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Jeff Monson
10-03-2011, 2:44 PM
I'm looking at replacing our sewer basin at our lake cabin, I found a product made by Liberty pumps,

http://www.pexuniverse.com/liberty-pumps-p382le51-submersible-sewage-pump-systems

I need a basin that is not very tall, a 24" model like the pro380 model. I'm having a problem calculating
which model I need. They refer to "shut off head" term on the specs. I'm not familiar on how to calculate this. My drain field is 25' away from the pump with a 6' uphill grade. The discharge pipe is 2". My current pump is a 1/2HP and does fine, I'd like to order this basin in a 1/2HP but I dont want the wrong one.

Lee Schierer
10-04-2011, 8:23 AM
Shut off head is the maximum lift capability of the pump. You will get zero flow if that pump has to lift 25 feet or more. Flow will increase as the height of the discharge is lowered. Manufacturers usually provide a pump curve that shows flow for any given lift height. This flow will also be reduced according to pipe losses for the system it is pumping through. There are ways to calculate pipe head loss as well.

Jeff Monson
10-04-2011, 8:58 AM
Lee, so are you saying this pump can pump liquids up to 25' vertically, with flow decreasing as the height increases? I'm assuming then that horizontal measurement does not matter much then?

Dan Hintz
10-04-2011, 9:22 AM
The horizontal measurement (and pipe diameter) is going to account for the majority of your pipe loss... compared to the vertical component, the horizontal run will have minimal impact unless it's a very small diameter...

Lee Schierer
10-04-2011, 11:07 AM
Lee, so are you saying this pump can pump liquids up to 25' vertically, with flow decreasing as the height increases? I'm assuming then that horizontal measurement does not matter much then?

At 25' you'll get no flow at all. At 24' you'll get some flow and you'll get more flow at 10' than at 20'.

Horizontal pipe losses add up and will reduce flow. For example each 90 degree elbow is equivalent to about 10 feet of pipe. Here's a link (http://www.engineeringtoolbox.com/pvc-schedule-40-pipe-friction-loss-diagram-d_1147.html) for figuring flow loss due to pipe length.