Design Criteria For Swine Waste Flushing Systems

Prepared by:
James C. Barker
Professor and Extension Specialist
Biological and Agricultural Engineering

L. Bynum Driggers
Professor and Extension Specialist
Biological and Agricultural Engineering

Ronald E. Sneed
Professor and Extension Specialist
Biological and Agricultural Engineering
North Carolina State University, Raleigh, NC

Published by: North Carolina Cooperative Extension Service

Publication Number: EBAE 080-81

Last Electronic Revision: March 1996 (JWM)

North Carolina swine production has consistently moved toward large confinement operations with animals housed in environmentally controlled or curtain side-walled buildings over concrete slab or slotted floors. Storage of waste for short periods of time on slab or for prolonged periods in underslat storage pits was a substantial improvement in waste handling over previous methods or drylot systems. Scraping or washing the solid floors often enough to prevent excessive odors became labor intensive. Preventing manure solids from settling to the bottom of storage pits and accumulating to the extent that they were difficult to agitate and remove became a management crisis for many producers. As anaerobic decomposition produced more odor and gases within the building, herd health and animal performance suffered.

Since lagoon treatment of animal wastes is widely utilized in the Southeast, recycling of lagoon effluent appeared to be the next step in expanding waste handling technology. For these reasons, waterwash (flush) systems have become quite popular over the last decade for frequent removal of wastes from underfloor pits and open floor gutters to a storage basin or lagoon (figure 1). Frequent loadings by flushing also enhance lagoon performance.

Advantages Several advantages result from frequent removal of wastes and associated anaerobic contaminants from production buildings. Reduced pit gases and odor improves the in-house environment, animal health and performance and employee working conditions. A reduction of these odorous gases exhausted from the building by pit ventilation systems is likely to reduce the potential for nuisance complaints. The solid buildup in the bottom of storage pits is no longer a handling problem, thereby improving labor and management efficiency. Corrosion and maintenance requirements by metallic components of the building are reduced. The capital costs of installing flush systems in new buildings is somewhat offset by the shallower underfloor pits required.

Ventilation Flushing technology should not become a substitute for ventilation. The primary purpose of ventilation is to remove moisture from a building during the winter and to control temperature during the summer. This basic requirement remains the same whether pits are flushed or not. Therefore, even though the primary source of gas and odor generation has been reduced by flushing, pit ventilation should still be provided.

Floor Type Flushing under slats or raised decks is recommended for all buildings while open floor gutter systems are a possible alternative only for gestation buildings. Disease, parasites and antibiotic transmission are potential problems where animals have direct access to the flush water.

Background Information on flush system design prior to 1980 was primarily confined to open gutter buildings less than 125 feet (ft) long with a slope of 1-2%. Variable-width, variable-slope gutters presented construction difficulties. Information for flushing longer buildings with wider underslat pits, flatter uniform slopes, and varying animal densities was limited. This article presents design criteria tailored toward individual building characteristics and constraints.

DESIGN PRODEDURE

Flow Rates Basic hydraulic rules were used to establish a link between channel slope, width and flow rate required for gutter cleaning. A minimum flow velocity of 3 feet per second (fps) was assumed for adequate cleaning. Table 1 presents minimum flow rates needed for varying flush channel slopes and widths. A discharge duration of 10 sec is desirable; therefore, an additional column in Table 1 establishes this minimum flush tank size. This flush volume may not be the governing value, however, as will become apparent in the following section. Table 2 lists pipe sizes or openings needed for discharge rates at varying hydrostatic heads.

Flush Volumes Flush volumes can be determined by manure viscosity, solids carrying capacity of the flush water, manure production or animal densities, and channel slope. A relationship can be developed between the minimum viscosity for adequate waste removal and the dry matter content or solids carrying capacity of the flush water. The waste density was assumed to be the same as water. Laboratory studies were conducted to develop an empirical relationship between viscosity and dry matter content in order to establish the solids carrying capacity of the water and correspondingly the water volume needed for waste removal. The amount of manure solids to be removed from the gutter can be determined from the animal densities and liveweights. The total mass including both the flush water volume and the manure solids can now be estimated. The flush volume required is the difference between the total mass and the weight of the manure solids. Table 3 presents tabulated water volumes recommended for varyi ng channel slopes and flush frequencies.

Detailed design procedures and assumptions are explained by Barker and Driggers, 1980.

