JPH04320766A - Seal device - Google Patents

Abstract

PURPOSE:To provide a seal device capable of realizing a superior sealing function over a wide temperature range without any lubrication. CONSTITUTION:Outer seal rings 28 and 29 made of resin material and having ends are axially piled up in two-stages within an annular groove 27 of resin material formed at an outer circumferential surface of a piston (a displacer) 19. An inner seal ring 30, having an end part formed similarly by resin material is installed inside these outer seal rings, and a coil spring ring 31 having an end part formed by winding a belt-like metallic plate in a helical form and a receiving ring 32 of the same material quality as that of the cylinder 15 are installed inside these outer seal rings. The coil spring ring 31 pushes the seal rings 28 and 29 against an inner circumferential surface of the cylinder 15 through the seal ring 30.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sealing device for sealing a gap between a cylinder and a piston without lubrication.

0002

2. Description of the Related Art There are various types of sealing devices for sealing the gap existing between a cylinder and a piston. Most of these seal devices employ a method in which the sliding parts are lubricated with lubricating oil.

However, some devices requiring cylinders and pistons do not like the lubricating oil used in sealing devices. A typical example of such a device is a cryogenic refrigerator that uses helium gas as a refrigerant. In this cryogenic refrigerator, if lubricating oil is used in the seal portion, it not only causes contamination of helium gas but also causes malfunction due to freezing. Therefore, lubricating oil cannot be used in such devices.

For this reason, in cryogenic refrigerators that use helium gas as a refrigerant, as shown in FIG. Sealing device 1
I try to seal it with 04.

The sealing device 104 is shown in FIGS. 13 and 14.
As shown in FIG. 1, a seal ring 106 made of resin and having an end is installed in an annular groove 105 formed on the outer circumferential surface of the piston 102 so that the outer circumferential surface contacts the inner circumferential surface of the cylinder 101. An end-shaped spring ring 107 is mounted inside the seal ring 106 to press the seal ring 106 against the inner peripheral surface of the cylinder 101. As shown in FIG. 15, abutment portions 108 are formed at both ends of the seal ring 106 for overlapping each other in the radial direction.

However, in the seal device 104 configured as described above, when the seal ring 106 is thermally shrunk at extremely low temperatures, the adhesion of the abutment portion 108, especially in the circumferential direction, tends to deteriorate. However, there is a problem in that the amount of helium gas leaking from this joint 108 increases, leading to an increase in the temperature of the cooling stage. In addition, for this type of sealing device, for example, a sealing device built into a cryogenic refrigerator, it is difficult to estimate the performance at cryogenic temperatures from a performance test at room temperature. .

[0007]

[Problems to be Solved by the Invention] As mentioned above, with conventional non-lubricant type sealing devices, the desired sealing performance cannot be obtained, especially when used at extremely low temperatures. For this reason, when it is incorporated into a cryogenic refrigerator, for example, there is a problem in that the refrigerating capacity is reduced. Furthermore, it has been difficult to estimate the performance of cryogenic refrigerators that are incorporated into cryogenic refrigerators at normal temperatures. SUMMARY OF THE INVENTION An object of the present invention is to provide a lubrication-free sealing device that can significantly improve sealing performance without complicating the structure.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the present invention is for sealing the gap existing between a cylinder and a piston without using lubricating oil.
an annular groove formed on the outer circumferential surface of the piston;
Ended first and second sheets installed in a stacked state
a third seal ring with an end, which is attached inside the first and second seal rings; Sea
and an end-shaped coil spring ring that is mounted inside the seal ring and presses the first and second seal rings against the inner circumferential surface of the cylinder via the third seal ring.

[0009]

[Operation] Since the three seal rings are arranged in the above relationship, each seal ring has a cut in the circumferential direction, for example, one
By spacing them 20 degrees apart and selecting a dimensional relationship that prevents each seal ring from moving in the axial direction within the annular groove, even if the width of each seal ring cut changes due to heat shrinkage, each cut will be can be completely covered by each seal ring, making it as if a continuous seal ring were used. At this time, the coil spring ring formed by spirally winding a band-shaped metal plate functions to press the three seal rings integrally and uniformly against the inner circumferential surface of the cylinder. Therefore, gas leakage through the sealing device can be significantly reduced, and when incorporated into a cryogenic refrigerator, for example, this contributes to improving the refrigerating capacity.

