Rod Seal

a. Field of Invention

This invention relates to gland type means for sealing between an apertured body and a moving or movable rod passing therethrough, e.g. a piston rod extending through an aperture in the end of a pump or an engine cylinder. Typically the aperture and rod have cylindrical surfaces.

B. Discussion of the Prior Art

Conventional gland type rod seals are subject to overtightening of the seal causing premature failure. This may be due to increased frictional engagement of the packing rings with the rod moving therethrough. Furthermore, conventional gland type rod seals are subject to incorrect adjustment or allow for no initial compression of sealing lips for sealing at low pressures or on worn surfaces. It is an object of the invention to overcome these problems.

The present invention provides a seal between an apertured body and a rod extending through the aperture in which controlled compression of the packing of the seal reduces chances of premature packing failure by eliminating overtightening of the packing during installation. Sufficient compression of the packing is allowed, however, thereby seal lips of the packing will be activated at low fluid pressures.

According to the invention a seal of the above type comprises lip type packing rings made of fabric reinforced elastomer, homogenous elastomer, or other conventional packing material. The rings are provided in their medial portions between their inner and outer peripheral lips with circumferentially disposed thin portions. Each packing ring is disposed between a pair of hard adapter rings made of metal or plastics or other strong material having protuberant portions adapted to engage the thin portions of the packing rings. Space is left between the adapter rings and packing rings and the adjacent rod and box into which space the packing ring material can flow. The packing assembly provided by the rings is loaded by means of a compression ring around the rod over the box. The protuberant portions of the adapter rings are tapered or otherwise shaped so that loading causes mostly axial compression of the thin section and only a small amount of radial expansion and contractions of the packing rings. Initial axial loading of the packing assembly squeezes the thin sections of the packing rings and causes radial flow of the material of the packing rings inwardly toward the rod and outwardly toward the box, activating the lip seals. Further loading tends to make the assembly go solid preventing overtightening, i.e. the thin portions will be so thinned out that even small absolute movements of the compression plate will represent a high percentage of the thickness remaining of the thin sections, requiring a large force to cause the movement. In this latter regard, recall that stress is proportional to the change in thickness divided by the total thickness, so that if the total thickness is smaller, the increase in strain for any given amount of movement will be greater. For that reason after the thin section becomes even thinner, under the initial compression, further compression requires a very large force not likely to be exerted, so that packing ring lips are not overly compressed against the rod.

Although it is only necessary to have a single packing ring, a plurality may be employed. The packing ring lips are directed to seal against the higher pressure on one side of the seal. If there is little pressure differential, the seal will function to prevent fluid flow in either direction, even though the lips may all be directed to seal against high pressure on one side of the seal. Although an adapter ring is desirable both above and below each packing ring, if there are plural packing rings a single adapter ring may serve for both a packing ring thereabove and one therebelow. Although it is preferred to provide concavities on both sides of each packing ring to form the thin section, other configurations are possible. Considering the mouth of the packing box as the top of the box, the compression ring could be combined with the uppermost adapter ring and the bottom of the packing box could be combined with the lowermost packing ring.

Typically the compression ring will be a nut screwed into the packing box, but it could be any other appropriate structure, e.g. an annular plate bolted to the body, e.g. around the mouth of the box and having an annular boss on its lower side bearing against the top adapter ring. Any suitable means for applying force to the compression ring can be employed.

The rod, body, and compression ring usually will be made of metal, e.g. steel, the packing rings of an elastomer, e.g. natural or synthetic rubber, plain or fabric reinforced, and the adapter rings typically will be made of hard plastics material which can be easily molded, although they may also be made of metal. Hardness ranges typically would be 60 to 95 on the Shore A scale for the packing rings, and 50 Durometer on the Shore D scale to R-120 for the adapter rings, if made of plastics. Suitable plastics materials for the adapter rings are filled phenolics and filled nylons.

The uncompressed thickness of the thin section should be in the range of 0.031 to 0.062 inch varying in accordance with the radial and axial thickness of the packing ring as a whole, the thickness of such thin section being in the range of about 15 to 30 percent of that of the adjacent thick sections.

For a further description of a preferred embodiment of the invention reference will now be made to the accompanying to scale drawings wherein:

FIG. 1 is an axial section through a rod seal embodying the invention;

FIG. 1A is a vertical section through one of the packing rings of the FIG. 1 rod seal separate from the seal of the packing assembly;

FIG. 2 is top view of one of the packing rings separate from the packing assembly;

FIG. 3 is a top view of a packing ring for a modified form of packing assembly;

FIGS. 4 and 5 are vertical sections of the modified packing assembly at planes 4--4 and 5--5 of FIG. 3;

FIG. 6 is a bottom view of the adapter ring of the FIG. 4 assembly.

