Seal for a joint or juncture – Seal between relatively movable parts – Relatively rotatable radially extending sealing face member
Patent
1991-01-04
1992-10-20
Cuchlinski, Jr., William A.
Seal for a joint or juncture
Seal between relatively movable parts
Relatively rotatable radially extending sealing face member
277169, 277177, 277206A, 277208, F16J 1516
Patent
active
051564106
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a combination seal for sealing between closely opposing surfaces of two machine elements, one of which has an open groove facing the other machine element, said groove having preferably a rectangular cross section, said seal comprising an expansion ring of an elastomeric material and designed to be positioned against the bottom of said groove, an intermediate sealing ring of a viscous-elastic synthetic material engaged by the expansion ring and shaped with a sealing surface for contact with the other machine element, and an outer ring of an elastomeric material and fitted into a separate groove on the sealing surface of the intermediate ring.
Such seals are known from the DK published patent specification No. 146050 and are especially used as piston seals or rod seals between mating cylindrical surfaces of two mutually mobile machine elements, e.g. a hydraulic cylinder and its working piston or a solid end wall of a cylinder and a piston rod piercing it. They are effective to provide efficient sealing for fluids as well as gases within a wide pressure range, e.g. for pressure differences varying from 0 to 500 bar. The intermediate ring that is biased by the elastomeric expansion ring may consist of polytetrafluoroethylene or of some other highly temperature-resistant synthetic material with a high elasticity modulus and low friction, provides an efficient dynamic sealing at relatively big pressure differences, whereas the elastomeric outer ring at the sealing surface of the intermediate ring assures an effective sealing even at minor pressure differences between the two sides of the seal.
The object of the invention is to widen the range of application of seals of the said type and provide an improvement of the known combination seal suitable in particular for gaseous fluids, e.g. to be applied in gas accumulators and heavily loaded shock absorbers.
In such cases, where combination seals of the said type often have to separate liquid and gas, it has proved difficult to get a sufficiently effective seal for both media. This is mainly due to the fact that during a working stroke a thin liquid film may pass from the high pressure side onto the outer ring fitted into the sealing surface of the intermediate ring. When subjected to heavy loads the prior art seals have not always been able to cause this liquid film to flow back during the return stroke. This can lead to a build-up of a liquid pressure depending on the working speed and may lead to a mechanical deformation of the sealing ring, whereby the outer ring is subjected to a damage risk through socalled "ribbling", i.e. cutting of material from the ring which under dynamic conditions performs pulsating movements. Thereby the sealing efficiency of the outer ring is impaired, and especially at high relative movements the sealing between the two machine elements may become deficient. This will often entail a need to supplement the known seal with additional seals specifically designed to counteract this drawback.
The invention solves this problem by means of a double acting combination seal, characterised in that the intermediate ring is designed with relatively sharp corners between the sealing surface and its end faces the parts of the sealing surface between each of said corners and said separate groove forming conical faces converging against the groove at a narrow slit angle.
With this design the seal an optimum pressure distribution over the sealing surface is obtained with a very narrow, nearly linear contact face and thus a maximum contact pressure at said corners which thus function as a kind of scraper edges.
At the same time the narrow slit angle entails for both of the said conical faces that a fluid film which during a working stroke may flow as a leakage flow to the outer ring is returned to the high pressure side during the return stroke, essentially in the same manner as it is known per se from DK patent No. 143667. Thereby one achieves an efficient hydrodynamic relief of the outer ring, ensuring that it is not even
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"Seals and Sealing Handbook": by R. H. Warring, pp. 220, 221, Gulf Publ. Co., priority date Jul. 1, 1986.
Abstract entitled "Pump or compressor piston seal--has radial thrust rings of material with lower expansion coeffficient than self-lubricating seal rings", 1987 Derwent Publications Ltd.
Edlund Roy
Hom Jorgen
Busak+Luyken GmbH & Co.
Cuchlinski Jr. William A.
Cummings Scott W.
W.S. Shamban Europa A/S (W.S. Shamban & Company A/S)
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