0010

Embodiments Hereinafter, embodiments will be described with reference to the drawings. FIG. 1 shows a Gifford-McMahon type refrigerator incorporating a sealing device according to an embodiment of the present invention.

This refrigerator is mainly composed of a cold head 1 and a refrigerant gas introduction and discharge system 2. The cold head 1 includes a closed cylinder 11, a piston or displacer 12 housed in the cylinder 11 so as to be able to reciprocate, and provides the displacer 12 with the power necessary for the reciprocating motion. It is composed of a motor 13.

The cylinder 11 is a large-diameter first cylinder 14.
and a small-diameter second cylinder 15 coaxially connected to the first cylinder 14. The boundary wall between the first cylinder 14 and the second cylinder 15 constitutes a first stage cooling stage 16, and the tip wall of the second cylinder 15 has a temperature lower than that of the first stage cooling stage 16. A second cooling stage 17 is constructed.

[0013] First cylinder 14 and second cylinder 15
is made of stainless steel material. In this embodiment, the inner circumferential surfaces of the first and second cylinders 14, 15, which come into sliding contact with the seal rings of seal devices 25, 26 (described later), are subjected to ion nitriding treatment, and The sliding contact portion is finished to have a surface accuracy of 3.2 μm or less.

The displacer 12 has a first cylinder 14
It is comprised of a first displacer 18 that reciprocates within the cylinder 15, and a second displacer 19 that reciprocates within the second cylinder 15. These first and second displacers 18,1
9 is made of a material obtained by adding polyimide resin to tetrafluoroethylene. And the first display
The displacer 18 and the second displacer 19 are coupled in the axial direction by a coupling mechanism 20. First displacer 1
A fluid passage 21 extending in the axial direction is formed inside the cooling member 8, and a cold storage material 22 formed of copper mesh or the like is accommodated in this fluid passage 21. Similarly, a fluid passage 23 extending in the axial direction is formed inside the second displacer 19, and a cool storage material 24 formed of lead balls or the like is accommodated in this fluid passage 23.

Between the outer peripheral surface of the first displacer 18 and the inner peripheral surface of the first cylinder 14 and the second displacer 1
Seal devices 25 and 26 are installed between the outer peripheral surface of cylinder 9 and the inner peripheral surface of second cylinder 15, respectively.

The sealing devices 25 and 26 are constructed as shown in FIGS. 2 to 6, for example, showing the sealing device 26 as a representative example. That is, the sealing device 26 includes an annular groove 27 formed on the outer peripheral surface of the second displacer 19;
Ended outer seal rings 28 and 29 are installed in this annular groove 27 in a two-stage structure in the axial direction with the outer circumferential surface in contact with the inner circumferential surface of the second cylinder 15;
An end-shaped inner seal ring 30 is installed inside the seal rings 28 and 29, and an outer seal ring 30 is installed inside the inner seal ring 30 and is connected to the outer seal ring 30 through the inner seal ring 30. the ring 28, 29 to the second cylinder 1
5, and a receiving ring 32 mounted inside the coil spring ring 31 so as to be in contact with the coil spring ring 31.

The outer seal rings 28, 29 and the inner seal ring 30 are made of the same material as the first and second displacers 18, 19, that is, polytetrafluoroethylene mixed with polyimide resin. It is made of added materials. The outer seal rings 28, 29 and the inner seal ring 30 are finished so that the surface accuracy of the outer circumferential surface, inner circumferential surface, and both end surfaces in the axial direction is 30 μm or less. The outer seal rings 28 and 29 have the same thickness in the axial direction and the same thickness in the radial direction. The inner seal ring 30 is
The thickness in the axial direction is equal to the sum of the axial thicknesses of the rings 28 and 29. The sum of the axial thicknesses of the outer seal rings 28 and 29 is equal to the thickness of the annular groove 27.
The dimensional accuracy is set to ±50 μm with respect to the width in the axial direction. The outer seal rings 28, 29 and the inner seal ring 30 formed as described above are shown in FIG.
As shown in , there is a cut 33 (3
4, 35), and each cut 33, 34,
35 are mounted in the annular groove 27 so as to be spaced approximately 120 degrees apart in the circumferential direction, as shown in FIG.

As shown in FIG. 4, the coil spring ring 31 is formed by spirally winding a thin band-shaped member 36 made of stainless steel. This coil spring ring 31 has 5
Inner seal ring 3 with a force of ~60kgf/cm2
The outer seal rings 28 and 29 are pressed against the inner circumferential surface of the corresponding cylinder via the outer seal rings 28 and 29. The receiving ring 32 is
As shown in FIG. 5, it is formed by butting semicircular members 37a and 37b made of the same material as the cylinder, that is, stainless steel.

