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Copyright 2005, Board of Trustees, University
."F 2C 190g
i;t'OcrsitY of Florid.
Some Devices for Flushing Animal Wastes
R.A. Nordstedt and L.B. Baldwin
Florida Cooperative Extension Service
Institute of Food and Agricultural Sciences
University of Florida
John T. Woeste, Dean
SOME DEVICES FOR FLUSHING ANIMAL WASTES
R.A. Nordstedt and L.B. Baldwin1
'Associate Professor-Extension Agricultural Engineer and As-
sociate Professor Emeritus, Agricultural Engineering Department,
University of Florida, Gainesville, FL 32611.
Flushing of animal wastes offers several advantages for the live-
stock producer, including labor efficiency and a more pleasant if not
actually more healthy environment in animal housing areas. This
report describes flushing facilities the authors designed or observed
to remove wastes from flush alleys under slatted floors in swine
houses, floors in dairy shade barns, and outdoor holding slabs for
Flush gutters up to about 3 feet (1 meter) wide can be flushed
successfully with small tanks made from 55- gallon (208 liter) drums
hung to swing on a longitudinal axle (Figure 1). The dump opening
is made by cutting out one quarter of the cylinder wall and replacing
it with a straight lip running at a tangent to the lower edge of the
opening. Steel scrap or lead counterweights are attached to hold the
tank with the opening spanning 12 to 3, or 9 to 12 o'clock, as viewed
from the ends. The tank can be filled with a hose bib mounted over
the tank opening. Upon dumping, the lip of the tank can strike the
concrete floor to stop rotation and discharge directly down the gutter.
To flush a 6-foot (2 meter)-wide alley, two drums welded end to end
and swung on a common axle may be used. The volume of flush
water is usually about 80% of the nominal size of the tanks, about
15 gal/ft (55 liters/meter) of gutter width. The striking force between.
tank lip and concrete floor is acceptable for both single and double
tanks. No shock control linkage or swing stops other than the floor
are needed. The drum tanks have been effective for calf and swine
wastes on troweled concrete up to about 80 feet (24 meters) in length
at 1% slope. Lengths greater than this require repeated, rather than
once or twice daily, flushing to clean the floor. Greater volume per
foot of alley width and increased floor slope will improve the flush
on longer gutters.
The use of long tilt tanks constructed from more than two 55-
gallon (208 liter) drums placed end to end is impractical due to the
light construction of the drums compared to the necessary axles and
supporting bearings needed to handle the weight involved. In order
to flush wider floors such as in feeding or loafing shade barns for
water supply -
4" x 3/8" flat steel cross
braces fit against drum
head and welded to rim.
I 3/8" o.d. x 50" long
steel pipe axle.
attach 651b.-701b. ballast of
I pc. 4" x 3/8" x 38 1/2" steel
and 4 pcs. 4" x 3/8" x 30"
steel or other materials of
equal weight. the tank should
hang in the position shown
cone. block or
~---~~-- ~ M
-- full safety screen
> <- flushing alley
Figure 1. Gator Gusher: Self-Dumping Tank
for Flushing Wastes.
S mount above lip radius
16 go. steel lip
cut out 1/4 of
wall but do not
22 1/2" dia. x 34 1/2"
55 gal. steel drum.
dairy cows, larger tanks may be selected. Multiple large tanks have
been used for a floor which was 30 feet (9 meters) wide and 80 feet
(24 meters) long, at a 2% slope. The finish was broomed for better
footing. Three standard 287-gallon (1086 liter) cylindrical tanks were
used. The openings and lip were in the same proportion as the smaller
drum tanks. Counterweights to hold the tanks in position while
filling were provided by pouring about 2 inches (5 centimeters) of
concrete in the tanks after mounting on the swing axle. A 4-inch (10
cm) steel pipe was used as a common axle for the three tanks, with
adequate spacing between tanks for pillow block bearings to support
the apparatus. Uniform filling of the tanks was accomplished by
perforating the axle inside each tank and supplying water through
a connection at one end of the axle.
