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This application claims benefit of provisional patent application Ser. No. 61/700,313, filed Sep. 12, 2012. 
    
    
     TECHNICAL FIELD 
     The present invention relates to molded plastic chambers having arch shape cross sections, for receiving, containing and dispersing stormwater when buried beneath the surface of the earth. 
     BACKGROUND 
     Arch shape cross section storm chambers made from injection molded plastics have been used for a number of years to handle stormwater. In a typical installation, multiple rows of strings of interconnected chambers are placed on the floor of a cavity made in the earth surface and are then backfilled with crushed stone or the like. Stormwater, such as might run-off from a paved parking lot or roofs of buildings is channeled to the chambers so the waters can accumulate and then be dispersed over time by either percolation into the surrounding soil or by controllably flowing to a water course. 
     Some types of arch shape cross section chambers, exemplified by a corrugated chamber described in Detullio U.S. Pat. No. 5,087,151, have closed ends and are interconnected by pipes. Those chambers might be made by thermoforming of thermoplastic sheet. Another type of chamber, of more relevance to the invention described herein, is exemplified by the chambers shown in Kruger U.S. Pat. No. 7,118,306. Those kinds of chambers are preferably made by injection molding. The chambers have open ends. A string of chambers is assembled by overlapping a first end of one chamber on the second end of a like chamber, when the like chamber has been previously placed within a cavity in the earth. After installation, the chambers are backfilled, typically with crushed stone, and the stone is covered to create a soil surface, often a paved surface which can be used by motor vehicles. 
     When so installed beneath the surface of the earth, stormwater chambers should have requisite strength and durability, particularly for bearing the overlying load of soil and any vehicular or other traffic. 
     Systems comprised of molded plastic arch shape cross section stormwater chambers are in functional- and cost-competition with other stormwater systems, including buried systems comprised of steel conduit and detention ponds. Generally, it is an objective to have storm chambers with larger and larger volumetric capacity per unit length, while of course still meeting the load bearing requirements. Whereas early plastic chambers used 20 years or more ago had a peak height of 12 inches, more recent chambers may be quite large. For example, a commercial Model 4500 stormwater chamber sold by Stormtech LLC, Rocky Hill, Conn. is 100 inches wide at the base, about 60 inches high, about 48 inches long, and weighs about 120 pounds. There is a generalized desire to commercialize even larger chambers. 
     There are practical problems encountered with large chambers. Among them are: First, it is not easy to mold large chambers because they require large molding machines and machinery for handling the just-molded products. Large and thus less common injection molding machines can be costly. 
     Second, large chambers present problems with respect to storing and shipping in economic fashion by truck —the most common mode. Typically chambers are nested one within the other to form a stack for shipment on pallet. But the basic height of a chamber is large to begin with, then that means not many chambers can be nested before the height capacity of a ordinary highway truck is exceeded. For example, if the load height capacity of a truck is about 100 inches from the bed surface, and one chamber is 60 inches high, then there is only an about 40 inches of space for containing nested chambers. If the stack height is about 6 inches (the spacing between one chamber and next-nested chamber), then only 6-7 chambers can be stacked on top of the bottom chamber. 
     Third, the weight of each individual chamber can exceed that which workers can handle manually, particularly at the site where the stormwater system is being constructed, necessitating the use of materials handling equipment. It is more convenient for installers to not have to use lifting devices. 
     SUMMARY 
     An object of the invention is to provide large stormwater chambers which have improved characteristics with respect to manufacturability, shipment and handling. Another object is to provide a chamber and associated handling shipping method which minimizes storage and shipping costs. 
     In accord with the present invention, a stormwater chamber is comprised of two half chambers. Half chambers of the present invention may be stacked as a nested multiplicity of half chambers on a pallet or the like for economical shipping, particularly by means of a motor vehicle transport truck. At or near the point of use, the half chambers are mated at coupling features to form a chamber which is in use configuration and which has a joint at the top of the chamber. Preferably, the half chambers are substantially identical and are made in the same mold. 
     Different embodiments of coupling features and joints may be used. Typically the joint is comprised of mating flanges, intermittent or continuous, which run along the length of the top of the chamber. The flanges may interlock, Clamps and latching means may be used to hold the half chambers relative to each other while they are handled and until they are buried in soil or the like for use. 
     The foregoing and other objects, features and advantages of the present invention will become more apparent from the following description of preferred embodiments and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a stormwater chamber comprised of half chambers mated at a top joint. 
         FIG. 2  is an end view of the chamber of  FIG. 1 . 
