KR920000043B1 - Hydraulic impact tool - Google Patents

Abstract

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Description

Hydraulic impact tools

1 to 5 are longitudinal front views illustrating the operation of the first embodiment of the present invention.

6 is a longitudinal front view of the second embodiment;

7 is a longitudinal front view of the third embodiment.

8 is a longitudinal front view of the fourth embodiment.

9 is a longitudinal front view of the fifth embodiment;

10 is a longitudinal front view of the sixth embodiment;

11 is a longitudinal front view of the seventh embodiment.

12 is a longitudinal front view showing operation in a different state.

13 is an essential part longitudinal front view of the conventional example.

* Explanation of symbols for the main parts of the drawings

15 cylinder 16: tool

17: large diameter 18: piston

19: upper small diameter portion 20: lower small diameter portion

21: upper large diameter portion 22: lower large diameter portion

23: the middle and small neck 25: the loss (上 室)

28: the middle room 29: the middle room

30: valve chamber 33: valve body

58: oil supply port 59: oil drain

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an impact tool for hydraulic operation, which is attached to a tip of a hydraulic powder (Shovel) or the like and used for dismantling a concrete structure, crushing rock, rock excavation, and the like.

The hydraulically operated impact tool is divided into two types, an accumulator type and a gas type.

The accumulator system accumulates oil in the accumulator as it rises and releases it from the stroke stroke to accelerate the piston.

In the gas system, when the piston rises by hydraulic pressure, it accumulates energy by compressing the gas above the piston, and in the stroke stroke, accelerates the piston using the expanding energy of the gas. This is posted in the publication.

FIG. 13 shows a known impact tool described in the above publication, and 1 is a cylinder in which a tool 2 such as a clisel or the like is freely mounted on the lower end.

In this cylinder 1, it has the large diameter part 3 in an intermediate part, previously made the piston 4 which strikes this tool 2 at the time of descending, and raises the upper part of the cylinder 1. The upper chamber 5 is provided with an upper chamber 5 sealed with a gas to which gas pressure is applied.

Moreover, the solid 6 and the bottom 7 are provided between the small diameter part of the upper-lower diameter part of the large diameter part 3 of the piston 4, and the inner periphery of the cylinder 1. As shown in FIG.

8 is a valve chamber provided in the side part of the cylinder 1, The valve body 10 which has a communication hole in the center is inserted in this valve chamber.

The upper and lower parts of the valve chamber 8 and the upper part of the solid chamber 6 and the lower part of the base 7 are connected to each other in a flow path, and the middle part of the cylinder 1 and the middle part of the valve chamber 8 are also connected to the flow path and the same flow path. It leads to the flow path which diverged on the way.

In addition, the upper and lower portions of the valve chamber 8 allow the oil outlet 11 and the oil inlet 12 to connect in series, and the plunger 13 which pushes down the valve body 10 through the oil passage through the oil inlet 12. Let the back of the) pass through.

This known impact tool is provided with hydraulic pressure from the oil supply port 12 to the basement 7 when the valve body 10 is at the lower limit, and the solid body 6 passes through the drain port 11 so that the piston 4 is moved. Ascending, the gas in the chamber 5 is compressed.

When the piston 4 rises, the oil supply port 12 leads to the flow path which pushes up the valve body 10, and the valve body 10 is raised by the action of hydraulic pressure so that the lower chamber 7 is connected to the valve body 10. The piston 4 descends due to the gas pressure of the upper chamber 5 by passing through the drain port 11 through the holes communicating with each other, and strikes the tool 2.

In the conventional impact tool which performs the above-mentioned action, since the valve body 10 is raised as described above in the stroke stroke of the piston 4 and the base 7 is led through the drain hole 11, the piston 4 When it violently violates immediately after hitting this tool 2, the pressure of the basement 7 falls rapidly, and the so-called cavitation phenomenon in which the bubble contained in hydraulic fluid grows rapidly arises.

Next, when the valve body 10 descends and the hydraulic pressure flows into the base 7, the grown bubbles instantly collapse and generate very high pressure and shock waves.

Since this phenomenon is repeated hundreds of times in one minute, when the impact tool is used for a long time, erosion occurs on the inner surfaces of the piston 4 and the cylinder 1.

An object of the present invention is to prevent occurrence of the above cavitation phenomenon and to eliminate erosion occurring on the surfaces of the piston 4 and the cylinder 1.

