Any SDopers work with pumps? Or, any MEs out there? The equation for specific speed for centrifugal pumps makes no sense to me. It relates speed (w in rpm), head (H in ft), and flowrate (Q in gpm) to some constant (N) known as “specific speed”. In theory, once I find this constant for a first set of conditions, I can find flow or head for a second set of conditions. But, isn’t this really bogus??? Consider this…
Surely it is possible for two distinct pumps to operate at the same speed AND yet their two distinct pump curves CAN intersect at one point? At this point of intersection, the two pumps would behave the same yeilding the same flow (Q) at the same head (H) on a graph of H (ft) vs. Q (gpm).
And, at this point of intersection, the equation for specific speed would yield the same value for this constant (N). Thus, when trying to find a second set of conditions from the first, one could NEVER be sure just which pump curve the solution is following!
Because of this, I say specific speed is bunk - unless there is some other charateristic to make the equation unique for each specific pump curve!
Does anyone know any more about this?
- Jinx, the Pump Head