Abstract:
Disclosed herein is a bulkhead fitting. The bulkhead fitting includes biasing means and a plurality of guide rings. In a preferred embodiment, a first guide ring is provided with an annular sidewall and a base extending radially outward from the sidewall, and a second guide ring is configured to mate with the first guide ring. Biasing means is positioned between the guide rings and radially outward of the sidewall to allow expansion and contraction of the first and second guide rings relative to one another, while preventing or inhibiting the biasing means from catching in the threads of the shaft or otherwise contacting the shaft.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a bulkhead fitting. More specifically, the invention relates to apparatus providing a substantially constant compression. 
     BACKGROUND OF THE INVENTION 
     Bulkhead fittings are a particular type of fitting used to create a sealed, mechanical connection through a wall, typically of a tank, or other fluid-containing vessel. The threaded versions of these fittings may include a body, a gasket, and a nut. Flange-type bulkhead fittings are also commercially available. Bulkhead fittings are typically constructed from metals and thermoplastics. The prior art includes U.S. Pat. No. 5,551,590, for example, which discloses a non-metallic pressure vessel fitting. 
     Tanks, especially those manufactured from thermoplastics, react mechanically to thermal changes due to temperature changes in the surrounding atmosphere, changes in temperature of the fluid contained in the tank, and changes due to solar heating. Additionally, tanks react mechanically to changes in internal pressure and changes in static head pressure of the fluid contained in the tank. These mechanical reactions can be generally described as (a) an expansion, or increase, in the tank dimensions due to increases in temperature and/or pressure, and (b) contraction, or a decrease, in tank dimensions due to decreases in temperature and/or pressure. Expansion of the tank dimensions results in a reduction of the wall thickness of the vessel, while contraction of the tank dimensions results in an increase of the wall thickness of the vessel. 
     As thermoplastic tank dimensions change, especially wall thickness, the initial compression imparted on the gasket may be affected. In particular as the tank expands, reducing wall thickness, a subsequent reduction in the initial compression imparted on the gasket may result in loosening of the fitting with the potential for a leak forming around the gasket. Further, as gasket compression is reduced by the continuous cycles of expansion and contraction, the load initially imparted between the threads of the nut and the threads of the body may be reduced. This may also result in the loosening of the fitting and the formation of potential leaks around the gasket. 
     Further, if the bulkhead fitting is manufactured from thermoplastic materials, the bulkhead fitting is subject to the same expansion and contraction changes that are imparted on the tank. Thus, the bulkhead fitting will be expanding at the same time the wall of the tank is getting thinner, exacerbating the decrease in the initial compression imparted on the gasket. If the fitting is manufactured from a thermoplastic material that has a coefficient of thermal expansion and contraction substantially different from the tank material, dimensional changes due to thermal or pressure changes may result in a further decrease in the initial compression imparted on the gasket. Additionally, the thermal expansion of the piping system attached to the bulkhead fitting can be of concern. 
     Also, if a bulkhead fitting is exposed to constant and excessive vibration, independent of, or combined with, physical changes in the tank due to thermal, or pressure changes, the bulkhead fitting may become loose, especially the nut portion of the bulkhead fitting. What is needed in the art is a bulkhead fitting that maintains a substantially constant pressure or constant compression on the gasket, in multiple conditions of use. 
     SUMMARY OF THE INVENTION 
     Preferred embodiments of the invention overcome these and/or other disadvantages and shortcomings of the prior art by providing an improved bulkhead fitting such that the bulkhead fitting provides a substantially constant compression. The bulkhead fitting comprises a body with a threaded shaft that extends through a tank wall and has a cavity to allow for fluid flow through the tank wall. The bulkhead fitting further comprises a gasket, a nut, a biasing means and a plurality of guide rings, each configured to allow the threaded shaft to extend therethrough. The plurality of guide rings can include a first guide ring with a sidewall adjacent the threads of the shaft and a base extending radially outward from the sidewall. The plurality of guide rings can include a second guide ring configured to mate with the first guide ring. A biasing means, which is preferably positionable between the first and second guide rings and radially outward of the sidewall, allows the first and second guide rings to expand and contract relative to one another, while preventing or inhibiting “catching” or “snagging” of the biasing means on the shaft threads. 
