BUILDING DRAINAGE SYSTEM PIPES WITH IMPROVED PERFORMANCE AT LOW FLOW

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/650,696 filed May 23, 2012 and U.S. Provisional Patent Application Ser. No. 61/748,549 filed Jan. 3, 2013, both of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to building drainage system pipes with improved performance at low flow.

BACKGROUND INFORMATION

Conventional sanitary and storm piping includes round circular tubes or pipes (right circular cylinders). These pipes are installed with a nonzero slope (i.e. not horizontally) in order to transport sewage by means of gravity to a point of disposal. There are several building codes in effect throughout the United States, and the building codes typically describe the capacity of the sloping sanitary pipes in terms of fixture units. Each type of plumbing fixture (e.g. shower, lavatory, water closet, etc.) is assigned a certain number of fixture units based on the fixture's discharge into the sanitary system. The appropriate pipe size and slope is then determined by adding the total number of fixture units connected to the pipe.

The pipes are intended to be only partially filled with sewage so that air can flow freely above the sewage. In this way, the system avoids the possible negative effects of differences in air pressure.

Sewage is a mixture of liquid and solids, and when a plumbing fixture such as a toilet discharges into a drain line, the solids are entrained in the flow. Flow is a general term that refers to the movement of the sewage through the pipe. As the sewage flows through the piping system, the solids will typically remain entrained if the velocity of the flow is 2 feet per second (fps) or greater. As it is used in the plumbing industry, the word “velocity” refers to the speed of the flow or the magnitude of the velocity vector. In addition, the velocity of the flow is not constant throughout the cross section of the pipe. Sewage that is very close to the pipe wall will be moving more slowly than the sewage further from the wall. However, these differences are not significant, and the “velocity” refers to the average velocity throughout the pipe cross section.

As the sewage flows through the pipe, the solids can remain entrained if the velocity is slightly less than 2 fps, but if the velocity is too low (perhaps 1.5 fps), the solids will separate from the flow and settle at the bottom of the pipe. If fixture use increases sometime later, the velocity will also increase. If the velocity rises to 2 fps, the fast moving water will scour the pipe and re-entrain the solids. Like a fast moving stream, everything is swept away. The velocity is, therefore, a critical element of the plumbing system design.

The velocity is directly related to the volume flow rate. The volume flow rate is the volume of fluid (in units of cubic feet for example) that flows through the pipe per unit of time (seconds, for example), and it is equal to the velocity of the flow multiplied by the area of the flow. So, Q=A×V where Q is the volume flow rate (cubic feet per second), A is the cross-sectional area (square feet), and V is the average velocity (feet per second).

Given a pipe with a certain size diameter that is installed with a certain slope, the velocity of the flow in the pipe will decrease as the volume flow rate decreases. Volume flow rates have been decreasing recently due to water conservation efforts. For example, typical toilet water consumption has dropped from 7 gallons per flush prior to 1980 to 1.6 gallons per flush for modern toilets, and there is a push to continue to reduce water use. As a result of the reduced volume flow rates, there is a reduced velocity in the pipe. The velocity reduction is sufficient enough that solids separate from the flow and settle at the bottom of the pipe. In addition, peak flows are sometimes too low to produce the necessary scouring velocity of 2 fps, and the solids remain on the pipe wall creating a blockage.

Therefore, there is a need for pipes that are large enough with sufficient capacity to handle peak volume flow while providing sufficient velocity at low flow when only a minimal number of fixtures are in use.

SUMMARY OF THE INVENTION

The present invention is directed to building drainage system pipes with improved performance at low flow. Low flow, as it is used here, means the volume flow rate in a pipe when a minimal number of fixtures are in use, and improved performance refers to a velocity that is greater than that of a round circular pipe which is the state of the art. The invention replaces or retrofits round circular pipes with bi-diameter pipes or sleeves of a different shape that maximize the velocity at low flow while maintaining capacity at peak flow. As used herein, the term “bi-diameter pipe” means a pipe having a non-circular cross section with at least two sections of the pipe having different radii of curvature, e.g., an upper section having a relatively large radius of curvature and at least one lower section having a smaller radius of curvature. The bi-diameter pipes may include a tubular member having a wall defining a cross-sectional shape including first and second partially circular portions, wherein the first partially circular portion has a radius smaller than a radius of the second partially circular portion. In certain embodiments, the bi-diameter pipes have two or more conjoined portions. At low flow, only the smaller portion contains sewage, and it provides a higher velocity than the state of the art by providing a greater hydraulic radius. The larger portion, on the other hand, is large enough to provide sufficient capacity at peak flow while maintaining sufficient velocity.

