SELF-COMPENSATING SEAL

Abstract: A self-compensating seal (10) has a substantially toroidally shaped seal body (12) and a plurality of axially separated annular wipers (14,16, 18) extending radially inwardly from the inner rim of the seal body in parallel arrangement. When a shaft or rod (36) (see Fig. 5) having a diameter greater than the inside diameter of the seal opening is inserted through the central seal opening, the wipers (14,16, 18) are bent or collapsed so as to extend in an axial direction. Each of the wipers (14, 16, 18) is radially inwardly biased by an O-ring (32, 34) so that wear at the sealing surfaces of the wipers caused by shaft movement is compensated for.

Description: The present invention relates to a seal for use in machines and mechanical devices having rotating or longitudinally reciprocating shafts. More particularly, the present invention relates to a mechanical seal which is used for sealing rotating or longitudinally reciprocating shafts and which is self-compensating for wear at the sealing surface of the seal. In many machines and mechanical devices having rotating or reciprocating shafts, mechanical seals or packings are required in order to prevent leakage past the rotating or reciprocating shafts. Such seals are often required internally in machines in order to prevent the mixing of two separated liquids and/or gases where the moving shaft communicates between both. Also, in the case where machinery has input and/or output shafts and a lubricant or other hydraulic material is utilized within the machine, a seal to prevent leakage of such material is required. As can be appreciated, the rotary or reciprocating movement of a shaft with respect to a seal or packing will cause the contacting surfaces of the seal or packing to wear. Eventually this wear becomes great enough that the seal no longer functions for its intended purpose and leakage past the seal occurs. Seal wear is a particularly acute problem in pumps which are utilized for pumping relatively abrasive liquid materials under high pressure, such as hydraulic paint pumps. Such pumps are utilized in the painting industry for pumping paint to a very high pressure so that the paint may be hydraulically atomized by means of a spray gun and thus deposited on the surface to be painted. For sealing the operating shafts of such pumps, whether a seal is required internally or externally to prevent leakage past the piston or its shaft, the usual chevron-type packings are utilized. Such a packing consists of a serially arranged plurality of profiled washer-like elements formed of plastic which are compressed together longitudinally so that the internal diameter of the packing compresses against the pump shaft or piston. Such multi-packings are used for the purpose of giving the seal a long footprint along the shaft so as to ensure against fluid finding its way between the packing and the shaft. In utilizing such chevron-type packings, extreme care must be exercised in the installation of the packing in the machine or pump with respect to the initial tightening thereof. Over tightening of the packing can result in excessive wear of the shaft and excessive consumption of power in moving the shaft. Insufficient tightening can result in leakage past the seal and eventual destruction of the seal. In the case where such packings are used externally, it is often possible to adjust or compensate for the resulting wear manually by tightening the gland nut which further compresses the internal diameter of the packing against the shaft. Obviously, such an adjustment of a packing or seal cannot be effected in the case where the seal is located internally within the pump or machine. In the latter case, it is necessary to completely dismantle the machine and rebuild the same with new packings and seals. As a leak initially occurs with such packings, particles of material pass the first of the series of plastic washers and, because of the fluid pressure in the case of a pump, these particles are eventually pushed past all of the sealing washers resulting in destruction of the seal. Another problem that the use of such packings internally can lead to is that when the seal leaks, which may not be realized because of its internal location, damage to the pump rod or piston may result before the problem becomes evident. Seals and particularly packings as described above, are formed of plastic material such as Teflon or polyethylene. Such materials tend to cold flow or set so that in the case of packings made therefrom, the grip on the shaft or piston is eventually relaxed with time, thus allowing leakage past the seal. In the case of a paint pump as described above where the paint is abrasive, this leakage can very quickly destroy the seal. DE-A-1 750 427 describes a self-compensating seal to be installed to effect a fluid tight seal between a shaft and a guide therefor by sealing against a surface to be sealed, said seal comprising: a) a toroidally shaped seal body; and b) a plurality of annular wipers extending in parallel substantially radially from said seal body, said annular wipers being spatially separated from one another in the axial direction and when the seal is installed to seal between the shaft and the guide, the annular wipers are partially collapsed against the surface to be sealed to extend in one axial direction. US-A-4,356,865 describes a pump plug for use in well operations, the pump plug having features substantially in accordance with the precharacterising portion of claim 1 appended hereto. It is a primary object of the present invention to provide an improved mechanical seal for use with rotating or reciprocating shafts or pistons of machines wherein the sealing properties of the seal are not diminished due to wear at the sealing surface