Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to an overflow unit, particu-
larly for rain-water overflow basins, rain retaining basins,
flood water retaining basins or the like.
This application is a divisional application of copend-
ing application No. 245,411 filed February 10, 1976.
It is known to throttle the outlet of overflow units
in combined storm-water and sewage systems inorder to achieve a
back-up or backwater in the event of increased inflow, so that
the overflow level is raised and the channel situated upstream
of it can be used as a storage volume (Lehr- und Handbuch der
Abwassertechnik (Textbook and Handbook of Sewage Technique),
Vol. 1, 1973, page 447). In this arrangement the overflow unit
is usually followed by a sufficiently long throttling section,
which is disposed in the sewage outlet pipe leading, e.g. to the
clarification plant. The known ouerflow unit nevertheless has
the disadvantage that the amount of water discharged through the
outlet fluctuates considerably, since it depends not only on the
fixed cross-section of the outlet pipe but also on the height of
the water level in the overflow unit. With high water levels in
the overflow unit it is therefore possible for far larger amounts
of water to be supplied through the outlet pipe to a clarifica-
tion plant which may be provided downstream of the overflow unit
than the plant can handle, so that an additional storm water
clarification tank is necessary in the region of the clarifica-
tion plant.
According to the present invention, there is provided a
water overflow unit, comp~ising a flow chamber having at least
one inlet, a discharge outlet from a lower region of the chamber
and an overflow outlet arranged to be utilised when a predeter-
mined capacity level is reached in the flow chamber, a restriction
device being provided for controlling the flow through the dis-
charge outlet, said device being displaceable by actuating means
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responsive to the liquid level in the overflow unit such that the
flow through the discharge outlet is increasingly restricted in
dependence upon a rise in the liquid level.
By the use of such an arrangement in a combined storm-
water and sewage system it is possible to keep the quantity of
sewage flowing through the discharge outlet to the treatment
plant substantially constant independently of the water level in
the overflow unit~ above a certain level, and so there is no need
to provide extra storage basins or reservoirs for the sewage
plant itself.
The adjustable restriction device can be actuated by a
float disposed in the overflow unit and may take the form of a
valve comprising a pivoted throttle flap or a sliding gate. When
the water level rises in the overflow unit, the float closes the
valve increasingly so that the discharge is further restricted
and is adapted to the higher pressure in the head water.
The float can be mounted on one end of a lever pivoted
intermediate its length at a point disposed above the maximum
water level in the overflow unit, a follower on the other end of
the lever engaging interchangeable cam means connected to the
restriction device. This feature makes it possible to adapt the
operation of the restriction device to various capacity levels
just by changing the cam means and ther~by varying the discharge
characteristics. Thus, when this feature is provided in a sewage
system where the inflow has increased, e.g. because of new hous-
ing and industrial development, the new discharge conditions can
be dealt with just by changing the form of the cam means.
The restriction device may be received in a shaft or
gallery or other discharge chamber disposed between the discharge
line and the flow chamber of the unit and communicating with the
flow chamber through the discharge opening. The float-operated
means for actuating the restriction device may be disposed in
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1094'~L4
that discharge chamber. If the restriction device comprises a
throttle flap instead of a gate, it will require no slide guides
likely to pick up pieces of foreign matter which may prevent
satisfactory operation. Placing the throttle flap in a special
shaft or gallery after the flow chamber ensures that even rela-
tively large pieces of foreign matter cannot upset its operation,
which is of particular significance, in a sewage system; in
addition, the actuating linkage for the throttle flap is not dis-
posed in the combined sewage flow chamber but is readily acces-
sible in the shaft or gallery for inspection and repair.
Conveniently, when the float for the restricting device
is disposed in the flow chamber of the overflow unit, a trash
board can be provided in that chamber to prevent the float from
being damaged by floating matter and to prevent the float from
being affected by differing flow pressures of the inflow.
The float for the restriction device can be alter-
natively disposed in the shaft or gallery or other discharge
chamber which follows on the overflow unit, the float being able
to rise and fall in said shaft or gallery in dependence upon the
water level there. Controlling the restriction devlce by the
tail water in this way has the advantage of improved throttle-
element regulation, since in tlle event ofa disturbance in the
discharge flow the water level in the shaft or gallery drops
; immediately and the throttle element opens fully. Any blockage
or ~amming or the like is then usually cleared rapidly by the
water entering the discharge at high pressure and above the
critical speed.
The invention will now be described in greater detail
with reference to the accompanying drawings, which also appear
in copending application No. 245,~11 which relates to other
features of overflow units and to overflow basins using such
units. In the present drawings:
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Fig. 1 is a view in longitudinal section of a storm
overflow basin provided with one embodiment of overflow unit
according to the invention,
Fig. 2 is a plan view of the installation of Fig. 1,
Fig. 3 shows on a larger scale a detail of Fig. 1,
showing the restriction or throttle device of the overflow unit,
Fig. 4 is a horizontal section, on the line IV-IV of
Fig. 3, of the arrangement of Fig. 3,
Fig. 5 shows a detail of Fig. 3 on a larger scale,
Fig. 6 is a plan view of the arrangement shown in Fig.
5,
Fig. 7 shows diagrammatically a vertical longitudinal
section of the restriction or throttle device in another embodi-
ment of the invention, and
Fig. 8 is a cross-section on the line VI-VI of the
arrangement of Fig. 7.
