Pumps performance
Pumps performance
(OP)
Hi,
There is one thing I am still struggling to understand about pumps which is the relation between BHP and capacity of pumps.
I know that on radial flow centrifugal pumps the higher the head the lower the capacity on a specific pump the less amps it draws and the lower the BHP requirement. What I do not understand is why the axial flow pumps behave in the opposite way. Is there a description in terms of fluid mechanics as to why is that? I mean what I understand is more flow means more fluid to be moved means higher BHP and more amps. The opposite is true for axial flow pumps.
There is one thing I am still struggling to understand about pumps which is the relation between BHP and capacity of pumps.
I know that on radial flow centrifugal pumps the higher the head the lower the capacity on a specific pump the less amps it draws and the lower the BHP requirement. What I do not understand is why the axial flow pumps behave in the opposite way. Is there a description in terms of fluid mechanics as to why is that? I mean what I understand is more flow means more fluid to be moved means higher BHP and more amps. The opposite is true for axial flow pumps.





RE: Pumps performance
This should explain. If it doesn't, tell us what you didn't understand here,
http://www.gouldspumps.com/cpf_0009.html
"We have a leadership style that is too directive and doesn't listen sufficiently well. The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward CEO, BP
**********************
"Being GREEN isn't easy" ..Kermit
http://www.youtube.com/watch?v=hpiIWMWWVco
http://vir
RE: Pumps performance
RE: Pumps performance
I still scratch my head, knowing more that it is true than exactly why it is true. Those were about 5K HP, so you couldn't monkey around much.
rmw
RE: Pumps performance
RE: Pumps performance
"We have a leadership style that is too directive and doesn't listen sufficiently well. The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward CEO, BP
**********************
"Being GREEN isn't easy" ..Kermit
http://www.youtube.com/watch?v=hpiIWMWWVco
http://vir
RE: Pumps performance
Is this what you are looking for in mathematical term -specifc speed - Ns
Ns = rpm x square root of flow @ BEP / H^3/4; this gives the impeller type.
Radial flow Ns is upto approx 1500
Francis vane upto approx 4500
Mixed flow upto approx 8000
Axial flow from 9000
RE: Pumps performance
Continuing along with my explanation, I'd say mathematically what's "going on" can be simplified to an equation for pump differential head vs flow, Q.
Head = A * Q^2 + B * Q + C
A is a coefficient relating H to fluid friction effect,
B is a coefficient relating H to linear friction effects, as Q relates directly to pump rotational speed, thereby also to friction of stuffings and bearings.
C is shutoff head (head at zero flow)
There are still friction effects when flow is zero; the pump is rotating, in which case it's the net effect H-Hfriction Q=0 = C, is what appears on the pump curve as shutoff head. (see attached)
For pumps with secondary curve components making those little waves, additional terms to those in the simple equation have to be included.
"We have a leadership style that is too directive and doesn't listen sufficiently well. The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward CEO, BP
**********************
"Being GREEN isn't easy" ..Kermit
http://www.youtube.com/watch?v=hpiIWMWWVco
http://vir