JP2582913Y2 - Relief valve - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a relief valve for relieving a high-pressure fluid having a predetermined pressure to a low-pressure side.

[0002]

2. Description of the Related Art Generally, in a fluid circuit for driving a crawler vehicle or the like, when a switching valve is switched to a flow position when the crawler vehicle stops, a fluid motor and the crawler vehicle continue to stop due to inertia. If the pressure in the circuit rises rapidly and the switching valve is switched to the neutral position during traveling of the crawler vehicle, the fluid motor rotates by a short time due to the inertial traveling of the crawler vehicle, so that the pressure in the fluid circuit rises rapidly. . For this reason, in such a fluid circuit, a relief valve is provided in the middle of the fluid passage connecting the fluid motor and the switching valve, and when any one of the fluid passages has a predetermined high pressure, the relief valve is connected through the relief valve. Thus, the high pressure fluid is relieved to the low pressure side.

Conventionally, various types of such relief valves have been proposed. In any case, the poppet valve body is urged by a spring to close the valve, and the valve is opened by any of the fluids. When the passage reaches a predetermined high pressure,
The high pressure is guided to a poppet valve body to move the poppet valve body against a spring.

[0004]

However, in such a conventional relief valve, since the valve opening pressure of the relief valve is determined by a spring,
The valve opening pressure is limited to one high pressure value,
When the fluid motor is started or braking is started as described above, the pressure rapidly rises to this high pressure, causing a problem that a large shock is applied to the fluid motor and the speed reducer.

An object of the present invention is to provide a relief valve capable of reducing a shock generated when a fluid motor is started or braking is started.

[0006]

SUMMARY OF THE INVENTION The object of the present invention is to provide a pair of supply / discharge passages 13 and 14 for connecting the switching valve 12 and the fluid motor 11 to each other.
And a case 50 in which a pair of supply / discharge passages 34, 35 constituting a part of the supply / discharge passages 13 and 14 are formed, and one of the supply / discharge passages 34 provided in the case 50. , 35 reach a predetermined pressure, and are pushed by the predetermined pressure and move in the valve opening direction while opposing the springs 67, 68, so that the fluid of the predetermined pressure is supplied to the supply / discharge passages 34, 35 on the low pressure side. A pair of poppet valve bodies 54 and 55 for relief, and a pair of fluid chambers 42 and 43 provided in the case 50 to accommodate the springs 67 and 68,
The tapered portions 56, 57 tapering toward the distal end on the distal end side of the poppet valve elements 54, 55 are tapered toward the distal end side.
Are provided at the boundaries between the pair of communication passages 36, 37 communicating the supply / discharge paths 34, 35 and the supply / discharge paths 34, 35, respectively. The tapered portions 56, 57 of the energized poppet valve bodies 54, 55 form valve seats 38, 39 with which the tapered portions 56, 57 come into pressure contact, respectively.
A pair of connecting holes 44, 45 into which the cylindrical portions 58, 59 of the poppet valve bodies 54, 55 are slidably inserted into the fluid chambers 4, 35 and the fluid chambers 42, 43.
In the relief valve 24 respectively connected by the above, the supply and discharge passages 34 and 35 and the fluid chamber 4 are provided in the poppet valve bodies 54 and 55, respectively.
Along with forming pores 60, 61 communicating with 2, 43, respectively, a piston 74 is slidably housed in the case 50, and one side of the piston 74 has one of the fluid chambers 42,
43, the other side of the piston 74 is the remaining fluid chamber 42,
A cylinder chamber 73 connected to 43 is formed, and among the pressure receiving areas where the pair of poppet valve bodies 54 and 55 receive the fluid force directed toward the rear end, the valve seats 38 and 39 and the tapered portions 56 and 57 are formed. The pressure receiving areas A1 and A2 located on the leading end side from the contact position are smaller than the pressure receiving areas B1 and B2 located on the trailing end side from the contact position. When the pressure reaches the first set pressure lower than the pressure, the fluid of the first set pressure passes through the pores 60, 61 of any of the poppet valve bodies 54, 55 and flows into the fluid chambers 42, 43, and the cylinder chamber The poppet valve element 5 is moved by pressing the piston 74 in the
A pressure difference is generated before and after 4, 55, and the poppet valve bodies 54, 5
5 is moved in the valve opening direction only until the piston 74 reaches the stroke end, and the fluid of the first set pressure is relieved to the low pressure side supply / discharge passages 34, 35. , 35 reach a predetermined pressure higher than the first set pressure, one of the poppet valve bodies 54, 55 is moved in the valve opening direction, and the fluid of the predetermined pressure is supplied to the low pressure side supply / discharge passages 34, 35. Can be achieved by relief.