thereof. This object, as well as others which will hereinafter become apparent, is accomplished in accordance with the present invention by the provision of a seal for sealing between a reciprocating or rotating shaft and guide therefor, as set forth in claim 1 appended hereto. Thus, the seal is in the form of a substantially unitary structure having a substantially toroidally shaped seal body and a plurality of annular wipers extending radially inwardly from the seal body in parallel arrangement and which are spatially separated in the axial direction. The annular wipers are given an initial slant or bend in an axial direction and the shaft to be sealed, which has a diameter slightly greater than the inside diameter of the seal, is inserted through the annular opening of the seal in this same axial direction causing the wipers to bend or collapse further in the same axial direction. Biasing means are associated with each wiper which cause the wiper to be pushed against the moving shaft and, as wear occurs at the wiper surfaces in contact with the moving shaft, the wiper is pushed by the bias acting thereon against the shaft so that this wear is compensated for automatically. According to another embodiment of the present invention, the annular wipers extend radially outwardly from the toroidally shaped seal body rather than inwardly. Such a seal can be utilized as a ring seal as on a reciprocating piston and functions essentially in the same way as the mechanical seal described above. Some ways of carrying out the present invention will now be described in detail by way of example with reference to drawings which show two specific embodiments of the present invention. In the drawings :- FIGURE 1 is a perspective view of a self-compensating seal according to the present invention; FIGURE 2 is a perspective view of the seal of FIGURE 1 having a portion thereof broken away; FIGURE 3 is a diametric cross-sectional view of the seal of FIGURE 1 with the biasing elements thereof removed; FIGURE 4 is a diametric cross-section of the seal similar to FIGURE 3 showing the biasing elements in place; FIGURE 5 is a diametric cross-sectional view of a portion of a seal according to the present invention shown in co-operation with a moving shaft; and FIGURE 6 is a diametric cross-sectional view of another embodiment of a self-compensating seal according to the present invention in co-operation with a piston and cylinder. Now turning to the drawings, there is shown in FIGURES 1 to 4 a self-compensating seal according to the present invention, generally designated 10, which is formed of a plastic material such as Teflon or high molecular weight polyethylene. Seal 10 is basically comprised of a substantially toroidally shaped outer seal body 12 whose inner rim or hub is provided with a plurality of substantially radially, inwardly directed annular wipers, designated 14, 16 and 18 which are parallel with one another and which define a central seal opening 20. Toroidally shaped outer seal body 12 has substantially parallel side faces 22 and 24 and an annular outer surface 26. Side faces 22 and 24 terminate radially inwardly at the inner rim of seal body 12. Although any number of inwardly directed annular wipers may be provided, at least two such wipers are required in order for the seal to function and it has been found that three are preferred. As clearly seen in FIGURE 3, each of the annular wipers 14, 16 and 18 is spatially separated from one another in the longitudinal or axial direction so that annular grooves 28 and 30 are defined between pairs of annular wipers 14, 16 and 16, 18, respectively. As clearly seen in FIGURES 2 and 4, O-rings formed of resilient material such as rubber and designated 32 and 34 are received in annular grooves 28 and 30, respectively. Annular wipers 14, 16 and 18 are bent or slanted in an axial direction so that the O-rings are thus, in effect, enclosed and restrained within the respective grooves because of the partial overlapping thereof by the slanted or bent annular wipers. As clearly seen in FIGURE 5, when seal 10 is used in conjunction with a reciprocating or rotating shaft, designated 36, the seal is positioned in annular groove 38 in the apparatus housing or guide 40 with shaft 36 passing through the central opening 20 of the seal. The purpose of seal 10 is to prevent leakage between guide 40 and shaft 36. Shaft 36 has a diameter slightly greater than the diameter of central opening 20 of seal 10, so that wipers 14, 16 and 18 are further bent or collapsed radially and a pre-squeeze is thereby put on the shaft at the surface 37 thereof to be sealed so as to initially prevent fluid leakage. Seal 10 is so arranged on shaft 36 that the axial direction of the slant of wipers 14, 16 and 18 is in the direction of the high pressure side of shaft 36. Seal 10 is tightened by tightening means 42, such as a gland nut or similar device, which clamps against side faces 22 and 24 of seal body 12 to establish static seals at side faces 22 and 24. This design eliminates operator error in installing the seal since an accurate tightening of the seal is unnecessary. The operator simply fully tightens tightening means 42 thereby clamping seal body 12. A back up, designated 44, is provided for annular wipers 14, 16 and 18 on the low pressure side of seal 10 and may be formed as part of tightening means 42. Back up 44 fits with a close tolerance annularly around shaft 36 and prevents the wipers from inverting their axial slant. Assuming that seal 10 of FIGURE 5 is utilized in a pump for pumping fluid under high pressure, then the space 46 on the lower side of seal 10 contains the high pressure fluid. The outer edge of the annular wiper exposed to the high pressure fluid, wiper 14 in FIGURE 5, at 48, is bevelled as clearly seen