An aspect of the present invention is to provide a pipe for use in building drainage systems, the pipe comprising a non-circular cross section comprising an upper portion having a radius of curvature and a lower portion having a radius of curvature less than the radius of curvature of the upper portion.

Another aspect of the present invention is to provide a building drainage system comprising multiple plumbing fixtures contained in a building, and at least one drain pipe contained in the building in flow communication with the multiple plumbing fixtures, wherein the at least one drain pipe comprises a non-circular cross section comprising an upper portion having a radius of curvature and a lower portion having a radius of curvature less than the radius of curvature of the upper portion.

These and other aspects of the present invention will be more apparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a conventional circular pipe.

FIGS. 2-4 illustrate various flow conditions through conventional circular pipes.

FIGS. 5-7 illustrate pipes with cross-sectional shapes in accordance with embodiments of the invention.

FIG. 8 illustrates pipe inserts for retrofitting conventional pipes in accordance with the embodiments of the invention.

FIG. 9 illustrates a pipe with a cross-sectional shape in accordance with another embodiment of the invention.

FIG. 10 illustrates a pipe with a cross-sectional shape in accordance with another embodiment of the invention.

FIG. 11 is a partially schematic illustration of a building containing multiple plumbing fixtures feeding into modified pipes in accordance with an embodiment of the invention.

FIG. 12 is an isometric view of a fitting for connecting two pipes of equal size in accordance with an embodiment of the present invention.

FIG. 13 is an isometric view of a fitting for connecting two pipes of different sizes in accordance with an embodiment of the present invention.

FIG. 14 is an isometric view of a T joint connecting pipes of the present invention.

FIG. 15 is an isometric view of a Y joint connecting pipes of the present invention.

DETAILED DESCRIPTION

The present invention provides building drainage system pipes and methods for improving performance during low flow. This is achieved by increasing the hydraulic radius of the bi-diameter pipes. In the art, conventional round circular pipes have an inherently small hydraulic radius at low flow due to their circular shape and relatively large wetted perimeter. In the present invention, by contrast, the shape of the bi-diameter pipe is such that the hydraulic radius is larger than that of the art at low flow due to its shape and its associated small wetted perimeter. Therefore, at low flow, the present invention will enable a larger velocity than the state of the art.

In accordance with an embodiment of the present invention, performance at low flow can be improved by altering the cross section of the pipe so as to increase the hydraulic radius. In certain embodiments, this may be achieved by adding a semicircular section at the bottom of the originally round pipe. The smaller semicircle can be sized so that the flow fills the semicircle at the lowest expected flow rate (e.g., the flow from a single toilet). For example, given a pipe with a radius r needed to handle the peak flow, append a semicircular area of radius b (b<r) to the bottom of the pipe to handle the low flow condition. The resultant cross-sectional shape of the bi-diameter pipe includes a lower portion extending downward a distance d that is greater than the radius r of the upper portion of the pipe.

In one aspect, the present invention is directed to a bi-diameter pipe with improved performance at low flow which can be easily sized using the current method of fixture units. Low flow, as it is used here, means the volume flow rate in a pipe when a minimal number of fixtures are in use, and improved performance refers to a velocity that is greater than that of a round circular pipe which is the state of the art. The invention replaces or retrofits round circular pipes with bi-diameter pipes of a different shape that maximize the velocity at low flow while maintaining capacity at peak flow. In certain embodiments, the new shape has two or more conjoined portions. At low flow, only the smaller portion contains sewage, and it provides a higher velocity than the state of the art by providing a greater hydraulic radius. The larger portion, on the other hand, is large enough to provide sufficient capacity at peak flow while maintaining sufficient velocity.

Referring to the drawings, FIG. 1 shows a conventional sanitary or storm pipe 10. A pipe is considered to be at maximum capacity when it is half-filled with sewage. FIG. 2 shows a cross-sectional view of a conventional pipe 10, with sewage 12 in the bottom half and air 14 in the top half.