[0007]

When the fluid motor is started or when the braking of the fluid motor is started, the pressure in one of the supply / discharge passage and the supply / discharge passage increases due to the inertia of the fluid motor or the like. Then, the increased pressure fluid passes through the pores of one poppet valve body, flows into the fluid chamber, and then flows into the cylinder chamber to push and move the piston. As a result, a pressure difference occurs due to a pressure drop before and after the one poppet valve element, and the force for closing the poppet valve element is substantially only the urging force of the spring.
At this time, the pressure fluid having the increased pressure acts on a large pressure receiving area on the rear end side of the poppet valve body from the contact position to apply fluid force in the valve opening direction to the poppet valve body. When the pressure in the supply / discharge passage rises to the first set pressure while the piston is being pressed and moved as described above, the fluid force acting on the wide pressure receiving area of the poppet valve body exceeds the biasing force of the spring and the like. As a result, the poppet valve body moves in the valve opening direction against the spring, and the tapered portion of the poppet valve is separated from the valve seat. As a result, the two supply / discharge paths communicate with each other, and the pressure fluid is relieved from the high pressure side supply / discharge path to the low pressure side supply / discharge path through the communication path. At this time, the pressure of the first set pressure also acts on the other poppet valve body, but this pressure acts on a narrow pressure receiving area on the tip side from the contact position of the other poppet valve body. It is smaller than the urging force, and the other poppet valve does not move. Then, when the piston moves in the cylinder chamber to the stroke end, the movement of the piston stops, so that the fluid does not flow through the pores of one poppet valve body, and the pressure difference before and after the poppet valve body disappears.
As a result, the poppet valve element is urged by the spring and moves in the valve closing direction until the tapered portion comes into pressure contact with the valve seat to stop the relief. Thus, the relief at the first set pressure is performed only until the piston reaches the stroke end. When the relief is stopped as described above, the pressure in the supply / discharge path rises above the first set pressure. When the pressure in the supply / discharge path reaches a predetermined pressure, the fluid force acting on the narrow pressure receiving area on the tip end side of the other poppet valve exceeds the biasing force of the spring, and the poppet valve acts on the spring. It moves in the valve opening direction in opposition, and the tapered portion is separated from the valve seat. As a result, the two supply / discharge paths communicate with each other through the communication path, and the pressure fluid is relieved from the high pressure side supply / discharge path to the low pressure side supply / discharge path. As described above, when the pressure in one of the supply / discharge paths reaches the first set pressure,
Once the relief is performed, and then the pressure is further increased to a predetermined high pressure, the relief is performed again, so that the shock applied to the fluid motor and the reduction gear is reduced. In addition, as described above, the poppet valve body which is relieved when the pressure becomes a predetermined pressure is acted upon by a fluid having a predetermined pressure on the pressure receiving area on the front end side from the contact position, and by a low pressure fluid on the pressure receiving area on the rear end side from the contact position. Therefore, the fluid flowing between the poppet valve element and the valve seat at the time of relief will flow while spreading toward the large diameter side around the tapered portion of the poppet valve element, and as a result, the predetermined pressure The rising relief static characteristics at the time are good.

Further, according to the present invention, the fluid pushed out of the cylinder chamber does not stay in the fluid chamber and hinders the movement of the poppet valve body. The relief operation can be performed at a predetermined pressure. Further, according to the third aspect of the present invention, the device can be easily manufactured and the size of the device can be reduced.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings. 1 and 2, reference numeral 11 denotes a fluid motor for driving a crawler vehicle, for example. The fluid motor 11 and the switching valve 12 are connected by a pair of supply / discharge passages 13 and 14. Further, the switching valve 12 and the fluid pump 15 are connected to a supply passage 16.
Thus, the switching valve 12 and the tank 17 are connected by the discharge passage 18. A counterbalance valve 19 is provided in the middle of the supply / discharge passages 13 and 14, and the counterbalance valve 19 is provided.
Supply and discharge passages 13 and 14 between the fluid motor 11 and the relief motor
24 are provided.