In order to achieve the above object, the present invention has a large diameter portion in a middle portion of a cylinder freely mounted with a tool such as a chisel at the lower end, and a piston striking the tool when descending, and an upper surface of the raised piston at the upper portion of the cylinder. The upper and lower chambers for applying gas pressure are installed, and between the upper and lower parts of the large diameter portion of the piston and the inner circumference of the cylinder, a solid and a chamber for raising and lowering the piston due to the change of hydraulic pressure are installed. In the impact tool which is connected by the valve chamber and flow path which it has, and raises and lowers the valve body by switching of the piston by the hydraulic pressure and gas pressure, and the switching of the hydraulic pressure accompanying the piston raising / lowering, In a stroke stroke of a piston, Immediately before hitting the tool, hydraulic pressure is introduced into the solid to increase the pressure in the basement in series with the solid. To the the oil pressure circuit.

In addition, a middle small diameter portion is provided in the middle portion of the large diameter portion of the piston, and the upper portion thereof is the upper large diameter portion, and the lower portion thereof is the lower large diameter portion, and the valve body is moved up and down by the flow path through the middle small diameter portion and the valve chamber. The hydraulic circuit is constructed and the hydraulic circuit is introduced into the chamber immediately before the piston strikes the tool in the piston striking process, and the hydraulic circuit is installed to raise the hydraulic pressure in the chamber and the upper and lower diameters of the piston are smaller than the lower diameter. The stroke stroke of the piston is performed by the difference between the gas pressure inside and the pressure applied by the hydraulic pressure applied to the upper and lower parts of the large diameter portion of the piston.

Since the valve body is at the lower limit and the piston is in the lowered position, the present invention has the above configuration, and the oil supply port and the basement communicate with each other while the solid is connected with the drain port so that the piston rises and compresses the lost gas.

The upward force of the hydraulic pressure applied to the valve body during the ascension of the piston surpasses the force pushing down the valve body, and the valve body rises, the basement and the solid flow through the drainage port, and then when the valve body reaches the upper limit, the solid and the basement When the piston lowered by the gas pressure hits the tool through the oil inlet, hydraulic pressure acts on the cylinder, so there is no sudden pressure drop due to piston repulsion, so no air bubbles in the hydraulic cylinder are generated and no cavitation occurs. .

In addition, a middle small diameter portion is provided in the middle portion of the large diameter portion of the piston, and the upper portion thereof is the upper large diameter portion, the lower portion thereof is the lower large diameter portion, and the valve body is moved up and down by the flow path through the middle small diameter portion and the valve chamber. In the hydraulic circuit, the hydraulic pressure flows into the chamber immediately before the piston strikes the tool in the piston striking process, and the hydraulic pressure in the chamber is raised to prevent the occurrence of cavitation.

Further, the diameter of the upper small diameter of the piston is smaller than that of the lower small diameter, and the impact effect is large because the piston is subjected to the striking step against the difference between the gas pressure in the chamber and the hydraulic pressure applied to the upper and lower portions of the large diameter portion of the piston.

The first embodiment 1 shown in Figs. 1 to 5 will be described.

In this embodiment, 15 is a cylinder in which the tool 16, such as a chisel, is mounted on the lower end freely. In this cylinder 15, the piston 18 which has the large diameter part 17 in the intermediate part, strikes the piston 16 which strikes this tool 16 at the time of descending, and raises the piston 18 in the upper part of the cylinder 15. The upper chamber 25 in which nitrogen gas under pressure is applied is installed on the upper surface of the chamber.

Moreover, the solid 28 and the lower chamber 29 are provided between the small diameter parts 19 and 20 of the upper and lower sides of the large diameter part 17 of the piston 18, and the inner periphery of the cylinder 15. As shown in FIG.

30 is a valve chamber in the valve box 31 provided in the side part of the cylinder 15, and the valve chamber 33 is provided with the valve body 33 which has the hole 32 connected in the center.

The upper and lower portions of the valve chamber 30, the upper portion of the solid chamber 28, and the base 29 are connected to the flow passages 35 and 36, and the intermediate portion of the cylinder 15 and the intermediate portion of the valve chamber 30 are also flow passages. The passage 38 is connected to the passage 38 branched in the middle of the passage 37 and the passage 38, but the passage 38 is much smaller than the other passages.

In addition, the inner circumferential grooves 40 and 41 through the flow paths 35 and 37 are provided above and below the solid 28, and the inner circumferential groove 42 through the flow path 36 is provided to the basement 29. As shown in FIG.

