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CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not Applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     This invention relates to hydrants attached to municipal water systems, and in particular to a device for simplifying the flushing of portions of water systems by hydrants attached in the system. 
     The need for periodically flushing portions of water systems, particularly dead-ends in the systems, has been recognized for many years, as shown for example in Lazenby III, U.S. Pat. No. 4,756,479. A summary of many of the problems requiring such flushing, as well as of the traditional solutions to those problems, is contained in my co-owned U.S. Pat. No. 5,201,338. More recently, such flushing operations have been automated, as described in McCarty, U.S. Pat. No. 5,921,270. The McCarty patent is owned by a company related to the assignee of the present invention. A similar approach is described in Newman, U.S. Pat. Nos. 6,035,704 and 6,358,408. Other approaches are shown in Poirer, U.S. Pat. No. 6,062,259, and Esmailzadeh, U.S. Pat. No. 6,467,498. 
     Although the prior art systems have met with some success, the complexity of the systems, the time and effort required to install and use them, and their consequent expense have limited their use. 
     BRIEF SUMMARY OF THE INVENTION 
     Briefly stated, the present invention provides a device and method for automatically flushing hydrants. The device is installed externally to an existing hydrant. The device comprises a nipple having an internally threaded collar for attaching the device to a hydrant outlet, a valve, and a control for automatically operating the valve. Preferably, the device includes a lockable box containing at least the valve, the box having an outlet for allowing water from the hydrant to pass from the valve to the exterior of the box. The box functions as an enclosure and may be of any desired configuration. 
     In accordance with an embodiment of the invention, the collar is rotatably mounted to the nipple externally of the box. In accordance with an embodiment of the invention, the control is mounted internally of the box. In an embodiment of the invention, the box includes a perforate lower wall through which water escapes. In other embodiments, a hose or pipe extends through a wall of the box to expel water; in some of those embodiments, the hose or pipe is connected to the valve in a closed system. The device is preferably supplied with a carrying handle for ease of transport and attachment to a hydrant. 
     Although the system of the present invention is not freeze-proof, it has been found that contrary to conventional wisdom, this is not a serious drawback. In many geographic areas, having particular problems with stagnant water, freezing is not generally a problem. Moreover, in temperate climates, the most severe problems with stagnant water generally occur in warm seasons. Further, because the device of the present invention is easily removable and portable, it can be brought to a site requiring its use on short notice and when temperature conditions are mild enough not to interfere with its use. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     In the accompanying drawings which form part of the specification: 
     FIG. 1 is a somewhat diagrammatic view in side elevation, showing a device of the present invention attached to a hydrant and flushing a water system through the hydrant. 
     FIG. 2 is a view in perspective of the device of FIG. 1, with a door of a box of the device opened to show the interior of the device. 
     FIG. 3 is a longitudinal cross-section of the device of FIGS. 1 and 2. 
     FIG. 4 is a view corresponding to FIG. 1, showing a discharge hose attached to the device. 
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several figures of the drawings. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following detailed description illustrates the invention by way of example and not by way of limitation. The description clearly enables one skilled in the art to make and use the invention, describes several embodiments, adaptations, variations, alternatives, and uses of the invention, including what is presently believed to be the best mode of carrying out the invention. 
     As shown in FIG. 1, an illustrative embodiment of the invention includes an automatic flushing device  1  attached to one outlet of a hydrant  10 . 
     The hydrant  10  is illustratively a so-called dry barrel hydrant, having a valve  11  below ground, generally below the local frost line, connecting the hydrant to a municipal water distribution system indicated generally at  12 . The valve  11  is self-draining, so that, when it is closed, water drains from the cast body  13  of the hydrant  10 . The valve  11  is opened and closed manually by attaching a wrench to a pentagonal head  15  extending from the top of the hydrant  10 . When the valve  11  is opened, the hydrant  10  fills with water. Three externally threaded outlets  16   a-c  threaded into the vertical wall  17  of the hydrant  10  are capped with caps  19   a-c  (the cap  19   a  being removed and not shown). The caps  19   a-c  are individually manually removable, using a wrench. The outlets, illustratively and conventionally, include two 2.5″ NST outlets  16   a  and  16   c  and one 4″ NST outlet  16   b . This construction is typical of a conventional fire hydrant, described for example in Ellis et al., U.S. Pat. Nos. 3,980,096 and 4,154,259. 