         FIG. 3  is an exploded view showing the upper portions of two half chambers which comprise a chamber like that shown in  FIG. 1 , showing how the half chambers couple to each other at a joint at the top of the chamber. 
         FIG. 4  is a vertical transverse cross section through the top portion of the chamber of  FIG. 1 . 
         FIG. 5  is a view like  FIG. 4 , showing an alternative joint configuration which comprises fasteners. 
         FIG. 6  is a view like  FIG. 4 , showing a chamber embodiment where C channels hold the mated half chambers to each other. 
         FIG. 6A  is a partial detail of a variation on the joint shown in  FIG. 6 . 
         FIG. 6B  is a partial detail of another variation on the joint shown in  FIG. 6 . 
         FIG. 7  is a partial perspective view of the top end of a half chamber, like that shown in  FIG. 6 . 
         FIG. 8  is a perspective view of a channel which may be used to hold to half chambers together at a top joint. 
         FIG. 9  is a view like  FIG. 4  showing a joint comprising an integral J channel and a C channel clamp. 
         FIG. 10  is a semi-diagrammatic illustration of half chambers mounted on a pallet for shipping to an assembly point. 
     
    
    
     DESCRIPTION 
     Embodiments of chambers of the present invention are preferably made of injection molded thermoplastic, preferably a polyolefin such as polyethylene or polypropylene. Exemplary chambers are comprised of half chambers which join to each other by coupling means at a joint proximate the top of the chamber. 
       FIG. 1  is a perspective view and  FIG. 2  is an end elevation view of a chamber  18  in its use configuration. The chamber is comprised of two mated chamber halves  22 ,  24  which have a joint  20  and opposing side base flanges  36  which lie in base plane HP. Chamber  18  has a length axis LL and a vertical lengthwise center plane CP which contains a vertical axis C, used as a reference in other Figures. 
       FIG. 3  is an exploded view showing how the upper portions of exemplary half chambers  22 ,  24  couple together.  FIGS. 4 ,  5 ,  6  and  9  are partial transverse cross section views showing features of joints of alternative embodiment chambers. An exemplary thermoplastic chamber will have a width WW of about 100 inches, a height H of about 60 inches, and a length of about 52 inches (so the effective length is 48 inches when the chambers are end to end overlapped). Alternating peak corrugations  48 ,  50  and valley corrugations  38 ,  40  run transverse to the length of the chamber. The corrugations provide cross section area for vertical load transfer and section modulus which imparts bending strength to the walls. Below, the terms “valley” and “peak” are shorthand references to the valley corrugations and peak corrugations. 
     Stormwater chambers and their use have been described in the art. In particular, reference may be made to commonly owned U.S. Pat. No. 7,118,306 of Kruger et al., entitled “Stormwater Management System” and U.S. Pat. No. 6,991,734 of Smith et al, entitled “Solids Retention in Stormwater System.” The disclosures of the foregoing patents are hereby incorporated by reference. When a chamber is buried within crushed stone or other soil material the arch shape of the chamber cross section maintains the integrity of the interior cavity of the chamber. Simply stated, the vertical forces of the stone, soil, and anything on the surface of the soil, are transferred along the curve of the arch to the base flanges. As is characteristic of arches (for instance, arches comprised of stone or brick pieces), there need not be significant capacity to bear shear forces within the curved structure in order to maintain the integrity of the structure once it is in place and subjected to foregoing kind of vertical loads. Thus, it will be appreciated that in the present invention the joint  20  at the top of the chamber need not have strength to resist high shear load. However, a joint will desirably have sufficient shear strength to enable lifting and other handling of a chamber, to move it from the point of assembly to its position within a to-be-filled cavity in the earth. 
     In one embodiment, half chambers are mechanically interlocked and optionally welded or otherwise secured at coupling features in vicinity of the joint. When the joint is planar it is preferably in the vertical center plane CP. When the joint is non-planar, the joint will be in proximity of the vertical center plane, with parts of the joint somewhat offset from the plane. 
       FIG. 3  shows the top portions of the two half chambers  22 ,  24 , as they appear when spaced apart and rotated away from each other to reveal the coupling features. Arrows A, B show how the half chambers  22 ,  24  mate with each other when the coupling surfaces are brought together to form a joint. The top of half chamber  22 , on the left, has a serpentine lip  30  and a discontinuous vertical top flange  26 . The flange  26  is comprised of a plurality of flat plates which close the ends of the valleys  38  that are between adjacent peak corrugations  48 . The lip  30  is shaped to mate with the serpentine interior surface  29  of the half chamber  24 , on the right in  FIG. 3 . Half chamber  24  has a top flange  28  lying in or close to the vertical plane CP which contains a vertical reference axis CC. See  FIG. 1 . Flanges  26 ,  28  may be discontinuous as shown, comprising a plurality of flat plates closing off the ends of the valleys. In an alternative embodiment flanges  26 ,  28  are continuous along the length of the top of each half chamber and close the underside cavity of the peak corrugations. See  FIG. 7 . 
