JP2006057610A5 - - Google Patents

Description

Shaft seal

  The present invention relates to a shaft seal, and more particularly to a shaft seal including a bellows type shaft seal that can also be used for a high-pressure reciprocating pump.

  In general, a reciprocating pump (a pump represents a general device for compressing and transferring a fluid, and includes a pump for liquid, a compressor for gas, a compressor, etc. The same shall apply hereinafter) is a piston or a piston rod (piston, plunger, And the piston rod together may be referred to as a shaft.) Has a shaft seal, thereby sealing the fluid in the pump from the atmosphere. Usually, as a shaft seal of a reciprocating pump, a gland packing, a V packing, a lip seal, a labyrinth type piston rod packing, a segment type piston rod packing or the like is used. However, these seals are mechanisms that seal while allowing the shaft and cylinder to slide, and since there is a sliding portion in the portion that seals the fluid, it is difficult to completely seal the internal fluid from the atmosphere. . In particular, when the internal fluid is in a gaseous state and has a high pressure, the leakage cannot be completely prevented structurally. The oil seal is not suitable for high pressure, and the oil-filled segmented piston rod packing is excellent in preventing fluid leakage, but requires oil circulation, and the seal structure is complicated and large. On the other hand, the diaphragm or bellows seal is a relatively simple seal that completely seals the internal fluid, and since it does not have a sliding portion, it can completely prevent leakage. However, the diaphragm has a small displacement and is not suitable for a large stroke. Due to its structure and material, if the pressure of the internal fluid is high, the bellows will break, and the pressure of the internal fluid that can normally be used for the bellows seal is about 0.3 MPa. Until now. For this reason, various studies have been made. For example, Patent Document 1 discloses a method of using a special lip seal structure for a shaft seal mechanism of a high-pressure compressor. However, although it is effective when the internal fluid is a harmless gas such as air, it is difficult to use it for hydrogen or the like where a small amount of leakage is not allowed.

JP 2003-222077 A

  An object of the present invention is to provide a bellows-type shaft seal that can completely seal leakage of high-pressure internal fluid into the atmosphere in a shaft seal of a reciprocating pump.

In order to solve the above problems, the present inventors have invented the following shaft seal in which an auxiliary seal or the like is combined with a bellows type shaft seal.
(1) In a reciprocating pump having a bellows type shaft seal, an auxiliary shaft seal is provided on a shaft on the atmosphere side of the bellows type shaft seal portion and a sliding portion of the cylinder, and the shaft or cylinder of the portion in contact with the auxiliary shaft seal Make the diameter equal to the effective diameter of the bellows, provide a primary seal on the pump side shaft and cylinder sliding part from the bellows type shaft seal part, and set the diameter of the shaft or cylinder in contact with the primary seal to the effective diameter of the bellows Shaft seal for reciprocating pumps equal to
(2) The shaft diameter on the pump side with respect to the primary seal is changed to the shaft diameter of the primary seal part, and the secondary seal is provided on the sliding part of the shaft and the cylinder where the diameter is changed. The space formed with the seal is a decompression chamber, the primary seal has a unidirectional structure that suppresses the inflow of fluid from the decompression chamber side to the bellows shaft seal side, and the secondary seal is from the pump side to the decompression chamber. A unidirectional structure that suppresses the inflow of fluid to the side, and a tertiary seal with a non-directional structure is provided on the shaft and cylinder sliding part on the pump side of the secondary seal, between the secondary seal and the tertiary seal. The shaft seal according to (1), wherein the space is electrically connected to the pump suction side.
(3) A primary seal having a unidirectional structure that conducts the space between the primary seal and the bellows type shaft seal to the pump suction side and suppresses the inflow of fluid from the pump side to the bellows type shaft seal side is provided ( The shaft seal according to 1).
(4) A liquid is sealed in the space between the bellows type shaft seal and the auxiliary shaft seal, and / or the non-directional structure of the shaft and cylinder sliding part between the primary seal and the bellows type shaft seal is four. The shaft seal according to any one of (1) to (3), wherein a secondary seal is provided, and a liquid is sealed in a space between the bellows-type shaft seal and the quaternary seal.

