CalculationsPRESSURE MANIFOLD CALCULATION TOOLMissouri Department of Health and Senior Services, Onsite Wastewater Treatment ProgramABSORPTION SYSTEM CALCULATIONSManual Calculation FormulaCalculated OutputInputUnitsResidential1Number of units (bedrooms, seats, etc.)Design input0Bedrooms2Flow per unit (Table 2A, Onsite Minimum Standards)Design input0120gpd3Design daily wastewater flowLine1 x Line20gpd4Trench depthDesign input018inches5Soil loading rate from soil reportDesign input0gpd/sq.ft.6Trench bottom area (minimum)Line3 / Line50sq.ft.Select7Effective trench width, based on type of trench materialDesign input0.0Selectfeet1.518" gravel8Total trench length (minimum)Line6 / Line70feet6224" gravel9Number of zonesLine7 / 1000 (Round up)06215" chamber10Design daily wastewater flow per zoneLine3 / Line90gpd212" EPS bundle11Length of trench per zone (minimum)Line7 / Line90feet2.08310" gravelless12Number of trenches per zoneLine11 / 100 (Round up)02.33322" chamber13Trench length, averageLine11 / Line120.0feet336" gravel14Zone dose volume0.5 x Line110gallons3.534" chamberFLOW CALCULATIONS0.0015Operating headDesign input4feet16Orifice (hole) diameterDesign input1/4inches5/3217Flow rate per orifice (see Table 2)11.79 x (Line16)2 x Line150.00gpm3/1618Flow rate per zone (target)Design input25gpm1/419Number of orifices per zone (approx.)Line18 / Line17(Round)05/1620Number of orifices per lateral (equal length)Line19 / Line12(Round)03/821Flow rate per lateral (equal length)Line17 x Line200.0gpm7/1622Number of orifices per zone (equal length laterals)Line20 x Line1201/223Flow rate per zone (equal length laterals)Line17 x Line220.0gpm9/1624Diameter of supply lineFrom Table 4inches5/825Type of PVC pipeDesign input4011/1626Velocity in supply/manifold pipeCheck Tables 1, 40.00feet/sec3/427Feet of lateral per orificeLine13 / Line200feet28Trench length tolerance (plus or minus, max)0.05 x Line240.0() feetTIMER CONTROL CALCULATIONS029Dose cycles per day (zone)Line10 / Line140.030Dose cycles per day (total)Line3 / Line140.031Dose time ON each cycleLine14 / Line230.0minutes32Time OFF between doses1440 / Line30 - Line310.0minutes33Pump run time per day (approx.)Line30 x Line310.0minutesTOTAL DYNAMIC HEAD CALCULATIONS34ELEVATION HEADDetermine at sitefeet35Length of supply lineFrom site layoutfeet length36Equivalent length of fittings, totalFrom mfg. or SSMPA tablesfeet length37Total equivalent length of supply lineLine35 + Line36 (round up)feet length38Supply line friction head / 100 feetFrom Table 1a or 1bfeet39Supply line friction headLine38 x Line37 /1000.0feet40Add on friction (if any)From component supplier(s)feet41FRICTION HEADLine39 + Line400.0feet42OPERATING HEADLine150.0feet43TDHLine34 + Line41 + Line420.0feetMINIMUM PUMP CAPACITY REQUIRED044Flow capacityLine23 + 20.0gpm45Head capacityLine430.0feet

Check minimum standards Table 2ACalculate flows from multiple sources separately and enter total in input column18" recommended (18" - 30" allowed); check with local authority about shallow placement modificationsGenerally, don't exceed lowest reported rate between the ground surface and 12 inches below the trench (Line2 +12")Trench bottom area can exceed calculated minimum for a more conservative designNarrow trenches are recommended to better use the available soil absorption areaTrench length can exceed calculated minimum for a more conservative designShould limit to less than 1,000 feet of trench per zone. However, more than 6 zones would require a distribution method other than an alternating valve, such as solenoid valves or duplex pumps.If demand dosing is used, zones will receive equal dose volumes and should be equal in sizeUse separate sheets for multiple zones with different trench lengthsGenerally, round up to use full length of trench productUse equal trench lengths if possible, and