Gravity flow rates and volumes in PVC pipe.
Gravity flow rates and volumes in PVC pipe.
(OP)
In trying to determine maximum gravity flow rates for water in 4" PVC pipe, I'm coming up with some really screwy looking numbers. For years I've use tables from the University of Iowa that are based on flow at 70% of pipe volume. Unfortunately I have misplaced them in an office move.
I used three methods to compute max flow rates for 30 lf of pipe at 1% slope
1. Hazen-Williams (V=1.318*CR^.63*S^.54), Chezy coef of roughness is 150 for new PVC
2. Mannings (1.486R^.67*S^.5)/n, n = .009 for PVC and
3. a reference I found in an Engineeering Handbook GPM = (2.56*X*d^2)/sqrt Y. this last one's a bit strange and I've never seen it before...X = horizontal distance in inches, d = pipe diameter in inches, Y= vertical distance in inches.
Problem is that I got very different answers for GPH for each method and all are considerably more than the rates I remember from the tables. Can't figure out why - except that maybe the last formula is a bust - but that offers no help with different flows using Mannings and Hazen-Williams.! Can anyone help me figure this out?
I used three methods to compute max flow rates for 30 lf of pipe at 1% slope
1. Hazen-Williams (V=1.318*CR^.63*S^.54), Chezy coef of roughness is 150 for new PVC
2. Mannings (1.486R^.67*S^.5)/n, n = .009 for PVC and
3. a reference I found in an Engineeering Handbook GPM = (2.56*X*d^2)/sqrt Y. this last one's a bit strange and I've never seen it before...X = horizontal distance in inches, d = pipe diameter in inches, Y= vertical distance in inches.
Problem is that I got very different answers for GPH for each method and all are considerably more than the rates I remember from the tables. Can't figure out why - except that maybe the last formula is a bust - but that offers no help with different flows using Mannings and Hazen-Williams.! Can anyone help me figure this out?





RE: Gravity flow rates and volumes in PVC pipe.
RE: Gravity flow rates and volumes in PVC pipe.
KRS Services
www.krs-services.com
RE: Gravity flow rates and volumes in PVC pipe.
https://www.forestry-suppliers.com/product_pages/view_catalog_page.asp?id=3400
Now I can spout off flows in a heart beat without fumbling with inches-feet conversion, hydraulic radius miscalcs, and simple math errors. I still have to produce the calcs in my Basis of Design, but now I have a very quick way to QC my work.
RE: Gravity flow rates and volumes in PVC pipe.
Hazen-Williams equations are NOT for gravity flow but for pressure flow and may only be used for water.
The "S" in both H-W and Mannings is the slope of the hydraulic grade line NOT the slope of the pipe.
Maximum flow in a circular pipe occurs at 0.92 of full depth.
In the H-W equations you must always be certain that you are using the correct units for diameter. The equations are sometimes written using inches and sometime written using feet. Leads to much confusion and many errors.
Using Mannings, I get Flow = 0.2749 cu ft/sec = 123.37 gpm = 7402 gph.
Russ
RE: Gravity flow rates and volumes in PVC pipe.
http://www.uni-bell.org/unibell_order.php
RE: Gravity flow rates and volumes in PVC pipe.
In my books, 4" pipe is reserved for single family residential. Shared services automatically get a 6" pipe. Those are my thoughts, but with over 16 years of fighting with capacity problems and maintenance issues over small pipe sizes.
KRS Services
www.krs-services.com
RE: Gravity flow rates and volumes in PVC pipe.
RE: Gravity flow rates and volumes in PVC pipe.
Regards,
Al