Patent Publication Number: US-6668851-B2

Title: Fool-proof plug in fluid system

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to plugs, and more particularly relates to plugs for selectively plugging one of two different flow passages. 
     BACKGROUND OF THE INVENTION 
     Although there may be other applications of the present invention, the present invention is particularly useful in oil pump applications for oil burner units. Oil burner units have in the past been provided with regulating valves interposed between the nozzles or nozzle which discharge fuel into the combustion chamber and the fuel pump which supplies fuel oil to the nozzles. Generally, these regulating valves open upon delivery of a predetermined supply pressure from the pump, regulate a substantially constant pressure flow to the burner nozzles, and shut off the supply of fuel oil to the nozzles when the pump is turned off upon shut down. In addition to regulating the pressure of fuel oil delivered to the burner nozzles, these valves have a bypass function of diverting an excess portion of the fuel oil pressurized and delivered by the pump back to the tank or pump reservoir so that only a portion of the fuel oil supplied by the pump is delivered to the nozzles. Oil pump units having a regulator valve for use with oil burner units are well known in the industry, and are generally disclosed in U.S. Pat. No. 5,692,680 to Harwath, U.S. Pat. No. 5,145,328 to Harwath, U.S. Pat. No. 3,566,901 to Swedberg, and pending U.S. patent application Ser. No. 10/017,153 to Mitchell, et al., the entire disclosures of which are hereby incorporated by reference. 
     Whether bypassed fuel is recirculated to the fuel tank or the local tank reservoir depends upon how the pump is set up. In either event, the oil pump units have two port openings, including a first port opening to allow for return to the local pump reservoir and a second port opening to allow for return to tank. In practice, the service technician or installing mechanic will typically plug one of the port openings to provide the desired flow path. To allow for selective installation, oil pump units are often sold with two different plugs, one to fit each different port opening. On occasion, service technicians or installing mechanics will make the mistake of installing both plugs at the same time which in turn can cause significant problems such as increasing upstream oil pressure and pump seal blowouts. 
     BRIEF SUMMARY OF THE INVENTION 
     To overcome the problems existing in the art, the present invention is directed toward a plug for plugging a first port and blocking insertion of a second plug into a second port of a fluid system. The plug includes a threaded plug portion and a blocking stem portion extending from the threaded plug portion. The stem portion extends sufficiently from the threaded plug portion such that when the plug is mounted in the first port, the stem portion projects into the second port and blocks insertion or mounting of a second plug and thereby keeps the second port unplugged. 
     According to one aspect of the present invention, the plug is mounted into the return port of a oil pump unit for an oil burner to block return flow to the local reservoir of the pump (when bypassed flow is recirculated to the fuel storage tank). This prevents two plugs from being inadvertently mounted into the pump and blocking all return flow. The plug thus prevents excess upstream pressure build up and blown seals caused by improper installation of two plugs. 
    