Large tanks tend to self-destruct when floor-lip contact is used as
a tilt stop during the dump. Shock absorbers may be used, or the
tanks may be mounted high enough to swing freely. The latter has
the advantage of simplicity of mounting. The major disadvantage of
a free swing dump is the tendency to drop the water vertically, with
resultant initial flow in all directions and a lower wave traveling
down slope. The dump can be given downslope direction by forming
a curved concrete wall behind the tanks and dumping against it.
The large tanks operated satisfactorily as described. The flush
water amounted to about 70% of the nominal size of the tanks,
providing 20 gal/ft (250 liters/meter) across the floor. Initially, the
tanks were allowed to dump every few hours to keep the loafing
barn floor quite clean. This practice resulted in sore hooves from
continually wet conditions on the hard floor. The tanks are presently
operated daily for two or three- dumps as rapidly as the tanks refill.
Although accurate costs were not obtained for the large, three-tank
installation, it is apparent that the device is costly. For most appli-
cations, it appears that tilt tanks' practicability extends to the 100-to-
150-gallon (380 570 liter) volume, but diminishes above that range
due to the necessity of supporting the greater weights and providing
shock absorber systems or curved backwalls, all of which are expen-
Piped Gravity Discharge
Large pipes or other conduits which deliver water by gravity are
sometimes called "siphons" even though they do not depend on atmo-
spheric pressure to function, as a true siphon does. This misnomer
is most frequently used when some sort of air trap is used as a
pressure-controlled valve. The devices discussed in this report are
not true siphons in that the discharge pipe does not run above the
stored water level (Figure 2).
NOTE: When water in tank fills to pipe trap
height H above lower lip of bell,
trapped air escapes down discharge
pipe and tank will drain.
Figure 2 Typical Arrangement of Air-Trap-Valve
to Initiate Discharge from Elevated
Flushing from elevated tanks by means of large pipes offers the
advantage of discharging large volumes of water with minimal in-
volvement of moving parts. It is necessary to support the weight of
the water for each flush which is usually an amount exceeding the
capability of standard building roofs. Discharge pipes can theoreti-
cally be sized or multiple-mounted to deliver any needed quantity
of water rapidly enough to develop a flushing wave. The materials
and equipment selected should be commercially available and
reasonable in price. A large swine building for farrowing and a nurs-
ery with flush alleys under slatted floors was equipped to de-
monstrate multiple-pipe discharge from elevated tanks. There were
two alleys 135 feet (41 meters) long and 7.7 feet (2.3 meters) wide,
and two alleys 90 feet (27 meters) long and 10 feet (3 meters) wide.
All alleys were sloped 2% with troweled finish, and a concrete sealer
was applied to reduce sticking. Concrete tanks were built on the
roof of a concrete block section of the housing facility. Additional
reinforcement was needed. The airtrap valve arrangement shown
in Figure 2 was used to automate flushing.
The 7.7-foot-wide alleys were each equipped with two 4-inch (10
cm) pipes with pipe traps formed from standard PVC plastic pipe
and fittings. Simultaneous discharge was achieved by mounting the
pipe inlets under a common airtrap bell fabricated from sheet
aluminum. Trap charging holes, and notches along the lower edge
of the bell, were provided for complete aspiration following discharge.
The 10-foot wide alleys were each equipped with three 4-inch pipes,
also under a common bell. Each of the four sets of discharge pipes
drained a concrete tank containing approximately 600 gallons (2300
liters). Discharge time was between 15 and 20 seconds, delivering
approximately 80 gallons/ft. (990 liters/meter) and 60 gallons/ft. (760
liters/meter) to the 7.7 and 10-foot-wide alleys, respectively. The
pipe outlets were set behind a 6-inch (15 cm)-high curb which ex-
tended across the upper end of each alley. The purpose of the curb
was to evenly spread the water entering the alley.
