U.S. patent application number 10/060649 was filed with the patent office on 2003-07-31 for baffle insert for drains.
Invention is credited to Rattenbury, John M., Sommerhein, Per.
Application Number | 20030141231 10/060649 |
Document ID | / |
Family ID | 27610058 |
Filed Date | 2003-07-31 |
United States Patent
Application |
20030141231 |
Kind Code |
A1 |
Rattenbury, John M. ; et
al. |
July 31, 2003 |
Baffle insert for drains
Abstract
A baffle insert for conversion of conventional gravity drains
into siphonic drains. The baffle insert is placed into a sump bowl
of a gravity drain and by nature of its design changes hydraulic
condition in the drain to a siphonic condition. The baffle insert
is composed of a baffle plate and a plurality of fin extensions
coupled to a bottom surface of the baffle plate. In a preferred
embodiment, the number of fin extensions is 12, and the bottom
surface of the baffle plate has a concave shape.
Inventors: |
Rattenbury, John M.; (Hull,
MA) ; Sommerhein, Per; (Lidingo, SE) |
Correspondence
Address: |
LAMBERT & ASSOCIATES, P.L.L.C.
92 STATE STREET
BOSTON
MA
02109-2004
US
|
Family ID: |
27610058 |
Appl. No.: |
10/060649 |
Filed: |
January 30, 2002 |
Current U.S.
Class: |
210/163 ;
404/4 |
Current CPC
Class: |
E04D 2013/0427 20130101;
E04D 13/0409 20130101; E04D 2013/0413 20130101 |
Class at
Publication: |
210/163 ;
404/4 |
International
Class: |
E03F 005/06 |
Claims
What is claimed is:
1. A baffle insert for drains, comprising: a baffle plate, having a
central axis, a lateral edge, a top surface, and a bottom surface;
a plurality of fin extensions coupled to the bottom surface of the
baffle plate.
2. The baffle insert of claim 1 wherein: each fin extension has an
outer edge, and a bottom edge.
3. The baffle insert of claim 1 wherein: the fin extensions are
arranged in a radial pattern with respect to the central axis of
the baffle plate.
4. The baffle insert of claim 1 further comprising: an inlet
entrance area located under the lateral edge of the baffle
plate.
5. The baffle insert of claim 1 wherein: the bottom surface of the
baffle plate is slopped upwards from the lateral edge towards the
central axis.
6. The baffle insert of claim 1 wherein: the bottom surface of the
baffle plate has a concave shape.
7. The baffle insert of claim 1 wherein: the lateral edge of the
baffle plate has at least one anchoring extension.
8. The baffle insert of claim 1 further comprising: means for
coupling of the baffle insert to a sump bowl of a drain.
9. The baffle insert of claim 1 wherein: the fin extensions are
spaced equidistantly from each other.
10. The baffle insert of claim 1 wherein: each fin extension has a
substantially vertical orientation.
11. The baffle insert of claim 1 wherein: the baffle insert is
integrated with a sump bowl of a drain.
12. The baffle insert of claim 1 wherein: the baffle plate has a
round shape.
13. A baffle insert for drains, comprising: a round baffle plate,
having a central axis, a lateral edge, a top surface, and a bottom
surface; a plurality of fin extensions coupled to the bottom
surface of the baffle plate, wherein the fin extensions are
arranged in a radial pattern with respect to the central axis of
the baffle plate, and wherein each fin extension has an outer edge,
and a bottom edge.
14. The baffle insert of claim 13 further comprising: an inlet
entrance area located under the lateral edge of the baffle
plate.
15. The baffle insert of claim 13 wherein: the bottom surface of
the baffle plate is slopped upwards from the lateral edge towards
the central axis.
16. The baffle insert of claim 13 wherein: the bottom surface of
the baffle plate has a concave shape.
17. The baffle insert of claim 13 wherein: the lateral edge of the
baffle plate has at least one anchoring extension.
18. The baffle insert of claim 13 further comprising: means for
coupling of the baffle insert to a sump bowl of a drain.
19. The baffle insert of claim 13 wherein: the fin extensions are
spaced equidistantly from each other and each fin extension has a
substantially vertical orientation.
20. The baffle insert of claim 13 wherein: the baffle insert is
integrated with a sump bowl of a drain.
