Seal for a joint or juncture – Seal between relatively movable parts – Circumferential contact seal for other than piston
Reexamination Certificate
2002-06-05
2004-08-17
Pickard, Alison K. (Department: 3676)
Seal for a joint or juncture
Seal between relatively movable parts
Circumferential contact seal for other than piston
C277S578000, C277S582000
Reexamination Certificate
active
06776419
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to sealing means for pumps and the like, and more specifically to a high pressure seal for use in reciprocating pumps and the like. The present seal has an external conical shape which conforms to a mating internal conically shaped seal retainer, with the assembly installed about the piston or plunger of a high pressure pump. The present seal is formed of a hard polyimide plastic material (e.g., Vespel®), which provides considerably greater durability than conventional softer seal material and also stabilizes the piston or plunger to increase efficiency and reduce wear.
2. Description of the Related Art
Reciprocating pumps are commonly used to provide high pressure liquid flow in various devices, such as car washes, pressure washers, etc. The plungers generally have a relatively small diameter and are adapted to provide quite high pressure. Yet, conventional practice has been to use seals formed of relatively soft materials in such pumps, in order for the seal material to “flow” and conform as liquid pressure distorts the seal and forces it against the stationary and moving surfaces of the pump.
Such conventional seals may be in the form of O-rings, cup seals, etc., but their common characteristic is their relative pliability and lack of resistance to wear and to internal forces within the pump assembly. This results in relatively short seal life, and also allows some limited lateral movement of the piston or plunger within its bore. The other than reciprocating motion results in lower efficiency and increased wear and vibration of the pump assembly in comparison to the ideal. Moreover, the relatively soft seals require replacement at relatively frequent intervals, with seal replacement obviously resulting in some down time for the pump and corresponding lost revenue for the operator.
The present invention provides a solution to the above problem of relatively soft seals in high pressure reciprocating pumps, by providing a seal formed of a hard plastic compound, e.g., Vespel® Vespel is a trademark of the DuPont Company); other suitable materials may be used. The present seal has a conical external face mating closely with an internal conical surface formed in a high pressure seal retainer which surrounds the plunger. A conventional O-ring is provided between the two conical faces to seal the two mating and relatively stationary seal surfaces. As the hard plastic seal wears against the plunger, the system operating pressure forces it downwardly into the mating internal conical retainer. While the material used is quite hard, it nonetheless has sufficient “flow” to be forced inwardly by the conical shape of the seal retainer, to fit closely about the plunger and provide a good seal about the sides of the plunger for the duration of the lifetime of the pump assembly.
A discussion of the related art of which the present inventor is aware, and its differences and distinctions from the present invention, is provided below.
U.S. Pat. No. 1,412,251 issued on Apr. 11, 1922 to Lewis C. Marshall, titled “Piston Packing,” describes mating conically faced piston rings for use in an internal combustion engine. Such rings are conventionally formed of cast iron and are relatively inflexible, in comparison to the hard plastic material of which the present seal is formed. As a result, Marshall requires that the rings have a split across their thicknesses, i.e., that they be circumferentially discontinuous, unlike the present seal. Moreover, the construction of the Marshall rings is essentially opposite that of the present seal, as Marshall grooves the piston to provide a seat for his rings. In contrast, the present seal is relatively stationary, and is secured by a retainer which is in turn secured immovably within the pump housing.
U.S. Pat. No. 1,698,546 issued on Jan. 8, 1929 to Loran L. Hoffman, titled “Piston Ring,” describes a ring constructions wherein the rings have mating conical faces. The Hoffman ring construction more closely resembles the ring construction of the Marshall '251 U.S. patent discussed immediately above, than it does the present invention, due to the rings being installed within grooves in the moving piston, rather than being retained immovably in the housing or cylinder. Moreover, the Hoffman rings are each formed of a series of segments, rather than comprising a single, unbroken toroidal shape, as in the present seal invention.
U.S. Pat. No. 1,838,669 issued on Dec. 29, 1931 to Edward J. Goodyear, titled “Piston Ring,” describes a piston ring set in which the rings have mating internal and external conical faces, much like the ring set of the Marshall '251 U.S. patent discussed further above. However, the bevel angle of the conical faces of the Goodyear rings extends inwardly in the direction away from the crown of the piston, rather than outwardly away from the crown, as in the case of Marshall. Otherwise, the same points of difference noted in the discussion of the Marshall '251 U.S. patent, are noted here as well, i.e., the relatively brittle nature of the cast iron used in conventional piston rings and the need to provide splits across the thicknesses of the rings, and the fact that the rings move relative to the cylinder bore rather than comprising a seal affixed within the bore or housing, as in the present invention.
U.S. Pat. No. 1,860,025 issued on May 24, 1932 to Francis R. Good, titled “Piston Ring,” describes a ring set for use in internal combustion engines as well as other motors, pumps, etc. No specific material is described, but the application of the Good ring set to internal combustion engines indicates that conventional cast iron is used. In fact, Good provides split ring construction, with a specially configured joint in the mating ends of each ring. Good also provides a mating conical face for the top ring, with the conical surface facing inwardly and away from the piston crown. However, the mating face has a spherical shape, contacting the upper ring only along a relatively narrow circumferential line.
U.S. Pat. No. 1,877,413 issued on Sep. 13, 1932 to Lewis C. Marshall, titled “Piston Packing For Internal Combustion Engines,” describes a series of ring embodiments, some of which include at least one tapered (i.e., conical) face. Each of the rings of the Marshall '413 U.S. patent is discontinuous and includes a split across its width or thickness, in order to allow for spread during installation about the larger diameter portion of the piston before seating in the ring groove. In contrast, the present seal forms a continuous toroidal ring, as it does not have to be distended to fit about the wider portion of a piston to seat within a ring groove, as in the case of the Marshall and other rings discussed to this point.
U.S. Pat. No. 2,080,579 issued on May 18, 1937 to Thomas Schaub, titled “Piston Ring,” describes a ring construction which closely resembles that disclosed in the Hoffman '546 U.S. patent discussed further above. Schaub discloses different embodiments of split type piston rings, with the difference between embodiments being that in one case the conical taper is oriented inwardly and upwardly toward the crown of the piston, and in the other case the taper is oriented inwardly and away from the piston crown. Schaub is silent regarding the material of which is rings are made, so it must be assumed that they are formed of a conventional and relatively brittle cast iron material, which cannot flow to fit the cylinder bore to accommodate wear. In contrast, the present seal is unbroken and is formed of a hard plastic which can flow to a certain extent to accommodate wear.
U.S. Pat. No. 2,081,040 issued on May 18, 1937 to Walter E. King, titled “Packing,” describes a series of embodiments of seals, each having a concave pressure face with bifurcated lips which are distended due to pressure to bear against the walls of the piston and cylinder. This type of seal is commonly known as a “cup” seal, due to its cross sectional s
Litman Richard C.
Patel Vismal
Pickard Alison K.
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