# Mechanical Engineering - Hydraulic Machines - Discussion

Discussion Forum : Hydraulic Machines - Section 1 (Q.No. 6)
6.
Discharge of a centrifugal pump is
directly proportional to diameter of its impeller
inversely proportional to diameter of its impeller
directly proportional to (diameter)2 of its impeller
inversely proportional to (diameter)2 of its impeller
Explanation:

Discharge of a centrifugal pump is directly proportional to (Diameter)^2 of its impeller.

Head of a centrifugal pump is directly proportional to (Diameter)^2 of its impeller.

Power Developed of a centrifugal pump is directly proportional to (Diameter)^4 of its impeller.

Discussion:
49 comments Page 1 of 5.

Kartheek said:   8 years ago
Discharge in centrifugal pump (Q) = pi * D * b * v.

where D = dia of the impeller at the inlet,
b = width of the impeller at the inlet
v = velocity of flow at the inlet.

So, according to the formula, discharge is directly proportional to Diameter of the impeller.

Discharge of centrifugal pump is Q = area* velocity of flow.

Q = (pi)(D1)(B1)(VF1) = (PI)(D2)(B2)(VF2).

Where B1 and B2 are width of impeller at inlet and outlet and B1 and B2 are diameter of impeller at inlet and outlet and VF1 and VF2 are velocity of flow at inlet and outlet.

Smith said:   8 years ago
The discharge flow rate of a centrifugal pump is directly proportional to diameter. Discharge head is directly proportional to the square of the diameter. And power is directly proportional to the cube of the diameter. You can understand all this with the help of affinity laws.

Utsav said:   6 years ago
No, the Discharge of a centrifugal pump is Directly proportional to Impeller diameter.

You can refer to below-given affinity laws.

Q1/Q2 = D1/D2.
H1/H2 = (D1/D2)^2,
P1/P2 = (D1/D2)^3.

Q Indicates Flow that is discharged,
P Indicates Power.
(1)

Sekhar mullapudi said:   5 years ago
The discharge flow rate is directly proportional to its diameter.

But here the question is an only discharge of centrifugal pump; So the answer is "directly proportional to the square of the diameter".

So, the correct option C is correct.

Muhammad Waqas said:   7 years ago
Q=πDb(V_f).

Where D=Diameter of impeller at inlet,
b=width of impeller at inlet,and
V_f=Velocity of flow at inlet.

Q=πDb(V_f).
Q=πDb(πDN/60).

Hence
Q is directly proportional to square of the diameter.

Hemanth G said:   6 years ago

I believe discharge refers to the outlet of the centrifugal compressor so

Q= π* D*B*Vf2 is the formula, that means A-option is the correct one to be chosen.

Deepak Rathva said:   6 years ago
Q= π x D x B x Vf.

Here, B also depends on D.
Vf depends on u means depends on DN,
So Q is directly proportional to D^3,
So all options are wrong.

Biswajit Das said:   5 years ago
Option C is correct.
That Q= π D b Vf.
Anyhow Vf is related to V and V is related to u and u =π D N /60.
So, Q is directly proportional to D^2.
(1)

Harry said:   8 years ago
As per Affinity Laws:

Speed is constant,

Q1/Q2 = (D1/D2)^3.

So, the answer is Discharge is inversely proportional to the cube of the diameter.