Description
FIELD OF THE INVENTION
[0001] This invention relates to baffle inserts for roof
drains.
[0002] Previously, two separate roof drain designs have been in
use, a gravity drain and a siphonic drain. In the United States,
gravity drains have been in a widespread use. They are
characterized as weir-type design in which the rainwater flows over
a rim and into a sump bowl before it enters the drainage pipe
system via a spigot outlet. With this particular design, the water
depth maintained on the roof is dependent on the circumference of
the outer rim and to a certain extent to resistance imposed by a
leaf guard. These viscous driven effects limit the rate of flow of
rainwater into the drain. Therefore, the diameters of the sump
bowls are relatively large in comparison to diameters of the spigot
outlets to maximize the circumferential weir length and, therefore,
the allowable flow rate.
[0003] A consequence of a gravity drain design is that the large
rim diameter in relation to the spigot outlet diameter means that
the water must flow radially inward for a certain distance along
the flat sump bowl to the spigot outlet before it enters the drain
piping system. Additionally, air enters the spigot outlet as well
and the rainwater flows on the inner sides of the piping in a thin
film. Therefore, the drain piping has to have a wide diameter in
order to have a large water intake capability.
[0004] The siphonic roof drainage has been utilized since the late
1960's starting in Scandinavia and spreading throughout the world
over, with the notable exception of the United States. Invented by
a Finnish engineer Olavi Ebling, the concept of siphonic drainage
is the achievement of full-bore flow within the drainage system
through a self-priming process and then of sustaining this flow
condition by eliminating the ingress of air through the roof drain.
Presently, the roof drains used for siphonic drainage are designed
as a whole unit with drain body, flashing hardware, and air baffle,
all designed together to achieve a siphonic performance. Such
drains include those designed, marketed and installed by
Sommerhein, A B and others. Since siphonic drains do not take in
air, the drain piping could accommodate greater volume of flowing
rainwater than same diameter drain piping in a gravity drain
system.
[0005] The key to the acceptance of siphonic roof drainage within
the United States is the production of drain devices by North
American drain manufacturers that are capable of supporting
siphonic drainage systems. Requiring the use of unfamiliar drainage
fixtures and pipe design techniques, siphonic drainage is currently
perceived by architects, engineers and contractors as "foreign" and
somewhat enigmatic technology.
[0006] What is needed is a simple and inexpensive way to convert
existing drain systems to a siphonic flow capability.
SUMMARY OF THE INVENTION
[0007] The present invention achieves this goal by placing a
specifically designed baffle insert into a conventional sump bowl
of the gravity drain. The baffle insert has a baffle plate and a
plurality of fin extensions protruding from the bottom surface of
the baffle plate. The design of the baffle insert allows for
creation of siphonic flow conditions inside of the drainpipe thus
converting a conventional gravity drain into a siphonic drain.
BRIEF DESCRIPTION OF DRAWINGS
[0008] These and other features, aspects and advantages of the
present invention will become better understood with reference to
the following description, appended claims, and accompanying
drawings where:
[0009] FIG. 1 is a side cross-sectional view of one of the
embodiments of the baffle insert.
[0010] FIG. 2 is a side cross-sectional view of one of the
embodiments of the baffle insert placed inside of a sump bowl of a
conventional drain.
[0011] FIG. 3 is a top view of one of the embodiment of the baffle
insert.
[0012] FIG. 4 is a bottom view of one of the embodiment of the
baffle insert.
[0013] FIG. 5 is a hydraulic analysis cross-sectional view partial
diagram of a section of the baffle insert placed inside of a sump
bowl.
DESCRIPTION OF THE INVENTION
[0014] This invention represents a baffle insert 50 depicted in
FIGS. 1-4. The idea behind the disclosed baffle insert 50 design is
to utilize existing conventional gravity drains used in the United
States and adopt them with an air baffle/anti-vortex plate to
achieve siphonic flow capability. This adaptation, however,
requires hydraulic analysis in order to ensure that the baffle
design is stable, will be capable of priming and minimizing the
depth of water on the roof as much as possible. By properly
configuring the baffle insert 50 geometry, the static pressure
beneath the baffle insert 50 can be controlled thereby ensuring
stable operation over a range of flows at a reasonable depth of
water over the spigot outlet 12.