The upper end of the first displacer 18 in the drawing is connected to a connecting rod 38, a Scotch yoke or a crankshaft 39.
It is connected to the rotating shaft of the motor 13 via. Therefore, when the rotating shaft of the motor 13 rotates, the displacer 12 reciprocates in synchronization with this rotation as shown by the solid line arrow 40 in the figure.

A refrigerant gas inlet 41 and an outlet 42 are provided in the upper part of the side wall of the first cylinder 14 , and these inlet 41 and outlet 42 are connected to the refrigerant gas introduction and discharge system 2 . The refrigerant gas introduction and discharge system 2 constitutes a helium gas circulation system via the cylinder 11, and has a discharge port 42.
is connected to the inlet 41 via a low pressure valve 43, a compressor 44, and a high pressure valve 45. That is, the refrigerant gas introduction and discharge system 2 compresses low pressure (approximately 5 atm) helium gas to high pressure (approximately 18 atm) using the compressor 44 and sends it into the cylinder 11. The low-pressure valve 43 and the high-pressure valve 45 are controlled to open and close in relation to the reciprocating motion of the displacer 12, as will be described later. The operation of the refrigerator configured in this way will be explained.

In this refrigerator, the part that generates cold, that is, the part that serves as a cooling surface, is in the first cooling stage 1.
6 and a second cooling stage 17. These cool down to about 30K and 8K, respectively, when there is no heat load. Therefore, there is a temperature gradient from room temperature (300K) to 30K between the upper and lower ends of the first displacer 18 in the figure.
Also, there is a distance of 30K between the upper and lower ends of the second displacer 19 in the figure.
There is a temperature gradient from to 8K. However, this temperature varies depending on the heat load of each cooling stage, and usually the first
In the stage cooling stage 16, the temperature is between 30 and 80K, and in the second stage cooling stage 17, it is between 8 and 20K.

When the motor 13 starts rotating, the displacer 12 reciprocates between the bottom dead center and the top dead center. When the displacer 12 is at the bottom dead center, the high pressure valve 45 opens and high pressure helium gas flows into the cold head 1. Next, the displacer 12 moves to top dead center. As mentioned above, there are gaps between the outer circumferential surface of the first displacer 18 and the inner circumferential surface of the first cylinder 14 and between the outer circumferential surface of the second displacer 19 and the inner circumferential surface of the second cylinder 15, respectively. Seal devices 25 and 26 are installed. Therefore, when the displacer 12 moves toward the top dead center, the high-pressure helium gas flows into the fluid passage formed in the first displacer 18.
A first-stage expansion chamber 46 and a second displacer formed between the first displacer 18 and the second displacer 19 pass through the fluid passage 23 formed in the first and second displacers 19. 19 and the tip wall of the second cylinder 15 . Along with this flow, the high-pressure helium gas is cooled by the cold storage materials 22 and 24, and eventually the high-pressure helium gas that has flowed into the first-stage expansion chamber 46 has a temperature of about 30K, and the high-pressure helium gas that has flowed into the second-stage expansion chamber 47 has a temperature of about 30K. It is cooled to about 8K.

At this point, the high pressure valve 45 is closed and the low pressure valve 43 is opened. When the low pressure valve 43 opens in this way, the first stage expansion chamber 46
The high-pressure helium gas in the inner and second-stage expansion chambers 47 expands to generate cold, and the first-stage cooling stage 16 and the second-stage cooling stage 17 absorb heat. Then, when the displacer 12 moves to the bottom dead center again, the helium gas in the first-stage expansion chamber 46 and the second-stage expansion chamber 47 is eliminated. The expanded helium gas cools the cold storage materials 22 and 24 while passing through the fluid passages 21 and 23, and is discharged at room temperature. Thereafter, the above-described cycle is repeated to perform the refrigeration operation.

In this type of refrigerator, the minimum temperature reached and the refrigeration efficiency are greatly influenced by the sealing performance of the sealing devices 25 and 26. Now, taking as an example the case where the temperature inside the first stage expansion chamber 46 is 30K and the temperature inside the second stage expansion chamber 47 is 10K, if a leak occurs in the sealing device 26, helium gas at 30K will be released. The helium gas enters the second stage expansion chamber 47 without contacting the cool storage material 24 in the second displacer 19, and conversely, 10K helium gas enters the first stage expansion chamber 47.
It will go inside. As a result, the first cooling stage 1
6 will fall, and the temperature of the second cooling stage 17 will rise.

