Abstract:
The present invention relates to systems for circulating water in a potable water piping network to prevent the stagnation of water in this piping network. Several systems are disclosed wherein partitioned pipes, pumps, partitioned headers, check valves, and scoop inserts are used to keep the water in movement inside the pipes. The present invention comprises several pumping arrangements for circulating water inside fire hydrant laterals and inside the branch pipes along dead-end streets where most of the water stagnation occurs. Although partitioned pipes are used and opposite flows are induced in opposite pipe halves, full pipe flow to each hydrant is maintainable in case of emergency. Inside buildings, the water is kept in movement inside a loop pipe that extends close to each water outlet such that the water is maintained fresh at each outlet.

Description:
FIELD OF THE INVENTION 
     This invention pertains to installations for circulating water in potable water piping systems and more particularly in the fire hydrants and dead ends of a municipal water distribution network. 
     BACKGROUND OF THE INVENTION 
     It is well known that microorganisms and suspended solids in potable water vary widely in composition depending on the source, and form microbial growth and sedimentation on the surfaces of piping and reservoirs wherever the water is contained. It is also well known that the sedimentation and the accumulation of microbial growth in still water promote the proliferation of various bacteria and cause the contamination of the water. 
     Plumbing regulations and plumbing codes are very explicit about preventing cross connections in a piping system and generally, licensed plumbers are apprehensive of these problems. A ‘cross connection’ is defined in plumbing code books as any actual or potential connection between a potable water system and any source of pollution or contamination. 
     It is generally well accepted that stagnant water should always be considered contaminated and non-potable. Further, it is believed that stagnant water is not only found in marshes and ponds, but is also found in water distribution piping systems and reservoirs that do not have sufficient flow to keep the water active, where water remains still for long period of time for example. Although the fact is often neglected, decaying water in a piping system is in direct contact with potable water and represents a cross-connection contamination that is believed to be harmful to the health of users supplied in water by that piping system. 
     Generally, municipal water distribution systems are flushed periodically to discharge stagnant water. It is often the case that the discharged water has a foul odor and filthy discoloration. Despite these periodic flushes, it is believed that the stagnation of water in municipal piping systems is a major cause of bad water taste, buildup of sediments in residential hot water reservoirs, and microbial growth in toilet reservoirs and in the drains of bathroom accessories. It is further believed that stagnant water in a piping system is a source of many persistent illnesses, digestive problems and the beginning of many diseases to those using and drinking water from these systems. 
     Another reason for periodically flushing water distribution systems is to eliminate concentrations of chlorine or other disinfectant used in water supply systems which tend to accumulate at regions of low flow or of stagnation. In addition to being detrimental to a good health, high concentrations of chlorine in particular, are known to change the PH value of the water and to deteriorate the protective coating inside water pipes. The material of fabrication of the pipes, which may contain traces of toxin substances are then exposed to the potable water. 
     The problem of water stagnation is particularly noticeable near water hydrants for example and at the ends of long branches of a piping system where the number of users on a branch pipe is not sufficient for ensuring a proper circulation of water. These situations are often found in newer or partly built subdivisions, and at the end of streets which are supplied in water by oversized pipes. Furthermore, a number of municipalities have water supply systems that were designed according to fire fighting requirements. The size of many branch pipes in these systems is often too large to ensure an adequate circulation of water within the pipe under normal conditions. 
     The problem of stagnant water in potable water distribution systems has been partly addressed in the past, as can be appreciated from the following prior art documents: 
     U.S. Pat. No. 2,445,414 issued on Jul. 20, 1948 to W. F. Zabriskie et al. This document discloses a partitioned riser pipe leading to a hydrant, in which water is circulated upward in one side of the pipe and down in the other side. The partitioned pipe is used to circulate water in the casing of the hydrant to prevent freezing of the water inside the hydrant head. 
