force main, overestimate?

[dicksewerrat]

I just got a call about a force main. They tell me it is 1100 feet long, fairly level( 10 feet differential), 8 inch line. This line is feed by a pump capable of 450 gpm at 31 feet total design head. But they also state that this line is operating at 150 psi. Since it is a sewer line, it outfalls to atmospheric. Can this operating pressure be possible?

 

[electricsub]

The 150 PSI, working pressure of the sewer line, seems way out. As i work in metric, when i converted the details, they were way over the top, the size of motor - did'nt even go that far.
However i think they may have got there figures wrong, when they spoke with you or have you been to site & checked ?
A quick check using a submersible pump would require something in the range of 6 to 7.5 kwatt motor, giving the required flow, normal solids handling say 4", velocity 1.0 m/sec ( sorry metric )
Even with a blocked or partial blocked line, they would still need one big big motor & for what to pump 450 gpm?
Suggest that you ask them to check there readings or visit site.

Electricsub

 

[dicksewerrat]

I called back and told them they were off base. Then they said'Oh the pumps will bring the pressure up to 30 psi. but we want the liner insert to be rated at 150 psi because that was what the old line was rated at. so now i can go ahead and design for 30 psi working and 45 psi surge.

 

[electricsub]

Glad to hear that your little problem has been resolved, now you can sit back a have a slight grin on your face & thinking " i told you so "

Also always remember, no matter what is wrong or goes wrong its always the pumps fault.

Electricsub