Referring now to FIGS. 1, 1A and 2, there is shown a body 11 having a cylindrical aperture 13 therethrough. A cylindrical rod 15 extends through the aperture in the body. A cylindrical box 17 is concentrically disposed around the rod at one end of aperture 13. The mouth of the box is provided with an internal constant diameter screw thread 19. A compression ring 21 is disposed over the mouth of the box around rod 15. Ring 21 has a boss 23 on its lower side. Boss 23 has an external constant diameter screw thread 25 correlative to thread 19. Preferably compression ring 21 has a radial flange 27 overlying body 11 to keep dirt out of the threads and to provide greater leverage for a wrench applied thereto. As is well known, flange 27 may be hexagonal or of other non-circular configuration to facilitate turning with a wrench.

Within box 17 is a packing means adapted to prevent fluid flow through aperture 13, especially from the lower end of the aperture to the upper and thereof. The packing means includes at the bottom of the box, i.e. the upstream end of the assembly, a thick lower seal ring or washer 29, made of some fairly hard incompressible material such as steel, brass, or plastics. Washer 29 is of constant thickness, and has cylindrical inner and outer peripheries fitting closely around the rod and within the box. Washer 29 effects a preliminary seal in that the fluid flow path therepast is fairly long and narrow, so that there is considerable pressure drop thereacross.

The packing means further includes a packing assembly between washer 29 and compression ring 21. The packing assembly includes packing rings 31, 33 alternating with adapter rings 35, 37, 39.

When positioned in box 17, the packing rings have inner peripheries that are cylindrical and in contact with rod 15 and have outer peripheral surfaces that are cylindrical and in contact with box 17. The inner and outer peripheries of the adapter rings are also cylindrical but are slightly spaced from the rod and box respectively.

The packing rings have downwardly pointing tapering inner and outer annular lips 41, 43 on their lower faces. Between these lips on each packing ring is an annular, rectangular cross-section groove 45 adapted to receive a correlative annular, rectangular cross-section tongue 47 on the upper face of each of the lower two adapter rings. The tongues are higher than the grooves are deep so that lips 41, 43 do not contact annular shoulders 49, 51 adjacent the tongues.

The upper faces of the packing rings are each provided with Acme cross-section (flat bottom, upwardly flaring) annular grooves 53 adapted to receive a correlative annular, Acme cross-section tongue 55 on the lower face of each of the upper two adapter rings. In cross section, the configuration of a tongue 55 received in a groove 53 resembles that of the cross section of an Acme screw thread, an illustration of which will be found at page 994 of Machinery's Handbook, 15th ed. (The Industrial Press, New York 1956). Tongues 55 are of the same height as grooves 53 and the generally flat horizontal upper surfaces of the packing rings adjacent the grooves are in contact with the generally flat lower surfaces of the two upper adapter rings adjacent the tongues. The inner and outer peripheries of the packing rings are beveled at their upper ends at 57, 59 and the bevels are engaged by correlative downwardly pointing, tapered, inner and outer annular, retaining lips 61, 63 on the lower faces of the upper two adapter rings.

From the foregoing description it will be apparent that each packing ring includes a medial web or thin portion 65 which will be compressed between tongues protuberant from the adapter rings above and below the packing ring. In addition, due to the taper of the Acme cross-section tongues above each packing ring, the packing rings will be stretched and contracted radially at their outer and inner portions respectively, when the compression ring is moved farther into the box.

When the compression ring is advanced sufficiently into the box, the thickness of webs 65 is reduced to the point where further compression is difficult. By this time there has been sufficient radial inward and outward movement of packing material to energize inner and outer lips 41, 43 to seal lightly against rod 15 and box 17.

Referring now to FIGS. 3-6, and more particularly to FIG. 4, there is shown a modified form of the packing assembly of the invention in which only a single packing ring 101 is employed and the top of tongue 103 on the lower adapter ring 105 is bevelled on its inner and outer peripheries at 107, 109. Tongue 103 is of greater height than in FIG. 1, having a height about equal to its width in vertical section. Packing ring 101 has a groove 111 whose edges are bevelled at 113, 115 correlative to the top of tongue 103. In the relaxed position of packing ring 101, i.e. when it is not in the seal box, the sides 117, 119 of groove 111 flare downwardly away from tongue 103. This causes these sides to press against the box and rod when initially installed, insuring instant sealing by lips 121, 123.

The principal modification introduced in the FIG. 4 construction is the substitution for grooves 53 of a plurality of conical sockets 125, azimuthally spaced, for example, by 30 degrees, annularly disposed about the top of packing ring 101. This results in a plurality of annularly disposed thin sections 127 spaced 30 degrees apart instead of the single ring shaped thin section 65 in each of the packing rings of FIG. 1. The FIG. 4 construction insures the integrity and strength of the packing rings while maintaining the compression limiting feature.

