Question
A six-stage centrifugal pump delivers 120 L $s^{-1}$ against a total head of 510 m. If the design speed of this pump is 1450 rpm, the specific speed of the pump will be ______________.
Centrifugal Pump Specific Speed Calculation
This solution details the calculation for the specific speed ($N_s$) of a centrifugal pump using its operational speed, flow rate, and head.
Calculation Steps
-
Identify Formula and Variables:
The specific speed ($N_s$) is a parameter used to classify pump impellers. A commonly used formula in metric units is:
$ N_s = \frac{N \sqrt{Q}}{H^{3/4}} $
Where:
- $N$ = Pump Speed (rpm)
- $Q$ = Flow Rate (Liters per Minute, LPM)
- $H$ = Total Head (meters, m)
- $N = 1450$ rpm
- Flow Rate = 120 L/s
- Total Head $H = 510$ m
- Convert Flow Rate Units: Convert the given flow rate from Liters per second (L/s) to Liters per minute (LPM): $ Q_{LPM} = 120 \, \text{L/s} \times 60 \, \text{s/min} = 7200 \, \text{LPM} $
-
Calculate Specific Speed:
Substitute the converted values into the specific speed formula:
$ N_s = \frac{1450 \times \sqrt{7200}}{(510)^{3/4}} $
First, calculate the square root of flow rate and the head term:
- $\sqrt{7200} \approx 84.85$
- $(510)^{3/4} \approx 171.57$
Was this answer helpful?
Important Questions from Pump Characteristics
- Impeller speed of a centrifugal pump is increased by $30\%$. The power requirement of the pump increases by $n$ times. The value of $n$ is ________. (Rounded off to two decimal places)
- A centrifugal pump having an overall efficiency of $75\%$ requires $6 \text{ kW}$ power at $1450 \text{ rpm}$ to deliver water against a suction head of $5 \text{ m}$ and a delivery head of $12 \text{ m}$. If the pump runs at $1650$ $\text{rpm}$ and frictional head losses are negligible, the total head developed by the pump in metres will be
- At a speed of 1800 rpm, a centrifugal pump discharges 50 L s$^{-1}$ at its best point of efficiency for a total head of 25 m. The specific speed of the pump in rpm (round off to 2 decimal places) is ________
- Discharge from a centrifugal pump operating at $1000$ rpm with a total head of $30$ m is $300$ L $min^{-1}$. The pump efficiency is $65\%$. If speed of the pump is increased to $1200$ rpm, the power required to operate the pump in kW is ________ (rounded off to $2$ decimal places).
Consider acceleration due to gravity = $9.81$ m $s^{-2}$. - The brake power of a centrifugal pump having an impeller diameter of 200 mm is 1.86 kW. If the impeller is replaced with another impeller of 180 mm diameter, the brake power of the pump in kW will be ________.
Need Expert Advice?