FIG. 7 shows the leakage rate of helium gas in the sealing device 26 (ratio of helium gas flowing through the sealing device 26 to the total amount of helium gas flowing into the second stage expansion chamber 47) and the rate of leakage of helium gas in each stage cooling stage. The results of calculating the relationship between − and temperature are shown. As can be seen from this figure, leakage at the sealing device 26 has a large effect on the temperature of each cooling stage. This applies not only to the sealing device 26 but also to the sealing device 25.

However, the sealing device 25 having the structure of this embodiment
, 26, the amount of leakage can be significantly reduced. As described above, the seal devices 25 and 26 use three seal rings consisting of the outer seal rings 28 and 29 and the inner seal ring 30, so the cuts 33, 34, and 35 are also There will be a total of 3 pieces. However, by shifting the positions of these cuts 33, 34, and 35 in the circumferential direction, it is possible to create a configuration that is substantially seamless and is equivalent to mounting a single seal ring that can be pressed against the inner peripheral surface of the cylinder. It is formed. And the annular groove 27
It is easy to prevent the outer seal rings 28, 29 and the inner seal ring 30 from moving in the axial direction during operation by selecting the axial width of the strip member 36. Since the three seal rings are pressed against the inner surface of the cylinder using the coil spring ring 31 formed by winding, unlike the coil spring ring formed from wire, it is easy to apply a force of 5 kg/cm2 or more. ,
Moreover, each part can be pressed uniformly, and as a result, gas leakage from the sealing devices 25 and 26 can be significantly reduced. Therefore, the temperature rise in the second cooling stage 17 can be suppressed, and the refrigerating capacity can be improved.

FIG. 8 shows outer seal rings 28, 2.
9 and the inner seal ring 30 against the inner circumferential surface of the cylinder, when a coil spring ring 31 formed by spirally winding the band member 36 as in this embodiment is incorporated, R1 When a coil spring ring formed by spirally winding a wire member is incorporated, R2
If a spring ring like the conventional device is installed, R3
A comparison of the leakage amount is shown. This was measured at room temperature under the same surface accuracy conditions for the three seal rings, mounting conditions, and cylinder surface accuracy conditions.

As can be seen from this figure, when the coil spring ring 31 formed by spirally winding the band member 36 is incorporated, the amount of leakage is significantly small in R1. this is,
The area of the part that actually contacts the inner circumferential surface of the inner seal ring 30 is large, and most of the reaction force due to deformation of the coil part is directed in the axial direction. This is because each part in the direction and the circumferential direction can be pressed uniformly. Therefore, the coil spring ring 31
contributes significantly to reducing the amount of leakage.

FIG. 9 shows a conventional refrigerator incorporating the sealing device shown in FIG. 14 and a sealing device 25 (26) shown in FIG.
The refrigeration curve for a refrigerator incorporating a refrigeration machine is shown. The horizontal axis represents the temperature (K) of the second cooling stage 17, and the vertical axis represents the heat load (W) applied to the second cooling stage 17. As can be seen from this figure, the refrigerator incorporating the sealing device 25 (26) of this embodiment has a greater ability to freeze at the same temperature. Therefore, the sealing device 25 (
It is understood that the refrigeration capacity can be improved by incorporating 26).

Note that in this embodiment, the first cylinder 14 (
Since the receiving ring 32 made of the same material as that of the second cylinder 15) is attached to the inside of the coil spring ring 31, the sealing performance at room temperature is reduced to the sealing performance at extremely low temperatures. - It is possible to estimate the performance of the system almost accurately. That is, the relative thermal contraction between the receiving ring 32 and the cylinder does not change even under extremely low temperatures. Therefore, the amount of strain given to the coil spring ring 31 during assembly at room temperature can be maintained even at extremely low temperatures, and as a result, the same performance as confirmed at room temperature can be exhibited at extremely low temperatures. .