Table 1. Channel Flow Rates for Cleaning Velocity



               ______________________________________________
               Channel   Channel    Flow    Flow   Min volume
                slope     width    depth    rate   for 10-sec
                                                   discharge
               ______________________________________________
                  %       feet     inches   gpm     gallons
                 0.5        2       3.5      783      130
                            3       3.2     1070      178
                            4       3.0     1367      228
                            5       3.0     1666      278
                            6       2.9     1967      328
                            8       2.9     2571      428
                           10       2.8     3175      529
                 1.0        2       1.9      416       69
                            3       1.8      594       99
                            4       1.7      773      129
                            5       1.7      953      159
                            6       1.7     1132      189
                            8       1.7     1492      249
                           10       1.7     1853      309
                 1.5        2       1.3      295       49
                            3       1.3      427       71
                            4       1.2      560       93
                            5       1.2      693      115
                            6       1.2      825      138
                            8       1.2     1091      182
                           10       1.2     1357      226
                 2.0        2       1.0      233       39
                            3       1.0      340       57
                            4       1.0      447       74
                            5       1.0      554       92
                            6       1.0      661      110
                            8       1.0      875      146
                           10       1.0     1089      182
               ______________________________________________

FLUSH TANK SELECTION

Several types of automated flush tanks and discharge mechanisms have been utilized successfully in North Carolina to deliver the required flush volumes at the desired flush frequencies. Tables 4 and 5 give the total water capacity of tanks of varying dimensions. A brief description of the more frequently used flush tanks follows.

Table 2. Water Volume Required for Flushing



           ______________________________________________________
           Channel            Number of flushes per day
           Slope    _____________________________________________
                       1      2*      3       4       6      12
           ______________________________________________________
              %      ------gallons per 100-lb hog per flush------
             0.5     3.21    1.61    1.07    0.80    0.54    0.27
             1.0     2.97    1.48    0.99    0.74    0.50    0.25
             1.5     2.84    1.42    0.95    0.71    0.47    0.24
             2.0     2.75    1.38    0.92    0.69    0.46    0.23
           ______________________________________________________

              * Recommended minimum flush tank design capacity.

Table 3. Flush Tank Discharge Rates



Hydro-Discharge           Nomimal Discharge Pipe Diameter, inches
staticPipe Exit ____________________________________________________________
Head  Velocity     2      3      4      6       8      10      12      15
____________________________________________________________________________
feet  ft per sec ____________________gallons per minute____________________
   1      4.01     39     88    158     353     628     982    1416   2210
   2      5.68     56    125    222     500     889    1389    2000   3126
   3      6.95     68    153    272     612    1089    1702    2450   3828
   4      8.02     78    177    314     708    1258    1964    2828   4420
   5      8.98     88    198    352     791    1406    2197    3163   4942
   6      9.82     96    217    385     866    1540    2406    3463   5414
   7     10.62    104    234    416     936    1663    2599    3742   5847
   8     11.35    111    250    444    1000    1778    2778    4001   6251
____________________________________________________________________________

Small-Diameter Single Siphon Figure 2 depicts this tank which offers automated dosing action with no moving parts. At the beginning of the fill cycle, air is trapped under the bell. As the tank fills with water, the air under the bell is slowly forced out of the siphon pipe until siphoning is triggered and the tank empties. Tank materials can either be metal or concrete. These tanks have met with mixed success since they are very sensitive to construction miscues and become impractical for long buildings especially in the flatter Coastal Plain regions due to the steep pit slopes required for cleaning. Table 6 gives construction dimensions.

Large-Diameter Multiple Siphon A larger, more successful version of the siphon tank (figure 3) allows multiple large-diameter discharge pipes to emerge from a common ground-level tank and siphon bonnet. Tank construction including the siphon bonnet is usually reinforced concrete. Initial positioning of the 2-in siphon trigger tube and discharge pipe relative to the pit floor and tank floor is important. This tank is more suited to flushing wider pits on flatter slopes. Table 7 gives construction dimensions.

Tipping Bucket Rotating tilt tanks similar to the sketch in figure 4 dump when they fill with water to a depth where the center of gravity is above the tank pivot point. Unless the tanks are constructed with a lid and controlled discharge outlet, the water is discharged at once, and any manure remaining after the first wave of water down the gutter will not be removed from the pit. These type of tanks are recommended primarily for small volume applications such as farrowing houses or nurseries. Metal tanks are expensive to construct, subject to corrosion, and require maintenance due to their frequent violent rotations.

