Seal

Details Seal Seal

1999-10-20

2001-11-13

Sandy, Robert J. (Department: 3626)

Seal for a joint or juncture

Seal between relatively movable parts

Relatively rotatable radially extending sealing face member

Reexamination Certificate

active

06315297

ABSTRACT:

THIS INVENTION relates to an improved seal. The invention is particularly, but not solely, directed to a mechanical seal for a slurry pump.
BACKGROUND ART
Slurry pumps are used in mining and other industrial applications to pump slurries and similar mixtures. A slurry pump typically comprises an impeller located within a pump housing, the impeller being mounted on a shaft extending into the housing. The shaft is normally driven by an electric motor outside the housing.
Due to the corrosive, toxic or otherwise aggressive nature of slurries, a reliable seal must be provided between the shaft and the housing of the slurry pump. This seal must be able to withstand the corrosive or aggressive nature of the slurry, as well as the high operating pressures and speed. Failure of seals leads to significant downtime while the seals are replaced. Since the slurry pumps often operate in remote locations, the sourcing and replacement of a seal may take a substantial period of time.
Known slurry pump seals have traditionally been based on conventional seal design. Such seals have a number of inherent disadvantages particularly when used in slurry pumps. For example, conventional seals are often unable to accommodate the relatively large amount of axial movement of the shaft which results from adjustment of the rotating part of the pump. Hence, it is necessary to physically undo the clamping rings or grub screws, move the rotating part of the pump, and then physically reset the clamping rings or grub screws whenever the impeller is adjusted. Due to the viscous nature of slurries, they tend to coagulate or clog in any small gap in their path. Hence, even if the seal drive clamp rings or grub screws are released, it is still difficult to move the rotating part of the pump through the seal due to the clogging caused by the slurry after even a relatively small amount of use.
Furthermore, known seals for slurry pumps generally cannot run dry, unless they have a water flush or some form of barrier fluid system from an outside source. In many applications, such as mining installations, sources of clean water are rarely available or are prohibitively expensive. Without a water flush or some other form of barrier fluid system, known seals often fail due to overheating and/or buildup of slurry as the seal is exposed to the slurry itself.
Where a water flush is available, the introduction of additional water to the pumped product may alter the desired characteristics of the product and/or require further processing in order to remove the added water.
Other known sealing arrangements involve complex installation of the seals such that the pump sleeve often has to be replaced. This often leads to incorrect fitting and premature failure.
Known sealing devices also fail regularly as a result of their inability to maintain the seal at higher pressures or during pressure spikes which occur when the slurry pump is part of a larger system which may involve other pumps.
It is an object of the present invention to provide an improved seal, particularly for slurry pumps, which overcomes or ameliorates the abovedescribed disadvantages, or which at least provides a useful alternative.
SUMMARY OF THE INVENTION
In one broad form, the invention provides a seal including
a housing having at least one stationary sealing surface,
a shaft assembly rotatable in the housing,
a sealing assembly mounted on the shaft assembly and rotatable therewith, the sealing assembly having at least one moveable sealing surface operatively abutting the stationary sealing surface,
wherein the shaft assembly is moveable axially relative to the sealing assembly.
In the preferred embodiment, the housing has two axially-spaced fixed radial sealing surfaces, and the sealing assembly has two moveable radial sealing surfaces, each operatively biased against a respective one of the stationary sealing surfaces. The sealing assembly also includes a spacer located between the two moveable sealing surfaces which are biased away from the spacer.
The spacer is preferably locked rotationally to the shaft assembly by a keylock, which still permits relative axial movement between the spacer and the shaft assembly. In this manner, the sealing assembly can maintain both dynamic seals even where there is relative movement between the shaft assembly and the sealing assembly.
The shaft assembly typically comprises a shaft having a sleeve fixed rotationally to the shaft.
The housing suitably provides a chamber around the sealing assembly which contains a lubricant. A paddle member may be provided on the spacer to promote circulation and misting of the lubricant within the chamber.
A pressure reducing plate may be fitted to the pump end of the seal to reduce the effect of pressure and/or pressure spikes on the inner dynamic seal.
The seal is particularly suitable for use in slurry pumps.
In order that the invention may be more fully understood and put into practice, a preferred embodiment thereof will now be described with reference to the accompanying drawings.


REFERENCES:
patent: 3547452 (1970-12-01), Hirata
patent: 3591188 (1971-07-01), Eisner
patent: 4294454 (1981-10-01), Cannings
patent: 4721311 (1988-01-01), Kakabaker
patent: 5409241 (1995-04-01), Bowers

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