In the drawings, 10 designates a storm overflow reser-
voir or basin which is disposed underground in a combined sewer
system somewhere near the sewer route. The storm over~low basin
comprises an elongated storage volume or tank or the like 12,
which is disposed below the surface 11 of the ground and is con-
nected to a trunk main 13 of the combined system, and a storm
overflow unit 14 which is connected to the tank or the like 12
at the downstream end thereof.
Both the overflow unit 14 and the storage tank 12 are
disposed underground somewhere near the sewer route, and the over-
flow unit has a flow chamber 15 whose inlet opening 16 is con-
nected to the storage tank 12 and is there provided with a baffle
or trash board 17.
On that side 18 which is opposite inlet 16 there is
situated a chamber outlet 19 to which a sewage discharge pipe 26
is connected which leads to the clarification plant (not shown~.
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The flow chamber 15 of the overflow unit 14 is bounded
on one side by a storm overflow 21, which separates the flow
chamber 15 from a flood relief channel 22 which leads to an out-
fall tnot shown). The storm overflow 21 comprises a fixed weir
sill 21a and a weir gate 21b which is pivotable about a horizon-
tal axis and is disposed above the weir sill.
The outlet 19 disposed at the bottom of the flow cham-
ber 15 is adapted to be closed by a restriction device comprising
a sliding gate 23, which is fastened at the bottom end of a guide
frame 24. The guide frame 24 is guided in guide rails 25, which
are secured at the rear end wall 26 of the overflow unit. At its
top end the frame 24 carries an exchangeable control cam plate
27, which has a control profile 28 in the form of a slot.
A two-armed lever 31 is pivotably mounted on a pivot
pin 30 disposed above the highest possible water level 29 in the
flow chamber 15 of the overflow unit 14. A float 34 is fastened
to the longer arm of the lever at end 33. The other end 35 of
the shorter lever arm 36 of the cranked lever 31 carries a pin
37 which engages in the control slot 28 of the cam plate 27.
It can be seen that the lever 31 pivots in the clock-
wise direction in the position shown in Fig. 3 when the float 34
rises. The pin 37 then slides to the left in the slot 28 and
pushes the cam plate 27 downwards, and with it the guide frame
24 and the gate 32 fastened thereon, so that with rising water
level in the overflow unit 14 the outlet 19 is increasingly
restricted.
;~ Depending on the construction and arrangement of the
cam plate 28, falling or rising movements of the gate 23 of
different magnitudes can be achieved for the same movement of
the float 34, so that for any level of water in the overflow
unit 14 the desired amount of water can be discharged through
the outlet 19.
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.
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In the embodiment shown in Figs. 7 and 8 the discharge
19 comprises a short tubular section 42 which is fitted into rear
end wall 41 of the chamber 15 and whose downstream end can be
closed by a restricting device 75 comprising a throttle flat or
gate 43. The throttle fla~ or gate is disposed in a shaft or
gallery or like discharge chamber 44 which follows on the unit
14 and which, like the flow chamber 15, has an open-top trough
45 to which a sewage line 20 extending to the treatment plant
(not shown) is connected. The throttle flap or gate 43 is
slidably mounted at the rear of the section 42 and can be actu-
ated by means of an actuating linkage operated by a float 50 that
is disposed in a shaft or gallery 44 forming a discharge chamber
~ which follows on from the flow chamber 15, the float 50 rising
- and falling in the gallery or shaft 44 in dependence upon the
- water level there. The float is secured to a cranked lever 116
of the linkage pivotally mounted at the point of cranking 117 on
a pivot 118 disposed in gallery 44, the free end of lever 116
being guided in the slot of a slider 108 (shown only diagrammati-
cally) which is connected to the throttle gate 43 for closing
the sewage discharge outlet 19. The linkage 47 is so devised
that the throttle gate closes increasingly as the water level in
the gallery 44 rises but remains fully open in dry weather flow
conditions when the quantity of water flowing only partly fills , -
trough 36 in the flow chamber 33.
If only a little sewage flows through the outlet 19 and
if the water level does not exceed a lower limit 115, the float
50 will rest on the inclined side walls 51 of a gutter or trough
45 forming the bottom of the discharge chamber. The throttle
gate 43 is then completely opened. If the water level in the
gallery 44 rises because of a greater pressure head, which may
rise to the high water level 65 in the flow chamber 15, a larger
amount of water flows through the outlet 19, the float is raised. I
16~ 4
It then increasingly closes the throttle gate 43.
Clearly, controlling the gate 43 in dependence upon
the water level in the shaft or gallery is much simpler than
controlling it in dependence upon the water level in the main
unit 14. Another advantage is the quicker response to distur-
bances, since the float drops very rapidly in the gallery in
response to a reduction or complete cessation of inflow into
the gallery because of a stoppage in the sewage discharge outlet
19. Also, the float and its linkage are less exposed to soil
than in the flow chamber 15, of the unit 14.
The overflow units described above are of use not only
in storm overflow basins but may be adapted for use generally in
systems for storm overflows, storm-water retention basins and
; storm-water clarification basins.
The illustrated arrangements can be modified as shown
for example in our copending application No. 245,511 by providing
a restriction device in the form of a throttle flap pivoted,
preferably at its top edge, instead of the sliding gate described
above. Also, when the float is located in the flow chamber a
trash board or baffle may be disposed upstream of it to avoid the
float being affected by variations of flow pressure in the cham-
ber. As regards the use of a cranked level to be operated by the
float, to keep the lever pivot mounting from being immersed, it
may be attached to the roof of the unit.
The constructions described may be varied in many other
ways obvious to those skilled in the art without exceeding the
scope of the invention.
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