Valved or Gated Discharge These tanks offer the advantage of simple ground level reinforced concrete or concrete and steel reinforced cinder block construction and the flexibility to either be flushed manually or with commercially available flush gate mechanisms. These tanks may be built adjacent to the end of the building using the building wall as a common wall to the tank or they may be free-standing unattached to the building. Figure 5 depicts a simple and reliable water-weighted valve opening mechanism which offers flexibility for opening multiple valves simultaneously at varying valve diameters without requiring electromechanical actuation. Figures 5a through 5e show the operating sequence of this valve opener and the adjustments necessary for it to function.

RECYCLE PUMPS

High-quality, low-pressure, self-priming centrifugal or submersible pumps control the filling of the flush tanks with lagoon liquid. Avoid significant oversizing of pumps to minimize high flow velocities through supply pipes and excessive turbulence in the pump cavity caused by throttling or valving the discharge. The pump should have enough capacity, however, to allow it to operate only one-half to two-thirds of the time. Consider placing the pump controls on a timer. Ensure that the suction line is large enough to prevent pump cavitation. (Rule of Thumb: The suction pipe diameter should be one standard size larger than the discharge pipe.) Also locate the pump as close to the high water level of the lagoon as possible to minimize suction lift. The pump intake is generally an open-ended suction pipe floating about 18 inches beneath the liquid surface of the lagoon. Remove fine mesh suction intake strainers. Intakes may be screened by a 1-inch mesh wire fence or basket with a diameter a t least 5 times the suction pipe diameter. The pump should be located as far as possible from the waste input.

Table 4. Rectangular Tank Capacity



_____________________________________________________________________________
Tank                             Tank Depth, feet
Width________________________________________________________________________
        2       3      4       5      6       7        8       9       10
_____________________________________________________________________________
feet ____________________gallons per foot of tank length____________________
  2     30      45     60      75     90      105      120     135      150
  3     45      67     90     112    135      157      180     202      224
  4     60      90    120     150    180      209      239     269      299
  5     75     112    150     187    224      262      299     337      374
  6     90     135    180     224    269      314      359     404      449
  7    105     157    209     262    314      367      419     471      524
  8    120     180    239     299    359      419      479     539      598
  9    135     202    269     337    404      471      539     606      673
 10    150     224    299     374    449      524      598     673      748
 12    180     269    359     449    539      628      718     808      898
 14    209     314    419     524    628      733      838     943     1047
 16    239     359    479     598    718      838      958    1077     1197
 18    269     404    539     673    808      943     1077    1212     1346
 20    299     449    598     748    898     1047     1197    1346     1496
_____________________________________________________________________________

Table 5. Circular Tank Capacity


____________________________________________________________________________
Tank                               Tank Depth, feet
Diameter ___________________________________________________________________
            2      3      4      5       6       7       8       9      10
____________________________________________________________________________
feet               ____________________gallons____________________
2            47     71    94     118     141     165     188     212     235
3           106    159   212     264     317     370     423     476     529
4           188    282   376     470     564     658     752     846     940
5           294    441   588     734     881    1028    1175    1322    1469
6           423    635   846    1058    1269    1481    1692    1904    2115
7           576    864  1152    1439    1727    2015    2303    2591    2879
8           752   1128  1504    1880    2256    2632    3008    3384    3760
9           952   1428  1904    2379    2855    3331    3807    4283    4759
10         1175   1763  2350    2938    3525    4113    4700    5288    5875
12         1692   2538  3384    4230    5076    5922    6768    7614    8460
14         2303   3455  4606    5758    6909    8061    9212   10364   11515
16         3008   4512  6016    7520    9024   10528   12032   13536   15040
18         3807   5711  7614    9518   11421   13325   15228   17132   19036
20         4700   7050  9400   11750   14100   16451   18801   21151   23501
____________________________________________________________________________

HIGH-VOLUME PUMP

Another technique which has been used effectively in North Carolina is a high-rate or high-volume pumping system connected directly to a distribution header inside the building (figure 6). These systems are especially useful for relatively flat slopes (<0.5%). These flat floors allow the capability to maintain 1-2 in of water in the pit between flushes to prevent adherence of the manure to a dry concrete floor. Recommended design pumping rates which have been field tested are 80 gpm per ft of channel width for channel lengths up to 150 ft and 100 gpm per ft of channel width for channels longer than 150 ft. Flow durations can be adjusted according to observed cleaning efficiency.