Adapter ring 129 has a plurality of conically tapered pins 131 on the lower side thereof, mating with sockets 125. Pins 131 take the place of tongues 55 of the FIG. 1 construction and function in a similar manner to effect primarily axial compression of the packing ring upon loading of the compression ring, but achieving sufficient radial flow of the packing ring material to energize lips 121, 123. As in the FIG. 1 embodiment, the top of packing ring 101 is bevelled on its inner and outer peripheries at 133, 135 and upper adapter ring 129 is provided with mating lips 137, 139.

It will be understood that the packing assembly shown in FIG. 4 is to be employed with the box and rod and other elements of the FIG. 1 construction and operated in the same manner.

As the result of a novelty search on the subject invention, the following references were found, same all being United States patents:

The foregoing patents illustrate various uses for the subject rod seal, such as the oil well plunger shown by Roy, the kelly seal shown by Beckman, the pump piston of Wheeler, and the valve stem seals of Gaillard and Dumazet, as well as the general purpose rod or shaft seals illustrated in all of the patents.

With regard to the first group of the above listed Wheeler (U.S. Pat. No. 1,964,237) shows packing rings of unequal density, Wheeler (U.S. Pat. No. 1,991,715) shows single lip packing rings, Roy shows single lip packing rings with mating tongues and groove, Showalter shows compression type packing rings with mating tongues and grooves, and Tucker shows single lip packing rings with a medial groove but no adapter rings.

Referring to the second group of the above listed patents, the Gould, Whittaker et al., Scannell, and Pippert (U.S. Pat. No. 3,915,463), patents each show a packing assembly including a plurality of grooved rubber double lip packing rings, but without any adapter rings therebetween, though Gould uses a filler strip in the grooves of his split packing and in the Whittaker constructions the shole stack of packing rings is sandwiched between upper and lower adapter rings.

None of the above discussed two groups of patents shows a medial thin portion as contemplated by the present invention nor the combination of a medial thin portion with adapter rings in engagement with both the upper and lower faces thereof.

Referring to the third group of the above listed patents, the Beckman, Bryant, and Gaillard patents show packing assemblies including alternating packing rings and compression rings but the packing rings do not incorporate medial portions that are thin.

In the Bryant construction, the packing rings have no thin portions and the adapter rings initially are out of engagement with the medial portions of the packing rings thereabove.

Beckman shows a packing assembly composed of alternating packing rings and metal adapter rings, the latter having inner edges, not medial portions, of reduced thickness. The portions of reduced thickness provide steps to interlock with annular tongues on the inner peripheries of the adapter rings. Only light sealing with the box is possible since the assembly rotates in the box. No lips are used.

The Gaillard patent shows a packing assembly employing alternating resilient packing rings and metal compression rings. The latter are not stated to be adapter rings in the sense of being provided with surfaces that mate with the packing rings. Although the compression rings have convex surfaces which press into the medial portions of the packing ring when the assembly is loaded, it is said that the packing rings are to be "flattended" by 20% during such loading, thereby to render them radially water-tight.

Gaillard also shows that the loading on a valve seal seat can be limited by placing a hard (graphite) washer between an annular tongue and groove on the body flange, but in this case the sealing means is in two pieces, in fact made of two different materials.

Referring to the fourth group of patents listed above the Dumazet and Pippert U.S. Pat. No. 3,248,088 patents relate to packing assemblies with means to limit compression.

The Dumazet patent shows compression limiting metal rings between inner and outer peripheral soft packing rings, whereby the degree of compression of the latter is limited when the metal rings engage. The inner and outer packing rings are not integral so that double the number of packing rings is required compared to the present invention.

Pippert U.S. Pat. No. 3,284,088 discloses a packing assembly including alternate packing rings and adapter rings. The packing rings each include a thin expended metal base having rubber molded thereto forming inner and outer lips with a very thin covering over the medial portion of the base so that the medial portion is substantially unyielding in compression. The adapter below each packing ring is out of contact with the medial portion of the base until the inner and outer lips are radially expanded. In other words, there is no medial compression of the medial section flowing rubber radially outwardly into the lips before axial travel is arrested. The thin section of this Pippert construction requires metal reinforcement to provide enough strength to keep it integral.

Applicant is also aware of U.S. Pat. No. 3,120,960 to Pippert and Heathcott which discloses a double lip packing ring.

In the following claims, the terms upper and lower will be used to indicate different parts of the packing assembly, having reference to the closed or bottom end of the box as being the lower end and the open end of the box as being the upper end, but it will be understood that the seal can be used in any position, e.g. with the "bottom" or closed end of the box uppermost, so that the terms upper and lower are merely relative, e.g. to the box, and not absolute or limiting with respect to the scope of the invention.