For steady and uniform flow conditions, the velocity of flow in a pipe due to gravity is given by both the Hazen-Williams Equation and Manning's Equation. Although these two equations are slightly different, they both have the same form given by:

V=C×R^m×Sⁿ

where V is the average velocity; C is a constant that depends on the pipe material (roughness); R is the hydraulic radius of the pipe; S is the slope of the pipe, and m and n are positive exponents. The velocity is thus relevant to three variables, C, R and S, and changing one or more of the variables, therefore, affects velocity. For example, if the slope, S, of the pipe is increased, the velocity will increase.

The velocity of any flow, therefore, can be increased by installing the pipe with a greater slope. The amount of slope is limited, though. A new building sewer must tie into the existing municipal sewer system, and if the slope is too great, the building sewer will be below the pipe to which it must connect. Increasing the pipe slope is also expensive due to the additional excavation and backfill required for installation. Therefore, the problem at low flow cannot simply be solved by increasing the slope. The roughness coefficient, C, also does not allow much manipulation. Thus, the key to achieving higher velocity at low flow is the hydraulic radius, R.

Despite the similar name, the “hydraulic radius” is not the same as the “radius” of a circular pipe. In fact, these two things differ greatly. The hydraulic radius is defined to be the area, A, of the flow in ft² divided by the wetted perimeter, P, in feet. So, R=A/P. The wetted perimeter is the length of the cross-sectional perimeter of the pipe that is in contact with the flow. While the radius of a circular pipe is a constant, the hydraulic radius of the same pipe is not constant. For example, FIG. 3 shows a pipe 10 that is half filled with a fluid 16. The remainder of the pipe contains air 18. The wetted perimeter 20 is that portion of the cross-sectional perimeter of the pipe that is in contact with the fluid. The cross-sectional area of the fluid is A. FIG. 4 shows a pipe 10 that includes a smaller amount of fluid 16. The remainder of the pipe contains air 18. The wetted perimeter 22 is that portion of the cross-sectional perimeter of the pipe that is in contact with the fluid. The cross-sectional area of the fluid is A′. A comparison of FIG. 3 with FIG. 4 will suggest that the ratio of the area of the flow to the wetted perimeter will change as the amount of fluid in the pipe changes. Indeed, in FIG. 3 both the area and the wetted perimeter are larger than that of FIG. 4, but the ratio of area to wetted perimeter is clearly greater than that of FIG. 4. This ratio is precisely the hydraulic radius. Therefore, the hydraulic radius varies as the cross-sectional area of the flow changes.

As an example, consider a round circular pipe of radius r that is half-filled with sewage. The area of the flow is one half of the pipe cross-sectional area, and the wetted perimeter is one half of the circumference of the pipe. The hydraulic radius is then given by:

R=A/P=(0.5×π×r²)/(0.5×2×π×r)=r/2.

This happens to be the maximum hydraulic radius for a circular pipe that is to be at least half-filled with air. As suggested by comparing FIG. 3 and FIG. 4, as the depth (and area) of the flow is reduced from the peak depth, the hydraulic radius will continuously decrease.

According to the Hazen-Williams Equation, if the pipe material and slope of the pipe are fixed, the velocity of the flow can be increased by increasing the hydraulic radius. Furthermore, the hydraulic radius, R=A/P, for a fixed area, A, can be maximized by minimizing the wetted perimeter, P. A reduced wetted perimeter is, therefore, desired.

As noted earlier, the pipes can only be partially filled with sewage so that air can flow above the sewage. Thus the sewage is bounded below and on the sides by the walls of the pipe, and it has a flat top boundary of air above it. This air boundary does not contribute to the wetted perimeter. Applying the result of a famous mathematical problem, for a given area of flow, the wetted perimeter will be a minimum when the shape of the flow is semicircular. Thus, for a given cross-sectional flow area, the hydraulic radius will be maximized if the shape of the flow is a semicircle. Hence, for a given slope and material roughness, the velocity will be maximized if the shape of the flow is a semicircle.

In accordance with an embodiment of the present invention, performance at low flow can be improved by altering the cross section of the pipe so as to increase the hydraulic radius. This may be achieved by adding a protruding portion at the bottom of the originally round pipe. In certain embodiments, at least a portion of wall of the protruding portion defines a section of a circle when viewed on a plane that is perpendicular to the longitudinal axis of the pipe. Such shapes may be compatible with the currently accepted method of determining pipe size based on fixture units.