  The shaft seal of the present invention has a bellows type shaft seal portion and completely seals the pump side and the atmosphere side, so that there is no leakage of the internal fluid to the atmosphere side. The bellows breakage occurs when a pressure difference is generated between the air side and the pump side of the bellows, and the bellows undergoes a deformation different from the deformation accompanying the reciprocating movement of the shaft, and thus a strong scavenging force acts on the bellows. In addition to the case where an abnormal pressure is applied to the pressure difference bellows between the air side and the pump side of the bellows, the bellows also changes in pressure due to the volume change of the closed space due to the movement of the components near the bellows due to the reciprocating movement of the shaft. According. The shaft seal of the present invention uses a pump action due to the volume change of the closed space in order to reduce the pressure difference applied to the bellows, and encloses an incompressible liquid in the atmosphere side space of the bellows, thereby reciprocating the pump. Therefore, it is possible to prevent deformation of the bellows because the volume of the incompressible liquid does not change even when high pressure or abnormal pressure is applied from the pump side of the bellows without changing the volume of the space in which the fluid is sealed. In other words, even if a compressive load is applied to the bellows, no shear load is applied, so that abnormal deformation and breakage of the bellows can be prevented.

  The shaft seal of the present invention will be described with reference to FIG. FIGS. 1a and 1b are explanatory views of one embodiment of the shaft seal of the present invention. The bellows type shaft seal portion is mainly shown, the lower side is the pump side, the upper side is the atmosphere side, and the drive unit side. The shaft 1 is on the left side and the cylinder 2 is on the right side. A bellows 5 is installed between the bellows chamber 3 that is in communication with the atmosphere side via the auxiliary shaft seal 6 and the bellows chamber 4 that is in communication with the pump side via the primary seal 8. Figure a shows the position where the piston is lowered most (referred to as bottom dead center), and Figure b shows the position where the piston is raised most up (referred to as top dead center). Bellows 5 is the most extended at the bottom dead center and the most contracted at the top dead center. The bellows 5 is a bent line for simplification of description, but any material or structure that serves as a bellows may be used. The optimum material and structure may be selected in consideration of the nature of the internal fluid of the pump, the pressure and temperature of the internal fluid, and the ease of manufacturing the shaft seal. In general, corrugated bellows, which are used as metal bellows, and corrugated bellows, a bellows close to a U-shape made by cutting Teflon (registered trademark), and a bellows made by molding resin Etc. are easy to use.

  What should be noted in the present invention is the diameter of the shaft 1 in contact with the auxiliary shaft seal 6 installed in the cylinder 2. It is necessary to make the diameter of the shaft 1 in this part equal to the effective diameter of the bellows 5. The effective diameter of the bellows 5 is a substantially cylindrical shape (a bellows-like cylinder) formed by alternately stacking bellows 5 on the horizontal surface of the bellows 5 and a bellows-like circumferential portion of the bellows 5, for example, a truncated cone-like plate. Is the length corresponding to the diameter of the circle. In other words, the effective diameter is an imaginary diameter for taking the bellows-like cylinder as a cylinder and taking out the volume. In FIG. 1, this effective diameter is represented by a line 7 in the bellows portion of the bellows chamber. The effective diameter 7 does not change with respect to the pump piston, that is, the reciprocating motion of the shaft 1 and the expansion / contraction of the bellows 5 that is interlocked. Therefore, if the diameter of the shaft 1 in contact with the auxiliary shaft seal 6 at the upper part of the bellows chamber 3 is the same as the effective diameter 7 of the bellows 5, the volume of the bellows chamber 3 partitioned by the auxiliary shaft seal 6 and the bellows 5 is It can be kept constant regardless of the reciprocation of the shaft. In other words, the bellows chamber 3 does not change in volume or pressure even if the shaft reciprocates. That is, a change in pressure does not occur in the bellows chamber 3 on the atmosphere side and the bellows is not damaged. Therefore, if the bellows structure can withstand the pressure inside the pump, more precisely, the pressure difference between the pressure in the pump side bellows chamber 4 and the pressure in the bellows chamber 3, the bellows 5 has a pressure difference caused by the pressure change in the bellows chamber 3. Will not be damaged.

