When it comes to choosing a centrifugal pump, you must start by knowing how to correctly identify the necessary power of the pump.
That is why, next, we will provide the main keys to perform the power calculation of a centrifugal pump.
Calculating the hydraulic power of a pump
There is a specific formula that allows the calculation of the power of any water pump, but to understand it we have to analyse its different components. The formula in question is as follows:
Power = (Pump Flow x Pump Pressure) / Performance
Now let’s see what each element means, since knowing that will be essential to apply it:
This is the quantity of kilos of the product that we are going to pump per unit of time. The operating curve of the pumps is usually calculated with water at 20°, the density of which is 1 kg per litre. Thus, the most common way to indicate the flow rate is in litres per second (l/s), litres per minute (l/min) or cubic meters per hour (m3/h).
The pump must give a pressure that is the sum of three factors: the geometric height, the pressure drops and the spearhead.
The geometric height is the height difference from the point where the pump is located to the drain point. If the fluid is to rise, it will be positive; but if the drain point is lower, the value will be negative. This is because gravity will help, and the pump will cost less to do the work.
The pressure drop is caused by the friction between the fluid and various elements of the installation itself, such as filters or valves. This loss will depend on the flow rate, the diameter of the pipes and the material with which they are made. Therefore, depending on the type of installation, there will be rules that determine the minimum and maximum flow rates that can be supported.
Finally, the spearhead refers to the pressure that the fluid will have when it leaves the conduit. This will be measured in bars.
In the formula analysed, the total performance of the centrifugal pump is formed by a combination of three different performance types: hydraulic, mechanical and electrical.
In this case, the hydraulic ŋ is the loss of power that occurs in the pump stator. On the other hand, the mechanic ŋ refers to the power lost in the different transmission elements, such as the cardan of the helical pumps.
The electric ŋ, finally, will be the performance of the motors themselves. This is usually around 98%.
Perform the calculation
Once the different elements that will affect the calculation of the power have been analysed, we can express the set mathematically:
P = Gravity * Q * H / (ŋ * 450) = Q* H / (ŋ * 450)
As we can see, it is the same formula as before, but broken down into all its elements. So, P is the power, and it will be expressed in horsepower. Gravity, on the other hand, will take 1 as the general value.
Q shall be the mass flow rate, expressed in litres per minute (l/min). H, for its part, will be the pressure expressed in bars. The number 450 is the conversion factor to obtain the horsepower. Lastly, the symbol ŋ will be the total yield.
FLUID model Consequently, this formula will be the one to be used for all centrifugal pumps, regardless of the model or type of installation. Only the internal characteristics of the pump in question and its installation shall be taken into account.
As we have seen, performing the power calculation of a centrifugal pump is a simple task. Knowing the different characteristics, and applying this formula, we will always be able to identify exactly whether the pump in question offers us the power we need, or whether we should opt for a different model.
Remember that if you need more information, or need personalized advice regarding our catalogue of centrifugal pumps, you just need to contact us. You can do this by filling out our contact form, also call us on +34 972 5820 40 or email us at email@example.com. We will help you find the model that covers your applications or your industrial activity without problems or errors.