An embodiment of a bi-diameter pipe 24 is shown in FIG. 5, including a tubular member 26 that defines a non-circular cross-sectional shape. The tubular member includes a top section 28 and a smaller bottom section 30 that is coupled to the top section. The cross-sectional shape of the top section is defined by an internal surface 32 that lies along a first circle 34. The radius of the first circle is shown as r. The cross-sectional shape of the bottom section is defined by an internal surface 36 that lies along a second circle 38. The radius of the second circle is shown as b. In certain embodiments, the ratio of r:b may range from 1.2:1 to 5:1, for example, from 1.5:1 to 3:1, or from 1.8:1 to 2.5:1. An internal surface of the protruding portion can have a substantially semicircular cross-sectional shape. First and second edges 40, 42 of the top section are connected to first and second edges 44, 46 of the bottom section, respectively. The location of the center 48 of the circle defined by the bottom section can be chosen such that the wall of the bottom section has a substantially semicircular shape. In the embodiment shown in FIG. 5, the center 48 of the bottom section lies on the first circle 34 of the top section 28.

The bottom portion can be sized so that the flow fills the bottom portion at the lowest expected flow rate (e.g., the flow from a single toilet). In the embodiment of FIG. 5, flow fills the bottom section when the top level of the flow is at the level shown by line 50. For example, given a pipe with a radius r needed to handle the peak flow, append a bottom section having an area of radius b (b<r) to the bottom of the top section to handle the low flow condition. The resultant cross-sectional shape includes a lower section that extends downward a distance d that is greater than the radius r of the upper portion of the pipe.

In other embodiments, a bottom section having internal surfaces that lie along portions of several semicircles of decreasing radius can be added to the bottom of the pipe in a line. Several semicircles of decreasing radius can be added to the bottom of the pipe either in a line (FIG. 6) or in a generally triangular shape (FIG. 7) or some other shape.

As shown in FIG. 6, a bi-diameter pipe 60 can include a top section 62 having an internal surface 64 positioned along a first circle 66, and a bottom section 68 having a first internal surface 70 positioned along a circle 72 and a second internal surface 74 positioned along a circle 76.

As shown in FIG. 7, a bi-diameter pipe 80 can include a top section 82 having an internal surface 84 positioned along a first circle 86, and a bottom section 88 having a first internal surface 90 positioned along a circle 92, a second internal surface 94 positioned along a circle 96, and a third internal surface 98 positioned along a circle 100.

FIG. 8 illustrates pipe inserts and sleeves for retrofitting existing pipes in accordance with embodiments of the invention. In FIG. 8, a sleeve similar to the bi-diameter pipe shown in FIG. 5 is installed inside a conventional circular pipe.

FIG. 8 illustrates a pipe insert (also called a sleeve) for retrofitting existing pipes in accordance with embodiments of the invention. In FIG. 8, a contoured insert 110 is installed in a conventional circular pipe 112. The insert includes a top section 114, wherein at least a portion 116 of the top section has a partially circular shape that conforms to an internal surface of the conventional circular pipe. A bottom section 118 of the insert is connected to the top section and has an internal surface 120 that lies along a portion of a circle 122.

FIG. 9 illustrates a pipe 130 having a cross-sectional shape similar to the pipe shown in FIG. 5. In FIG. 9, the pipe 130 includes a top section 132, wherein at least a portion 134 of the top section has an internal surface 134 that lies along a circle 136. A bottom section 138 of the pipe is connected to the top section and has an internal surface 140 that lies along a portion of a circle 142. In the embodiment shown in FIG. 9, the center of the bottom section 138 lies above the circle 136 of the top section 132, e.g., at the same vertical height as the intersecting edges of the internal surfaces 134 and internal surface 140 of the top and bottom sections 132 and 138, respectively.

FIG. 10 illustrates a non-circular tube 226 in accordance with another embodiment of the present invention. The tube 226 includes a top section 228 and a smaller bottom section 230 that is coupled to the top section 228 by substantially flat transition walls 232. The transition walls 232 are arranged tangentially with respect to the top section 228 and the bottom section 230. The top section 228 has an internal radius r that is larger than an internal radius b of the bottom section 230.

FIG. 11 schematically illustrates a building drainage system 300 contained in a building 302 in accordance with an embodiment of the present invention. Several sets of plumbing fixtures 304, 305, 306 and 307 are provided at different locations and different elevations inside the building 302. Sewage from the fixtures 304, 305, 306 and 307 flows downward through conventional pipes into substantially horizontal bi-diameter pipes 314, 315, 316 and 317 having cross-sectional shapes in accordance with embodiments of the present invention. The bi-diameter pipes 314, 315, 316 and 317 may have cross-sectional shapes such as those shown in the embodiments of FIGS. 5-10.

