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QUESTION
I am trying to track down a reference that states maximum velocities for force mains. Ten states has minimum but no max.
This is just to get a reference point for a sewer study. The study will investigate the ability to increase the flow in an existing sanitary discharge line.
REPLIES
BarryEng
Major power agencies (hydroelecticity) have a max of about 10 m/s for a cement mortar lined steel pipe. Beyound this, initial imperfections in joints etc will cause spalling of the lining. BUT there cannot be ANY changes of direction, reducers, connections etc etc. So this maximum velocity is not a practical max for small pumping mains.
For a well constructed large pipeline, a practical max would be about 5 to 7 m/s.
If you have a look at Davis Stephenson’s book on water supply, he has developed a graph showing that the ‘economical’ velocity of about 1.5 m/s for a small pipe up to 2.5 m/s for a large pipe.
rconner
You have received some good advice. Actually, I believe at least the 2004 edition of the Ten States Standards for Wastewater contains the following,
33.45 High Velocity Protection.
Where velocities greater than 15 feet per second (4.6 m/s) are attained, special provision shall be made to protect against displacement by erosion and impact.
Many other engineering references, e.g. ASCE MOP No. 36 (WPCF MOP No. 8), ASCE MOP No. 37 (WPCF MOP. No. 9), the ASCE book, “Pressure Pipeline Design for Water and Wastewater”, and civil engineering texts such as Metcalf & Eddy and Fair & Geyer also contain copy arguably more definitively aimed at maximum force main velocity. The specific numbers in the latter references may even be a little more restrictive than the Ten States Standards, although I believe there is a reference in one of them to the effect that clear water velocities of up to 40 fps have been found to cause no harm to some concrete surfaces.
I believe you could also find in a short web search (as well as the archives of these lists) that many authorities/utilities are further limiting (due to past unexpected experience/concerns involving water hammer or fatigue etc.?) the maximum velocities of some specific weaker material force mains to much lower numbers than in these traditional references.