     When half chamber  22  and half chamber  24  are engaged with each other, the upper end of half chamber  24  rests on the surface of the serpentine lip  30 . Flange  28  has a multiplicity of horizontally extending pins  34  which fit into the female cavities of sockets  32  on the flange  26 , to help align the coupling features with each other. The pin-socket engagements provide some shear strength to the joint. 
       FIG. 4  is a transverse vertical cross section showing portions of half chambers  22 ,  24  when they are mated to form a chamber  18  as shown in  FIG. 2 . The parts are shown as they are ready for welding, as by ultrasonic, heat gun, hot plate, or other known means, for example at joints  70 ,  20 A. Note how typical valley  40  of half  24  rests on lip  30  of half  22 . The engagement of the vertical flange  26  on one half chamber with the vertical flange  28  on a mating half chamber is helped by pins  34  and sockets  32 , or by means of substitutional functionally-equivalent features. The pins and socket features help locate the mating half chambers with respect to each other and also provide some vertical direction strength to the joint. 
     Optionally, as shown in  FIG. 4 , lip  30  (which has the ability to elastically deflect downwardly) may have a lengthwise ridge or a series of upward projecting protuberances  66  which are received in mating recesses  68  on the undersides of typical valleys  40 , to modestly hold the half chambers together at the joint prior to welding. 
     While welding is preferred with the  FIG. 4  joint design, it is within contemplation that chambers having joints like those shown in  FIG. 4  may be useful for assembling chambers at the point of installation without adding the welding step. Other fastening or securing means may be used with the  FIG. 4  embodiment, as described below. 
       FIG. 4  also shows in phantom one of several optional stiffeners  42  which may be molded into the center one or more valleys  40  of typical half chamber part  24 . Like stiffeners may be used on the other half  22 , as well. 
       FIG. 5  shows a portion of an alternate another embodiment of the invention, chamber  318 , where a bolted joint  20  is formed between half chamber  322  and half chamber  324  —which half chambers have configurations largely like chambers  22 ,  24 . A multiplicity of exemplary threaded fasteners  27 A,  27 B inserted in holes, and associated nuts  333 ,  335 , are used to join vertical flanges  326 ,  328  to each other and to join lip  330  with valley  40 . Preferably, a multiplicity of fasteners will be spaced apart along the length of the joint. 
       FIG. 6  is a view like the view of  FIGS. 4 and 5 , showing a portion of another embodiment of the invention, chamber  118 . Mating half chambers  122 ,  124  have respective peak corrugations  148 ,  150  and valley corrugations  138 ,  140 . The half chambers  122 ,  124  meet at lengthwise flanges  126 ,  128 .  FIG. 7  is a partial view of the upper end of a half chamber  122 , showing that flange  126  is preferably continuous, as is flange  128 . In variations on this embodiment, the flanges may be intermittent as shown in connection with  FIG. 3 . Referring again to  FIG. 6 , lengthwise vertical lips  58 ,  60  run along the undersides of valleys  138 ,  140 . The lips  58 ,  54  and the upper ends of flanges  126 ,  128  are respectively clamped together by channels  52 ,  54 .  FIG. 8  is a perspective view of typical channel  52  which is preferably made of a metal or fiber reinforced plastic. The width of channel  52  is dimensioned so that there is an elastic force in the channel when the clamp is forcibly engaged (as with a rubber hammer) with the mated flanges  126 ,  128 . Channel  54  is similarly dimensioned with respect to the vertical lips  58 ,  60 . 
       FIG. 6A  is a detail of a portion of an alternative embodiment of the joint shown in  FIG. 6 . Flanges  326 ,  328  correspond with flanges  126 ,  128 . The lengthwise vertical lips  358 ,  360  are L shape in cross section, so that when mated as shown they present as a T shape cross section. Alternate embodiment channel  354  is C shape in cross section, so it is vertically captured in place by the T shape cross section. 
       FIG. 6B  shows another variation which may be used with the  FIG. 6  embodiment and other embodiments. Vertical flange  226  has a recess and vertical flange  228  has a protuberance  62  which fits in the recess. The recess and protuberance may be round as shown in  FIG. 3 , or may comprise lengthwise running portions. In the chamber  118  and in other embodiments of the invention, the mating flanges may have even more contoured and interlocking features than have been shown by example. 