Table 6. Small-diameter single siphon dimensions


                ____________________________________________
                Pipe                   Symbol
                diam.  _____________________________________
                a       b    c     e     f      g    h    i
                ____________________________________________
                     ______________inches______________
                  2     36   48   1.5    5.0   1.0    6    9
                        48   60   1.5    6.0   1.0    8    9
                        60   72   1.5    6.5   1.0    9    9
                  3     36   48   1.5    6.0   1.0    9   11
                        48   60   1.5    7.5   1.0   12   11
                        60   72   1.5    8.5   1.0   14   11
                  4     36   48   1.5    8.0   1.0   14   12
                        48   60   1.5    7.5   1.0   12   14
                        60   72   1.5    8.0   1.0   13   15
                  6     36   48   2.0    9.5   1.5   18   16
                        48   60   2.0    9.5   1.5   17   18
                        60   72   2.0    9.5   1.5   16   20
                  8     36   48   2.5    9.5   2.0   17   22
                        48   60   2.5    9.5   2.0   17   24
                        60   78   2.5   11.5   2.0   20   24
                ____________________________________________

Table 7. Large Diameter Multiple Discharge Siphon Dimensions


Nom pipe
 dia,in            4                      6                       8
_______________________________________________________________________________
No. disch
  pipes    1   2  3   4   6   8   1   2   3   4   6   8   1   2   3   4   6   8
_______________________________________________________________________________
 symbol              ----------siphon dimensions, inches-----------
    a     12  12 18  18  24  24  12  18  24  24  30  36  18  24  30  30  36  42
    b    3.3 2.53.1 2.8 3.3 3.4 2.9 2.6 3.4 2.9 2.9 3.3 2.9 2.8 2.5 3.4 2.6 3.2
    c     39  39 39  39  39  39  39  39  39  40  40  42  39  39  40  42  42  42
    d    6.714.57.911.2 8.712.616.112.4 9.614.113.111.710.111.210.515.616.415.8
    e     23  16 22  19  21  17  14  18  20  15  16  15  20  19  19  11  11  11
    f      3   3  3   3   3   3   3   3   3   4   4   6   3   3   4   6   6   6
    g      6 5.35.8 5.6 4.3 6.3 5.7 5.3 6.1 6.7 6.5 5.8 5.7 5.5 6.3 9.2 8.2 7.9
    h      6   6  6   6   6   6   6   6   6   6   6   6   6   6   6   6   6   6
 Q*, gpm 293 589880117617622350 63712761903256438265101107921593268439065188691
_______________________________________________________________________________


Nom pipe
 dia,in                  10                                12
____________________________________________________________________________
No. disch
  pipes      1    2     3    4     6     8     1    2    3    4      6     8
____________________________________________________________________________
 symbol           ------------siphon dimensions, inches-------------
    a       18   30    36   36    48    54    24   30   42   48     54    60
    b      2.7  3.0   2.5  2.7   2.6   2.6   3.3  3.2  3.1  2.8    3.4   2.5
    c       40   40    42   42    42    42    40   42   42   42     42    42
    d     18.3 11.0  11.5 17.3  13.4  14.4  12.7 17.8 11.9 12.2   15.6  17.5
    e       11   18    16   10    13    11    16    9   15   15      9     6
    f        4    4     6    6     7     8     4    6    6    6      8    10
    g      6.4  6.8   8.3  8.4   6.7   7.2   7.1  8.9  8.8  8.5    7.8   8.5
    h        6    6     6    6     7     8     6    6    6    6      8    10
 Q*, gpm  1691 3374  5147 6854 10211 13614  2368 4805 7212 9635  14375 19166
____________________________________________________________________________

* Discharge or flow rate, gallons per minute (gpm)

SALT BUILDUP

Many lagoon liquid recycling systems have experienced a buildup of a grayish-white crystalline salt on the internal pumping and pipe surfaces. This compound is predominantly magnesium ammonium phosphate sometimes referred to as struvite. Predicting the occurrence of salt crystallization is very difficult since exact causes and remedies for the deposition are not well defined. The following design, maintenance and management techniques help in many cases to minimize the buildup.