     U.S. Pat. No. 3,481,365 issued on Dec. 2, 1969 to A. R. Keen. This patent discloses various partitions in a piping system to divert the water flow near the branch valves in that piping system. The partitions are used to prevent stagnation of water near the branch valves. 
     U.S. Pat. No. 5,476,118 issued on Dec. 19, 1995 to Ikuo Yokoyama. This document discloses the use of a venturi eductor and venturi tube in an active water pipe to draw water from a valve body in a branch pipe connected to this water pipe, to prevent stagnation of water in the valve body. 
     U.S. Pat. No. 6,062,259 issued on May 16, 2000 to Blair J. Poirier; the applicant of the present patent application. This document describes a system for recirculating water in the branches of a municipal water distribution system. The main feature of this invention consists of a pumping system having means to draw water from the far end of a branch pipe relative to the water main and to convey this water into the near end of the branch pipe to circulate the water in the branch pipe. 
     CA 2,193,494 issued on Dec. 07, 1999 to Perry et al. This document discloses a method of cleaning and maintaining potable water distribution pipe system with a heated cleaning solution. The heated cleaning solution is circulated in the piping system to dislodge and flush all accumulated contaminants. 
     Although substantial efforts have been made in the past to propose solutions to prevent the stagnation of water in piping systems, these proposals continue to be treated with uncertainty by water system designers. For this reason basically, it is believed that there continues to be a need for a better solution which is more practicable than the prior art proposals. 
     SUMMARY OF THE INVENTION 
     In the present invention, however, there is provided three potable water circulation systems which are related to each other due to several common features. The potable water circulation systems according to the present invention are relatively easy to build, easy to install and to operate. The water circulation systems according to the present invention are believed to be compatible with the current waterworks design practices and fire prevention requirements of a municipal water distribution system. 
     Broadly, in accordance with one aspect of the present invention, there is provided a potable water circulation system for circulating water in a municipal water distribution network which has a water main and at least one branch pipe extending from the water main. As it is often the case, the branch pipe has a dead end therein at a distance from the water main. The potable water circulation system comprises a conduit system inside the branch pipe, connected to the dead end and to the water main for circulating water from the water main to the dead end and back into the water main. The potable water circulation system also comprises a pump and check valve arrangement connected to the conduit system to cause a minimal circulation of water in the conduit system when a water demand in the branch pipe is lower than the nominal capacity of the pump, and to cause the circulation to reverse when the demand in the branch pipe exceeds the nominal capacity. 
     The major advantage of this circulation system is that the minimal circulation through the dead end of the branch pipe during low demand periods eliminate the risk of water stagnation in this dead end, while allowing full pipe flow in the branch pipe in the case of an emergency when a fire hydrant is opened for example. 
     In accordance with another aspect of the present invention, the conduit system is formed by a partition inside the branch pipe and a return gap in this partition at the dead end. One of the advantages associated with such partitioned pipe of that its installation does not require more excavation work than the installation of a conventional municipal water distribution pipe. 
     In accordance with another aspect of the present invention, there is provided a potable water circulation system for circulating water in a municipal water distribution network comprising a water main and a branch pipe extending from the water main and having a dead end therein at a distance from the water main. The potable water circulation system comprises a first longitudinal partition mounted inside the branch pipe and defining a first and second pipe halves, and a first gap in the first longitudinal partition at the dead end. The potable water circulation system also has a first and second takeoff pipes connected respectively to the first and second pipe halves and separately to the water main. A check valve is mounted in the first takeoff pipe. The check valve has an unchecked side near the water main and a checked side away from the water main. There is also provided a pump having an intake pipe and a discharge pipe connected to the first takeoff pipe, astride the check valve, on the unchecked and checked sides respectively. The pump is operable to cause a circulation of water from the water main, into the first pipe half, through the first gap and back to the water main along the second pipe half, to prevent water stagnation in the dead end. 