The relief valve 24 has a main body block 25 in which a pair of main passages 26 and 27 are formed. Reference numerals 28 and 29 denote a pair of holders inserted and fixed in the main body block 25.
Chambers 30 and 31 are formed at the distal ends (inner ends) of the pipes 8 and 29, respectively, and the chambers 30 and 31 and the main passages 26 and 27 are communicated by a plurality of holes 32 and 33. Main passages 26 and 2 described above
7, the chambers 30, 31, and the holes 32, 33 are a pair of supply / discharge paths 34, 3 as a whole.
The supply / discharge passages 34, 35 constitute the supply / discharge passages 13, 1
Form part of 4. The chambers 30, 31 and the main passages 27, 26 are provided in the holders 28, 29 on the tip side of the chambers 30, 31,
A pair of communication passages 36 and 37 for communicating the 34 and 35 with each other are formed, respectively. The communication passages 36 and 37 and the chamber 3
0, 31, that is, the boundaries between the supply and discharge passages 34, 35 are valve seats 38, 39 with which a poppet valve body described later contacts in a liquid-tight state. Also the room
A pair of fluid chambers 4 is provided in holders 28 and 29 behind 30 and 31.
2 and 43 are formed, and the pair of fluid chambers 42 and 43 and the chambers 30 and 3 are formed.
1, that is, the supply / discharge paths 34, 35 are connected by a pair of connection holes 44, 45. At the rear ends of the fluid chambers 42, 43, receivers 46, 47 for closing the fluid chambers 42, 43 are accommodated, and these receivers 46, 47 are stoppers screwed and fixed to the rear ends of the holders 28, 29. Exit is regulated by 48 and 49. Main body block 25, holders 28 and 29, receiver 4 described above
6, 47, stoppers 48, 49 are all
The case 50 is constituted.

Reference numerals 54 and 55 denote a pair of poppet valve bodies. These poppet valve bodies 54 and 55 have tapered portions 56 and 57 tapering toward the front end, and the tapered portions 56 and 57 at the rear end side. Are provided, respectively. These poppet valve bodies 54 and 55 are housed in holders 28 and 29, respectively.
8, 39 can be contacted, and cylindrical parts 58, 59
Are slidably inserted in the connection holes 44 and 45 in a liquid-tight state. And in both poppet valve bodies 54 and 55,
The pressure receiving areas A1, A2 located on the tip side from the contact positions of the valve seats 38, 39 and the tapered portions 56, 57 are smaller than the tapered portion pressure receiving areas B1, B2 located on the rear end side from the contact position. Has formed. The outer diameters of the cylindrical portions 58, 59 are larger than the diameters of the valve seats 38, 39, and the supply / discharge passages 34, 35 and the fluid chambers 42, 43 are connected in the poppet valve bodies 54, 55. Pores 60 and 61 are formed, and apertures 62 and 63 are formed in the middle of the pores 60 and 61. 67 and 68 are a pair of springs housed in the fluid chambers 42 and 43, respectively.
7, 68 are interposed between ring-shaped receivers 69, 70 formed at the rear ends of the poppet valve bodies 54, 55 and the receivers 46, 47,
The poppet valve bodies 54 and 55 are urged toward the distal end so that the tapered portions 56 and 57
Are brought into pressure contact with the valve seats 38 and 39, respectively, to close the relief valve 24. One cylinder chamber extending in the case 50, specifically, the main body block 25, so as to intersect with the holders 28, 29.
A piston 73 is formed in the cylinder chamber 73.
74 are slidably housed. And this piston
The cylinder chamber 73 on one side from 74 and the fluid chamber 42 are
The cylinder chamber 73 and the fluid chamber 43 are connected to each other through a hole 75 formed in the cylinder 28 and a passage 76 formed in the main body block 25, and a hole 77 formed in the holder 29 and They are connected via a passage 78 formed in the main body block 25.

Next, the operation of the first embodiment of the present invention will be described. Now, the switching valve 12 is switched from the neutral position to the flow position, and the high-pressure fluid from the fluid pump 15 is supplied to the fluid motor 11 through one of the supply / discharge passages, for example, the supply / discharge passage 13, and the fluid motor 11 is started. To start. At this time, since the fluid motor 11 and the crawler vehicle continue to stop due to inertia, the pressure in one of the supply / discharge passages, here, the supply / discharge passage 13 increases, and at this time, the supply / discharge passage 34 and the supply The pressure in the communication path 37 which is always in communication with the discharge path 34 also increases.