longest trenches, up to 100 feet, that will fit the site. Minimum of two required1/2 gallon per foot of trench, recommended; add volume needed to fill supply line if it drains back to pump tankSet operating pressure with a valve on each lateral line. Use between 2 feet and 8 feet. (default is 4 feet)Use to optimize pump flow capacity (default is 1/4-inch)Read from Table or calculateInitial value used to help optimize pump capacity and cycle time. Compare pump manufacturer's cycle time recommendations with Line31. Confirm actual flow capacity (Line44) with pump performance curve.Initial value used to select actual number of orifices per lateralUse reason when selecting a different number of orifices, as it will affect required pump capacityActual flow. 10 to 40 gpm is typical. Confirm sufficient pump capacity (line44 and 45) using pump performance curve.Only used to proportion distribution in unequal length trenches in a zoneFor unequal length trenches, length per orifice should not vary by more than 5%Difference in elevation (vertical distance) from low water level in pump tank to high point in pressure systemTypically 2 or less doses per day and should not exceed 4 dosesAdd time needed to fill supply line if it drains back to pump tank. In the field, you can start with a drained system and time how long it takes to start to discharge at farthest lateral.Total doses for all zonesTotal pump run time not including time needed to fill supply lineRound up to nearest 10 feetPressure losses in filters, alternating valves, etc. (if in psi, multiply by 2.31 to obtain feet of head)Zone flow rate plus allowance of 2 gpm for flow through 5/32" siphon break or weep holeCheck minimum standards Table 2ASelect pipe size for which flow rate (Line23) results in between 2 and 5 feet per second (fps)Length of supply/manifold pipe from pump to the last lateral lineRecommend using tables, such as from pipe manufacturer or SSPMA. If tables are used, carry manual calculations through line 43. (Calculator estimates equivalent length at 20% of straight length of supply/manifold pipe; be sure to include other losses on Line40.)When flow and head capacity are plotted on a pump's performance curve, that point must fall below the curveCalculated value assumes equivalent length of fittings = 20% of the length of the supply pipe. Use with caution and be sure to include any additional friction in Line40Reset FormPrint CalculationsPrint Instruction SheetsPrint TablesSchedule 40 for example

Notes, InstructionsPRESSURE MANIFOLD CALCULATION SHEET INSTRUCTIONSThis calculator is a tool and not intended to substitute for sound design judgement. It is not the only method fordesigning pressure manifold systems. Site factors may dictate different trench lengths or other modifications.Comply with all state and local standards and permit requirements.See manifold schematic diagrams below.MANUAL CALCULATIONS:ACalculate using line# formulas and tables. Double check manual calculations.BDefaults are provided below as a starting point. Adjust default numbers to optimize pump requirements or to use a prefered pump.ELECTRONIC CALCULATIONS:AClick on Calculations Sheet tab. For new calculations, you can click the reset button to start with the default numbers.BEnter data in the ORANGE cells. (Use 'Enter' or the down arrow key to move to next cell. Use "Backspace" to clear a cell)CDefaults are provided as a starting point. Adjust default numbers to optimize pump requirements or to work with a prefered pump.DEnter data in the yellow cells (optional), to adjust for site conditions or to make the design more conservative. For example, to useshorter trenches, increase total length, or round up trench lengths. Entries less than the minimum calculated values are not allowed.EUse of the timer control calculations is optional, but