The hydraulic chamber 45 is installed in the upper portion of the valve chamber 30, and the plunger 46 slides in the lower portion of the hydraulic chamber 45 to freely move the lower end of the plunger 46. The upper end of the sieve 33 is in contact. The valve body 33 has a large diameter portion 47 at the upper portion and a small diameter portion 48 at the lower portion thereof. The valve body 33 is freely fitted into the large diameter portion and the small diameter portion of the valve chamber 30, and the large diameter portion 47 is provided. An operating chamber 49 is formed between the lower surface of the valve body and the valve body 30.

The outer circumferential groove 50 is formed below the small diameter portion 40 of the valve body, and the inner circumferential grooves 52, 53 are formed in the large diameter portion of the valve chamber 30 from the upper portion, and the inner circumferential groove 54 is formed in the small diameter portion. 55,56).

The inner circumferential grooves 53, 54, and 56 pass through the flow paths 37, 38, and 36, respectively, and the oil inlets 58 installed in the valve box 31 are the hydraulic chamber 45 and the inner circumferential groove 55. The drain port 59 communicates with the inner circumferential groove 52.

Further, the cross sectional area difference between the large diameter portion 47 and the small diameter portion 48 of the valve body 33 is larger than the cross sectional area of the plunger 46.

Next, the operation of the first embodiment will be described.

In FIG. 1, the piston 18 and the valve body 33 are at the lower limit positions, and when the pressure oil is supplied to the oil inlet 58 in this state, the pressure oil is in the inner circumferential groove 55 → the outer circumferential groove 50 → the inner circumferential groove. 56 flows from the flow path 36 to the base 29, and hydraulic pressure is applied to the lower end surface of the large diameter part 17 of the piston 18. As shown in FIG. At this time, the solid 28 is connected to the flow path 35 → the upper portion of the valve chamber 30 → the inner circumferential groove 52 → the drain port 59 so that the piston 18 compresses the nitrogen gas in the upper chamber 25. Ascends. At this time, the oil pressure flows into the hydraulic chamber 45 from the oil supply port 58, and the valve element 33 is pressed downward by pressing the plunger 46 downward.

Next, when the piston 18 is further raised and the lower end surface of the large diameter portion 17 is in the state of FIG. 2 through which the inner circumferential groove 41 and the base 29 are connected, the pressure oil of the base 29 is increased in the inner circumferential groove ( 41) → flow path 37 → operation chamber 49, and the hydraulic pressure acts on the lower end surface of the large diameter part 47 of the valve body 33.

The working area of the lower end surface of this large diameter part 47 of the valve body 33 is larger than the cross-sectional area of the plunger 46, and the valve body 33 starts moving upwards.

When the valve body 33 is raised to the position shown in FIG. 3, the inner circumferential grooves 55 and 56 are blocked and the lower portions of the inner circumferential grooves 54 and 55, the inner circumferential groove 56 and the valve chamber 30 are located. The chamber 29 is connected to each other by a flow passage 36 → an inner circumferential groove 56 → a lower portion of the valve chamber 30 → a hole 32 that communicates with the drainage port 59. As the pressure decreases, the piston 18 starts lowering due to the pressure of the nitrogen gas in the chamber 25.

Even if the lower end of the large-diameter portion 17 of the piston 18 blocks the inner circumferential groove 41 from the base 29 during the lowering, the hydraulic oil is supplied from the inner circumferential groove 54 to the small diameter flow passage 38 to the flow passage 37. As the supply to the operating chamber 49 continues, the valve body 33 continues to rise. When the valve body 33 rises further to reach the upper limit position, the upper surface of the large diameter portion 47 blocks the drain port 59 at the upper portion of the valve chamber 30, so that the oil in the basement 29 is solid. Inflow to (28). 4 shows a state where the valve body 33 is raised to reach the upper limit position.

When the piston 18 descends to the state of FIG. 5 and the upper end surface of the large diameter portion 17 passes through the inner circumferential groove 41, the hydraulic pressure flows from the inner circumferential groove 55 to the inner circumferential groove 54 to the small diameter flow path ( 38) flows into the flow passage 37 and the inner circumferential groove 41, and the pressure in the solid 28 rises.

In connection with this, the pressure of the basement 29 which is connected to the solid chamber 28 also rises, and the piston 18 carries out the tool 16 in the state which the pressure of both chambers of the solid chamber 28 and the basement 29 rose. By hitting, even if the piston 18 rebounds after hitting, the hydraulic pressure in the undercarriage 29 does not drop rapidly, and air bubbles in the oil are not generated.