As shown in FIG. 11, the bi-diameter pipes 314, 315, 316, and 317 feed into a vertical down pipe, which transitions into another horizontal bi-diameter pipe 318 having a non-circular cross-sectional shape as described above. The bi-diameter pipe 318 exits the building 302 via an outlet section 320 that may feed into a municipal system, i.e., a public sewer or the like.

FIGS. 12-15 illustrate fittings and couplings in accordance with embodiments of the present invention. In the embodiment shown in FIG. 12, a fitting 400 includes an inlet section 402 and an outlet section 405, which have non-circular cross sections similar to the bi-diameter pipes described above. The fitting 400 shown in FIG. 12 may be used to connect two equally sized bi-diameter pipes together.

FIG. 13 illustrates a connector 410 including an inlet end 412 and an outlet end 415. In this embodiment, although both the inlet end 412 and outlet end 415 are both non-circular, they are sized to accommodate and connected two bi-diameter pipes of differing sizes.

FIG. 14 illustrates a T-connector 420 in accordance with an embodiment of the present invention. The T-connector 420 includes a first section 422 and a second section 425 that intersects the first section 422 at a 90 degree angle. In the embodiment shown, the T-connector may be used to connect three bi-diameter pipes having the same sizes.

FIG. 15 illustrates a Y-connector 430 in accordance with an embodiment of the present invention. The Y-connector 430 includes a first section 432 and a second section 435 that intersects the first section 432 at an angle of less than 90 degrees. In the embodiment shown, the Y-connector 430 may be used to connect three bi-diameter pipe sections together having the same sizes.

Given any number of fixture units to be connected to the pipe and given any minimum flow requirement, the present bi-diameter pipes can be sized (i.e. the various radii can be selected) and the slope can be selected to maximize the velocity at low flow while providing sufficient capacity at peak flow. This can be accomplished using the standard charts of the building code by adding the fixture units accommodated by the smaller semicircular bottom portion of the pipe (diameter 2×b) to the fixture units accommodated by the larger upper portion of the pipe (diameter 2×r).

An example of a building code pipe chart is shown in Table 1.

TABLE 1
Building Drains and Sewers

	Maximum Number of Drainage Fixture Units Connected to
	Any Portion of the Building Drain or the Building
Diameter	Sewer, Including Branches of the Building Drain
of Pipe	Slope per foot

(inches)	1/16 inch	⅛ inch	¼ inch	½ inch

1¼	—	—	1	1
1½	—	—	3	3
2	—	—	21	26
2½	—	—	24	31
3	—	36	42	50
4	—	180	216	250
5	—	390	480	575
6	—	700	840	1,000
8	1,400	1,600	1,920	2,300
10	2,500	2,900	3,500	4,200
12	3,900	4,600	5,600	6,700
15	7,000	8,300	10,000	12,000
For SI: 1 inch = 25.4 mm, 1 inch per foot = 83.3 mm/m.

Furthermore, given requirements for peak flow, minimum flow, and several intermediate flows, the bi-diameter pipes can be sized (i.e. the various radii can be selected) to maximize the velocity at low flow while providing sufficient velocity at the other flow conditions. The bi-diameter pipes of the present invention can be easily sized using current methods of fixture units. The small diameter semicircular section at the bottom can be sized for the minimum flow such as flow from a single toilet, while the larger diameter section at the top can be sized for peak flow. In certain embodiments, when installing the bi-diameter piping of the present invention, the total number of fixture units may not exceed the maximum number of fixture units allowed for a larger circular pipe alone.

As described above, bi-diameter pipes constructed in accordance with embodiments of the invention can provide improved performance at low flow which can be incorporated into the currently accepted method of fixture units are disclosed. The bi-diameter pipes can replace round circular pipes or retrofit round circular pipes with tubes or sleeves of a different shape that maximize the velocity at low flow while maintaining capacity at peak flow. In certain embodiments, pipes having the disclosed shape include two or more conjoined portions. At low flow, only the smaller portion contains sewage, and it provides a higher velocity than the state of the art by providing a greater hydraulic radius. The larger portion, on the other hand, is large enough to provide sufficient capacity at peak flow while maintaining sufficient velocity. The fixture unit capacity of the bi-diameter pipes can be determined by adding the fixture unit capacity of the distinct portions of the pipe.

Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.