At this time, since the pressurized fluid in the supply / discharge passage 34 flows into the fluid chamber 42 through the small holes 60 of the poppet valve 54, the pressure fluid is communicated with the fluid chamber 42 through the hole 75 by the piston 74. The pressure fluid also flows into the cylinder chamber 73 on the side, and the piston 74 in the cylinder chamber 73 moves toward the stroke end on the other side. At this time, the fluid in the cylinder chamber 73 on the other side of the piston 74 passes through the supply / discharge passage 35 on the low pressure side.
The gas is discharged through the holes 78, the holes 77, the fluid chamber 43, and the fine holes 61. As a result, a pressure difference is generated due to a pressure drop before and after the one poppet valve element 54, and the force for moving the poppet valve element 54 in the valve closing direction, that is, the force for pressing the valve seat 38 is substantially the same as the biasing force of the spring 67. Become.

When the pressure in the supply / discharge passage 13 rises to the first set pressure during the movement of the piston 74, the fluid force acting on the large pressure receiving area B1 located on the rear end side of the poppet valve body 54 causes the spring to move. To exceed the bias of 67,
The poppet valve element 54 moves in the valve opening direction against the spring 67, and the tapered portion 56 of the poppet valve element 54 is separated from the valve seat 38. As a result, the pressure fluid is relieved from the high pressure side supply / discharge path 34 to the low pressure side supply / discharge path 35 through the communication path 36. Such relief at the first set pressure is performed only until the piston 74 reaches the stroke end on the other side. At this time, the first set pressure acts on the pressure receiving area A2 on the tip side from the contact position of the other poppet valve body 55, and a fluid force directed in the valve opening direction is given. Since the pressure is smaller than the pressure receiving area B1, the fluid force is smaller than the urging force of the spring 68 at the first set pressure,
As a result, the other poppet valve element 55 cannot move and cannot be opened.

Next, when the piston 74 moves within the cylinder chamber 73 to the stroke end on the other side and stops moving, fluid stops flowing through the fine holes 60 of the poppet valve element 54, and the poppet valve element 54 The pressure difference before and after is eliminated. As a result, the one poppet valve element 54 receives the urging force of the spring 67 and the fluid force from the fluid in the fluid chamber 42, moves in the valve closing direction, and the tapered portion 56 is pressed against the valve seat 38.
Thereby, the relief from one poppet valve body side stops.

When the relief stops, the pressure in the supply / discharge passage 13 further increases. Then, when the pressure in the supply / discharge passage 34 exceeds the first set pressure and rises to a predetermined pressure (hereinafter, referred to as a second set pressure), the pressure receiving area A2 on the distal end side from the contact position of the other poppet valve body 55 becomes smaller. The acting fluid force exceeds the biasing force of the spring 68, and the poppet valve body 55
Moves in the valve opening direction against the spring 68, and
57 is separated from valve seat 39. As a result, the high pressure side supply / discharge path 34
Is connected to the supply / discharge passage 35 on the low pressure side.
Relieved through 37. When the pressure in the supply / discharge path 34 reaches the first set pressure which is lower than the predetermined pressure (the second set pressure), the supply / discharge path 34 is temporarily relieved from the supply / discharge path 34 to the supply / discharge path 35,
Thereafter, when the pressure rises to a predetermined high pressure (second set pressure),
Since the supply / discharge path is relieved again from the supply / discharge path, the shock applied to the fluid motor 11 and the reduction gear is reduced.

Such an operation is performed in the same manner when braking the fluid motor 11 or when the supply / discharge passage 14 is on the high pressure side. Further, as described above, the poppet valve body 55 which is relieved when the pressure reaches the predetermined pressure (the second set pressure) has a predetermined pressure fluid in the pressure receiving area A2 on the distal side from the contact position, and the fluid on the rear end side from the contact position. Since the low pressure fluid is acting on the pressure receiving area B2, the poppet valve body 55 and the valve seat 39
And the fluid flowing through the space between the tapered portion 57 and the tapered portion 57 of the poppet valve body 55 is relieved while expanding toward the large diameter side. As a result, the rising relief static characteristic at a predetermined pressure is improved. . In addition, since the length of the cylinder chamber 73 is not particularly limited, the stroke of the piston 74 can be freely changed, whereby the shock absorption time at the first set pressure can be appropriately adjusted.