When the piston 18 rebounds, the pressure in the solid chamber 28 is instantaneously higher than the pressure in the base 29, and the upper portion of the valve chamber 30 is also higher in pressure than the lower portion, so the valve body 33 is pressed downward. . When the upper end surface of the large diameter part 47 of the valve body 33 passes through the inner circumferential opening 52, the solid 28 and the basement 29 are connected to the drain port 59 together, and the pressure drops rapidly, and the operation Since the pressure of the seal 49 also lowers, the valve body 33 will be in the lowered position shown in FIG. 1 by the pushing force of the plunger 46. As long as the pressurized oil is supplied from the oil supply port 58, the above operation is repeated.

In the first embodiment, the hydraulic chamber 45 is provided as a means for always pushing the valve body 33 downward, and the plunger 46 slides so as to freely move and contact the valve body 33. However, in the second embodiment shown in FIG. 6, the middle diameter portion 60 is added above the large diameter portion 47 of the valve body 33 as a means to replace the upper portion of the valve chamber 30. A thread 61 is formed from the middle diameter part 60, and this thread 61 is connected to the constant oil supply port 58 in a flow path. The cross-sectional area difference of the large diameter part 47 and the middle diameter part 60 of the valve body 33 is made smaller than the cross-sectional area difference of the large diameter part 47 and the small diameter part 48. As shown in FIG.

In this second embodiment, when the inner circumferential groove 41 and the base 29 are connected in series, and the same hydraulic pressure as that applied to the chamber 61 is applied to the operation chamber 49, the inner and outer grooves 41 and the base 29 are applied to the upper and lower surfaces of the large diameter portion 47. The valve body 33 reaches the upper limit due to the pressure difference, and when the operating chamber 49 passes through the drain port 59, the valve body 33 is lowered by the hydraulic pressure in the chamber 61.

Other configurations and operations are the same as in the first embodiment.

In the first and second embodiments described above, when the piston 18 is raised and the lower end surface of the large diameter portion 17 is brought into a position where the inner circumferential groove 41 and the lower chamber 29 are connected to each other, It flows into the operation chamber 49 and operates the valve body 33 upward.

Further, in order to ensure the operation of the valve body 33 upward, the pressurized oil flows into the inner circumferential groove 55 → inner circumferential groove 54 → small diameter flow path 38 → flow path 37 → operation chamber 49. .

In the third embodiment shown in FIG. 7, the middle diameter portion 60 is added to the upper end of the valve body 33 to form the seal 63, and the large diameter portion 47 of the valve chamber 30 is An inner circumferential groove 64 is formed in the inner circumference of the sliding valve chamber 30 so as to be connected to the oil supply port 58 in a small diameter flow path 65. The inner circumferential groove 64 rises to block the inner circumferential grooves 55 and 56 and the inner circumferential groove 56 and the lower portion of the valve chamber 30 communicate with each other when the valve body 33 rises. The lower end surface of the large diameter part 47 is formed in the position which communicates with the operation chamber 49 and the inner peripheral groove 64 in succession.

In the above configuration, the inner circumferential groove 64 communicates with the operation chamber 49 in a state where the valve body 33 reaches a strong vicinity, and the pressure oil in the small-diameter flow path 65 passes through the operation chamber 49. The pressure acts on the lower surface of the large diameter portion 47 to maintain the valve body 33 at the upper limit. Therefore, the small diameter flow paths 38 of the first and second embodiments are closed.

Other configurations and operations are the same as in the first and second embodiments. 8 shows a fourth embodiment. In this figure, the parts of the structure similar to the said 1st-3rd embodiment attach | subject the same code | symbol, abbreviate | omit description, and demonstrate only a difference.

In this fourth embodiment, the upper large diameter portion 21 and the lower large diameter portion 22 are formed between the injured small diameter portions 19 and 20 of the piston 18, and the middle small diameter portion 23 is formed therebetween. do.

In the middle portion of the inner circumference of the cylinder 11, upper and lower inner circumferential grooves 43 and 44 which are connected to the middle small diameter portion 23 at the same time at the lowering position of the piston 18 are provided.

The upper inner circumferential groove 43 is connected to the inner circumferential groove 52 of the valve chamber 30 by the flow passage 34, and the inner circumferential groove 44 is the inner circumferential groove of the valve chamber 30 by the flow passage 37. The flow passage 37 is connected to the inner circumferential groove 54 by the small diameter flow passage 38.

In addition, the flow passage 36 is connected to the inner circumferential groove 55 by the small flow passage 39.