     In yet another aspect of the present invention, there is provided a fire hydrant lateral connected to the branch pipe. This fire hydrant lateral has a second longitudinal partition therein defining a third and fourth pipe halves there along. The fire hydrant lateral also has a hydrant base defining an end thereof and a second gap in the second longitudinal partition in the hydrant base. In this aspect of the present invention, the third and fourth pipe halves communicate with the first pipe half and form with the first pipe half and the second gap a serial conduit. 
     In yet a further aspect of the present invention, the fire hydrant lateral connected to the branch pipe comprises a directional/bypass valve to selectively direct a flow of water along the third and fourth pipe halves there through, and divert a flow of water from the third pipe half to the fourth pipe half. 
     In yet another aspect of the present invention, the directional/bypass valve comprises a butterfly valve having an upstream side and a downstream side, and partitioned adapters mounted on the upstream and downstream sides. These adapters have a simple structure manufacturable by conventional metalworking processes or by moulding or casting for examples. This directional/bypass valve is thereby manufacturable with commercially available components and tooling. 
     The potable water circulation systems according to present invention reduces the difficulties and disadvantages of the prior art water circulation proposals, as the circulation systems described herein are compatible with conventional design and installation practices applicable in this field of waterworks. The potable water circulation systems according to the present invention are manufacturable using current technologies, and do not adversely affect the emergency capacity of a municipal water distribution network. 
     Other advantages and novel features of the present invention will become apparent from the following detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Three embodiments of the present invention are illustrated in the accompanying drawings, in which like numerals denote like parts throughout the several views, and in which: 
     FIG. 1 is a cross-section view of a municipal water circulation system according to the first preferred embodiment of the present invention, including a water main, a branch pipe along a dead-end street, a fire hydrant lateral, and a pumping system to circulate water in the dead-end branches and in the base of fire hydrants; 
     FIG. 2 shows a cross-section view of the branch pipe shown in FIG. 1, taken along the line  2 — 2  in FIG. 1, and of all the other partitioned pipes shown in the accompanying drawings; 
     FIG. 3 is an illustration of the partition inside the branch pipe in FIG. 1, as seen when looking inside the end of the branch pipe, substantially along line  3 — 3  in FIG. 1; 
     FIG. 4 is a cross-section view of a municipal water circulation system according to a second preferred embodiment of the present invention, including a water main, a closed-loop subdivision, a number of laterals including three fire hydrant laterals, a dead-end branch pipe, a supply pipe to the sprinkler system of a building, and a pumping system to circulate water in this closed-loop subdivision, laterals and branches; 
     FIG. 5 illustrates a cross-section view of a scoop insert mounted inside the tee fitting shown in the detail circle  5  in FIG. 4; 
     FIG. 6 is a cross-section view of the scoop insert as seen along line  6 — 6  in FIG. 5; 
     FIG. 7 is a cross-section view inside a fire hydrant lateral as seen when looking inside the fire hydrant lateral, substantially along line  7 — 7  in FIG. 1, showing the directional/bypass valve in an open position; 
     FIG. 8 is a cross-section side view of the directional/bypass valve in a closed position; 
     FIG. 9 is a cross-section top view of the directional/bypass valve in a directional mode; 
     FIG. 10 is a cross-section top view of the directional/bypass valve in a bypass mode; 
     FIG. 11 is a symbol of a four-way spool valve indicating an alternate embodiment of the directional/bypass valve; 
     FIG. 12 is a symbol of a four-way ball or barrel valve indicating another alternate embodiment of the directional/bypass valve; 
     FIG. 13 is a diagram of a potable water circulation system according to the third preferred embodiment of the present invention for circulating domestic water in the piping system of a building; 
     FIG. 14 is a valve header used at some of the water outlets in the water circulation system shown in FIG. 14; and 
     FIG. 15 illustrates an alternate embodiment for circulating water in a hydrant lateral extending from a water main such as illustrated in the lower left corner of FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     While this invention is susceptible of embodiments in many different forms, there are illustrated in the drawings and will be described in details herein three specific embodiments of the present invention, with the understanding that the present disclosure is to be considered as an example of the principles of the invention and is not intended to limit the invention to the embodiments illustrated and described. The three embodiments are presented herein to better illustrate various manners of construction, installation and operation of the potable water circulation systems according to the present invention. 
