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Inverted Siphon

LMNO Engineering, Research, and Software, Ltd.




Inverted Siphon (Depressed Sewer) Design Calculation LMNO Engineering, Research, and Software, Ltd. To: LMNO Engineering home page [email protected] Unit Conversions Register  Trouble printing? nverte! siphons "also calle! !epresse! se#ers$ allo# storm#ater or #aste#ater se#ers to pass un!er obstructions obstructions such as rivers. Our calculation allo#s up to %ive parallel siphons to go un!er the river. river. Unli&e the main se#er pipe' the siphon pipes %lo# un!er un!er  pressure an! must have %lo# velocities greater than ( %t)s "*.+ m)s$ to &eep material suspen!e!, there%ore' several siphons having smaller !iameters than the main se#er ma- be reuire!. Our calculation computes the siphon siphon !iameters' velocities' an! inlet chamber #all heights an! siphon invert elevations. Overall /iagram: 0lan vie# o% inlet chamber "( siphons$: 1ection 232 "e4plo!e! scale$: 5or ease o% %abrication' all siphon inverts can be locate! at the elevation o% the lo#est siphon invert. Register  to %ull- enable the 6Clic& to Calculate6 button in the calculation belo#: Units: cm7centimeter' c%s7cubic %eet per secon!' %t7%eet' gpm7U1 gallons per minute' gph7U1 gallons per hour' gp!7U1 gallons per !a-' m7meters' M8/7Millions o% U1 gallons per !a-' s7secon! Lin&s on this page: ntro!uction Euations 9ariables Manning n coe%%icients 8lossar- Error messages an! vali!it- Re%erences Introduction 1torm#ater an! #aste#ater se#ers o%ten encounter obstructions such as rivers' other  pipes' sub#a-s' tunnels' or valle-s. To pass these obstructions' a common metho! is %or the se#er pipe to !rop sharpl-' then run horiontal un!er the obstruction' an! %inall- rise to the !esire! elevation. The piping going un!er the obstruction is tra!itionall- calle! an 6inverte! siphon6' but since the pipe is not actuall- acting as a siphon' a better term is 6!epresse! se#er6 "Metcal% an! E!!-' ;+<;$. Unli&e the main se#er pipe' the siphon pipe"s$ %lo# un!er pressure. 1pecial care must  be ta&en in inverte! siphon !esign since losses are greater %or pressurie! %lo#' an! the velocit- in each siphon pipe must be at least ( %t)s "*.+ m)s$ %or se#age or = %t)s ";.> m)s$ %or storm #ater "Metcal% an! E!!-' ;+<;$. There%ore' even i% there is onl- one main se#er pipe' several siphons ma- be reuire!. Equations and Methodology ac& to calculation Euations are primaril- %rom Metcal% an! E!!- ";+<;$ but are supplemente! beuations in Cho# ";++$ an! 9iessman an! Aammer ";++<$. Note that ManningBs euation is empirical' an! its %orm in the %ollo#ing euations reuires use o% meters an! secon!s %or the units. Compute the ma4imum %lo# in the main se#er pipe using ManningBs euation %or %ull  pipe %lo#: Compute the !iameter o% each siphon' / i' or the %lo# through each siphon'  i' using ManningBs euation %or %ull pipe %lo# through each siphon: Compute the #all heights' - D "relative to main invert$' in the inlet bo4. The #alls separate the siphons %rom each other. The #all heights are the same height as the #ater !epths' - D' in the main pipe correspon!ing to the !ischarge through the siphons. Aere'  D7; is the !ischarge through siphon ;'  D7> is the !ischarge through siphons ; an! >' an! so on. ManningBs euation %or a partiall- %ull main pipe is use!' but is solve!  bac&#ar!s "numericall-$ in or!er to compute - D. e allo# up to %ive siphons "%our #alls$. Compute the siphon invert elevations in the inlet chamber. 2ccor!ing to Metcal% an! E!!- ";+<;$' there is no loss in the inlet bo4 %or %lo# going %rom the main culvert to the %irst siphon since the %lo# travels in a straight path. Ao#ever' %or siphons > through n the %lo# must turn +* o to go over the chamber #all "a hea! loss o% ;. velocit- hea!s$ an! has an a!!itional hea! loss o% one velocit- hea! as the %lo# enters siphon i. There%ore' %or i7> to n siphons an! D7> to n3; #alls: #here Ei is relative to the invert o% the main pipe. Note that %or the %irst siphon' Ai7*' an! %or the last siphon - D is replace! b- / m. O%ten' all siphon inverts are locate! at the same elevation "the elevation o% the lo#est siphon$ %or ease o% construction. ac& to calculation Variables  A j75lo# area in the main pipe %or computing height o% #all D Fm >G.  Di7/iameter o% siphon i FmG.  Dm7/iameter o% main pipe FmG.  E 7Main invertBs elevation !rop %rom inlet chamber to outlet chamber FmG. Use! to compute h-!raulic gra!e line' 1 s' %or siphon pipes.  E i71iphon i inlet invert elevation relative to invert o% main culvert FmG. These are ma4imum elevations. 2n- siphon can be place! lo#er than E i. 5or ease o% %abrication' all siphon inverts are o%ten place! at the elevation o% the lo#est siphon invert.  