impeller trimming calculation 1

[rajm008]

hii everyone,

I have a pump model which underwent UL testing and i got 2 flow points. 50 and 100 gpm , each flow points has got a pressure range too.

50 gpm- (120 to 133 psi)
100 gpm -(112 to 127 psi)

max impeller dia of this model is 272 and minimum is 260.

so to get 100 gpm @ 127 psi i used my maximum impeller.

Now i need to know how much i should trim the impeller to get 50 gpm @ 120 psi. for this i used affinity law. (d1/d2)3= q1/q2 , (d1/d2)2=h1/h2, (d1/d2)5= p1/p2.

multiplying all these equations i got d2 as 241 mm . but it is out of the approved impeller range tht is 260- 272 mm.


Please help me. Please tell me where i went wrong.

 

[rajm008]

Sorry for my late reply ..i was out of station for few days. I realy appriciate for kind heart to help me patiently.

Actully the model was tested for rated flow point 100 gpm with maximum and minimum impeller. Out of 8 points taken for plotyin the graph one point was tp gpm. And they gave us this pressure ranges for 100 and 50 gpm from same model.

Now my manufacturer is confused about hw to trim that impeller to get t0 gpm rated point. They only know to get one rated gpm from one casing.

Thier question to me is how can ul get two rated flow plint from model just by trimming impeller and nt changing inlet dia.of impeller and casing. They know to get different pressure ranges for one flow point b trimming impeller bt don know hw to get another rated flow.