in FIGURES 3 and 4. Thus, the pressure in space 46 exerted on bevel 48 of wiper 14 is directed radially to thereby increase the wiper pressure on shaft 36 enhancing the seal thereat. Also, as the sealing surface of annular wiper 14 wears, the pressure exerted thereon by the high pressure fluid maintains wiper 14 in effective sealing contact with shaft 36. If after a prolonged period of operation of the machine, some pressurized material gets by the first wiper 14 and enters into the space or cavity between wipers 14 and 16, the pressure exerted by this material acts upon annular wiper 16 to further increase the pressure exerted by wiper 16 on shaft 36. When seal 10 is installed as in FIGURE 5, the wipers are further bent or partially collapsed so that wipers 16 and 18 are wrapped around resilient O-rings 32 and 34 to compress the resilient material of the O-rings and effect a radially inwardly directed bias on annular wipers 16 and 18. This biasing action on wipers 16 and 18 increases the sealing pressure exerted by the wipers on shaft 36 and, as the sealing surfaces of the wipers become worn, the biasing action of the O-rings continues to force the sealing surfaces of the wipers against shaft 36 so as to compensate for this wear. In FIGURE 6, another embodiment of the seal of FIGURES 1 to 5 is shown wherein the seal, designated 110, is in the form of a ring seal utilized as a seal on a reciprocating piston 136 which is adapted to reciprocate within cylinder wall 140. As can be seen, annular wipers 114, 116 and 118, rather than being inwardly directed from seal body 112, are outwardly directed toward cylinder wall 140. Seal 110 is so positioned that wipers 114, 116 and 118 are directed, because of their inclination as well as their collapsed situation, toward the area of high compression 146 of piston 136. Thus, seal 110 operates substantially in an identical manner to that described in connection with seal 10 of FIGURES 1 to 5. The O-rings 132 and 136 bias the collapsed wipers 116 and 118 outwardly so that the wear at the sealing surfaces of the wipers is compensated for. The high pressure of the material being pumped by piston 136 acts on bevel 148 of annular wiper 114 to increase the pressure of the wiper against cylinder wall 140 in a manner identical to the operation of the pressure in space 40 on wiper 16 of seal 10 as described in connection with FIGURE 5.

Claims: A self-compensating seal (10;110) to be installed to effect a fluid tight seal between a reciprocating or rotating shaft (36;136) and a guide (40;140) therefor by sealing against a surface (37;140) to be sealed, said seal comprising: a) a seal body (12;112); b) a plurality of annular wipers (14,16,18;114,116,118) extending in parallel substantially radially from said seal body (12;112), said annular wipers being spatially separated from one another in the axial direction so as to define a groove or grooves (28,30) between a pair or pairs of annular wipers and when the seal is installed to seal between the shaft (36;136) and the guide (40;140), the annular wipers are partially collapsed against the surface (37;140) to be sealed to extend in the axial direction of higher fluid pressure; c) biasing means (32,34;132,134) disposed in the groove or grooves for biasing said partially collapsed annular wipers (14,16,18;114,116,118) radially against said surface (37;140) to be sealed; characterised in that the seal body (12;112) is toroidally shaped and in that the annular wiper (14;114) adjacent the high fluid pressure is bevelled so that in the collapsed state the pressure exerted on said annular wiper (14;114) by the high fluid pressure is radially directed to force said annular wiper against the surface to be sealed. The self-compensating seal (10;110) as defined in claim 1, wherein said parallel annular wipers (14,16,18;114,116,118), when the seal is not installed, are initially inclined in the same axial direction that the axial wipers extend when the seal is in the installed position and said wipers are partially collapsed against the surface (37;140) to be sealed. The self-compensating seal (10;110) as defined in claim 1 or 2, wherein said biasing means includes an O-ring (32,34;132,134) formed of resilient material disposed in each said groove (28,30) between pairs of annular wipers, when said annular wipers are partially collapsed in the installed condition of the seal, the annular wipers associated with O-rings (32,34;132,134) wrap around the associated O-ring to compress the resilient material thereof so that a radial bias is effected thereby on said associated annular wipers. The self-compensating seal (10) as defined in claim 1 wherein said shaft guide is provided with an internal annular groove (38) in which said seal body (12) is axially clamped, and said annular wipers (14,16,18) extend substantially radially inwardly from said seal body (12). The self-compensating seal (110) as defined in claim 1 wherein said shaft (136) is provided with an annular groove (144) in which said seal body (112) is axially clamped, and said annular wipers (114,116,118) extend substantially radially outwardly from said seal body (112). The self-compensating seal (110) as defined in claim 5 wherein said shaft is a piston (136) and said guide (140) is a cylinder. The self-compensating seal (10:110) as defined in any preceding claim wherein said seal body (12;112) and said plurality of annular wipers (14,16,18;114,116,118) are formed of plastic or Teflon or high molecular weight polyethylene. The self-compensating seal as defined in any preceding claim wherein three of said parallel annular wipers (14,16,18;114,116,118) are provided.

Inventors: GEBERTH, JOHN DANIEL, JR.
Applicants: GEBERTH, JOHN DANIEL, JR.
Application year: 1987
Main classification: F16J15
IPC codes: F16J15