     Referring firstly to FIGS. 1 to  3 , the first preferred embodiment of the present invention applies to the circulation of water inside a long branch pipe  20  of a municipal water distribution system, such as along a secondary street, and in one or more fire hydrant laterals  22  extending from the branch pipe. Most importantly, the branch pipe  20  is a partitioned pipe as illustrated in FIG. 2, having a partition  24  there along dividing the pipe cross-section in two pipe halves  26 ,  28 . The branch pipe  20  can be several hundred feet long and have numerous residential and commercial takeoffs connected there along. These takeoffs have not been illustrated because they do not constitute the focus of the present invention. 
     The illustrations in FIGS. 1 and 4 in particular, represent cross-section plan views of a piping network as seen substantially along a median plane across the pipes such as along plane A—A in FIG.  2 . 
     In the first preferred embodiment, a pair of spaced apart takeoff pipes  30 ,  32  extend from a water main  34  and are joined at a distance from the water main  34  by a crossover pipe  36 . A first tee fitting  38  is mounted in the crossover pipe  36  and has a medial partition  40  extending along the takeoff section thereof and separating the straight section thereof and the crossover pipe  36  in two segments  42 ,  44 , which respectively communicate with one of the pipe halves  26 ,  28  of the branch pipe  20 . 
     A check valve  50  is mounted in the takeoff pipe  30 . A pump  52  is provided to draw water from the water main  34  and to force this water into the branch pipe  20 . The pump has an intake pipe  54  communicating with the takeoff pipe  30  on the unchecked side of the check valve  50  and a discharge pipe  56  communicating with the checked side of the valve  50 . 
     In the embodiment illustrated in FIG. 1, the hydrant lateral  22  extends from a second tee fitting  60  which has a three-way partition  62  therein. The partition  62  joins the longitudinal partitions  24  in the branch pipe  20  to another longitudinal partition  24 ′ in the hydrant lateral  22 . A directional/bypass valve  64  is installed along the hydrant lateral  22 , to selectively isolate the hydrant lateral from the branch pipe  20 . 
     In this first preferred embodiment, the directional/bypass valve  64  is a butterfly valve in which the blade  66 , when opened, constitutes a partition through the valve body to maintain straight the flow of water across the valve and along both pipe halves  26 ′,  28 ′ of the hydrant lateral  22 . 
     The partition  24 ′ in the hydrant lateral  22  does not extend the full depth of the hydrant base  68  such that the water can circulate from one pipe half  26 ′ into the hydrant base  68  and into the other pipe half  28 ′. For this purpose, the partition  24 ′ defines a return gap  70  in the base of the hydrant  68 , as illustrated in FIG.  7 . This return gap  70  has a length ‘B’ and a height corresponding to the diameter of the pipe  22 . The dimension ‘B’ is determined to provide with the diameter of the pipe  22 , an open area inside the hydrant base  68  which is larger than the cross-section area of one of the pipe halves  26 ′,  28 ′. The dimension ‘B’ is also selected to provide this return gap  70  with a low friction coefficient similar to a smooth return bend. 
     It should be noted that the three-way partition  62  in the second tee fitting  60  intersects the first pipe half  26  in the branch pipe  20 . The return gap  70  and the pipe halves  26 ′, 28 ′ form a serial conduit with the first pipe half  26  to circulate water in and out of the hydrant lateral  22 . When the pump  52  operates, a forced circulation of water is established along the pipe halves  26 ,  26 ′, through the hydrant base  68 , and along the other pipe half  28 ′, to prevent the stagnation of water in the hydrant base  68 . 