     The illustrative device  1  of the present invention is designed to be mounted to one of the 2.5″ NST outlets of the hydrant  1 . 
     The device  1  includes a box  21  made of sheet aluminum and having a rear wall  23 , sides  25 , a front door  26  hinged to one of the sides  25 , a top  27 , and a bottom  29 . The front door  26  is supplied with a keyed lock  31  to hold the door shut by engaging an angle  32  welded to the sidewall. 
     As shown in FIG. 3, at the upper portion of the rear wall  23 , two identical flanges  33  and  34  are bolted to the inside and outside of the wall, respectively, by bolts, not shown, extending through openings in the rear wall  23  and connecting the flanges  33  and  34 . The outside flange  33  supports a 2.5″ NST×2″ male iron pipe swivel  35 . The swivel  35  includes a lugged collar  37  designed to form a water-tight fit when threaded onto a 2.5″ NST externally threaded outlet of the hydrant  10 . This type of coupling is well known in the art and is described, for example, in Porter, U.S. Pat. No. 6,227,463. 
     Inside the box  21 , the flange  34  forms a fluid connection between the swivel  35  and a pipe  38  having external 2″ iron pipe threads. The pipe  38  is connected by a tee  39  to an inlet of an electrically-operated valve  41 . The valve  41  is illustratively a 2″ Model P-220 plastic irrigation valve sold by The Toro Company. The valve  41  is a diaphragm valve in which line pressure exerted over the diaphragm holds the valve closed, and opening of a bleed port by a solenoid relieves pressure in the diaphragm chamber and causes the valve to open. The construction of the P-220 valve is described in Toro Form No 490-2991 (October 1999) incorporated by reference herein. The construction and operation of such valves are well known in the art and are described for example in Hunter et al., U.S. Pat. No. 5,996,608 and Scott, U.S. Pat. No. 5,979,482. The valve  41  is oriented with its inlet  43  up and its outlet  45  directed down. The valve  41  is manually adjustable to permit flow rates from a trickle to in excess of two-hundred-fifty gallons per minute. 
     The solenoid plunger  46  of valve  41  is controlled by a Toro Remote 1000 Series battery-operated valve controller  47 . The controller  47  is described in Toro Form No. 490-3008 (May 2000). The controller  47  includes a housing having a socket sized to fit over the casing  48  of plunger  46 . Within the housing, the socket is surrounded by a coil connected to a battery and programmable circuitry for activating the coil to operate the solenoid. The Remote 1000 Series controller is described in U.S. Pat. No. 5,797,417, issued to DeLattre et al. As set out in this patent, the illustrative control is a removable, bistable, programmable actuator for a solenoid. The controller  47  is battery powered and includes manually operable buttons for setting the operating cycle to twice per day, once per day, once per two days, and once per week, for setting the run time from six seconds to almost twenty-four hours, and for setting the beginning of the run time for zero hours, four hours, eight hours, or twelve hours after programming is completed. The controller  47  may be removed from the valve  41  for programming. 
     The lower wall  29  of the box  21  is formed with 0.5″ perforations  51  to diffuse water emanating from the outlet  45  of the valve  41  inside the box  21 . A cut-out  53  directly under the outlet  45  permits installation of a diffuser plate  55 , or alternatively of a pipe nipple extending from the outlet  45  through the lower wall  29 , as shown in FIG.  4 . When used, the nipple  57  is preferably threaded to receive a hose  59  or diffuser to distribute water expelled through the device  1  to a desired remote location. 
     The upper wall  27  of the box  21  is provided with a strap handle  61  for carrying the device  1  and for positioning it while installing it on a hydrant. 
     The device  1  is assembled by threading the swivel  35  into the external flange  33 , threading the tee  39  into the inlet of the valve  41 , threading the internal flange  33  onto the inlet end of the tee  39 , applying gaskets to the flanges  33 , and bolting the flanges  33  together through the rear wall  23  of the box as indicated at  62  in FIG.  4 . This assembly method allows the box to be nearly the same width and depth as the valve  41 . The controller  47  may be pre-installed on the valve  41  or not as desired. Because the controller may be programmed before it is installed on the valve, it is frequently more convenient to program one or more controllers at a central location, for later installation on devices  1 . 