recommended.FAs an alternative to completing the TDH calculations, pump suppliers can assist if you provide the site elevations and supply line length.GUse buttons at top of calculation sheet to print worksheets.ABSORPTION SYSTEM CALCULATIONSNotes/Recommendations1Number of unitsCheck Minimum Construction Standards Table 2A in the Onsite Sewage Rule2Flow per unitCheck Minimum Construction Standards Table 2A in the Onsite Sewage Rule3Design daily wastewater flowCalculate flows from multiple sources separately and enter total in input column4Trench depth18" recommended (18" - 30" allowed); check with local authority about shallow placement modifications5Soil loading rate from soil reportGenerally, don't exceed lowest reported rate between the ground surface and 12 inches below the trench (Line4 +12")6Trench bottom area (minimum)Trench bottom area can exceed calculated minimum for a more conservative design7Effective trench widthNarrow trenches are recommended to better use the available soil absorption area8Total trench length (minimum)Trench length can exceed calculated minimum for a more conservative design9Number of zonesShould limit to 1,000 feet of trench per zone. However, more than 6 zones would require a dist. method other than an alternating valve, such as solenoid valvess or duplex pumps.10Design daily wastewater flow per zoneIf demand dosing is used, zones will receive equal dose volumes and should be equal in size11Length of trench per zoneUse separate sheets for multiple zones with different trench lengths12Number of trenches per zoneUse equal trench lengths if possible, and longest trenches, up to 100 feet, that will fit the site. A minimum of two trenches is required13Trench length, average (minimum)Generally, round up to use full length of trench product14Zone dose volume1/2 gallon per foot of trench, recommended; add volume needed to fill supply line if it drains back to pump tankFLOW CALCULATIONS15Operating headSet operating pressure with a valve on each lateral line. Use between 2 feet and 8 feet. (Default is 4 feet)16Orifice (hole) diameterUse to optimize pump flow capacity (Default is 1/4-inch)17Flow rate per orifice (see Table 2)Read from Table 2 or calculate using the formula provided18Flow rate per zone (target)Initial value used to help optimize pump capacity and cycle time. Compare pump manufacturer's cycle time recommendations with Line31. Confirm actual flow capacity (Line44) with pump performance curve. (Default is 25 gpm)19Number of orifices per zone (approx.)Initial value used to select actual number of orifices per lateral20Number of orifices per lateral (equal length)Use caution in selecting a different number of orfices, as it will affect required pump capacity21Flow rate per lateral (equal length)22Number of orifices per zone23Flow rate per zoneActual flow. 10 to 40 gpm is typical. Confirm sufficient pump capacity (line44 and 45) using pump performance curve.24Diameter of supply lineSelect pipe size for which flow rate (Line23) results in between 2 and 5 feet/second (fps)25Type of PVC pipeSchedule 40 for example26Velocity in supply/manifold pipeIf velocity < 2 fps, smaller pipe is recommended; if > 5 fps, larger pipe is recommended27Feet of lateral per orificeOnly used to proportion distribution in unequal length trenches in a zone (see next note)28Trench length tolerance (plus or minus, max)For unequal length trenches, the length per orifice should not vary by more than 5%TIMER CONTROL CALCULATIONSRecommended as an alternative to demand dosing29Dose cycles per day (zone)Typically less than 2 doses and should not exceed 4 doses30Dose cycles per day (total)Total doses for all zones31Dose time ON each cycleAdd time needed to fill supply line if it drains back to pump tank. In the field, you can start with a drained system and time how