Seal for a joint or juncture – Seal between relatively movable parts – Diverse and distinct dynamic seals
Reexamination Certificate
1996-04-05
2001-10-23
Knight, Anthony (Department: 3626)
Seal for a joint or juncture
Seal between relatively movable parts
Diverse and distinct dynamic seals
C277S387000, C277S408000
Reexamination Certificate
active
06305691
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a shaft sealing apparatus for various kinds of pumps handling various low boiling point inflammable fluids such as butane, methane, ethane, propane, LNG (Liquefied Natural Gas) and etc.
2. Prior Art
Conventionally, in the case of pumps handling low boiling point and highly inflammable fluids such as butane, methane, ethane, propane, LNG and etc., it has been usual that a reservoir L is used so as to store and supply or pressure-supply a buffer solution or a sealing solution used for the mechanical seal M of a shaft sealing apparatus whereby a fluid leaking from the contact type seal is released outside (for example, into the flare) instead of being introduced into the atmosphere.
Further, there has been used a shaft sealing apparatus as described in Japanese Unexamined Patent Publication H6-42650 which has a favorable and stabilized sealing function in a high-pressure condition or with respect to a volatile or low boiling point fluid such as liquid ammonium.
However, the above-mentioned conventional shaft sealing apparatuses have had the following various problems. That is, where the above-mentioned reservoir L is used, the entire apparatus becomes large-sized or the manufacturing cost increases.
Further, since the gas in the purge fluid area flows into the reservoir L without any resistance, where a high-pressure sealing fluid leaks from the mechanical seal, the pressure of the purge gas as a sealing fluid for a dry gas seal (i.e., non-contact type mechanical seal) drastically changes in such a manner that it rises up immediately and then drops at once failing to enable a stable dry gas sealing operation to be carried out.
Moreover, where the purge gas discharge line is directly coupled to the flare, since harmful gases from other various facilities of the plant gather in the flare, there is a danger of the harmful gases concentrated into the flare entering into the shaft sealing apparatus. Therefore, when these harmful gases enter into the purge gas area of the sealing apparatus, they tend to leak from the sealing surface of the dry gas seal toward the atmosphere.
In addition, where the high-pressure sealing fluid leaks from the mechanical seal, the pressure of the purge gas as a sealing fluid of the dry gas seal immediately rises up so that the sealing fluid penetrates near the sealing surface of the dry gas seal. As the sealing fluid used in the sealing apparatus is highly inflammable and the dry gas seal also allows a small quantity of purge gas to leak, there is a danger of gas explosion at the bearings or drive device outside the sealing apparatus.
Lastly, in the case of the latter (i.e., the shaft sealing apparatus described in Japanese Unexamined Patent Publication No. H6-42650), since it lacks a purge gas supply system, the density of the sealing gas leaked into the purge fluid area becomes high so that the leakage of the high-density sealing gas into the atmosphere can not be prevented.
SUMMARY OF THE INVENTION
The present invention has been developed in order to solve the above-described problems and an object of the invention is to provide a shaft sealing apparatus which is capable of preventing vaporized gases from the gas seal or purge fluids from leaking into the atmosphere until the pressure switch operates due to a pressure rise resulting from the leakage of the gases from the mechanical seal of the apparatus.
To achieve the above object, the shaft sealing apparatus of the present invention is characterized in the following points.
According to a first aspect of the invention, the shaft sealing apparatus comprises a seal casing and a rotary shaft passing through the former wherein a mechanical seal and a dry gas seal are mounted on the rotary shaft in line with each other so as to seal a target sealing fluid area from the atmosphere through two purge fluid areas formed between both of the seals. With this structure, a purge fluid from an external supply line is supplied to one of the purge fluid areas adjacent to the sealing surface of the dry gas seal and is released outside from the other purge fluid area adjacent to a spring retainer of the dry gas seal through a relief line having an orifice.
According to a second aspect of the invention, the shaft sealing apparatus comprises a seal casing and a rotary shaft passing through the former wherein a mechanical seal and a dry gas seal are mounted on the rotary shaft in line with each other so as to seal a target sealing fluid area from the atmosphere through two purge fluid areas formed between both of the seals. Further, a non-contact seal section is provided so as to establish communication between the purge fluid area adjacent to the seal surface of the dry gas seal and the purge fluid area adjacent to a spring retainer of the dry gas seal and a purge fluid from outside is supplied to the dry gas seal side purge fluid area through a supply line having an orifice and the supplied purge fluid is then released outside from the purge fluid area adjacent to the spring retainer of the dry gas seal through a relief line.
According to a third aspect of the invention, in association with the first aspect of the invention, the purge fluid is supplied to the dry gas seal surface side purge fluid area from the supply line having the orifice.
According to a fourth aspect of the invention, in association with the first, second and third aspects of the invention, a bypass line having an electromagnetic valve and a pressure switch is provided on the purge fluid relief line so as to bypass the orifice of the latter.
According to a fifth aspect of the invention, in association with the fourth aspect of the invention, when it is assumed that the supply pressure of the purge fluid be P
2
, the preset pressure of a seal section including the purge fluid areas between both of the orifices be P
2
, the pressure of the area between the orifice of the relief line and outside be P
3
and the operating pressure of the pressure switch be P
s
, the relationships of P
1
>P
s
>P
2
>P
3
are established.
As the non-contact seal section with respect to the rotary shaft, a labyrinth seal, liner seal or liner ring (such as a carbon bush fixed to the seal casing) may be used. These non-contact seal sections can not completely prevent the flow of the purge fluid but allow for the passage of the purge fluid and make it difficult to transmit a pressure change in one area to the other area.
The shaft sealing apparatus according to the first aspect of the present invention make it possible to reduce the rapid pressure fluctuation width of the purge fluid area (i.e., the sealing fluid area of the dry gas seal) and enable the dry gas seal to be operated in a stable manner by the provision of an orifice in the purge fluid relief line. Further, it prevents the pressure fluctuation of the flare from being transmitted thereto to thereby prevent the entry of harmful gases from the flare thereinto.
The shaft sealing apparatus according to the second aspect of the present invention has a structure such that the purge fluid supply line is provided with an orifice and the non-contact seal section which allows the passage of the purge fluid between purge fluid area adjacent to the sealing surface of the dry gas seal and the purge fluid area adjacent to the spring retainer (i.e., the mechanical seal side) of the dry gas seal so that even when the sealing fluid leaks from the mechanical seal, it is possible to reduce the pressure fluctuation width of the purge fluid area on the dry gas seal surface side and to prevent purge gases containing the leaking fluid from coming close to the sealing surface of the dry gas seal. Consequently, the dry gas seal can be operated in a stable manner and to prevent the leakage of harmful gases from the sealing surface of the dry gas seal.
The shaft sealing apparatus according to the third aspect of the present invention can further reduce the pressure fluctuation of the purge fluid area even when the sealing fluid leaks since, due to
Armstrong, Westerman, Hattori, McLeland & Naughton, LLP.
Knight Anthony
Nippon Pillar Packing Co. Ltd.
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