     The free end of the tee  39  is provided with a sampling bibb  63  for periodically manually taking samples of water to be tested. A ball valve shut-off  65  protects the bibb from leaking. 
     The use of the device  1  is simple. The device  1  is carried to a hydrant  10 , and the cap of a 2.5″ NST outlet of the hydrant is manually removed. The device  1  is then held in position with the handle  61  while the collar  37  is threaded onto the outlet. The device  1  is thereafter held above the ground by the swivel  35  and flange  33 . The controller  47  is programmed to a desired start and stop time, and to a desired cycle time. The door  26  is unlocked and opened, the controller  47  is placed on the electrically controlled valve, and the door is closed and locked. The pentagonal head  15  of the manual valve  11  is turned to open the valve  11 . The device  1  will thereafter open the valve  41  at a desired time for a desired interval in accordance with a desired cycle (twice daily, daily, bi-daily, or weekly) to flush the system. If desired, a chain may be passed through chain holes  67  and locked around the hydrant  10 . 
     When the device  1  has done its job, or when it is needed at another location, the hydrant  10  is manually closed by closing the manual valve  11 , the device  1  is unthreaded from the hydrant  10 , the cap is replaced on the hydrant, and the device  1  is moved to another location. When prolonged freezing temperatures are expected, the hydrant  10  is shut off (and drains automatically) and the device  1  is removed until weather conditions permit its reuse. 
     As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. 
     Merely by way of illustration, because the device operates substantially independent of the construction of the hydrant (other than requiring an outlet to which it can be attached), the device may be installed to hydrants other than the illustrative dry barrel fire hydrant  10 . For example it can be attached to a flushing hydrant such as the one described in Lazenby III, U.S. Pat. No. 4,756,479, or else to a wet barrel type of hydrant. It is presently being sold by The Kupferle Foundry Company with its Model 77 flushing hydrant. The swivel  35  may be externally threaded, for example if the external outlet  16  is removed from the hydrant body. 
     A feed chemical such as dechlorination tablets may be placed in the water path, as for example by placing them on the bottom wall  29  of the box. 
     Whether the flushed water is diffused through the perforated lower wall  29  or is carried away by a pipe or hose  59 , various types of splash guards or other water control devices may be utilized, including for example those shown in DiLoreto, U.S. Pat. No. 6,056,211 or Grimes, U.S. Pat. No. 6,116,525. Flushed water may also be routed to a sewer line, drain field, or storm drain. 
     Instead of a T, a street L may connect the valve  41  to the swivel  35 , if a sampling valve is not required. 
     The swivel  35  may be a tamper-proof design, or the swivel  35  may be positioned inside the box  21  if a separate support in the box is provided for the valve  41 , although this may make attachment of the device to a hydrant less convenient. Numerous tamperproof designs such as the one shown in Sigelakis, U.S. Pat. No. 5,549,133 are well known and may be utilized. When the device is used in circumstances where security is not a problem, the box  21  may be eliminated. 
     Other valves and other controls may be utilized, although the preferred solenoid valve and control are particularly simple. As set out in DeLattre et al, U.S. Pat. No. 5,797,417, the control may be powered in various ways, such as a rechargeable battery charged by solar or wind power, and may be controlled in various ways such as infra-red, telephone, or radio communication, either one-directional or bi-directional. As also set out in that patent, condition sensors rather than a timer may be used for controlling the operation of the device; it is therefore to be understood that the “periodic” operation of the valve need not occur on a strict timetable. More complex controls may also be used, as for example those described in Waltzer et al., U.S. Pat. No. 4,799,142, Kendall, U.S. Pat. No. 4,189,776, and Kendall et al., U.S. Pat. No. 4,165,532. 
     These variations are merely illustrative. 
     All of the patents and printed publications mentioned herein are incorporated herein by reference.

Summary:
A device and method for automatically flushing hydrants. The device is installed externally to an existing hydrant. The device comprises a nipple having an internally threaded collar for attaching the device to a hydrant outlet, a valve, a control for automatically operating the valve, and a lockable box containing at least the valve, the box having an outlet for allowing water from the hydrant to pass from the valve to the exterior of the box. The box functions as an enclosure and may be of any desired configuration.