In addition, in this embodiment, the outer seal ring 28 is made of tetrafluoroethylene resin to which polyimide resin is added.
, 29 and an inner seal ring 30, respectively. The addition of polyimide resin is extremely effective in improving wear resistance, and the sealing device 25 (
26) The amount of leakage does not increase rapidly. Figure 10 shows S1 when a seal ring made of tetrafluoroethylene added with polyimide resin is used, and S2 when a seal ring made of tetrafluoroethylene added with carbon is used. The rate of increase in leakage amount with respect to the elapsed operating time is shown for S3 and S3 when a seal ring made only of tetrafluoroethylene is used. As can be seen from this figure, in S1 when a seal ring made of tetrafluoroethylene added with polyimide resin is used,
The rate of change in leakage amount with respect to elapsed operating time is extremely small. This is due to the improvement in wear resistance due to the addition of polyimide resin.

Furthermore, in this embodiment, the outer circumferential surfaces of the first cylinder 14 and the second cylinder 15, which are made of stainless steel, constitute the sealing device 25 (26).
The portions that come into contact with the seal rings 28 and 29 are subjected to ion nitriding treatment, and are finished so that the surface accuracy is 3.2 μm or less. The presence of this ion nitrided layer contributes to improving the wear resistance of the outer seal rings 28, 29.

FIG. 11 shows a case T1 in which a ceramic coating layer is provided on the inner circumferential surface of a stainless steel cylinder, and a case in which an ion nitriding treatment is applied to the inner circumferential surface of a stainless steel cylinder. T2 when using a cylinder made of stainless steel only, and T3 when using a cylinder made only of stainless steel.
The rate of increase in leakage amount with respect to the elapsed operation time is shown. As can be seen from this figure, the rate of increase in the amount of leakage is extremely small in T1 when a cylinder provided with a ceramic coating layer is used and in T2 when a cylinder subjected to ion nitriding treatment is used. This is because the ceramic coating layer and the ion nitriding layer contribute to suppressing wear of the seal ring.

Furthermore, in this embodiment, the sealing device 25 (2
The surface accuracy of the outer circumferential surface, inner circumferential surface, and both end surfaces in the axial direction of the outer seal rings 28, 29 and the inner seal ring 30 constituting 6) is finished to 30 μm or less,
Furthermore, the surface accuracy of the portions of the first cylinder 14 and the second cylinder 15 that contact the outer seal rings 28, 29 is finished to 3.2 .mu.m or less. Therefore, due to these relationships, the outer seal ring 2
The amount of leakage between the outer seal rings 28, 29 and the inner peripheral surface of the cylinder, and between the end surfaces of the annular groove 27 and both end surfaces of the outer seal rings 28, 29 and the inner seal ring 30 can be sufficiently reduced.

Furthermore, in this embodiment, the width of the inner seal ring 30 in the axial direction is larger than that of the outer seal rings 28, 29.
This width is set to a value that is the sum of the axial width of the annular groove 27, and this width is set to have a dimensional accuracy of ±50 μm with respect to the axial width of the annular groove 27. Therefore, outer seal ring 2
The amount of leakage between the end surfaces of the annular groove 27 and both end surfaces of the inner seal ring 30 and the annular groove 27 can be sufficiently reduced. In addition, the outer seal ring 2 is made of the same material as the first and second displacers 18 and 19.
8, 29 and the inner seal ring 30, the axial heat shrinkage of the outer seal rings 28, 29 and the inner seal ring 30 can be made equal to that of the annular groove 27, so that By maintaining the above-mentioned dimensional accuracy when installed even at extremely low temperatures, it is possible to prevent an increase in leakage due to differences in thermal contraction.

Note that the present invention is not limited to the embodiments described above. That is, in the above embodiment, the first and second displacers 18, 19 are made of the same material as the outer seal rings 28, 29 and the inner seal ring 30, that is, polytetrafluoroethylene added with polyimide resin. However, it may also be formed from a material having approximately the same thermal shrinkage rate as this, such as tetrafluoroethylene, or tetrafluoroethylene to which carbon or glass fiber is added. Further, it is not necessary to form the entire displacer with these, and only the portion where the annular groove 27 will be formed may be formed with these. Similarly, the receiving ring 32 does not need to be made of the same material as the cylinder, but may be any material that has a heat shrinkage rate comparable to that of the cylinder constituent material. In addition, in the embodiment described above, ion nitriding is applied to the inner peripheral surfaces of the first and second cylinders 14 and 15, but ion nitriding is applied only to the sealing device side, which is more affected by gas leakage, that is, to the second cylinder 15. A nitriding treatment may also be performed. The cylinder constituent material is not limited to stainless steel, but the same effect can be obtained by using a titanium-based material that is subjected to ion nitriding treatment or coated with ceramic. It is also effective to make the portion of the inner circumferential surface of the cylinder that comes into sliding contact with the sealing device from ceramic. Furthermore, it goes without saying that the sealing device according to the present invention can be applied not only to cryogenic refrigerators but also to similar devices in general that require no lubrication.

