Quote:
Originally posted by Dix Dogfight
myv65
Do you dissagree that it takes 6.5W of power to move 1200l/h to a height of 2m with a 100% effective pump?
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Actually, I do disagree. Your statement would be true only if the pressure on the suction side of the pump was atmospheric. If you were running the pump, say, 2m above a reservoir, then the true pump lift would be 4m. If you had a reservoir 10m above the pump, the pump would effectively be "in the way" of natural, gravity-fed flow.
Useful flow energy
is flow rate multiplied by pressure rise. In a closed system, vertical lift really has no meaning and you need to look at total head loss through the system. Note that I've also left out flow loss to get it up those two meters. What if you're going through a 1/4" ID line? What if you've got elbows or other restrictions in the way? All you are considering is the gravity lift. All the pump knows is total head, a number that includes suction as well as discharge resistance. How those resistances are generated make no difference to the pump.
Even so, all one needs to do is read a pump curve (one that include pump efficiency). The folks that make most pumps have already done this work for us. The pumps we use
at the flow situations we have usually run less than 50% efficient and often below 30%.