Piping System Use nonmetallic pipe and fittings. Polyvinyl chloride (PVC,white), polyethylene (PE, black), and acrylonitrile- butadiene-styrene (ABS,black) are typical pipe materials being utilized. The black PE and ABS pipes are reported to give slightly less salt troubles than the PVC. The minimum pressure rating of recharge pipes should be 80 psi. Consult with pump experts to size pipe diameters large enough to maintain flow velocities between 3-5 feet per second. The minimum pipe diameter at any point in the system should be 1.5 inches. Table 7 gives flow capacities for various PVC Class 125 sizes to keep the flow velocity between 3-5 feet per second. Minimize sharp bends such as elbows and tees with rolled PE pipe and long sweep elbows for direction changes. Piping systems not in continuous use should be planned for draining between pumping events.

Electrostatic Charges Direct grounding of the pump housing helps to discharge any static charges or stray voltage believed to contribute to salt deposition. A metal ground rod should be driven 10-12 feet into moist soil near the lagoon edge. Check cable edge. Check cable connections at the ground rod and pump periodically for corrosion.

Table 7. Maximum Flow Rate for Class 125 PVC Pipe


                     __________________________________
                     Nominal pipe   Flow velocity, fps
                     diameter, in      3          5
                     __________________________________
                                    -------gpm---------
                     1.5                  25         40
                     2                    37         60
                     2.5                  55         90
                     3                    80        130
                     4                   130        220
                     6                   285        475
                     __________________________________

Lagoon Treatment Primary lagoons should be properly sized with adequate treatment capacities to minimize salt buildup potential and to achieve odor control and a lagoon liquid suitable for flush recycling. Current recommendations are 1.5 cubic feet of liquid volume per pound of live animal weight as primary treatment plus another 0.5 cubic feet per pound as storage either in the primary lagoon or a second-stage lagoon. New lagoons should be charged at least half full of water prior to startup and the liquid level brought up to design levels as soon thereafter as possible. Rainfall during normal years dilutes lagoon liquid concentrations while extended periods of hot, dry weather increase nutrient and salt levels and the rate of salt buildup in recycling systems. During these periods, flushing with fresh water or irrigating a portion of the lagoon contents replaced by fresh water may be advisable.

Acid Cleaning Salts can be dissolved from internal pump and pipe surfaces with dilute acid treatments. Removal of heavy buildups require several dosings followed by flushing of the acid and dissolved salt solutions or an acid recirculation loop. A recirculation loop consists of an acid-resistant reservoir tank with capacity to supply enough solution to fill the pipe length to be cleaned as determined from Table 8 plus some reserve to keep the pump primed. The flush pump suction is switched from the lagoon and connected to the bottom of the acid tank with a quick-connect coupling. A 1-inch line from the end of each pipe section treated returns acid to the tank.

Muriatic (hydrochloric) acid (30% (20o) technical grade) is diluted (one gallon acid added to 9 gallons water). Extreme caution must be exercised since mixing of acids with water can be very hazardous. Never try to add water to the concentrated acid. Always partially fill the tank with water, then add the acid to the water very slowly. Heat will be generated. Eye protection is advisable. Recirculations ranging from two hours to overnight will be required depending on the degree of salt buildup. This dilution should not hurt metal although prolonged contact should be avoided. A heavy buildup may render the acid usable only one time; although it should be retained after the first use and reused to see how much strength remains. Spent acid may be dumped to the lagoon.

Table 8. Class 125 PVC Pipe Volumes


                        _____________________________
                        Nomimal pipe    Gallons per
                        diameter, in   foot of length
                        _____________________________
                            1.0             0.06
                            1.5             0.13
                            2.0             0.20
                            2.5             0.30
                            3.0             0.44
                            4.0             0.73
                            6.0             1.58
                        _____________________________

FLUSH FREQUENCY

High density housing units such as finishing buildings, grower units, and caged nurseries should be flushed as least 4 times daily for adequate solids removal and odor control. This frequency requires automated flushing equipment. Farrowing houses and flat deck nurseries might be flushed less frequently to conserve heat in the winter since the waste quantities produced in these houses are greatly reduced. A standpipe drain (figure 7) would allow pit recharging with the option of storing waste as long as a week between flushes. This management mode provides a similar degree of gas and odor control as more frequent flushings. Both options greatly improve in- house conditions when compared to prolonged pit storage of manure.

