Extending Force/Rising Main

[heatherhills]

We are looking to extend a rising main (forcemain for those in the US) and I need to calculate the additional head on the pump. The rising main will actually be going downhill but will not be flowing by gravity as the friction head loss will be more than the elevation difference. When calculating the additional head on the pump can I deduct the elevation difference from the friction head loss to calculate the net additional head that the pump will need to overcome?

 

[bimr]

You use the difference between the starting elevation and the endpoint elevation plus the headloss in the pipe. Your pump must also have enough dicharge head to be able to pump the water over a high spot in the middle of the force main (if the endpoint has lower elevation than the high spot).

Your pump must have the necessary power to initially push the water over the summit. Once operating, the pump opeating HP will drop as you recover the energy. If you do not add the extra power to the pump, you may not be able to push the water over the summit.

 

[heatherhills]

That's great thanks, that's what I thought.

 

[stanier]

Suggest you download this freeware and model the scenarios.

http://www.pumpsystemsmatter.org/content_detail.aspx?id=110

If you like the software and have much larger systems in terms of the number of nodes then you can invest in AFT's Fathom or for free Epanet. If you want to model transients then you can use AFT's Impulse or Hytran.