In the case of the fourth embodiment, the piston 18 and the valve body 33 are in the lowered position as shown in FIG. 8, and when the pressure oil is supplied to the oil inlet 58 in this state, the pressure oil is changed from the inner circumferential groove 55 to the outer circumference. Hydraulic pressure is applied to the lower end surface of the lower large diameter portion 22 of the piston 18 by flowing from the groove 50 to the inner circumferential groove 56 to the passage 36 to the base 29.

At this time, the solid chamber 28 is connected to the flow path 35 → the upper portion of the valve chamber 30 → the inner circumferential groove 52 → the drain port 59, so that the piston 18 is nitrogen gas in the upper chamber 25. Rises while compressing. At this time, the oil pressure flows into the hydraulic chamber 45 from the oil supply port 58, and the valve body 33 is pushed downward by pushing the plunger 46 downward.

Next, when the piston 18 is further raised so that the lower end surface of the lower large diameter portion 22 passes through the inner circumferential groove 44 and the lower chamber 29, the pressure oil of the lower chamber 29 flows from the inner circumferential groove 44 to the flow path. (37) → It flows into the actuator chamber 49, and hydraulic pressure acts on the lower end surface of the large diameter part 47 of the valve body 33, and moves the valve body 33 upwards.

The displacement of the valve body 33 becomes a certain amount and at the same time the inner circumferential grooves 55 and 56 are blocked, and the inner circumferential grooves 55 and 54, the inner circumferential groove 56, and the lower part of the valve chamber 30 communicate with each other. The base 29 is connected to the flow path 36 → the inner circumferential groove 56 → the lower portion of the valve chamber 30 → the hole 32 passing through the air passage → the drain port 59, and the pressure in the base 29 is lost. The piston starts to descend by the pressure of the nitrogen gas of (25).

Even if the lower end of the lower large diameter part 22 of the piston cuts off the inner circumferential groove 44 from the base 29 during the lowering, the hydraulic oil flows from the inner circumferential groove 55 to the inner circumferential groove 54 to the small diameter flow path 38 to the flow path. (37) → The valve body 33 continues to ascend as it is continuously supplied to the operation chamber 49. When the valve body 33 rises further and reaches near the upper limit, the oil in the base 29 is blocked by the upper end surface of the large diameter portion 47 blocking the upper portion of the valve chamber 30 from the inner circumferential groove 52. Flows into).

At this time, the pressure oil flows into the inner circumferential groove 55 → the micro gas passage 39 → the flow passage 36 → the chamber 29 so that the pressure of the chamber 29 rises. In connection with this, the pressure of the solid 28 also rises.

Since the cross sectional area difference between the upper small diameter portion 19 and the upper large diameter portion 21 is the same as the cross sectional area difference between the lower small diameter portion 20 and the lower large diameter portion 22, the pressures in both the basement 29 and the solid 28 are equal. Thus, the downward movement of the piston 19 is not disturbed.

When the piston 10 is lowered and the inner circumferential grooves 43 and 44 are connected to each other by the central small diameter portion 23, the operation chamber 49 is the inner circumferential groove 53 → the flow passage 37 → the inner circumferential groove 44 →. By flowing into the inner circumferential groove 43 and passing through the drain port 59 by the flow path 34, the pressure in the operating chamber 49 is rapidly lowered, and the valve body 33 is removed by the plunger 46. It is pushed down to the lowered position shown at 8 degrees.

At this time, the pressurized oil may be supplied from the small diameter oil passage 38 to the oil passage 37. However, since the inflow flow rate into the operation chamber 49 is limited by the small diameter oil passage 38, it is important to the movement of the valve body 33. Does not affect As long as the buty pressure oil is supplied to the oil supply port 50, the above operation is repeated.

In the fifth embodiment shown in FIG. 9, the configuration and operation of the cylinder 15, the piston 18, and the valve body 33 are the same as those of the fourth embodiment in FIG. Since the apparatus for pushing downward is the same as that of the second embodiment in FIG. 6, the same reference numerals as in FIG. 6 are used, and description thereof is omitted.

In addition, since the sixth embodiment shown in FIG. 10 uses the same operation circuit as that of the third embodiment in FIG. 7, the valve box 31 and portions of the valve body 33 are used. Is the same reference numeral as in FIG.

In the above structure, the inner circumferential groove 64 connects to the operation chamber 49 in a state where the valve body 33 reaches the upper limit, and the pressure oil in the small diameter flow path 65 flows into the operation chamber 49. The pressure acts on the lower surface of the large diameter part 47 through and maintains the valve body 33 to an upper limit. Therefore, the small diameter flow path 38 of the fifth embodiment is closed.