     A similar return gap  72  having a length ‘C’ and a height corresponding to the diameter of the branch pipe  20  is formed in the end portion  74  of the branch pipe  20 . The return gap  72  is illustrated in FIG.  3 . The dimension ‘C’ of the return gap  72  is also determined to limit pressure losses in the flow of water through this gap. 
     As it will be appreciated, the operation of the pump  52  causes the water to circulate from the water main  34 , into the first takeoff pipe  30 ; along a first pipe half  26  of the branch pipe  20  and the along the first pipe half of the hydrant lateral  22 ; into the hydrant base  68 ; inside the dead end  74  of the branch pipe; and back into the water main  34  through the second takeoff pipe  32 . Gate valves  78  may be provided along the takeoff pipes  30 ,  32  and along the intake and discharge pipes  54 ,  56  of the pump to control the flow of water through these pipes. 
     The capacity of the pump  52  is selected to provide a head which is about 10-12 feet above the highest elevation along the piping system in which the water is circulated, and a preferred flow velocity along each pipe half  26 ,  28  of at least about 0.1 ft/sec. 
     It will be appreciated that when the demand of water is large in the branch pipe  20  such as when a fire hydrant is opened, the water can flow freely through the check valve  50  along the takeoff pipe  30  thereby bypassing the pump  52 . In these circumstances, the flow in the second takeoff pipe  32  is reversed and the flows in both pipe halves  26 ,  28  are oriented toward the point of use to supply this demand surge. Therefore, in high demand periods or in emergency situations, the maximum flow of water along the branch pipe  20  and along the hydrant lateral  22  is substantially the same as the capacity of an unpartitioned pipe, being only reduced by the thickness of the partition  24 . Because of the arrangement of the pump  52  mounted astride the check valve  50 , and of the takeoff pipes  30 , 32 , the force circulation system is present only in low water demand periods when the water is susceptible of stagnation. 
     Referring now to FIG. 4, a second preferred embodiment of the present invention is illustrated therein. In this embodiment, a pump  52  and check valve  50  are mounted along a closed loop pipe  80 , such as around a subdivision in a municipal water distribution system, to cause a circulation along the closed loop pipe  80 . Again, the closed the loop pipe  80  can extend several hundred feet and may have numerous secondary takeoffs there along which have not been illustrated. In some configurations, the closed loop pipe  80  may be formed by the water distribution pipes extending along two parallel streets for example, with a crossover pipe at the far end or at both ends of the streets. 
     The closed loop pipe  80  is connected to a water main  34  by means of two takeoff pipes  82 ,  84  each having a check valve  86  mounted therein. Each of the check valves  50  and  86  has an unchecked side toward the water main  34  and a checked side away from the water main. Water is free to flow from the water main  34  through all three check valves in peak demand periods, as previously explained and as illustrated by the double-headed arrows  88 . In low water demand periods, the pump  52  maintains a minimum flow along the closed loop pipe  80  to prevent stagnation in the branches and laterals connected to this closed loop pipe. 
     In the illustration of FIG. 4, a combination of a branch pipe  20  and a hydrant lateral  22  is shown downstream from the pump  52 . The branch pipe  20  is connected to the closed loop pipe  80  using a medially partitioned tee fitting  38 . A same type of tee fitting  38  is also used to join a supply pipe  90  of a sprinkler system of a building to the closed loop pipe  80 . One or more partitioned elbows  92  may be used along a partitioned pipe as can be appreciated from this illustration. The piping system illustrated in FIG. 4 also shows a hydrant lateral  22  connected directly to the closed loop pipe  80  in a similar manner using a medially partitioned tee fitting  38 . It will be appreciated that in periods of strong water demand, such as when a fire hydrant is opened, the flow of water can come from both pipe halves of each partitioned pipe and around the return gap of every branch and hydrant lateral, to reach the point of high demand. 