long it takes to start to discharge at farthest lateral.32Time OFF between doses33Pump run time per day (approx.)Total pump run time not including time needed to fill supply lineTOTAL DYNAMIC HEAD CALCULATIONS34Elevation headDifference in elevation (vertical distance) from low water level in pump tank to high point in pressure system35Length of supply lineLength of supply/manifold pipe from pump to the last lateral line36Equivalent length of fittings, totalRecommend using tables, such as from pipe manufacturer or SSPMA. If tables are used, carry manual calculations through line 45. (Calculator estimates equivalent length at 20% of straight length of supply/manifold pipe; be sure to include other losses on Line40.)37Total equivalent length of supply lineRound up to nearest 10 feet38Supply line friction head / 100 feet39Supply line friction head40Add on friction (if any)Pressure losses in filters, alternating valves, etc. (if in psi, multiply by 2.31 to obtain feet)41Friction headUse equivalent length of fittings can be more accurate. Compare with calculated value.42Operating head43TDHIf friction is calculated manually using equivalent lengths of fittings, enter TDH on line 45MINIMUM PUMP CAPACITY REQUIRED44Flow capacityZone flow rate plus allowance for flow through 5/32" siphon break or weep hole45Head capacityWhen flow and head capacity are plotted on a pump's performance curve, that point must fall below the curveINSTALLATION1 Manifold line with tee at each lateral2 Valve used to adjust pressure at each lateral3 Tee with threaded adapter to attach standpipe or a cap with a hole4 Yard box for access5 Dam to prevent effluent from draining into manifold trench6 Capped pipe with drilled holes7 Any accepted conventional gravity trench material or productInstall system with a standpipe, or a cap with a hole drilled in it, at #3. Use valve,#2, to adjust equal head or squirt height in each lateral. Install solid caps at #3.The manifold and supply pipes should drain completely, either back to thepump tank or to the trenches

1234567Photo example of short pipe with 4 orifices to insert into a gravity lateral trench systemSchematic showing components of manifold and short pipe into a gravity lateral trenchDiagram of manifold system with 3 conventional gravity trenches

TablesP V C PIPE TABLESTable 1a:Pressure Loss per 100-feet of Schedule 40 PVC and Velocityas a function of flow rate and nominal pipe diameter in inches1/23/411 1/41 1/2FlowPressure DropVelocityPressure DropVelocityPressure DropVelocityPressure DropVelocityPressure DropVelocitygphgpmfeetpsifpsfeetpsifpsfeetpsifpsfeetpsifpsfeetpsifps6010.980.431.060.250.110.600.080.030.3712023.551.552.110.900.391.200.280.120.740.070.030.4318037.533.273.171.910.831.800.590.261.110.160.070.640.070.030.47240412.825.574.223.261.412.411.010.441.480.260.110.860.120.050.63300519.398.425.284.932.133.011.520.661.860.400.171.070.190.080.79360627.1711.816.346.912.993.612.130.922.230.560.241.290.260.110.95480846.3020.108.4511.775.094.813.631.572.970.950.411.720.450.201.266001017.797.706.025.492.383.711.440.622.150.680.291.589001537.6916.329.0211.635.035.573.061.323.221.440.622.3612002019.818.587.425.212.254.292.461.063.1515002529.9512.969.287.873.415.363.721.613.9418003011.044.786.445.212.264.7321003514.686.367.516.933.005.5224004018.808.148.588.873.846.3027004523.3910.129.6511.044.787.0930005013.425.817.8836006018.808.149.464200704800805400906000100750012590001501050017512000200Note: Values in shaded areas are at velocities over 5 fpsH = 10.44 * L * (Q/C)1.852 * D-4.871H (feet) = Pressure loss(feet per second) and should be selected with caution.Q (gpm) = Flow in pipe segmentD (inches) = Actual pipe inside diameterL (feet) = Pipe length ( = 100 for table)C is a constant ( = 150 used for PVC)Table 1b:Pressure Loss per 100-feet of Schedule 40 PVC