FIGS. 3 and 4 show a second embodiment of the present invention. In this embodiment, the main passage
A check passage 82 connecting the 27 and the cylinder chamber 73 on the other side of the piston 74 is formed, and a check passage 83 connecting the main passage 26 and the cylinder chamber 73 on one side of the piston 74 is formed.
In the middle of these check passages 82 and 83, balls 84,
Check valves 80 and 81 each including an 85 and seat surfaces 86 and 87 are provided. The check valves 80 and 81 are connected to the main passage.
Fluid flowing from 27 and 26 to cylinder chamber 73 is transferred to balls 84 and 85
Seated on the seat surfaces 86 and 87, respectively,
On the other hand, the fluid pushed out of the cylinder chamber 73 by the movement of the piston 74 is guided to the low-pressure supply / discharge passages 35 and 34 by the balls 84 and 85 separating from the seat surfaces 86 and 87, respectively. When such check valves 80 and 81 are provided, when the piston 74 moves, the fluid pushed out from the cylinder chamber 73 pushes and opens the check valves 80 and 81 to promptly open and close the low pressure side supply / discharge passage 3.
5 and 34, the fluid from the cylinder chamber 73 stays in the fluid chambers 42 and 43 and its pressure increases, and the poppet valve body
The movement of the poppet valve bodies 54, 55 can be accurately opened and relieved at a predetermined pressure, and the fluid in the supply / drain passages 35, 34 can be prevented. Does not flow into the cylinder chamber 73 through the check passages 82 and 83.

FIG. 5 is a diagram showing a third embodiment of the present invention. In this embodiment, in the poppet valve bodies 54 and 55,
Specifically, a check valve 90 is provided in each of the fine holes 60 and 61. Here, each check valve 90 is housed and fixed in the fine holes 60 and 61 and has a cylindrical sheet body 92 having a seat surface 91, and a cylindrical shape housed and fixed in the fine holes 60 and 61 on the distal end side of the sheet body 92. Stopper 93, the pores 60 between the sheet body 92 and the stopper 93,
The ball 94 is seated on the seat surface 91 and blocks the flow when the fluid is going to flow from the supply / discharge passages 34 and 35 to the cylinder chamber 73. On the other hand, when the fluid is going to flow from the cylinder chamber 73 to the supply / discharge paths 34 and 35, the ball 94 separates from the seat surface 91 to allow the flow. 62 and 63 are apertures as a part of the pores 60 and 61 formed in the sheet member 92. With the configuration as in this embodiment, the production is easier and the apparatus can be downsized as compared with the second embodiment.

FIG. 6 is a diagram showing a fourth embodiment of the present invention. In this embodiment, a through-hole 95 different from the pores 60, 61 having throttles 62, 63 in each poppet valve body 54, 55.
A check valve 90 comprising a sheet body 92 having a seat surface 91 similar to that described above, a stopper 93, and a ball 94 is provided in the middle of the pore 95. In this embodiment, unlike the third embodiment, no aperture is formed in the sheet member 92. Also, in this embodiment, similarly to the third embodiment, when the fluid is going to flow from the supply / discharge passages 34, 35 to the cylinder chamber 73, the ball 94 is seated on the seat surface 91.
When the fluid is to flow from the cylinder chamber 73 to the supply / discharge passages 34 and 35 while the
94 separates from the seat surface 91 to allow the flow.

FIG. 7 is a diagram showing a fifth embodiment of the present invention. In this embodiment, the fine holes 60 and 61 similar to the fine holes 60 and 61 having the throttles 62 and 63 described in the fourth embodiment are inclined with respect to the axes of the poppet valve bodies 54 and 55,
The other end is not the other end face of the poppet valve body 54, 55, but the pore 95
It is opened halfway. The other structure and operation are the same as in the fourth embodiment.

[0022]

As described above, according to the present invention, the shock generated at the time of starting or braking the fluid motor can be effectively reduced while having a simple structure and a small size. It is also possible to make the rising relief static characteristics good under pressure.

[Brief description of the drawings]

FIG. 1 is a front sectional view partially showing a symbol showing a first embodiment of the present invention.

FIG. 2 is a sectional view taken along the line II of FIG.

FIG. 3 is a front sectional view, partly represented by a symbol, showing a second embodiment of the present invention.

FIG. 4 is a sectional view taken along the line II-II in FIG.

FIG. 5 is a sectional view showing the vicinity of a poppet valve according to a third embodiment of the present invention.