  In FIG. 1, the auxiliary shaft seal 6 is installed on the cylinder 2 side and is slid with the shaft 1, but conversely, the auxiliary shaft seal 6 is installed on the shaft 1 side and the cylinder The structure which slides with 2 may be sufficient. In this case, “the diameter of the shaft 1 in contact with the auxiliary shaft seal 6 installed in the cylinder 2 is necessary. It is necessary to make the diameter of the shaft 1 in this portion equal to the effective diameter of the bellows 5.” "The diameter of the cylinder 2 in contact with the auxiliary shaft seal 6 installed on the shaft 1 is read. It is necessary to make the diameter of the cylinder 2 in this portion equal to the effective diameter of the bellows 5." Just do it. The auxiliary shaft seal 6 may be any type of seal, but may be used in combination with a seal having a unidirectional structure such as a gland packing, an O-ring, a V packing, a lip seal, or a lip seal with a spring. The auxiliary shaft seal 6 is not required to have a particularly directional seal for fluid sealing, and a gland packing, an O-ring or the like is suitable.

  FIG. 1 c and FIG. D are also one embodiment of the shaft seal of the present invention. The structure is the same as in FIGS. a and b except that the bellows is joined to the shaft at the upper part and joined to the cylinder at the lower part. Therefore, the bellows chamber 3 on the atmosphere side is on the cylinder side, and the bellows chamber 4 on the fluid side of the pump chamber is on the shaft side. Further, the piston is at the uppermost part (top dead center) in the case of FIG. C, and is at the lowest part (bottom dead center) in the case of FIG. Although the position of the atmosphere side bellows chamber 3 is opposite to that described in FIGS. A and b, the same effect as described above can be obtained if the effective diameter of the bellows 5 and the diameter of the shaft in contact with the auxiliary shaft seal 6 are equal. can get.

  Up to this point, the description has focused on the bellows chamber 3 on the atmosphere side of the shaft seal of the present invention, but the same can be said for the bellows chamber 4 on the pump side. 1A and 1B, the primary seal 8 isolates the internal fluid and the bellows chamber 4 in the same manner as the auxiliary shaft seal 6. FIG. There is no volume change or pressure change of the bellows chamber 4 due to reciprocation of the shaft, that is, expansion and contraction of the bellows 5. Thereby, the bellows 5 hardly changes in the differential pressure between the air side and the pump side due to expansion and contraction, and the possibility of damage due to the pressure change due to the reciprocating pump with respect to the bellows 5 is further reduced. The primary seal 8 may be a seal of any structure as long as it is a unidirectional structure that suppresses the inflow of fluid to the bellows chamber 4 side, but a V packing, a lip seal, a spring having a relatively simple structure. An attached lip seal is economical and suitable. Normally, as the primary seal 8, since the pressure on the pump side is higher than the pressure on the bellows chamber 4 side, a seal having a check valve function such as a V-packing or lip seal is used as a fluid for the bellows chamber 4 side. Install in a unidirectional structure to prevent inflow.

  Furthermore, as a desirable mode, there is a structure shown in FIG. In addition to the structure of the shaft seal shown in FIGS. 1c and 1d above, the diameter of the shaft 1 on the pump side with respect to the primary seal 8 is changed to the diameter of the shaft 1 of the primary seal portion, and the changed shaft 1 A secondary seal 9 is provided on the sliding portion of the cylinder 2. Incidentally, in FIG. 2, the diameter of the shaft 1 is changed thinly. The space between the primary seal 8 and the secondary seal 9 is a decompression chamber 12, and the primary seal 8 suppresses the inflow of fluid from the decompression chamber 12 side to the bellows chamber 4 side and from the bellows chamber 4 to the decompression chamber 12 side. The secondary seal 9 has a unidirectional structure that suppresses the inflow of fluid from the pump side to the decompression chamber 12 side and allows the fluid to flow from the decompression chamber 12 to the pump side. Further, a tertiary seal 10 is provided in the sliding portion between the shaft 1 and the cylinder 2 on the pump side relative to the secondary seal 9, and a conduction path 11 to the pump suction side is provided in the space between the secondary seal 9 and the tertiary seal 10. The pressure in this space is the same as the pump suction side. The primary seal 8 has a unidirectional structure that suppresses the inflow of fluid from the decompression chamber 12 side to the bellows chamber 4 side, and the secondary seal 9 has a unidirectional property that suppresses the inflow of fluid from the pump side to the decompression chamber 12 side. Structure.