    
     Other objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention, and together with the description serve to explain the principles of the invention. In the drawings: 
     FIG. 1 is cross sectional view of a plug installed in a fluid system according to a preferred embodiment of the present invention, in which the plug blocks one port and prevents installation of a second plug into a second port. 
     FIG. 2 is a similar cross section to FIG. 1, but illustrates how the plug of the preferred embodiment allows for installation of a conduit into the unplugged port over the blocking stem portion of the plug. 
     FIGS. 3 and 4 are schematic drawings of the plug shown in FIG. 1 incorporated in an oil pump unit according to two alternative hydraulic circuit arrangements. 
     FIGS. 5 and 6 are side and end views of the plug illustrated in FIG.  1 . 
     While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     For purposes of reference, a preferred embodiment of the present invention has been depicted as a fool-proof plug  10  arranged in a fluid circuit shown herein as an oil burner circuit or pump circuit  12  in FIGS. 3 and 4. It will be understood that the plug  10  is particularly useful in the illustrated environment of the pump circuit  12 . However, it will also be understood that the plug may be used in other applications or environments and certain broader claims appended hereto are meant to include-such alternative applications or environments. 
     Other than the aspects relating to the plug  10 , the pump circuit  12  is conventional and includes a pump  14  for pumping fuel oil from a storage tank  16  to one or more nozzles  18  arranged in a combustion chamber  20  of an oil burner. Typically, the pump  14  has a local reservoir  22  that receives fuel through an inlet conduit  24  connected to the main storage tank  16 . The pump also includes a fuel regulator  26  that is adapted to regulate flow of fuel oil from the pump  14  to the combustion chamber  20 . The fuel regulator  26  recirculates or bypasses excess fuel flow delivered by the pump  14  through a bypass conduit  28 . Typically, the bypass conduit  28  passes through a lubrication chamber  30  where the fuel oil can lubricate the rotating shaft  32  that drives the pump  14 . The lubrication chamber  30  is sealed typically through a wiper seal  34 . Further details of exemplary oil pumps and pump circuits can be had with reference to U.S. Patents and patent application referenced above. 
     The bypass conduit  28  can recirculate and return fuel oil either to the main storage tank  16  or to the local pump reservoir  22  through two different ports  36 ,  38 . The smaller diameter port  36  is connected to a pump return passage  40  extending through the pump housing to the local pump reservoir  22 . The larger port  38  can be connected through a tank return conduit  42  to the main fuel storage tank  16 . In practice, one of the ports  36 ,  38  is plugged while the other remains unplugged to provide for return flow to either the storage tank  16  or alternatively to the local pump reservoir  22  as shown in FIGS. 3 and 4, respectively. As shown in FIGS. 1-4, the ports  36 ,  38  are coaxially aligned in spaced relation. 
     In accordance with the present invention, the plug  10  of the disclosed embodiment ensures that only one of the ports  36 ,  38  are closed. The plug  10  includes a threaded plug portion  44  and a stem portion  46 . In the illustrated embodiment, the plug portion  44  threads into the threaded opening  48  of the smaller diameter port  46 . The plug portion  44  plugs the smaller diameter port  36  leading to the pump return passage  40 . The stem portion  44  also blocks insertion or mounting of a second plug  52  into the larger diameter port  38 . 
     The stem portion  44  is of a small enough diameter or width so as not to block the larger diameter port  38 . When the pump circuit shown in FIG. 3 is selected, a pipe fitting  54  is threaded into the threaded opening  56  of the larger diameter port  38  to establish the tank return conduit  42 . Although the pipe fitting  54  surrounds the plug stem portion  44 , the inner diameter of the pipe fitting  54  is sufficiently large and the outer diameter or width of the stem portion  44  is sufficiently small that an annular gap  58  between the stem portion  44  and the pipe fitting  54  exists to provide for return oil flow through the larger diameter port  38  and return conduit  42  leading to the storage tank  16 . 
     The stem portion  44  of the plug  10  also may provide a tool engaging surface that can be engaged to a torquing tool (e.g. a screwdriver, allen wrench or hex wrench/socket). In the disclosed embodiment the tool engaging surface is an outer hexagonal surface  60  on the stem portion  44 . The hexagonal surface  60  provides a means for receiving a tool to facilitate rotation and mounting of the plug  10  into the smaller diameter port  36 . 
     Preferably, the threads  50  of the plug  10  (and the corresponding threads of the threaded opening  48 ) are of non standard threads (e.g. a {fraction (1/16)}-27 (PTF−⅞) thread characteristic) such that a mechanic will have a very difficult time finding a substitute off-the-shelf replacement plug to fit the hole. This better ensures that only the fool-proof plug  10  is used. 
     Although the disclosed embodiment has been illustrated as a plug  10  for plugging the smaller diameter port  36  and blocking insertion of the second plug  52  into the larger port  38 , it will be understood that an embodiment may also be a plug for the larger port  38  that includes a stem projecting into and block the smaller port  36 . With this type of an embodiment, the tool engaging surface (e.g. a hex socket for receiving an allen wrench or screw driver slot) would be on the plug portion rather than the extending stem portion. 
     All of the references cited herein, including patents, patent applications, and publications, are hereby incorporated in their entireties by reference. 
     The foregoing description of various embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Numerous modifications or variations are possible in light of the above teachings. The embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.