     Another advantage of the potable circulating systems illustrated in FIGS. 1 and 4 is that there could be a water filtration system  94  mounted next the pump  52 , to filter the water distributed to this particular subdivision or suburb. This filtration system  94  is illustrated in dashed lines because it is considered optional. Although a water filtration system is mentioned, this installation could comprise other water treatment systems such as a chlorination treatment system, a de-chlorination system, a fluorination system and an UV treatment system. This filtration system  94  is particularly appreciable to correct problems being developed in a water distribution system between the water treatment plant and the point of use. 
     It should be noted at this point that the illustrations in FIGS. 1 and 4 should not be scaled. As mentioned before, the branch pipe  20  and the closed loop pipe  80  shown therein can extend several hundred feet and have a number of hydrants and other laterals and residential takeoffs connected to them. Similarly, the lengths of the takeoff pipes  30 ,  32 ,  82 ,  84  can be limited to a few feet inside a pump house for example. The illustrations in FIGS. 1 and 4 depict the basic principles and operation of two circulation systems according to the present invention, in sufficient details to provide the person skilled in the art with the knowledge required to apply these concepts and principles to various configurations of municipal water distribution systems. 
     A hydrant lateral  22  may also be connected to the water main  34 , using a partially partitioned tee fitting  100 , as shown by label  98  on the lower left corner of FIG.  4 . The partially partitioned tee fitting  100  is better illustrated in FIGS. 5 and 6. This tee fitting  100  consists of a regular tee fitting, in which there is mounted a scoop insert  102 . The scoop insert  102  is mounted in the takeoff portion  104  of the tee fitting  100  and extends across the straight portion  106 , a distance of about half the diameter of the straight portion. When the takeoff portion  104  is two (2) denominations smaller than the straight portion  106 , six (6) inch and ten (10) inch respectively for example as it is customary with these takeoff tee fittings, and the flow in the water main is about 0.5 ft/sec, it is believed that the scoop insert  102  diverts about 4-5% of the flow in the water main into the hydrant lateral  22 . This belief is based on theoretical pressure loss calculations made with principles and instructions found in an engineering manual entitled: Fundamentals of Fluid Mechanics, third Edition, by Munson, Young and Okiishi, published by John Wiley &amp; Sons, Inc. 1998. When the hydrant lateral is connected to an active water main, a flow of this magnitude is considered sufficient to prevent water stagnation in the hydrant base  68 . 
     The scoop insert  102  consists of a tubular element  108  enclosing a cross-like blade  110 . The blade  110  has a two-way deflector  112  on its end, to divert a flow of water from either direction in the straight portion  106 , and into the takeoff portion  104 . The two-way deflector  112  defines the end of the blade  110  extending halfway across the straight portion  106 . A flange  114  is provided around the tubular element  108 . 
     The scoop insert  102  is preferably made of a mouldable plastic material. The dimension of the tubular element  108  and of the flange  114  are preferably selected to mount fitly into the takeoff portion  104  of a standard tee fitting. The tubular element  108  and the blade  110  extend outside the takeoff portion  104 , beyond the flange  114 . In use, the blade  110  is joined to or otherwise meets with the partition  24 ′ inside the partitioned pipe  22 . The joining of the blade  110  to the partition  24 ′, or the joining of two adjoining partitions  24  is not illustrated herein because this could take numerous forms and does not constitute the focus of the present invention. The scoop insert  102  may be readily mounted in a standard tee fitting and fastened to the tee fitting by its flange  114  during the mounting of the tee fitting to an adjoining pipe. 
     As mentioned before, the fire hydrant lateral  98  illustrated in FIG. 4 is connected to an active water main  34  with a flow of about 0.5 ft/sec. It will be understood that this hydrant lateral  98  can also be connected to a closed loop pipe  80  around a subdivision. In this case, the pump  52  is selected to cause a flow in the closed loop pipe  80  which is sufficient for inducing a desired flow of water through the hydrant lateral  98 . 
