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FIELD OF THE INVENTION 
     The present invention relates to arrangements for securing fire hydrant operating valves. More particularly, the present invention relates to magnetically operated devices for securing fire hydrant operating valves. 
     BACKGROUND OF THE INVENTION 
     Municipal and county water departments are frequently confronted with unauthorized use of fire hydrants by members of the public, who, on occasion, open the valves of the hydrants to obtain water to cool-off on hot days or for the purpose of filling tank trucks with fresh water which is then sold for various purposes, such as filling swimming pools. In cities, open fire hydrants can result in a drop in water pressure to customers and can occasionally endanger a community by reducing the availability of water necessary to fight fires. 
     In attempts to secure fire hydrants from unauthorized use, fire companies have employed locking devices such as the magnetic valve locks of U.S. Pat. Nos. 4,620,428 and 5,596,893. The particular valve lock disclosed in the &#39;428 patent utilizes a magnetic detent, normally disposed in a center post fixed to a hydrant operating nut, to couple the operating nut of the fire hydrant to an outer body in the form of a capped sleeve, which is normally freely rotatable with respect to the hydrant operating nut. The magnetic detent is attracted by a second magnet permanently mounted in a wrench which cooperates with the outer body to rotate the outer body. Upon coupling the outer body to the center post, rotation of the outer body by the wrench rotates the hydrant operating nut to release water from the hydrant. In the &#39;428 patent the center post is attached to the valve operating nut of the hydrant by a pin that passes laterally through both the center post and the hydrant operating nut. Since the pin has a relatively small diameter, persistent vandals have an opportunity to defeat these devices. 
     The &#39;893 patent discloses a center post configured inner sleeve with a polygonal opening for receiving the operating nut of the fire hydrant. Since the particular valve lock of &#39;893 patent is only suitable for use with a valve operating nut of one size and configuration, it is necessary to have a different center post for different sized and configured hydrant operating nuts. In that the center post is a brass casting, considerable expense is involved in maintaining an inventory of center posts that are compatible with most, if not all fire, hydrant operating nuts. This problem becomes acute when replacing old fire hydrants with new fire hydrants that may have different hydrant operating nuts. A frequent response is to dispose of these magnetic valve locks and buy new ones at considerable expense. 
     SUMMARY OF THE INVENTION 
     In view of the aforementioned considerations, a valve operator securing arrangement is provided for fire hydrants having valve stems connected to hydrant operating valves wherein the valve stems have hydrant operating nuts with particular polygonal exterior shapes. Rotation of the valve stems by gripping and rotating the hydrant operating nuts opens and closes the valves. The arrangement includes a device comprising a center post having a first end with a first recess of a selected shape therein, which first recess opens outwardly therefrom. The center post also has a second end defining a first coupling element. At least one insert is disposed non-rotatably within the recess of the center post. The insert has an axial opening therein of a polygonal shape complementing the polygonal exterior shape of the hydrant operating nut for non-rotatably receiving the hydrant operating nut therein, wherein rotation of the center post positively rotates the hydrant operating nut. An outer body is rotationally mounted over and around the center post for rotation with respect to the center post. The outer body includes a second coupling element. A movable magnetizable element is provided which is urged to a first position, decoupling the first and second coupling elements, and is movable to a second position coupling the first and second elements in a non-rotational relationship, wherein rotation of the outer body rotates the center post to rotate the valve stem and operate the valve. Upon employing a wrench with a permanent magnet and mechanically interlocking the wrench with the outer body, the outer body is enabled for rotating the hydrant operating nut when the magnetizable element is moved from the first to the second position. 
     In a further aspect of the invention, the particular polygonal exterior shape of the hydrant operating nut is a pentagon, a square or a hexagon. 
     In a further aspect of the invention, the first recess in the center post has a polygonal shape and the insert has a polygonal exterior shape which compliments the polygonal shape of the recess to lock the insert and center post in a non-rotatable relationship. 
     In a still further aspect of the invention, the insert is slidable into the first recess in an axial direction. 
     In a still further aspect of the invention, the arrangement comprises a system having plurality of inserts each having the same exterior shape as the shape of the first recess and each having an axial opening of a polygonal shape complementing one of the particular polygonal exterior shapes of the hydrant operating nuts. 