Other configurations and operations are the same as in the fifth embodiment.

In the above embodiments, the diameters of the small diameter portions 19 and 20 are the same, but the diameters of the small diameter portions 19 and 20 are different in the seventh embodiment shown in FIGS.

This seventh embodiment is an improvement of the fifth embodiment of FIG. 9, and the circuit configuration is the same as that of the fifth embodiment, but the upper small diameter portion 19 of the piston 18 is smaller than the lower small diameter portion. When the hydraulic pressure of dynamic pressure acts on the solid body 28 and the basement 29, the downward force acts on the piston 19. If the upper small diameter portion 19 and the lower small diameter portion 20 of the piston 10 have the same diameter, since the hydraulic oil supplied from the pump is not consumed in the piston stroke stroke, the pressure on the oil supply port 58 side is reduced by the piston 18. ) Will be higher than the pressure during the upstroke.

In order to solve the above problem, an accumulator was attached to the pipeline on the oil supply port 58 side to reduce this pressure fluctuation as much as possible.

However, when the diameter of the upper small diameter portion 19 is smaller than the diameter of the lower small diameter portion 20 as in the seventh embodiment, oil is consumed in the striking process of the piston 18, so that the upward stroke of the piston Since the pressure is not higher than the hydraulic pressure, the pressure fluctuation is small, and the accumulator can be omitted. This configuration can also be used in the above embodiments.

In this embodiment, the lower portion of the valve body 33 is longer than the outer peripheral groove 50, and the lower portion of the valve chamber 30 is also longer than the inner peripheral groove 55. At the time of the rise of 33, the upper end of the valve body 33 becomes the upper part of the inner circumferential groove 52 as shown in FIG. 12, so that the hole 32 which connects the valve body 33 in communication with the drainage port 59 is blocked. After that, the lower end of the valve body 33 is above the lower edge of the inner circumferential groove 57 so as to pass through the lower end of the hole 32 to be connected to the base 29.

By carrying out the valve mechanism as described above, the basement 29 is led to the lower oil supply port 58.

As a result, the base 29 is maintained at a higher pressure than that of the other embodiments, whereby the generation of bubbles due to the pressure drop is suppressed, and the erosion by cavitation is further facilitated.

The impact tool of the present invention, in the stroke stroke of the piston, pressurized oil into the solid immediately before the piston strikes the tool to increase the pressure in the basement connected to the solid, or in the stroke stroke of the piston Just before the piston strikes the tool, hydraulic pressure flows into the chamber, increasing the pressure in the chamber. Therefore, even if the piston repulses after hitting, bubbles are not generated in the oil in the cellar, and cavitation can be prevented, and the effect of not causing erosion on the surfaces of the cylinder and the piston can be obtained.

Claims (3)

The cylinder is equipped with a large diameter portion in a middle portion in a cylinder freely mounted on the lower end of the tool, and a piston for striking the tool when it is lowered is fitted therein, and an upper portion of the cylinder is provided with a loss for providing gas pressure to the upper surface of the raised piston. Between the upper and lower diameters of the large diameter portion of the piston and the inner circumference of the cylinder, a solid and a chamber are provided for raising and lowering the piston due to the change of hydraulic pressure. In an impact tool that allows the valve body to be raised and lowered by the lifting and lowering of the piston by hydraulic and gas pressures and the switching of the hydraulic pressure accompanying the raising and lowering of the piston. Flows into the solid to increase the pressure in the basement Hydraulic impact tool characterized in that the pressure circuit. 2. The valve body according to claim 1, wherein a middle small diameter portion is provided in the middle portion of the large diameter portion of the piston, the upper portion thereof is the upper large diameter portion, and the lower portion thereof is the lower large diameter portion, and the valve body is formed by a passage through the middle small diameter portion and the valve chamber. A hydraulic impact tool comprising a hydraulic circuit for up and down, and a hydraulic circuit for increasing hydraulic pressure in a chamber by introducing hydraulic pressure into the chamber before the piston strikes the tool in the piston striking process. The piston stroke stroke according to claim 1 or 2, wherein the upper small diameter portion of the piston is smaller than the lower small diameter portion so that the stroke stroke of the piston is performed by the difference between the gas pressure in the chamber and the pressure applied by the hydraulic pressure applied to the upper and lower portions of the large diameter portion of the piston. Hydraulic impact tool, characterized in that.

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