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An injection molded plastic corrugated leaching or storm water chamber has a peak corrugations segment with a flattened and thickened web. The web is the portion of the corrugation which runs from the peak to the floor of the adjacent valley. Preferably, flattened web segments are at the apexes of a

An injection molded plastic corrugated leaching or storm water chamber has a peak corrugations segment with a flattened and thickened web. The web is the portion of the corrugation which runs from the peak to the floor of the adjacent valley. Preferably, flattened web segments are at the apexes of adjoining corrugations, to create an increased thickness band region, running lengthwise along the chamber from an injection nozzle location or sprue. The flattened web segments enable better melted plastic flow during molding, without increasing nesting height.

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We claim: 1. In an injection molded thermoplastic arch shape cross section corrugated chamber, useful for receiving and discharging water beneath the surface of the earth; wherein the chamber has an arch top and opposing sides disposed on either side of a lengthwise vertical centerplane, running up

We claim: 1. In an injection molded thermoplastic arch shape cross section corrugated chamber, useful for receiving and discharging water beneath the surface of the earth; wherein the chamber has an arch top and opposing sides disposed on either side of a lengthwise vertical centerplane, running upwardly to the arch top; wherein the chamber has a multiplicity of alternating peak corrugations separated by valleys, wherein each of said peak corrugations and valleys has a length which runs transverse to the chamber length and up a first side of the chamber, across the arch top of the chamber, and down the opposing side of the chamber; wherein each peak corrugation comprises a pair of opposing-side webs, one of which webs runs to a valley running on along one lengthwise side of the peak corrugation, and the other of which webs runs to a valley running along the opposing lengthwise side of the peak corrugation; wherein the webs of said pair are angled relative to each other and thereby have an associated Peak Web Angle therebetween; the improvement which comprises: at least one peak corrugation having at least one segment of peak corrugation length characterized by (a) a Peak Web Angle which is substantially greater than the Peak Web Angles which characterize portions of said at least one peak corrugation which are adjacent to each of the lengthwise ends of said at least one segment; and, (b) web thicknesses which are substantially greater than the thicknesses of the webs of portions of said at least one peak corrugation which are adjacent to each of the lengthwise ends of said at least one segment. 2. The chamber of claim 1 wherein nesting height of a stack of like chambers is limited by contact of a multiplicity of said webs of a multiplicity of said peak corrugations. 3. The chamber of claim 1 characterized by a multiplicity of said peak corrugations, each peak corrugation having at least one segment of the length thereof which is characterized by: (a) a Peak Web Angle which is substantially greater than the Peak Web Angles which characterize portions of said at least one peak corrugation which are adjacent to each of the lengthwise ends of said at least one segment; and, (b) web thicknesses which are substantially greater than the thicknesses of the webs of portions of said at least one peak corrugation which are adjacent to each of the lengthwise ends of said at least one segment. 4. The chamber of claim 1 further comprising: at least one sprue positioned within one of the valleys which runs along each opposing lengthwise side of said at least one peak corrugation. 5. The chamber of claim 4 further comprising: a second sprue positioned in one of the valleys which runs alongside said at least one peak corrugation; wherein, the first sprue and second sprue are located on opposing sides of said vertical center plane of the chamber. 6. The chamber of claim 3 wherein all of said multiplicity of segments are at the top of the chamber. 7. The chamber of claim 3 wherein some of said multiplicity of segments are on a first side of the lengthwise vertical centerplane of the chamber and some of said multiplicity of segments are on the second side of said lengthwise vertical centerplane. 8. The chamber of claim 1 wherein said Peak Web Angle associated with said at least one segment is at least about 8 degrees greater than Peak Web Angle associated with said adjacent portions of said at least one peak corrugation. 9. The chamber of claim 8 wherein said Peak Web Angle of said at least one segment is about 40 degrees and wherein the Peak Web Angle of said adjacent portions of said at least one peak corrugation is about 12 degrees. 10. The chamber of claim 1 wherein the web thickness in said at least one segment is at least 20 percent greater than the thickness of the web in the said adjacent portions of said at least one peak corrugation. 11. The chamber of claim 1 wherein the thickness of at least one of the webs of said pair of webs of said at least one segment is greater in thickness near the center of the segment than it is at either end of the segment. 12. The chamber of claim 1 wherein at least one of said webs of said at least one segment comprises one or more plastic flow channels running in the lengthwise direction of the chamber. 13. The chamber of claim 1 wherein the opposing sides and arch top lie along a continuous curve path which defines the upper bound of said arch shape cross section. 14. In an injection molded thermoplastic arch shape cross section corrugated chamber, useful for receiving and discharging water beneath the surface of the earth; wherein the chamber has an arch top and opposing sides disposed on either side of a lengthwise vertical centerplane, running upwardly to the arch top; wherein the chamber has a multiplicity of alternating peak corrugations separated by valleys, wherein each of said peak corrugations and valleys has a length which runs transverse to the chamber length and up a first side of the chamber, across the arch top of the chamber, and down the opposing side of the chamber; wherein each peak corrugation comprises a pair of opposing-side webs, one of which webs runs to a valley running along one lengthwise side of the peak corrugation, and the other of which webs runs to a valley running along the opposing lengthwise side of the peak corrugation; wherein the webs of said pair are angled relative to each other and thereby have an associated Peak Web Angle therebetween; the improvement which comprises: forming at least one segment of the length of at least one of said webs so that (a) the Peak Web Angle which characterizes the segment is substantially greater than the Peak Web Angles which characterize portions of said at least one peak corrugation which are adjacent to each of the lengthwise ends of said at least one segment; and, (b) the thickness of at least one of the webs of said at least one segment is substantially greater than the thicknesses of the webs of portions of said at least one peak corrugation which are adjacent to each of the lengthwise ends of said at least one segment. 15. The chamber of claim 14 characterized by forming a multiplicity of said at least one segments on a multiplicity of different peak corrugations, so all the segments are aligned within a zone which runs lengthwise along the chamber length and parallel to said lengthwise vertical centerplane. 16. In the method of forming a thermoplastic injection molded arch shape cross section corrugated chamber, having an arch top, and opposing sides disposed on either side of a lengthwise centerplane, running upwardly to the arch top; wherein the chamber has a multiplicity of alternating peak corrugations separated by valleys, wherein said peak corrugations and valleys have lengths which run transverse to the chamber length and up a first side of the chamber, across the arch top, and down the opposing side of the chamber; wherein each peak corrugation comprises a pair of opposing-side webs, each of which runs to a valley which runs alongside of the peak corrugation; wherein the webs of said pair are angled relative to each other and thereby have an associated Peak Web Angle therebetween; the improvement which comprises: forming at least one segment of the length of at least one web of at least one peak corrugation so that (a) the Peak Web Angle of the segment is substantially greater than the Peak Web Angles of portions of said at least one peak corrugation which are adjacent to said at least one segment; and (b) the thicknesses of at least one of the webs of said at least one segment is substantially greater than the thicknesses of the webs of portions of said at least one peak corrugation which are adjacent to said at least one segment, to thereby improve the flow of melted plastic within the mold which forms the part during injection molding. 17. The method of claim 16 which further comprises: providing a multiplicity of peak corrugations with one or more segments similar to said at least one segments; and, positioning at least one of said segments in vicinity of a sprue of the molded chamber. 18. The method of claim 17 wherein said segments are disposed on alternating fashion on both sides of said vertical lengthwise centerplane.