[0015] The baffle insert 50 is comprised of a baffle plate 1 having
a central axis 2, a top surface 4, a bottom surface 5, and a
lateral edge 3. A plurality of fin extensions 6 is coupled to the
bottom surface 5 of the baffle plate 1 as depicted in FIGS. 1, 2
& 4. Each fin extension 6 has an outer edge 7, and a bottom
edge 8, as depicted in FIGS. 1 & 2. The baffle insert 50 has an
inlet entrance area 33 located under the lateral edge 3 of the
baffle plate 1.
[0016] The baffle insert 50 is designed for insertion into a
conventional gravity drain depicted in FIG. 2. Normally, the
gravity drain has a sump bowl 11 with a rim 10 and the collected
rainwater exits the sump bowl 11 by flowing through a spigot outlet
12 into a pipe 13. To convert the gravity drain into a siphonic
flow drain, the baffle insert 50 is placed inside of the sump bowl
11 over the spigot outlet 12 as depicted in FIG. 2. The baffle
insert 50 rests on the bottom of the sump bowl 11 with the bottom
edges 8 of the fin extensions 6 being in contact with the sump bowl
11.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0017] In a preferred embodiment, the baffle insert 50 has 12 fin
extensions 6 since this number was proven to be sufficient for
achievement of desired results during experimental testing. The
baffle plate 1 is circular in shape. The fin extensions 6 are
spaced equidistantly from each other and in a radial pattern around
the central axis 2, as depicted in FIG. 4. The bottom surface 5 of
the baffle plate 1 has a concave shape to improve hydraulics under
the baffle plate 1. Furthermore, the baffle insert 50 could have at
least one anchoring extension 35 protruding from the lateral edge 3
of the baffle plate 1, where the anchoring extension 35 has means
for coupling to the sump bowl 11 for prevention of spinning of the
baffle insert 50 inside of the sump bowl 11. The means for coupling
of the anchoring extension 35 to the sump bowl 11 are any means
well known in the art such as a clamp or a simple contact with any
protrusion on the inside of the sump bowl 11 as shown in FIG. 2.
Alternatively any means well known in the art could be used for
coupling of the baffle insert 50 with the sump bowl 11, such as
welding of the bottom edges 8 of the fin extensions 6 to the bottom
of the sump bowl 11. However, there is no absolute need to
physically affix the baffle insert 50 to the sump bowl 11. Simple
placement of the baffle insert 50 into the sump bowl 11 is enough
for achievement of siphonic drain water flow.
[0018] Following is an analysis of the hydraulics involved in the
design of the disclosed baffle insert 50 which should be considered
with reference to a FIG. 5.
[0019] The introduction of a baffle insert 50 into the sump bowl 11
creates a restriction to the water flow path in the horizontal
plane. When water flows radially inward beneath the baffle plate 1
from all sides surrounding the baffle insert 50, the available
volume decreases and, therefore, the velocity must increase under
the principle of continuity (i.e. Velocity.times.Area Constant).
According to Bernoulli's principle of energy conservation, the
increase in velocity also results in a reduction in static
pressure.
[0020] Starting with Bernoulli's Equation: 1 P r + V r 2 2 g + Z r
= P 0 + V 0 2 2 g + Z 0
[0021] Where .rho. is water density expressed in pounds mass (Lbm)
per cubic foot. We can eliminate the P.sub.0 term when referencing
atmospheric pressure as zero (gauge). Also, the velocity at the
water surface away from the inlet entrance area 33 of the baffle
insert 50 is nearly zero. By eliminating these terms and
rearranging to express P.sub.r explicitly we have: 2 P r = ( Z 0 -
Z r ) - V r 2 2 g
[0022] Because the top surface 4 of the baffle insert 50 is nearly
dry or covered only by a couple of inches of water, it can be
assumed that atmospheric pressure prevails on the top surface 4 of
the baffle insert 50 (i.e the Zo-Zr term is insignificant). Thus,
the static pressure at any point under the baffle plate 1 is less
than atmospheric. The pressure profile along the radius of the sump
bowl 11 during siphonic flow conditions is defined by what is
called "Barlow's Curve" which is obtained by a formula derived from
Bernoulli's principle while neglecting frictional flow losses under
the baffle.
