Seal for a joint or juncture – Seal between relatively movable parts – Diverse and distinct dynamic seals
Reexamination Certificate
2000-05-16
2001-12-04
Sandy, Robert J. (Department: 3626)
Seal for a joint or juncture
Seal between relatively movable parts
Diverse and distinct dynamic seals
C277S400000
Reexamination Certificate
active
06325380
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a face seal assembly. The invention relates in particular, but not exclusively, to a face seal assembly suitable for sealing the drive shaft of a charge compressor in an internal combustion engine relative to a compressor housing.
2. Description of the Related Art
Particular attention has to be paid in regard to the special operating conditions when sealing the drive shaft of e.g. an. turbine-driven centrifugal or screw compressor or a turbocompressor driven by an exhaust gas loaded turbine. For instance the drive shafts of such compressors generally have a very small diameter, e.g. less than 40 mm. These shafts rotate at very high speeds of e.g. 10
5
min
−1
and more. Further the seal may be subjected to pressures above as well as below atmospheric pressure conditions prevailing in the housings of such compressors. Moreover the gaseous medium to be sealed, which is generally air, must be kept free of non-gaseous constituents such as oil particles. Oil particles may be contained in a portion of the compressor located externally of the compressor housing for accomodating roller bearings or the like for supporting the shaft, relative to which portion the interior of the compressor has to be sealed. In view of the critical operating conditions, labyrinth seals have long been preferred for such applications although labyrinth seals have the inherent disadvantage of a relatively high leakage. A face seal assembly has not yet been take into consideration as alternative to labyrinth seals for such applications despite of the much lower leakage of face seals. It has been found that the seal rings of prior face seal assemblies because of a dry running became so hot that a premature break-down of the seal occurred. Similar results were obtained with prior face seal assemblies when these were subjected to negative pressure conditions and the operating speeds significantly reduced.
An object of the invention is to provide an improved face seal assembly. Another object of the invention is to provide a face seal assembly having minimum danger of dry running and a reduced leakage under operating pressures above as well as below atmospheric pressure conditions. Still another object of the invention is to provide a face seal assembly suitable for sealing the shafts of turbo compressors having a small diameter.
SUMMARY OF THE INVENTION
A face seal assembly in accordance with the present invention includes a pair of co-operating seal rings of which one is provided for mounting on a rotary component and the other on a stationary component. The seal rings have substantially radially aligned seal faces, during operation a seal gap is provided therebetween for sealing a zone peripherally outward of the seal faces relative to a zone peripherally inward thereof. A plurality of peripherally spaced recesses effective for pumping a gas is provided in at least one of said seal faces, said recesses extending from one periphery of the seal face towards the other periphery thereof, but the ends of said recesses being radially spaced from, the latter. On the said one seal face comprising said recesses a surface area ratio F
GFA
/F
G
is provided, which is in a range between 0.35 and 0.65, preferably 0.4 and 0.6, wherein F
GFA
=the total surface area of the recesses when seen as a projection onto the seal face, and F
G
=the total surface area of the seal face.
In particular, the invention envisages that the number of recesses effective for pumping a gas (hereinafter also gas recesses) present in the seal face of one of the seal rings is such that the surface area occupied by these gas recesses occupies approximately 35 to 65% of the total surface area of the seal face. In contrast to conventional face seal assemblies, this means a very large number of gas recesses provided in the seal face. Moreover the portions of the seal face free of gas recesses are reduced to a minimum. Thus, the ratio of the radial dimension of a recesses-free dam portion relative to the radial dimensions of the seal face may be only approximately 0.2 to 0.3, whereas the dam portion in conventional face seal assemblies occupies a substantially greater part of the seal face. As a consequence of the present invention it is ensured that a stable gas cushion is formed between the co-operating seal faces in every operational state, etc., even when the face seal assembly is subjected to a low pressure by the medium (air) to be sealed. Furthermore, in accordance with a preferred embodiment of the invention, a load ratio k, defined as the ratio of an effective surface area of the face seal assembly hydraulically loaded by the pressure of the medium to be sealed to the total surface area of the seal face, should lie in a range between 0.5 and 1.2. The load ratio k should be in the lower part of the range for low pressure conditions and in the upper part for overpressure conditions. Moreover, in order to ensure that any non-gaseous constituents included in the gases do not enter into a space which is to be sealed, from the outer environment, it is preferred that the gas recesses originate at the inner periphery of the seal face. This causes a leakage current to always flow from this space in a direction towards the outer environment and not vice versa. It also prevents non-gaseous constituents from getting between the seal faces which could lead to operational disturbances of the face seal assembly. The entry of non-gaseous constituents into the face seal assembly can be reduced still further by a means for retaining non-gaseous constituents, which is disposed upstream of the side of the face seal assembly remote from the medium to be sealed.
For a more complete understanding of the invention and the objects thereof, reference should be made to the accompanying drawing and the following detailed description wherein a preferred embodiment of the invention is illustrated and described.
REFERENCES:
patent: 5071141 (1991-12-01), Lai et al.
patent: 5531458 (1996-07-01), Sedy
patent: 6213472 (2001-04-01), Bondarenko et al.
Feigl Peter
Plewnia Bernd
Feodor Burgmann Dichtungswerke GmbH & Co.
Sandy Robert J.
Schwing Karlena D.
LandOfFree
Face seal assembly does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Face seal assembly, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Face seal assembly will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2580927