PIT CONSTRUCTION

A pit depth of 24 in below the slats or deck is recommended to separate the manure and urine on the pit floor between flushes from the animal's breathing zone and to allow the underfloor ventilation system to remove the gases. Pit dividers as shown in Figures 6 and 9 are necessary for wide pits to channel the flush water and prevent meandering around heavy waste accumulations. Flush channels no wider than 4 ft have given the best performance. Animals on slats were observed to establish dunging habits along the edge of pens resulting in heavy waste accumulations in outside channels rather than uniform distribution of manure across the entire pit width. This would either suggest making those channels with the heavier waste buildups narrower, distributing more water to them, and/or flushing more frequently.

DRAIN CONSTRUCTION

The flushed waste must be collected and removed from the building such that flow is not restricted. Inadequate drain capacities leave undesirable solids deposition at the lower end of the flush channels. A cross gutter inside the building across the end of the flush channels 16 in wide and sloping from 4 to 8 in below the pit floor conveys the flushed waste to a collection box on one side of the building (figures 8 and 9). Drain pipes must be large enough to handle the discharge rate from the gutter. An 8-in diameter pipe is the smallest drain recommended for wastewater transport. The entire cross sectional area of the drain pipe should be below the collection gutter to ensure that the pipe flows full (figure 10). Table 9 gives flow capacities for various size drainpipes at different slopes. Drain pipes should extend into the lagoon at least to the toe of the bank slope. For better odor control, a turn-down collar at the end of the drain pipe for discharge below the liquid surface is preferred.

Table 9. Flow Capacities of Round Sewer Drainpipe


               _______________________________________________
               Nominal              Slope of Pipe, %
               Drainpipe  ____________________________________
               Diameter     0.1    0.5     1.0     1.5     2.0
               _______________________________________________
               inches      --------gallons per minute--------
                   2          4      9      13      16      19
                   3         12     28      40      48      56
                   4         27     60      85     105     121
                   6         80    179     253     309     357
                   8        172    385     544     666     769
                  10        312    697     986    1210    1390
                  12        507   1130    1600    1960    2270
                  14        765   1710    2420    2960    3420
                  15        919   2060    2910    3560    4110
                  16       1092   2440    3450    4230    4880
                  18       1490   3340    4730    5790    6690
                  20       1980   4420    6260    7660    8850
                  22       2550   5700    8070    9880   11400
                  24       3220   7200   10200   12500   14400
               _______________________________________________

SUMMARY AND CONCLUSIONS

Basic hydraulic relationships were used in conjunction with a laboratory developed empirical relationship between manure viscosity and dry matter content to develop predictive data and design criteria for planning swine waste flushing systems. Field verification of these recommendations has resulted in widespread implementation of flushing systems in North Carolina which are responsive to the needs of large as well as small operators.

Specific conclusions are:

Flushing systems are not a substitute for ventilation.
Flush system discharge rates must sustain a 3 fps flow velocity for adequate manure removal.
Recommended minimum flush tank volumes range from 1.4 - 1.6 gals/100- lb hog.
Recommended minimum flush frequencies for finishing buildings are 4 times per day.
High-volume pump systems should deliver between 80 - 100 gpm per foot of flush channel width.
Drain systems should have enough capacity to prevent flow restrictions.

REFERENCE

Barker, J.C. and L.B. Driggers. 1980. Design criteria for alternative swine waste flushing systems. Livestock Waste: A Renewable Resource, Proc 4th International Symposium on Livestock Wastes, American Society of Agricultural Engineers, St. Joseph, MI. pp. 367-370, 374.

Not Included:
Figure 2. Small-diameter single siphon flush tank
Figure 3. Large-diameter multiple siphon flush tank
Figure 4. Free-swinging flush bucket (Univ. of Tenn. Plan No. T4044)
Figure 5. Ground level flush tank with water weighted valve opener
Figure 6. High-volume flush pump distribution header
Figure 5a. Beginning of fill cycle. Tank empty; valve closed; 2-3" slack in valve chain; reservoir empty.
Figure 5c. Just prior to valve opening. Tank full; valve closed; valve chain taut; water rapidly filling reservoir.
Figure 5e. Just prior to valve closing. Tank empty. When all water drains from reservoir, valve closes, valve chain becomes slack, and fill cycle begins.
Figure 5b. Water beginning to enter reservoir. Tank nearly full; valve closed; 2-3" slack in valve chain; some water in reservoir.
Figure 5d. Valve fully open. Tank emptying; valve open; valve chain taut; reservoir about 2/3 full of water.
Figure 7. Pit drain standpipe valve
Figure 8. Waste collection box
Figure 9. Pit drain collection gutter
Figure 10. Drainpipe connection

Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.

EBAE 080-81