FIG. 6 is a sectional view showing the vicinity of a poppet valve body according to a fourth embodiment of the present invention.

FIG. 7 is a sectional view showing the vicinity of a poppet valve body according to a fifth embodiment of the present invention.

[Explanation of symbols]

 11 ... Fluid motor 12 ... Switching valve 13, 14 ... Supply / discharge passage 24 ... Relief valve 34, 35 ... Supply / discharge passage 36, 37 ... Communication passage 38, 39 ... Valve seat 42, 43 ... Fluid chamber 44, 45 ... Connection hole 50 ... Case 54, 55 ... Poppet valve body 56, 57 ... Tapered part 58, 59 ... Cylindrical part 60, 61 ... Pores 67, 68 ... Spring 73 ... Cylinder chamber 74 ... Piston 80, 81 ... Check valves A1, A2 ... Pressure receiving area located at the front end side B1, B2 ... Pressure receiving area located at the rear end side

Claims (3)

(57) [Scope of request for utility model registration] An air supply / discharge passage is provided in the middle of a pair of air supply / discharge passages connecting a switching valve and a fluid motor.
A case 50 in which a pair of supply / discharge passages 34, 35 forming a part of 3, 14 is formed, and a case 50 is provided in the case 50. A pair of poppet valve bodies 54 and 55 that are pressed by a predetermined pressure and move in the valve opening direction while opposing the springs 67 and 68 to relieve the fluid at the predetermined pressure to the supply / discharge passages 34 and 35 on the low pressure side. A pair of fluid chambers provided in the case 50 to accommodate the springs 67 and 68
42, 43, and a tapered portion 56, 57 tapered toward the tip on the tip side of the poppet valve element 54, 55, a cylindrical portion 58 continuous with the tapered portion 56, 57 on the rear end side. A poppet valve body biased by the springs 67 and 68 is provided at a boundary between the pair of communication passages 36 and 37 that communicate the supply and discharge paths 34 and 35 and the supply and discharge paths 34 and 35, respectively. The taper portions 56, 57 of 54, 55 form valve seats 38, 39 with which the pressure contact is made, respectively,
A relief in which the supply / discharge passages 34, 35 and the fluid chambers 42, 43 are connected by a pair of connection holes 44, 45 into which the cylindrical portions 58, 59 of the poppet valve bodies 54, 55 are slidably inserted. valve
24, the supply / discharge path is provided in each of the poppet valve bodies 54 and 55.
In addition to forming pores 60 and 61 for communicating the fluid chambers and 43 with the fluid chambers and 43, respectively, a piston 74 is slidably housed in the case 50, and one side of the piston 74 is connected to one of the fluids. The other side of the piston 74 is connected to the chambers 42 and 43 to form a cylinder chamber 73 connected to the remaining fluid chambers 42 and 43,
Further, of the pressure receiving areas where the pair of poppet valve bodies 54 and 55 receive the fluid force directed toward the rear end, the pressure receiving area A located on the tip side from the contact position between the valve seats 38 and 39 and the tapered portions 56 and 57.
1, A2, the pressure receiving area B located on the rear end side from the contact position
1, smaller than B2.
When 5 becomes the first set pressure lower than the predetermined pressure, the fluid of the first set pressure is supplied to the pores of one of the poppet valve bodies 54 and 55.
By passing through the fluid chambers 42 and 43 through the passages 60 and 61, and pressing and moving the piston 74 in the cylinder chamber 73, a pressure difference is generated between the poppet valve bodies 54 and 55 before and after the poppet valve bodies 55. By moving the valves 54 and 55 in the valve opening direction only until the piston 74 reaches the stroke end, the fluid at the first set pressure is relieved to the supply / discharge passages 34 and 35 on the low pressure side, When the pressures of the passages 34 and 35 reach a predetermined pressure higher than the first set pressure, one of the poppet valve bodies 54 and 55 is moved in the valve opening direction, and the fluid of the predetermined pressure is supplied to the supply / discharge passage 34 on the low pressure side. A relief valve characterized in that the relief valve has a relief of 35. 2. The cylinder chamber 73 is moved by the movement of the piston 74.
A pair of check valves (80, 81) for guiding the fluid pushed out of the pump to the supply / discharge passages (35, 34) on the low pressure side, respectively.
The relief valve as described. 3. The poppet valve body 54, wherein the check valves 80 and 81 are
The relief valve according to claim 2, wherein the relief valve is housed in each of 55.