     In still a further aspect of the invention, the selected shape of the first recess in the center post and the exterior shape of each insert is pentagonal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various other features and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood when considered in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the several views, and wherein: 
     FIG. 1 is a side view showing a valve operator securing arrangement in accordance with the present invention mounted on a fire hydrant; 
     FIG. 2 is an exploded view of the fire hydrant securing arrangement of FIG. 1 showing the separate components thereof; 
     FIG. 3 is a side elevation showing the components of FIG. 2 assembled; 
     FIG. 4 is a top view of an outer body providing part of the arrangement of FIGS. 1-3; 
     FIG. 5 is an elevation taken along lines  5 — 5  of FIG. 4; 
     FIG. 6 is a side elevation of a mating collar used with the arrangement of FIGS. 1-3; 
     FIG. 7 is a top view of a magnetizable detent used with the arrangement of FIGS. 1 and 2; 
     FIG. 8 is a side view of the matnetizable detent of FIG. 7; 
     FIG. 9 is a side elevation of a center post used with the arrangement of FIGS. 1-3; 
     FIG. 10 is a top view of the center post of FIG. 9; 
     FIG. 11 is a bottom view of the center post of FIG. 9; 
     FIG. 12 is a bottom view of a master pentagon cast in the center post casting of FIGS. 9,  10  and  11 ; 
     FIG. 13 shows an insert having a pentagonal shape, and 
     FIG. 14 shows an insert having a square shape. 
    
    
     DETAILED DESCRIPTION 
     Referring now to FIG. 1 there is shown a fire hydrant securing arrangement  10  configured in accordance with the present invention. The arrangement  10  is mounted on the domed top  12  of a fire hydrant  14  which is in turn connected to a water main  16  by a valve stem  18  that opens and closes a hydrant operating valve  20 . Upon opening the valve  20 , water flows through an outlet  22  for fighting fires and occasionally for other purposes. The fire hydrant securing arrangement  10  is operated by a key wrench  24  which receives and mates with an outer body  26 , which has a cruciform top  28  that is positively engaged within a cruciform recess within the key wrench  24 . The outer body  26  has a lower end  30  which is received through an upper end  32  of a mating collar  34  that abuts the domed top  12  of the hydrant  14 . The only elements of the fire hydrant securing arrangement  10  which are normally visible are the outer body  12  and the mating collar  34 . The key wrench  24  is normally carried on fire trucks and is not available to the general public. Rotation of the outer body  26  can not open the valve  20  unless the key wrench  24  is used to couple the outer body  26  to the valve stem  18 . Without the key wrench  24  being used, the outer body  26  simply spins with respect to the mating collar  34 . 
     Referring now to FIG. 2 where the elements of the fire hydrant security arrangement  10  are separately shown in an exploded view, it is seen that the mating collar  34  covers a hydrant operating nut  40  which is fixed to the valve stem operator  18  that is used to open the valve  20 . Partially within the mating collar  34 , and covered by the outer body  26 , is a center post  42 . The center post  42  is secured by an attachment bolt  44  that passes axially through the center post and is threaded into a threaded bore  45  formed in the hydrant operating nut  40 . The center post  42  has a first end  46  with a polygonal first recess  47  that receives the polygonal nut  40 . A magnetizable detent  50  is received in a top recess in the center post  42  and is slidable in an axial direction with respect to the center post in order to non-rotatably couple the outer body  36  to the center post. 
     After the center post  42  is attached to the hydrant operating nut  40  and the magnetizable detent is placed in the center post, the outer body  26  is coupled to the center post  42  in an axial direction by a sheer ring  52  that is received in an annular groove  56  disposed around the center post  42 . The sheer ring  52  is also received in a groove Within the outer body  26  so as to hold the outer body on the center post  42 . To facilitate coupling the outer body  26  to the center post  42  by using the sheer ring  52 , the sheer ring  52  is radially split so that it can expand and contract in a radial direction. Upon axially pushing the outer body  26  over the center post  42 , the sheer ring  52  is radially pushed into the groove  56  in the center post and expands into the groove  98  (See FIG. 3) in the outer body to rotationally couple the center post to the outer body 
     FIG. 3 shows in more detail elements of the fire hydrant securing arrangement  10  assembled on the dome  12  of the fire hydrant  14 . The separate elements combined in FIG. 3 are shown isolated from one another in FIGS. 4-13. The mating collar  34  (FIG. 6) is placed on the domed top  12  first with a beveled end  60  thereof resting against the domed top. The center post  42  (FIGS. 9-11) is then inserted into the opening  32  through the mating collar  34  with the hydrant operating nut  40  received in the first recess  47  in a first opening  64 , a first end  66  of the center post  42 . The first end  66  of the center post  42  rests on an annular shelf  68  projecting radially inwardly from the mating collar  34 . 
     Disposed within the first opening  64  of the center post  42  is an insert  70  (FIGS. 11-13) which has a polygonal inner surface  74  that has a shape corresponding to the polygonal external surface  76  of the hydrant operating nut  40  so that the center post  42  is non-rotatably coupled with the hydrant operating nut  40 . The insert  70  abuts a shoulder  76  on the center post  42  (see FIG. 9) and is axially slidable in and out of the polygonal opening of the center post  42 . In order to prevent rotation of the insert  70  with respect to the center post  42 , the insert  70  has a polygonal outer surface  78  which complements a polygonal inner surface  80  of the center post  42  defining a polygonal recess  81 . Consequently when the center post  42  is rotated, it is rotationally locked to the hydrant operating nut  40 . 
