or sleeve) respectively. These kinds of changes must be considered obvious.

(40) With respect to the front and rear support surfaces (322, 323) they are not required to be equal and can be modified according to the hammer operation requirements. Moreover, those surfaces (322, 323) can be reduced to almost cero just mismatching the angles of those surfaces with respect to the front valve support surface (311) of the probe carrier (310) and the rear valve support surface (301) of the valve carrier (300), respectively. In both cases the effect is achieve an earlier change in the state of the valve (320) because surfaces (322, 323) would be always subject to the rear chamber (230) and front chamber pressures (230).

(41) In FIG. 5, the probe carrier (310) and the rear sub (20) have surficial undercuts to avoid the need of alignment between the ports (48) and passageways (29) and between passageways (29) and passageways (315). Because this is an obvious design solution, those undercuts are not considered critical features of the invention.

(42) Valve System Biasing

(43) The valve system described before allows to increase the DTH hammer power. In situations where increase the efficiency is also important, which means improve the DTH hammer power to pressurized fluid consumption ratio, or the flow rate coming from the source of pressurized fluid is limited, a biasing surface (326) can be added to the valve (320).

(44) FIG. 8 shows a longitudinal cross section view of a DTH hammer with a Type F Flow System and the first preferred embodiment of the valve system of the invention when the valve (320) is in its close position, and it has a biasing thrust area (326). Whereas FIGS. 9 and 10 show the valve (320) of the first preferred embodiment and the valve (320) of the second preferred embodiment respectively, both having a biasing thrust area (326).

(45) When the valve (320) is closed, the pressure acting on the biasing thrust area (326) is equal to the pressure generated by the source of pressurized fluid (stagnation pressure). The force exerted on the biasing thrust area (326) is added to the force exerted on the rear support surface (323) and the rear thrust surface (325) due to the pressure inside the front chamber (240). In this way, the effect of the biasing thrust area (326) of the valve (320) is delay the opening of the valve (320).

(46) In a similar fashion, when the valve (320) is open, the pressure acting on the biasing thrust area (326) is also equal to the pressure generated by the source of pressurized fluid (stagnation pressure), but the force exerted on the opposite side, on the additional portion of the front support surface (322), is lower due to the drop in the pressure caused by the flow of pressurized fluid in between the front support surface (322) of the valve (320) and the rear valve support surface (301) of the valve carrier (300). In this way, the second effect of the biasing thrust area (326) of the valve (320) is achieve an earlier closing of the valve (320).