     Although a flow of water in a hydrant lateral of about 4-5% of the flow in the water main is believed sufficient for preventing a stagnation of the water in the hydrant base  68 , there may be some exceptional circumstances where a larger flow is required in a hydrant lateral. Also, there are cases where the flow in the water main is insufficient to induce a minimum flow through the tee connection  100  and the hydrant lateral  98 . For these reasons, the arrangement illustrated in the lower left corner of FIG.  4  and in FIGS. 5 and 6, is believed to be appropriate for only a majority of hydrant laterals connected to water mains. 
     In other exceptional cases, an alternate embodiment of a circulating system is proposed. This alternate embodiment is only remotely related to the present invention, but is nonetheless presented herein for convenience, to provide additional resources to the designers of the circulation systems according to the present invention. This alternate embodiment is illustrated in FIG.  15  and comprises a pumping unit  115  mounted next to the water hydrant  116  and having an intake pipe  117  connected to the hydrant base  68  and a discharge pipe  118  connected to the water main  34 . This pumping unit  115  is described in U.S. Pat. No. 6,062,259 issued to the Applicant of the present application. This pumping unit  115  may be powered by an electrical power source or from a solar panel  119  mounted next to the fire hydrant. 
     Referring back to FIGS. 7-10, another important aspect of the present invention will be described. The preferred directional/bypass valve  64  is a butterfly valve  120  having a gear drive actuator  122  requiring several turns on a handle (not shown) to open or close the valve. The butterfly valve  120  has a nominal size of at least one (1) denomination larger than the nominal size of the adjoining pipe  22 . For example, a butterfly valve having a nominal size of eight (8) inch should be used on a partitioned pipe of six (6) inch or smaller. The directional/bypass valve  64  also comprises an expanding and reducing adapters  124 ,  126  on the upstream and downstream sides of the butterfly valve  120  respectively. 
     Each of the adapters  124 ,  126  has a contoured partition  130  therein. In use, the contoured partitions  130  are joined to the partition  24 ′ in the adjoining pipes  22 . Again, the joining of the partitions  130  and  24 ′ can take different forms which are not illustrated herein for not being the focus of the present invention. Each contoured partition  130  has a curved edge  132  which is a precise fit around the curvature of the valve&#39;s blade  66 . This precise fit is preferably a close contact fit but may also form a gap ‘D’ having a clearance of up to about ¼ inch, without adversely affecting the performance of the forced flow circulation systems according to the present invention. It is believed that a gap ‘D’ of {fraction (1/16)} inch will allow only about 10% of the flow in the upstream pipe half to traverse there through. This flow loss increases to 18-20% with a gap size ‘D’ of ⅛ inch, and to about 30% with a gap ‘D’ of ¼ inch. These secondary flows across the valve are shown as labels  138  in FIG.  9 . This belief is also based on theoretical pressure loss calculations made using principles and instructions found in the aforesaid engineering manual entitled: Fundamentals of Fluid Mechanics. It will be appreciated that such loss of flow across the valve does not compromise the effectiveness of the circulation systems according to the first and second preferred embodiments. 
     When the valve  64  is open, such as illustrated in FIGS. 7 and 9 in particular, the flow of water in both pipe halves of the partitioned pipe  22  are respectively directed across the valve. When the valve is closed, as illustrated in FIGS. 8 and 10, the blade  66  isolates the upstream end of the hydrant lateral  22  from the downstream end, and opens a return path  140  across both pipe halves  26 ′,  28 ′, thereby allowing a flow of water from one pipe half to the other. Because the size of the butterfly valve  120  is one (1) denomination larger than the nominal size of the pipe  22 , the height and width ‘E’ of the return gap  140  define a bypass area which is substantially larger than the cross-section of one pipe half  26 ′ or  28 ′ of the partitioned pipe  22 . The flow through the return gap  140  is thereby minimally restricted. When the valve blade  66  is closed, the hydrant base  68  is isolated from the branch pipe  20  or  80  and the flow of water is maintained substantially undiminished along the branch pipe  20  from which the hydrant lateral depends. 