[0023] We can express V.sub.r as follows using the principle of
continuity with Ar being the flow area at the inlet entrance area
33 of the baffle insert 50: 3 A r = 2 rh A r .times. V r = Q V r =
Q 2 rh
[0024] The term Q is the volumetric flow rate. By substituting the
above expression for V.sub.r into Bernoulli's equation: 4 P r = ( Z
0 - Z r ) - Q 2 8 2 r 2 h 2 g
[0025] This equation represents Pr in terms of the radial position
beneath the baffle insert 50 at a given flow Q. It teaches that the
static pressure beneath the baffle insert 50 decreases with the
inverse square of the radius with an unbounded limit when r
approaches zero.
[0026] The design of any air baffle, such as the baffle insert 50,
needs to follow three main principles. It first needs to be able to
prime the connected piping quickly. Thus, the height of the baffle
plate 1 above the bottom of the sump bowl 11 needs to be minimized.
This will help achieve a high Reynolds Number beneath the baffle
plate 1 and the necessary turbulence for proper air to water
mixing. Second, the baffle insert 50 must not introduce a limiting
effect with respect to maximum flow. In other words, it is
advantageous for the drain to be limited in maximum flow capacity
by the fixed spigot outlet 12 diameter and not by the introduction
of a baffle insert 50. Finally, the first two goals must be
balanced with the desire to have a minimum of water depth on the
roof above the baffle insert 50, which means that the resistance of
the baffle insert 50/drain combination should be minimized.
[0027] The static pressure (in this case, negative pressure) under
the baffle insert 50 is an important parameter for any baffle
design because there is a limit to negative pressure under the
baffle. If the static pressure beneath the baffle reaches water's
vapor pressure at the ambient temperature, spontaneous flashing of
water into vapor will occur resulting in a phenomenon known as
"cavitation." This condition is characterized by alarming noise,
vibrations and a disruption in flow. Thus, there is an upper limit
to flow capability through the drain in siphonic action.
[0028] The flat sump bowl 11 design of conventional roof drains
precludes the efficiency of a flat plate or convex baffle as this
geometry compounds the drop in static pressure as water flows
radially toward the spigot outlet 12. Our approach to the baffle
insert 50 design was to limit the maximum velocity beneath the
baffle insert 50 to minimize the Barlow Curve effects. It is
possible to maintain a stable static pressure beneath the baffle
plate 1. Since the direction of flow is horizontal, potential
energy effects do not come into play. If the effects of friction
losses are ignored, the development of the static pressure along
the radial dimension is controlled only by the velocity head term
in Bernoulli's energy equation. In order to maintain and control a
maximum static pressure drop, the velocity must be limited to some
maximum value in the direction of flow.
[0029] This requirement is possible to achieve if the baffle plate
1 is given an upward slope on the bottom surface 5 from the lateral
edge 3 towards the central axis 2. This concave geometry, shown in
FIGS. 1, 2 & 5, is intended to maintain a limit to the water
velocity beneath the baffle plate 1.
[0030] The first step in determining the dimensions of the baffle
insert 50 is to set the minimum height of H.sub.i at the inlet
entrance area 33 where the water enters the drain. The first
principle design feature is to allow the system to prime quickly,
but there is a minimum height above the sump bowl 11 that will
assure the achievement of the second principle, to ensure that the
maximum velocity below the baffle plate 1 does not exceed the
velocity within the spigot outlet 12. Since the drain manufacturer
fixes the radius of the spigot outlet 12, the velocity at the
spigot outlet 12 V.sub.o, sets the maximum velocity at the inlet
entrance area 33. We want V.sub.i to be less than or equal to
V.sub.o. We can express the velocity in the spigot outlet 12 in
terms of the water flow rate as follows: 5 V 0 = Q R 0 2
[0031] Where Q is the volumetric flow rate and Ro is the spigot
outlet 12 radius.
[0032] The water velocity at the inlet entrance area 33 can also be
expressed in terms of the flow and the inlet entrance area 33
geometry. The analysis of the cross-sectional area below the baffle
plate 1 needs to account for the presence of the fin extensions 6.
These fin extensions 6 are an integral part of the baffle insert 50
design. They serve three main purposes:
[0033] 1. They prevent or diminish the rotation of the inflowing
water (i.e. vortices).