     In accordance with a first preferred embodiment of the invention, the first guide ring has a substantially U-shaped half cross-section, and the second guide ring has a substantially T-shaped half cross-section. In accordance with a second preferred embodiment of the invention, the first guide ring has a substantially L-shaped half cross-section, and the second guide ring has a substantially rectangularly-shaped half cross-section. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, reference is made to the following detailed description of exemplary embodiments considered in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a front exploded perspective view showing a bulkhead fitting constructed in accordance with a first exemplary embodiment of the present invention, the bulkhead fitting including a lower guide ring with a half cross-section having a U-shape and an upper guide ring with a half cross-section having a T-shape; 
         FIG. 2  is a rear exploded perspective view showing the bulkhead fitting of  FIG. 1 ; 
         FIG. 3  is an assembly view showing the bulkhead fitting of  FIGS. 1 and 2 ; 
         FIG. 4A  is a cross-sectional view of the bulkhead fitting of  FIGS. 1-3  taken along section line  4 A- 4 A of  FIG. 3  and shown in combination with a tank, the fitting being shown in a relaxed state; 
         FIG. 4B  is the cross-sectional view of  FIG. 4A  with the fitting being shown in a compressed state; and 
         FIG. 5  is a cross-sectional view showing a bulkhead fitting constructed in accordance with a second exemplary embodiment of the present invention, the bulkhead fitting being including a lower guide ring with a half cross-section having an L-shape, and an upper guide ring with a half cross-section having a rectangular shape. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIGS. 1-4B , a bulkhead fitting  10  constructed in accordance with an exemplary embodiment of the present invention is shown to include a body  12 , a compression gasket  14 , a first guide ring  16 , a biasing means  18 , a second guide ring  20 , and a nut  22 . Each of the body  12 , the compression gasket  14 , the guide rings  16 ,  20 , the biasing means  18 , and the nut  22  shall be described below. 
     The body  12  comprises a flange  24  and a threaded shaft  26  extending therefrom. The threaded shaft  26  defines therethrough a central axially extending passage  28  for the outflow of fluid from a tank  30 . The compression gasket  14  is substantially annular with a central opening sized to receive the threaded shaft  26 . In preferred embodiments, the compression gasket  14  may be an elastomer gasket. 
     Regarding the guide rings  16 ,  20 , the first guide ring  16  is substantially annular in shape and sized to receive the threaded shaft  26  therethrough. The first guide ring  16  includes an annular base  32  and at least one sidewall  34 . The sidewall  34  is positioned at an inner radius of the annular base  32 , such that, when assembled, sidewall  34  extends substantially concentric with the threaded shaft  26 . Thus the first sidewall  34  acts as inner guide for biasing means  18  to prevent or inhibit the biasing means  18  from moving inwards towards the threaded shaft  26  of the body  12 . In preferred embodiments, such is the case, even when the bulkhead fitting is positioned substantially or at least partially horizontal with respect to ground. The first guide ring  16  can further include an outer sidewall  36  proximal an outer radius of the annular base  32  and concentric with the sidewall  34  and threaded shaft  26 . In this regard, the first guide ring  16  can be said to have a U-shaped half cross-section. An annular gap  38  is formed between the first guide ring  16  and the gasket  14  for receiving the tank  30 . 
     Biasing means  18  is preferably substantially annular and sized to receive the threaded shaft  26  therethrough. Biasing means  18  can include a wave spring or belleville washer, for example. The biasing means  18  is preferably formed of metal and is more preferably formed of stainless steel. While  FIGS. 1-5  depict an “open” wave spring as the biasing means  18 , it should be noted that the wave spring  18  can be provided as a “full” ring style. Regardless of shape or material of construction, the biasing means  18  is preferably configured to contract and expand into compressed and relaxed states, respectively. 
     The second guide ring  20  is preferably substantially annular, sized to receive the threaded shaft  26  and configured to mate with first guide ring  16  while the biasing means  18  is positioned therebetween. The second guide ring  20  can have a base  40  and a sidewall  42  extending radially therefrom, such that the second guide ring  20  can be said to include a half cross-section having a T-shape. In view of the sidewall  42 , the second guide ring  20  and the first guide ring  16  cooperate to be spaced apart a distance (1) in which said biasing means  18  is positioned, and (2) which defines a maximum compression of the biasing means  18  (e.g., a minimum length of the biasing means  18  in a compressed state thereof). 
     The nut  22  is substantially annular and configured to threadably engage the threaded shaft  26  of the body  12 . The body  12 , the first and second guide rings  16 ,  20 , and the nut  22  are preferably manufactured from thermoplastic materials, such as polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC), natural polypropylene, etc, but could also be manufactured from metal materials. 
     Referring to  FIGS. 4A and 4B , methods of using the bulkhead fitting  10  shall be discussed with further detail. The inclusion of the biasing means  18  in the bulkhead fitting  10  acts to maintain a substantially constant compression on the compression gasket  14  and the nut  22 . It is contemplated that the bulkhead fitting  10  will primarily be assembled to a predefined dimension based on the interaction of the first guide ring  16  and second guide rings  20 , which will result in a predefined biasing means  18  compression that is independent of the geometry of the tank, or vessel, to which it is assembled. This configuration also allows the user the option of adjusting, e.g., reducing or increasing, the amount of biasing means  18  compression, if desired, by loosening the nut  22  of the bulkhead fitting  10 . Retention of compression in compression gasket  14  inhibits leakage around the compression gasket  14 , through the hole in the tank  30 . Maintaining a load on the nut  22  via the compressive load transferred through the second guide ring  20  results in continuous engagement of the threaded shaft  26  of the body  12  by nut  22 , preventing unwanted loosening of nut  22 . 