and Velocityas a function of flow rate and nominal pipe diameter in inches22 1/2346FlowPressure DropVelocityPressure DropVelocityPressure DropVelocityPressure DropVelocityPressure DropVelocitygphgpmfeetpsifpsfeetpsifpsfeetpsifpsfeetpsifpsfeetpsifps601120218032404300536060.080.030.5748080.130.060.76600100.200.090.960.080.040.67900150.430.181.430.180.081.010.060.030.651200200.730.321.910.310.131.340.110.050.871500251.100.482.390.460.201.680.160.071.091800301.540.672.870.650.282.010.230.101.300.060.030.762100352.050.893.350.860.372.350.300.131.520.080.030.882400402.631.143.821.110.482.680.380.171.740.100.041.012700453.271.414.301.380.603.020.480.211.950.130.061.133000503.971.724.781.670.723.350.580.252.170.150.071.263600605.572.415.742.341.014.020.810.352.600.220.091.514200707.413.216.693.121.354.691.080.473.040.290.121.764800809.494.117.653.991.735.361.390.603.470.370.162.0254009011.805.118.614.962.156.031.720.753.910.460.202.270.060.031.00600010014.346.219.566.032.616.702.090.914.340.560.242.520.080.031.1175001259.123.958.383.171.375.430.840.363.150.110.051.39900015012.795.5410.054.441.926.511.180.513.780.160.071.67105001755.902.567.601.570.684.410.210.091.94120002007.563.278.682.010.875.040.270.122.22Note: Values in shaded areas are at velocities over 5 fpsH = 10.44 * L * (Q/C)1.852 * D-4.871H (feet) = Pressure loss(feet per second) and should be selected with caution.Q (gpm) = Flow in pipe segmentD (inches) = Actual pipe inside diameterL (feet) = Pipe length ( = 100' for table)C is a constant ( = 150 used for PVC)Table 2:Orifice Flow Rate in gallons per minute (gpm)as a function of pressure head and drilled hole diameter in PVC pipePressure HeadOrifice diameter (inches)feetpsi1/85/323/167/321/49/325/1611/323/813/327/1615/321/29/165/811/163/410.430.180.290.410.560.740.931.151.391.661.952.262.592.953.734.615.576.631.50.650.230.350.510.690.901.141.411.712.032.382.763.173.614.575.646.838.1220.870.260.410.590.801.041.321.631.972.342.753.193.664.175.286.517.889.382.51.080.290.460.660.891.171.471.822.202.623.083.574.104.665.907.288.8110.4931.300.320.500.720.981.281.621.992.412.873.373.914.495.116.467.989.6511.493.51.520.340.540.781.061.381.742.152.613.103.644.224.855.516.988.6210.4312.4141.730.370.580.831.131.471.872.302.793.323.894.515.185.907.469.2111.1513.264.51.950.390.610.881.201.561.982.442.963.524.134.795.506.257.919.7711.8214.0752.160.410.640.931.261.652.092.573.123.714.355.055.796.598.3410.3012.4614.83psi = pounds per square inchQ = 11.79 * D2 * hQ (gpm) = Flow through orificeD (inches) = Orifice diameterh (feet) = Pressure head at orificeTable 3:Nominal Pipe Diameter to Actual Inside Diameter Conversion (inches)Pipe Class/ Schedule1/23/411 1/41 1/222 1/2346SUPPLY ID125NANANA1.5481.7842.229NA3.2844.2246.2170160NANANA1.5321.7542.1932.6553.2304.1546.115Col200NA0.9301.1891.5021.7202.1492.6013.1664.0725.99303150.7160.8941.1211.4141.6182.0232.4492.9623.8345.643Row400.6220.8241.0491.3801.6102.0672.4693.0684.0266.0654800.5460.7420.9571.2781.5001.9392.3232.9003.8265.761Table 4Flow Rate (gpm) Needed to Effectively Scour Schedule 40 PipeNominal Pipe Diameter (inches)gpm for 2 fps (minimum recommended)gpm for 5 fps (maximum recommended)15.413.51.259.323.31.512.731.7220.952.32.529.874.6346.0115.22 fps is the generally accepted minimum pipe scouring velocityTable 5:Pipe storage capacity - gallons per 100-feetas a function of nominal pipe diameter and class/ schedulePipe Class/ ScheduleDiameter (inches)1/23/411 1/41 1/222 1/2346125NANANA9.813.020.3NA44.072.8157.7160NANANA9.612.619.628.842.670.4152.6200NA3.55.89.212.118.827.640.967.7146.53152.13.35.18.210.716.724.535.860.0129.9401.62.84.57.810.617.424.938.466.1150.1801.22.23.76.79.215.322.034.359.7135.4V = * (D/24)2*L*7.48V (gallons) = Pipe volume= 0.0408 * (D)2*LD (inches) = Inside DiameterL (feet) = Pipe length ( = 100' for table)