H i7Aea! loss %or %lo# %rom main pipe to siphon i FmG.  L s7Total length o% one siphon FmG. 2ssumes all siphons are appro4imatel- the same length.  Lw7all length insi!e inlet chamber FmG. 2lso &no#n as #eir length. nm7ManningBs n coe%%icient o% main pipe. n s7ManningBs n coe%%icient %or the siphon pipes.  P  j7ette! perimeter o% main pipe %or computing height o% #all D FmG. Qi75lo#rate "!ischarge$ through siphon i Fm()sG. Qm75lo#rate "!ischarge$ through main pipe #hen %lo#ing %ull Fm ()sG. Q j75lo#rate "!ischarge$ through main pipe #here D represents the sum o% siphons ; through D Fm()sG. 5or instance' i% D7(' then  j71H2H3. Use! to compute height o% #all D.  R j7A-!raulic ra!ius o% main pipe %or computing height o% #all D FmG. S m71lope o% main pipe Fm)mG. 9ertical)Aoriontal. S  s72llo#able h-!raulic gra!e line %or siphon pipes Fm)mG T  j7Top #i!th o% main pipe %or computing height o% #all D FmG. V i79elocit- o% #ater %lo#ing through siphon i Fm)sG. V m79elocit- o% #ater %lo#ing through main pipe #hen %lo#ing %ull Fm)sG. V  j79elocit- o% #ater %lo#ing through main pipe %or computing #all heights D Fm)sG. - j7ater !epth in main pipe %or computing #all heights D FmG. - D is measure! relative to the main invert. There%ore' i% the bottom o% the inlet chamber is belo# the main invert' the #all #ill actuall- be - D plus the elevation !i%%erence bet#een the main invert an! the  bottom o% the chamber. n the %igure title! 61ection 2326 at the top o% this page' the  ph-sical #all heights are -;HE; an! - >HE;' since siphon ; has the lo#est invert o% the three siphons sho#n in the %igure. Manning n Coefficients ac& to calculation Manning n values are %rom Metcal% an! E!!- ";+<;$' 21 ";+<*$' an! %ootnote! items in re%erences %or pipes in goo! con!ition. ipe Material Uncoate! cast iron Commercial #rought iron 3  blac&  Manning n ipe Material *.*;( Coate! cast iron Commercial #rought iron 3 *.*;( galvanie! 1mooth loc&bar an! #el!e! 1mooth brass an! glass *.*;* 6O/6 Rivete! an! spiral steel pipe *.*; Corrugate! Metal Common cla- !rainage tile *.*;> 9itri%ie! se#er pipe ric& in cement mortar' bric& *.*;( 8lae! bric&#or& Manning n *.*;> *.*;= *.*;; *.*>>I *.*;( *.*;> se#ers Cement mortar sur%aces *.*;> Neat cement sur%aces *.*;; oo! stave pipe *.*;; Concrete pipe *.*;( Corrugate! 0ol-eth-lene "0E$ #ith smooth inner #alls  a'b *.**+3*.*; Corrugate! 0ol-eth-lene "0E$ #ith corrugate! inner #alls  c *.*;<3*.*> 0ol-vin-l Chlori!e "09C$ #ith smooth inner #alls  !'e *.**+3*.*;; I Corrugate! metal pipe n value can var- signi%icantl- #ith pipe !iameter an! t-pe o% corrugations "values can range %rom *.*;> to *.*(($ 3 21 ";+<*$. ac& to calculation !lossary nlet chamber 3 usuall- concrete manhole #here main culvert branches into several siphon pipes. nvert 3 insi!e bottom o% pipe. Main 3 culvert through #hich %lo# occurs be%ore an! a%ter the siphon. 1iphon 3 pipe or pipes %lo#ing %ull an! un!er pressure #hich go un!erneath the obstruction. Not siphons b- the true !e%inition. True siphons %lo# uphill then bac& !o#n. 1iphons use! here go !o#n then bac& up. ac& to calculation Error Messages and Validity  Initial input checks. The %ollo#ing messages are generate! %rom improper input values: "Need 1e-9*<. Utah ater Research Laborator-' Utah 1tate Universit-. Logan' Utah. ;+<<. c  ar%uss' 1teven an! . 0aul Tullis. 5riction %actor test on high !ensit- pol-eth-lene  pipe. A-!raulics Report No. >*<. Utah ater Research Laborator-' Utah 1tate Universit-. Logan' Utah. ;++=. e  ishop' R.R. an! R.. eppson. A-!raulic characteristics o% 09C se#er pipe in sanitar- se#ers. Utah 1tate Universit-. Logan' Utah. 1eptember ;+. Cho#' 9. T. ;++. Open3Channel A-!raulics. Mc8ra#3Aill' nc. "the classic te4t$ Aammer' M. . an! M. . Aammer' r. ;++. ater an! aste#ater Technolog-. 0rentice Aall' (e!. Metcal% an! E!!-' nc. ;+<;. 8. Tchobanoglous' e!itor. aste#ater Engineering: Collection an! 0umping o% aste#ater. Mc8ra#3Aill' nc. "Note that there are some errors in the invert elevations compute! on p. ;.$ !  Neale' L.C. an! R.E. 0rice. 5lo# characteristics o% 09C se#er pipe. ournal o% the 1anitar- Engineering /ivision' /iv. 0roc +*12(' 21CE. pp. ;*+3;>+. ;+=.  b  Tullis' . 0aul' R.P. at&ins' an! 1. L. ar%uss. nnovative ne# !rainage pipe. 0rocee!ings o% the nternational Con%erence on 0ipeline /esign an! nstallation' 21CE. March >3>' ;++*. 9iessman' . an! M. . Aammer. ;++<. ater 1uppl- an! 0ollution Control.  2!!ison3esle-' e!.  $ %&&% 'M Engineering* "esearch* and Software* 'td+ (,ll "ights "eserved) LMNO Engineering' Research' an! 1o%t#are' Lt!. <* 2ngel Ri!ge R!. 2thens' Ohio =*; U12 "=*$ +>3;<+* [email protected] http:))