[0034] 2. They assist in the mixing of water and air during the
initial phase of priming thus minimizing the priming time for the
device and the connected piping.
[0035] 3. The fin extensions 6 transfer the force created by the
differential pressures across the baffle insert 50 to the bottom of
the sump bowl 11.
[0036] The number of fin extensions 6 is optional, however, in
order to minimize rotation and maximize air mixing, 12 fin
extensions 6 have been chosen for this design. The fin extensions 6
occupy a certain area that has to be considered when calculating
velocities beneath the baffle plate 1.
[0037] At the inlet entrance area 33 of the baffle insert 50, we
apply the same principle of continuity to express the inlet
velocity (Vi) in terms of the flow rate as follows:
A.sub.i=2.pi.R.sub.dH.sub.i-ntH.sub.i
[0038] In this expression, the area at the inlet entrance area 33
is the circumference of the baffle plate 1 (if the baffle plate 1
is round) times the height less the area taken up by the fin
extensions 6 where n is the number of fin extensions 6 and t is
their thickness.
[0039] Thus: 6 V i = Q 2 R d H i - n t H i
[0040] By setting Vi=Vo, we see that the flow rate drops from the
analysis and only the two areas are left (i.e. the cross-sectional
flow areas at each station must be equal). After some rearranging:
7 H i = R 0 2 2 R d - n t
[0041] For the 4" outlet drain (102 mm), the spigot outlet 12
radius (Ro) is 2.0 inches (51 mm), the baffle plate 1 radius is set
at 4.33 inches (110 mm), the number of fin extensions 6 chosen is
12 and the fin extensions' 6 thickness is 0.25 inches. Substituting
these numbers into the above equation, the minimum height at the
inlet entrance area 33 (Hi) is 0.52 inches. In our design, we set
the height well above that minimum height to 1.1 inches (28 mm) to
ensure a stable design. The primary reason for this is to assist in
limiting the resistance value of the baffle insert 50 while still
maintaining a reasonably minimum clearance to assist in quick
priming.
[0042] The goal of the design at this stage is to then set the
radial velocity Vr to a maximum allowable value beneath the baffle
plate 1. This is achieved by pitching the bottom surface 5 of the
baffle plate 1 upward and away from the flat bottom of the sump
bowl 11. The desired result of this pitch is to allow a velocity
head no greater than that achieved in the fixed spigot outlet 12.
Thus, the maximum flow capacity of the drain is limited only by the
spigot outlet 12 dimension and not the baffle insert 50. The flow
cross-sectional area can be expressed for any value of r between Rd
and Ro as follows:
A.sub.r=(2.pi.r-nt)(H.sub.i+(R.sub.d-r)tan .alpha.)
[0043] Alpha is the slope of the bottom side 5 of the baffle plate
1. In this case the height of the inlet entrance area 33 is no
longer a constant value as it would be if the baffle plate 1 was a
flat disc--the height increases as r decreases. Again setting the
spigot outlet 12 area equal to the flow cross-sectional area below
the baffle plate 1, we get: 8 = arctan [ R 0 2 ( R d - r ) ( 2 r -
n t ) - H i ( R d - r ) ]
[0044] The point just before the spigot outlet 12 would have the
highest velocity if the baffle plate 1 were not pitched. Thus,
solving for alpha at r=Ro will give the minimum pitch required.
With Ro=2, Rd=4.33, Hi=1.1, n=12, and t=0.25 we find the value of
alpha to be a minimum of 5.2 degrees.
[0045] With this resulting pitch, we go back to compute the
velocity head in the spigot outlet 12 at a unit flow of 1 cubic
foot per second. With the inner diameter being 4", the resulting
velocity head is 2.04 ft. The velocity head of the water just
before it reaches the edge of the spigot outlet 12 is computed to
be also 2.04 ft. The velocity head at the inlet entrance area 33 of
the baffle is 0.45 ft. Thus, the designed geometry allows the
converted drain to operate at its highest possible capacity while
maintaining a safe design without cavitation effects.
[0046] The tested prototype has an inner slope on the bottom
surface 5 of the baffle plate 1 of 5.0 degrees for simplicity of
construction. During flow tests, the baffle insert 50 performed
according to theory and should constitute a safe and stable design
when put into production.
* * * * *