The discharge and alley dimensions appeared to be well matched.
Measured flow depth at the lower end of the alleys was about 3
inches (7.5 cm). Wastes were removed satisfactorily with a single
flushing, twice daily.
Expanding on experience with the facility just described, a dual
tank facility was designed with four 4-inch pipes under a common
bell in each tank with a 2-inch (5 cm) air line connecting the bells
for simultaneous discharge. The floor to be flushed was 24 feet (7.3
meters) wide and 150 feet (46 meters) long, sloped at 3%. The floor
surface was grooved irregularly for better footing. The building was
designed to house beef brood cows for feeding and loafing.
Several innovations were used in this flushing facility. It was
constructed using a pole-supported platform, 10 feet (3 meters) high,
outside the building, for two standard 660- gallon (2500 liters) stock-
watering tanks. These tanks were 2 feet (.6 meter) deep. Air-trap
bells were made from smaller, shallower sheep-watering tanks,
placed in an inverted position over pipe intakes. Trap charging and
bell aspirator holes were provided. The air line connecting the bells
was equipped with a manually operated valve to vent the bells to
the atmosphere and initiate the flush.
One discharge pipe trap was selected to be the trigger for auto-
mated discharge. This is often necessary with large, multi-pipe de-
vices because the water fill rate is not adequate to overcome initial
spillover in all the tubes and continue to increase the tank level to
cause air escape and discharge. A piece of plastic tubing was installed
across the top loop of the trap to reduce the length of the water
column resisting discharge by about 1 inch (2.5 centimeters). This
method can be used to correct a trap that is too long for the available
tank head without cutting and reassembling the trap.
Automatic discharge (when the increasing water level in the tanks
causes the bells to vent air down the pipes) has not been entirely
satisfactory with this two-tank, two-bell facility. The air purge by
this means results in about 30 seconds of low flow down all eight
pipes before air flow finishes and the main surge of water occurs.
This diminishes the flushing wave. When the discharge was
triggered by opening the air valve above the bells, full water flow
was quickly started and discharge of the approximately 1000 gallons
(3800 liters) occurred in about 20 seconds, providing about 42 gallons/
foot (520 liters/meter) of floor width.
Like large tilt tanks, multiple pipes for large volume flushing can
become tricky to design and expensive to construct, particularly the
support of elevated water tanks. The air bell for single or multiple
discharge tubes can be operated as a quick discharge valve by venting
the bell manually, as described above. This would require controlling
the fill level to prevent overflow. The relative cost of air-trap valves,
either automatic or manually operated, in place of one or more large,
quick opening mechanical valves should be considered.
Gated Discharge Floor Level Tanks
Tanks built at floor level or on a slightly elevated floor can be
sized to contain large volumes of water at low cost. Several gates
are commercially available to empty large tanks rapidly enough to
create a flush wave. Also, homemade gates can be devised. Gates
can be automated, but most producers prefer manual operation
which avoids the hazard of unexpected operation and reduces cost.
Floor level tanks with low sides can sometimes function as watering
tanks. They are usually constructed of reinforced concrete block with
cement plaster or other lining that will provide waterproofing.
Examination of several floor level tank flush systems for feedlots
and wide dairy feed and loafing lanes reveals a wide range in the
volume of water used for each flush and in the number of flushes
per day. Manufacturers of flush gates usually recommend flush vol-
ume based on floor width, slope, and length. The more common
volumes recommended are up to 120 gallons per foot of floor width
(1000 to 1500 liters/meter) for floors at 2% slope and up to 150 feet
(46 meters) long. Greater floor length requires proportionally more
water. Animal density and the time animals remain on the flush
floor determine flushing frequency. Twice-a-day flushing is often
employed at dairies to correspond with the milking and feeding cycle.
Enclosed buildings may be flushed more frequently for better odor
High Volume Pumping
Another method of flushing is the use of high volume pumping to
produce sustained flow for periods of several minutes up to an hour.