     For the practicality of the design, the preferred directional/bypass valve  64  has been described as a butterfly valve  120  enclosed between two partitioned adapters  124 ,  126 . Such a butterfly valve is readily available commercially, and it is believed that the manufacturing of the adapters  124 ,  126  does not present any difficulties for the person skilled in the art. However, it will be appreciated that this particular design is not essential to the operation of the circulation systems according to the present invention. Other types of valve can be used to perform the same function. As a first example, it is known that a spool valve, as illustrated by the symbol  150  in FIG. 11 can be made to provide directional and bypass features as previously described. As a second example, it is known that a ball valve or a barrel valve as represented by the symbol  152  in FIG. 12 may also be made and used to obtain the same function as the butterfly valve  120  and the adapters  124 ,  126 . And of course, one may also consider the use of a pair of gate valves or other combination valves connected in parallel, with a third valve mounted across their upstream sides. 
     As can be appreciated, the circulation systems described in the first and second preferred embodiments are made with components that are readily available or easily manufacturable. The configuration of these systems does not depart from common water piping technologies. It is believed that the capital cost for designing and installing a circulation system according to the concepts and principles described in these preferred embodiments is similar to the current prices paid by municipalities for building conventional piping systems. 
     Referring now to FIG. 13, a schematic diagram of a potable water circulation system according to a third preferred embodiment of the present invention is illustrated therein. This third preferred embodiment is adapted to circulate water in the potable water distribution system of a building. This system comprises a water inlet pipe  178 , a loop pipe  180  connected to the water inlet pipe  178 , and a pump  182  mounted in series with a primary loop pipe  180  to circulate the water in the primary loop pipe. A plurality of secondary takeoff loops  184  or secondary loop pipes, are connected to this primary loop pipe  180  to feed various water outlets  186  such as an outdoor tap and a drinking fountain for examples. Each of the secondary loop pipes  184  has a U-like shape with a pair of leg pipes  188 ,  188 ′ connected to diametrically opposite sides of said primary loop pipe  180 . Each outlet is connected to a valve header  190  connected to one of the secondary takeoff loops  184 . The flow through the primary and secondary loops are controlled by a number of flow control valves  192 . This system may also comprise a timer-controlled dumping valve  194  to periodically drain the reservoir  196  of a drinking fountain for example. 
     The principal feature of this third preferred embodiment consists of the structure of the valve header  190 . The valve header has a U-like construction with a main flow along a U-shaped path  198  and a takeoff portion  200  extending from a mid-point on the U-shaped path. A valve  202  is mounted in the takeoff portion for selectively shutting off a flow of water through the takeoff portion  200 . A partitioned pipe  204  extends from the takeoff portion beyond the valve  202  to a water outlet such as a faucet. 
     There is provided a divider  206  extending inside the valve header  190  across the U-shaped path  198  and forming a gap  208  near the valve  202 , in a manner which is similar to the previously described gap ‘D’. The dimension of this gap  208 , however, should be selected to cause a flow along the partitioned pipe  204  of only about 1-5% of the flow along the U-shaped path  198 . This structural limitation is advantageous for allowing the installation of several valve headers  190  in series in a same secondary loop  184  without causing significant pressure losses. Also, the flow of water in the primary and secondary loop pipes  180 ,  184  can be reversed as shown by the double-headed arrows  88  to supply a large demand of water to one of the outlets  186 . 
     While three embodiments of the present invention have been described hereinabove, it will be appreciated by those skilled in the art that various modifications, alternate constructions and equivalents may be employed without departing from the true spirit and scope of the invention. It will also be appreciated that the feature of one embodiment can be used in another and vice-versa. Therefore, the above description and the illustrations should not be construed as limiting the scope of the invention which is defined by the appended claims.