[0037]

As described above, according to the present invention, it is possible to exhibit a good sealing function over a wide temperature range despite the simple structure. In particular, by using a coil spring ring formed by spirally winding a band member, the seal ring can be pressed against the inner peripheral surface of the cylinder with strong force and uniformly, further enhancing the sealing function. can be improved.

[Brief explanation of drawings]

FIG. 1 is a schematic vertical cross-sectional view of a Gifford-McMahon refrigerator incorporating a sealing device according to an embodiment of the present invention.

[Figure 2]
A diagram of the refrigerator cut along line C-C in Figure 1 and viewed in the direction of the arrow.

[Fig. 3] A view cut along DD in Fig. 2 and viewed in the direction of the arrow.

[Fig. 4] A plan view showing a partially extracted coil spring ring incorporated in the sealing device.

[Fig. 5] Plan view of the receiving ring incorporated in the sealing device

[
Figure 6: Side view showing the end of the seal ring incorporated in the sealing device

[Fig. 7] A diagram showing an example of calculating the temperature change of each cooling stage when there is a leak in the sealing device.

[Fig. 8] A diagram showing the relationship between pressing force and leakage amount when various spring rings are installed in the sealing device.

FIG. 9 is a diagram showing a comparison of the refrigerating capacity characteristics of a refrigerator incorporating a sealing device according to the present invention and a refrigerator incorporating a conventional sealing device.

[Fig. 10] A diagram showing the relationship between elapsed operating time and leakage amount when various seal rings are installed in the seal device.

[Figure 11]
Diagram showing the relationship between the inner surface treatment of the cylinder and the amount of leakage in the sealing device

[Figure 12] Seat installed between cylinder and piston
Diagram showing the device

[Fig. 13] A view cut along line A-A in Fig. 12 and viewed in the direction of the arrow.

[Fig. 14] A view cut along the line BB in Fig. 13 and viewed in the direction of the arrow.

FIG. 15 is a sectional view showing an end portion of a seal ring incorporated in a conventional sealing device.

[Explanation of symbols]

1...Cold head,
2... Refrigerant gas introduction and discharge system, 11... Cylinder,
12...displacer, 13...motor, 14...
1st cylinder, 15...2nd cylinder,
16...first stage cooling stage, 17...second stage cooling stage, 18...first displacer, 19...second displacer,
22, 24... Cold storage material, 25, 26... Seal device, 27... Annular groove, 28, 2
9...Outer seal ring, 30...Inner seal ring, 31...Coil spring ring,
32... Reception ring, 33, 34, 35... Cut,
36...Band-shaped member, 46...1-stage expansion chamber, 47...2-stage expansion chamber.

Claims (5)

[Claims] Claim 1: A device for sealing a gap existing between a cylinder and a piston without using lubricating oil,
an annular groove formed on the outer circumferential surface of the piston;
Ended first and second sheets installed in a stacked state
a third seal ring with an end, which is attached inside the first and second seal rings; Sea
and an end-shaped coil spring ring that is attached to the inside of the cylinder ring and presses the first and second seal rings against the inner circumferential surface of the cylinder via the third seal ring. A sealing device characterized by: Claim 2: A device for sealing a gap existing between a cylinder and a piston without using lubricating oil,
an annular groove formed on the outer circumferential surface of the piston;
Ended first and second sheets installed in a stacked state
a third seal ring with an end, which is attached inside the first and second seal rings; Sea
an end-shaped coil spring ring that is attached to the inside of the cylinder ring and presses the first and second seal rings against the inner peripheral surface of the cylinder via the third seal ring; A sealing device comprising a receiving ring mounted on the inside in contact with the coil spring ring. 3. The sealing device according to claim 2, wherein the receiving ring is made of a material having a heat shrinkage rate that is the same as or close to that of the material that makes up the cylinder. 4. The first, second, and third seal rings include:
3. The sealing device according to claim 1, wherein the sealing device is made of a resin containing a polyimide resin. 5. The cylinder is made of stainless steel or titanium, and includes at least the first and second seals.
3. The sealing device according to claim 1, wherein a portion in contact with the sealing ring is subjected to ion nitriding treatment or ceramic coating.