This method is used to flush gutters under layer cages by introducing
flow of 80 to 100 gallons per minute per foot of pit width (1000 to
1500 liters/min/meter) on slopes of around 0.5%. Flows of the mag-
nitude required are obtained at reasonable costs with low-head
pumps using the waste lagoon as a water source. This system is less
attractive if potable water from a well is to be used.
Large, irregularly shaped floors which are sloped can be flushed
by introducing a flow of water along the upper end of the slope. Such
a system was constructed at the IFAS dairy research farm. The floor
was a holding area about 200 feet (60 meters) long and 32 feet (10
meters) wide. Slope was about 3%, running across the floor. The
flush system utilized a high pressure irrigation pump and barn waste
water collected in a pit. Flush water was discharged along the 200-
foot (60 meter) top of slope by means of 4-inch (10 cm) steel pipe,
perforated with 3/8 inch (.95 cm) holes at 18-inch (46 cm) intervals.
Discharge was estimated at about 4.5 gpm per foot (57 pm/meter).
The system was operated daily for an hour or more, with some
The capability to flush animal wastes reduces labor requirements
and generally improves the appearance and the environment of ani-
mal housing and holding areas. Where daily or more frequent clean-
ing is required, flushing devices generally do not increase total water
requirements. Waste water can often be reused for flushing. Disad-
vantages of flushing can be waste volume increase in some cases
and higher capital costs for waste management. Capital costs and
maintenance of flushing devices can be minimized by the use of
simple principles and economical, long lasting materials.
The key to successful flush cleaning is proper layout and construc-
tion of the floors and gutters to be flushed. Surge or wave flushers
are particularly dependent upon uniform slopes and floor finishes.
Experience indicates that the frequency and number of flushes can
be altered to compensate for changes in manure accumulation, drying
manure, or other variables. On the other hand, it is difficult to design
a flush system to operate satisfactorily on irregularly sloped or flat
Pits or gutters under slatted floors or cages should have a smooth
surface. Wide areas can be flushed more efficiently if they are divided
into 4-to-6-foot (1.2 to 1.8 m) alleys with curbs. Flush surfaces oc-
cupied by animals may be grooved either transversely or with a
diamond pattern. Grooves which would lead flowing water to one
side of the flush alley should be avoided.
All flush systems require storage or outflow capacity at the foot
of the flush area to prevent ponding on the area. Reduced water
velocity will result in settlement of waste solids and poor cleaning.
Deep cross gutters can be used to achieve this, but they must be
drained and perhaps independently flushed to prevent filling with
The corrosive atmosphere near manure accumulation, particularly
when waste water is being used for flushing, make the use of intricate
steel linkages and structures undesirable. Some manual operation
may be preferred to long term dependence on float valves and
switches which may corrode, fail, and result in power and water
waste. Low maintenance design is critical to the continued proper
functioning of waste management facilities.
Safety is an ever present factor when heavy loads and quick moving
devices, such as tilt tanks and drop gates, are involved. Initial design
and construction to assure adequate support, and enclosures to block
entry to danger areas should be of primary concern in planning flush
COOPERATIVE EXTENSION SERVICE, UNIVERSITY OF FLORIDA, INSTITUTE
OF FOOD AND AGRICULTURAL SCIENCES, John T. Woeste, director, in cooper-
ation with the United State Department of Agriculture, publishes this information to
further the purpose of the May 8 and June 30, 1914 Acts of Congress; and is
authorized to provide research, educational information and other services only to
individuals and institutions that function without regard to race, color, sex, age, .
handicap or national origin. Single copies of extension publications (excluding 4-H
and youth publications) are available free to Florida residents from county extension offices. Information
on bulk rates or copies for out-of-state purchasers is available from C.M. Hinton, Publications Distribu-
tion Center, IFAS Building 664, University of Florida, Gainesville, Florida 32611. Before publicizing
this publication, editors should contact this address to determine availability. Printed 8/90.