       FIG. 9  is a vertical cross section like the view of  FIG. 6 , showing a portion of a chamber  218  comprised of half chambers  222 ,  224  having mating respective lengthwise vertical top flanges  226 ,  228 , intermittent in valleys  238 ,  240 . Alternately, the flanges are continuous. In the locations of the valleys, flange  226  has a top portion  64  shaped to create a pocket  74  within which is received the upper edge of flange  228 . The upper part of flange  226  may be characterized as a J shape channel (which defines the pocket  74 ). 
     While the joint is preferably formed at the at the center plane of the chamber, as has been shown in several embodiments here, in the generality of the invention the joint may be offset transversely somewhat from the center plane; and thus the term half chamber in such instances would be construed in nominal and not exact terms. 
     In one method of making and shipping chambers within the scope of invention, when half chambers are molded, they may be mated and optionally welded in the factory and shipped as one piece chambers. 
     Alternatively, in another method of making and shipping chambers, half chambers may be shipped to an assembly point remote from the point of molding on a pallet  80  (or equivalent device) as a nested stack  82  as shown (for representative half chambers  24 ) in  FIG. 10 . Typically, a pallet with chambers in such transport configuration will be carried by a semi-trailer connected to a motor vehicle tractor truck. The point of assembly can be at the job site or in a vicinity of the job site where the less efficient transport of whole chambers is not a big economic factor. The following more completely states this process: A method of manufacturing and transporting an injection molded plastic corrugated chambers for receiving water when buried beneath the surface of the earth, wherein each chamber has a length, opposing side base flanges running lengthwise and lying in a base plane, an arch shape wall running upwardly to a chamber top from the opposing side base flanges, thereby the wall defining an arch shape cross section chamber interior, the wall characterized by alternating peak corrugations and valley corrugations running transverse to the chamber length, and a vertical center plane running intersecting the chamber top, comprises:
         (a) injection molding a multiplicity of first half chambers and second half chambers, each half chamber comprising one of said base flanges, about half of said arch shape wall, and a coupling portion connected to the wall in vicinity of the top of a chamber which is formed by mating a first half chamber with a second half chamber; the coupling portions shaped for mating first half chambers with second half chambers to form whole chambers;   (b) placing the first half chambers and second half chambers on a pallet in nested fashion, transporting the pallets and said half chambers on a motor vehicle truck to a point of assembly;   (c) removing the half chambers from the pallet at the point of assembly;   (d) mating and securing the coupling portion of each first half chamber with and to the coupling portion of each second half chamber, to thereby form a multiplicity of whole chambers; and   (e) placing each whole chamber with in a cavity in the earth for use.       

     The invention enables more compact and economic shipping, by shipping unassembled half chambers, compared to shipping whole chambers. The invention also enables fabrication of large chambers which are beyond the plastic-weight molding capacity of, or the platen size of, a particular injection molding press, where the half chamber is within such capacity. 
     The present invention has relationship with the invention of a commonly owned provisional application 61/700,315 of Moore, Jr. et al., and a non-provisional patent application claiming benefit of same, bearing Ser. No. 14/025,773, entitled “Molded Plastic Stormwater Chamber Having a Hinged Top Joint,” filed on even date herewith. The disclosures of both applications are hereby incorporated by reference. The related applications describe chambers which are made from half chambers, where the half chambers are connected to each other by one or more hinge joints at the top of the chamber. Application Ser. No. 14/025,773 describes ways of locking one hinged half chamber to a mating hinged half chamber. The locking means, and in particular a longitudinal running locking rod, may be used in the present invention. The application also describes preferred ways of molding half chambers, so the resultant chambers are well-suited to overlapping end-to-end installations. That method of making may be used in the present invention. 
     The invention, with explicit and implicit variations and advantages, has been described and illustrated with respect to several embodiments. Those embodiments should be considered illustrative and not restrictive. Any use of words which relate to the orientation of an article pictured in space are for facilitating comprehension and should not be limiting should an article be oriented differently. Any use of words such as “preferred” and variations thereof suggest a feature or combination which is desirable but which is not necessarily mandatory. Thus embodiments lacking any such preferred feature or combination may be within the scope of the claims which follow. Persons skilled in the art may make various changes in form and detail of the invention embodiments which are described, without departing from the spirit and scope of the claimed invention.

Summary:
A molded plastic arch shape cross section stormwater chamber having a corrugated wall comprises separately molded half chambers which are connected by coupling features at a joint at the top of the chamber. Preferably, the half chambers are substantially identical and are made in the same mold. The half chambers may be compactly stored and transported. Near the point of use, the chambers may be assembled.