     The center post  42  has a beveled opening  80  extending axially therethrough which receives the bolt  44  (see also FIG.  9 ). In order to axially fix the center post  42  on the fire hydrant operating nut  40  the threaded hole  45  is tapped through the hydrant operating nut  40  so that the bolt  44  can axially fix the center post  42  on the hydrant operating nut. 
     The magnetic detent  50  (see also FIGS. 7 and 8) is received in a second recess  90  (see also FIG:  10 ) in the top end center post  42  and rests on a rectangular shelf  92  with the top surface  94  of the magnetizable detent being flush with the top surface  96  of the center post  42 . Consequently, when the outer body  26  is mounted on and over the center post  42 , the outer body will be freely rotatable on the center post as long as the magnetizable detent  50  remains in the slot in a first position in which it rests on the shelf  92 . 
     The outer body  26  (FIGS. 4 and 5) is secured over the center post by the split ring  52  which is received in the annular, outwardly facing groove  56  in the center post and an annular inwardly facing groove  98  in the outer body  26 . The split ring  52  is compressed into the slot  56  when a sleeve portion  100  of the outer body  26  is slid over the center post  42 . Upon the groove  98  aligning with the groove  56 , the resilient sheer ring  52  expands radially into the groove  98  thereby axially securing the outer body  26  to the center post  42 . The lower end  102  of the sleeve portion  100  of the outer body  26  extends into the opening  32  and abuts a shelf  104  on the center post  26 . 
     Within a cap portion  106  of the outer body  26  there is a square recess  108  which receives the magnetizable detent  50  when a magnet in the key wrench  24  (FIGS. 1 and 2) attracts the magnetizable detent and pulls the magnetizable detent into the square recess  108 . Since the recesses  108  and  90  are both polygonal in that they are square, the outer body  26  is positively locked to the center post  42  so that when the key wrench  24  locks with the cruciform projection  28  and is rotated, torque is transmitted through to the hydrant operating nut  40  enabling a fireman to open the valve  20  of FIG.  1 . 
     FIGS. 11,  12 ,  13  and  14  disclose embodiments for the structure of the insert  70 , as well as the structure of the first end  66  of the center post  42  (see also FIG.  9 ). The insert  70  has a polygonal or non-round outer surfaces  78 ,  78 ′ and  78 ″, while the center post  42  has a polygonal or non-round inner wall  80 . In the preferred embodiment of FIGS. 11-14, the polygonal inner wall  80  on the center post  42  has five abutting walls and is in the shape of a pentagon. The insert  70  shown in FIG. 11 has a pentagonal outer wall  78 , which complements the illustrated pentagonal inner wall  80  of the center post  42  when the insert is slid into the pentagonal recess  81  defined by the inner wall  80 . In the embodiment of FIG. 11, the recess  70  has a pentagonal inner wall  74  (see also FIG. 9) that defines the first recess  47  that receives the hydrant operating nut  40  (see FIGS.  2  and  3 ). 
     It is emphasized that while the inner wall  80  of the center post  42  is disclosed as pentagonal, the wall may have any other polygonal shape. For example, the wall  80  may be square or hexagonal. Pentagonal is the preferred shape of the wall  80  because it provides a thickness for the first end  66  of the center post  42  which is sufficient to withstand assaults by vandals who may attack the securing arrangement  10  with heavy implements such as sledge hammers. 
     In FIG. 13 the recess  47 ′ of the insert  70 ′ is pentagonal, but relatively small, for example about 1 ⅛ inch, whereas the pentagonal recess  47  in FIG. 11 is relatively large, for example about 1 and {fraction (11/16)} inch. In FIG. 14 the opening  47 ″ in the insert  70 ″ is square in order to mate with a square fire hydrant operating nut  40 . The square recess  47 ″ may relatively large, having sides which are about 1 ¼ inch. However, the square recess  47 ″ of FIG. 14 can be of any dimension, as long as it is not larger than the external area defined by the insert  70 ″. In still other embodiments the recess  47  can be a hexagon of any size necessary to complement a hexagonal hydrant operating nut  40 . For large hexagonal operating nuts (for example, nuts having a diameter of about 1 {fraction (13/16)}), the opening  81  of FIG. 12 can be reconfigured as a hexagon and the center post  42  used without an insert  70 . 
     From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing form the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.

Summary:
A fire hydrant securing arrangement utilizes a magnetic detent to couple an outer body to a center post so that when a wrench with a permanent magnet is mated with the outer body, the magnetic detent connects the outer body to the center post. The center post has an end with a polygonal recess which complements the shape of the hydrant operating nut. The recess is within an insert that has a polygonal periphery engaged by a polygonal inner wall of the center post. The insert is interchangeable with other inserts having recesses of different sizes and configurations so that the securing arrangement is readily acceptable to fire hydrants having different operating nuts of different sizes.