  Thereby, with the reciprocation of the shaft, the bellows chamber 4 and the decompression chamber 12 are restrained from increasing in pressure even in the pump compression process. Since the decompression chamber 12 has a higher compression ratio than the decompression chamber 4, the decompression chamber 12 and further the bellows chamber 4 can be decompressed by a reciprocating motion when combined with a one-way seal of the pump. Thereby, even if the pressure of the pump suction part is higher than the atmospheric pressure, the pressure in the bellows chamber 4 can be made close to or lower than the atmospheric pressure, and the pressure difference between the bellows chamber 4 and the bellows chamber 3 is 0.1 MPa or less. It can be. Further, since the space between the secondary seal 9 and the tertiary seal 10 is electrically connected to the pump suction side, it does not become higher than the pressure on the pump suction side. Therefore, the bellows chamber 4 does not always become higher than the pressure of the pump suction port. In this way, the pressure in the bellows chamber 4 is further stabilized, and the risk of damage to the bellows 5 becomes smaller. The material and structure of the secondary seal 9 may be appropriately selected according to the nature, pressure, temperature, etc. of the fluid operated by the pump, as with the primary seal 8. For example, it is desirable to provide a seal having a check valve function, such as a simple V-packing, lip seal, or lip seal with a spring, with a unidirectional structure that suppresses the inflow of internal fluid from the pump side. The tertiary seal 10 may be any seal similar to the auxiliary shaft seal 6. For example, an O-ring, piston ring, V packing, lip seal, lip seal with spring, rod packing, etc. are convenient and convenient. Further, in the explanatory diagram, the seal is shown to be installed on the cylinder side and slides with the shaft, but may be installed on the shaft side and slide with the cylinder.

  As a simpler shaft seal than the shaft seal of the above aspect, a shaft seal having a structure in which the primary seal 8, the secondary seal 9, and the decompression chamber 12 are omitted is also an effective shaft seal. In this case, although shown by the tertiary seal 10 in FIG. 2, it is a primary seal in terms of function. For example, a seal having a check valve function such as a simple V-packing, lip seal, or spring-loaded lip seal is pumped. It is desirable to provide a unidirectional structure that mainly suppresses inflow from the side. Thereby, the pressure of the bellows chamber 4 does not always become higher than the suction side pressure of the pump.

  As a more preferable mode of the shaft seal, a space formed by the bellows chamber 3 and the auxiliary seal 6 and / or a space formed by the bellows chamber 4 and the quaternary seal provided on the side of the bellows chamber 4 of the primary seal 8 of the shaft 1 is formed. It is desirable to enclose the liquid. The liquid is preferably incompressible, hardly vaporized in the temperature range of use, and has little thermal expansion. As the liquid, it is preferable to use a liquid that does not easily leak from the auxiliary shaft seal 6 to the atmosphere side, such as lubricating oil. However, if the viscosity is too high, resistance to reciprocation of the shaft and expansion / contraction of the bellows will cause resistance. Therefore, it is necessary to select the liquid in consideration of the reciprocating speed of the piston. Normally, machine oil or the like may be used. However, when a pump is used in a low temperature environment such as liquefied gas, it is necessary to pay attention to selection of a liquid in accordance with the temperature of the bellows chamber. When liquid is sealed in the bellows chamber 4, a quaternary seal is provided on the side of the bellows chamber 4 of the primary seal 8 of the shaft 1. The quaternary seal may be any seal similar to the auxiliary shaft seal, but a non-directional seal having no directionality in the sealing function such as a gland packing is desirable.

  Further, the primary seal 8, the secondary seal 9, the tertiary seal 10, and the quaternary seal may not be installed on the piston shaft, but may be installed on the piston. In the case of a plunger pump where there is no distinction between the pump and the piston, the shaft described in the present invention means the plunger.