     Continuing with references to  FIGS. 4A and 4B , the biasing means  18 , such as a wave spring or belleville washer, for example, can be flattened during installation.  FIG. 4B  depicts a compressed state of the biasing means  18  of the bulkhead fitting  10  and  FIG. 4A  depicts a relaxed state. By flattening the biasing means  18 , it is at a heightened level of stored energy, and in a position to “activate” when the conditions of initial compression on compression gasket  14 , or initial preload on the nut  22  change, especially in states of expansion within the system. For example, in a condition of increasing system temperature, resulting in an expansion of the tank dimensions and related decrease in the wall thickness of the tank, the biasing means  18  would “extend” from its flattened condition imparting reactive loads on the first guide ring  16  and second guide ring  20 . The compressive load imparted on the second guide ring  20  would be transferred as a tensile load via the nut  22 , through the body  12 , which would result in a substantially constant compression on the compression gasket  14 . At the same time, the compressive load imparted on the first guide ring  16  serves to keep the first guide ring  16  anchored against the tank  30 . It is contemplated that a plurality of wave springs and belleville washers can be stacked to influence, e.g., increase, spring rate. 
     To install the bulkhead fitting  10 , a mechanic or other user attaches the compression gasket  14  over the threaded shaft  26  of body  12  and adjacent to the flanged end  24  of body  12 . This sub-assembly can be placed through a hole in the wall  30 , such that the compression gasket  14  and the flanged end  24  of the body  12  remain inside the tank  30 , with the substantially cylindrical, threaded shaft  26  of the body  12  extending through the hole in the tank  30 . The first guide ring  16  is positioned about the threaded shaft  26  of body  12 , and is positioned against the tank  30 . The biasing means  18 , is positioned adjacent the first guide ring  16  so as to be radially outward of the sidewall  34  thereof. The second guide ring  20  is positioned adjacent the biasing means  18 . The nut  22  is threaded onto the threaded shaft  26  of the body  10 , and is tightened, for example, until the biasing means  18  is flattened. 
     It is preferable for the biasing means  18  to be radially outward of thesidewall  34  so as to inhibit “snagging” or “catching” of the biasing means  18  on the threaded shaft  26 . For example, as a wave spring is compressed (or expanded), the spring is prevented or inhibited from entering the grooves created by the threaded shaft  26 . The geometry of the “T” and “U” shaped half cross-sections (and the geometries of  FIG. 5  discussed below), for example, are shaped so that the inner annular leg, e.g., sidewall  34 , acts as an inner guide for the biasing means  18  and prevents or inhibits same from moving inward to the threaded shaft  26  of the body  12 , where it might catch or snag. Furthermore, in the case of the “T”-shaped half cross-section, the fitting  10  further provides an outside guide for the biasing means  18 . 
     Preferred embodiments of the present invention are further advantageous in that compression of the biasing means  18  might occur within that distance by which the first and second guide rings  16 ,  20  are spaced apart by the sidewall  34  (thereby inhibiting over-compression). Furthermore, such minimum distance is preferably “fixed” and repeatable to define a maximum compression of the biasing means  18  independent of the dimensions of the tank  30  with which the fitting  10  may be assembled. Moreover, preferred embodiments of the present invention provide for user-adjustability, e.g., reducing (or increasing) the amount of spring compression, by loosening the nut  22  of the bulkhead fitting  10 . 
     With respect to  FIG. 5 , a bulkhead fitting  110  is shown constructed in accordance with a second embodiment of the present invention. Elements of the bulkhead fitting  110  that are substantially the same as those described above in connection with bulkhead fitting  10  are designated with like reference numerals increased by one hundred. In the embodiment of  FIG. 5 , a first guide ring  116  has an “L”-shaped half cross-section and a second guide ring  120  has a rectangularly-shaped half cross-section. The second guide ring  120  is configured to mate with the first guide ring  116  while a biasing means  118  is positioned therebetween and radially outward of a sidewall of the first guide ring  120 . 
     It will also be understood that the embodiments of the present invention described herein are merely exemplary and that a person skilled in the art may make many variations and modifications without departing from the spirit and the scope of the invention. All such variations and modifications, including those discussed above, are intended to be included within the scope of the invention as defined in the appended claims.