3 replies to this topic

[iplan]

Dear members,

In the absence of the Pump Characteristic curve by pump manufacturer, I am required to estimate the shutoff head of the pump. I came across a relation between speed of the pump and the impeller diameter as below.

Shutoff Differential head H = D^2 * ( N/1750)^2

where D - Impeller diameter in inches

N = Speed in RPM

H = Shutoff Differential head in feet

I would like to know from respected members their views on the correctnes and usage of the above relation for estimating the shutoff head of centrifugal pump.

Many thanks in advance.
Iplan

[Padmakar Katre]

Dear members,

In the absence of the Pump Characteristic curve by pump manufacturer, I am required to estimate the shutoff head of the pump. I came across a relation between speed of the pump and the impeller diameter as below.

Shutoff Differential head H = D^2 * ( N/1750)^2

where D - Impeller diameter in inches

N = Speed in RPM

H = Shutoff Differential head in feet

I would like to know from respected members their views on the correctnes and usage of the above relation for estimating the shutoff head of centrifugal pump.

Many thanks in advance.
Iplan

Dear,
This formula gives you the head and not the shut-off head. To calculate the shut-off head you need to have the slope of the Head Vs Flow curve.

[Erwin APRIANDI]

Hi iplan,

This is what I ussually use, I will estimated the shut off pressure and convert it the shut off head
to calculate the shut off pressure the following equation can be used

Usually, discharge design pressure is calculated adding operating pressure of the suction drum to the shut-off ΔP of the pump (equation 1)
Equation 1 ; Pc (Shut Off P) = PsMax + [ (dMax/10.2)*(hsMax + (1+K) * ΔHmax) ]

or adding the suction vessel design pressure to the operating ΔP of the pump (equation 2)
Equation 2 ; Pc (Shut Off P) = PsDesign + [ (dMax/10.2)*(hsMax + ΔHmax) ]

Or more conservative estimation, consists in adding the suction vessel design pressure to the shut-off ΔP of the pump (equation 3)
Equation 3 ; Pc (Shut Off P) = PsDesign + [ (dMax/10.2)*(hsMax + (1+K) * ΔHmax) ]

Where
PsMax = Maximum Operating Suction Pressure
PsMax = Suction Design Pressure
dMax = max specific gravity of the pump product
hsMax = height difference liquid suction to pump suction
ΔHmax = Pump diffential head
K = calculation coefficient of pressure (normally we use 20%)

after you get the shut off pressure, just convert it to head by multiply the results with (10.2/dMax)

[sheiko]

Iplan,

I agree with Padmakar. I would just add that your formula is based on the following "rule of thumb":
- At 1750 rpm. Shut off head = Diameter (inch sizes) of the impeller squared

Edited by sheiko, 11 January 2011 - 04:22 PM.