Reference example

A shaft seal which is a reference example of the present invention will be illustrated. FIG. 3 is a cross-sectional view of the shaft seal of the liquid hydrogen plunger pump. Although not shown, a liquid hydrogen pump unit is provided at the lower portion, and is cooled and kept at approximately -253 ° C. At the top is a plunger drive, not shown. In the figure, the left side of the center line shows the state where the plunger is at the bottom dead center. The right side of the center line indicates that the plunger is at the top dead center. The bellows 5 is a metal bellows, and the auxiliary shaft seal 6 is an O-ring at room temperature. The primary seal 8 and the secondary seal 9 use V packing, and the tertiary seal 10 is a seal such as a piston ring. The primary seal 8 and the secondary seal 9 are installed in a unidirectional structure that suppresses the flow of internal fluid hydrogen from the pump side to the bellows-type shaft seal portion. Although not all shown, the conduction path 11 is connected to the pump suction portion. Even in the pump compression process, such a shaft seal returns to the suction portion through the conduction path 11 even if the compressed hydrogen passes through the tertiary seal 10, and the space between the secondary seal 9 and the tertiary seal 10. Will not be higher than the pressure on the pump suction side. The decompression chamber 12 has a function of a pump that discharges fluid from the bellows chamber 4 side to the space side between the secondary seal 9 and the tertiary seal 10. That is, the fluid in the bellows chamber 4 is discharged to the decompression chamber 12, and the fluid in the decompression chamber 12 is discharged to the space side between the secondary seal 9 and the tertiary seal 10. Therefore, the bellows chamber 4 is kept below the pressure of the decompression chamber 12, and further below the pressure of the suction port.

  On the other hand, in the bellows chamber 3, which is the space on the atmosphere side from the bellows 5, the effective diameter (B) of the bellows and the diameter of the shaft 1 in contact with the auxiliary shaft seal 6 are the same. The volume does not change. That is, the bellows chamber 3 is always kept at a constant pressure unless the bellows 5 is deformed only by expansion and contraction due to the pump reciprocation and is not deformed due to pressure fluctuation of the pump bellows chamber 4. That is, the differential pressure applied to both sides of the bellows 5 is constant regardless of the movement of the piston, and there is no risk of damage due to the pressure difference between the two sides of the bellows. When the differential pressure applied to both sides of the bellows 5 is large, filling the atmosphere-side bellows chamber 3 with lubricating oil that does not easily leak from the auxiliary seal 6 causes a reaction force with the same pressure as the pump-side bellows chamber 4. Since the same pressure is applied to both sides of 5, the differential pressure is almost zero.

  The shaft seal of the present invention is suitable for various reciprocating pumps, particularly for reciprocating pumps that reliably prevent leakage of internal fluid and handle high-pressure internal fluid without providing a complicated sealing mechanism.

FIG. 1 is an explanatory view of a shaft seal of the present invention. FIG. 2 is an explanatory view of another aspect of the shaft seal of the present invention. FIG. 3 is a cross-sectional view for explaining a shaft seal as a reference example of the present invention.

a: Explanatory drawing of the state where the piston of the shaft seal of the present invention is at the top dead center when the atmosphere side bellows chamber is on the shaft side b: The shaft seal of the present invention when the atmosphere side bellows chamber is on the shaft side Fig. 3c is an explanatory diagram of a state where the piston is at bottom dead center c: An explanatory diagram of a state where the piston of the shaft seal of the present invention is at top dead center when the atmospheric side bellows chamber is on the cylinder side. Explanation e of the state where the piston of the shaft seal of the present invention is at the bottom dead center when it is on the cylinder side e: The piston of the shaft seal of the present invention is bottom dead when a decompression chamber is added to the figure c of FIG. Explanation of the state at the point f: Explanation of the state where the piston of the shaft seal of the present invention is at the bottom dead center when the decompression chamber is added to the d diagram of FIG. 1A: Diameter of the shaft of the auxiliary shaft seal portion B: Effective diameter of bellows C: Diameter of shaft of bellows part D: Of secondary seal part Shaft diameter 1: Shaft 2: Cylinder 3: Atmospheric side bellows chamber 4: Pump side bellows chamber 5: Bellows 6: Auxiliary shaft seal 7: Virtual line representing effective diameter of bellows 8: Primary seal 9: Secondary seal 10: Tertiary seal 11: Conduction path 12: Decompression chamber