A question about the nameplate of a mechanical pump
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During the inspection upon arrival, I checked the nameplate of the pump and saw that its power rating was 45.4 KW; the power of the accompanying motor was also 45 KW. They said this was incorrect, as the power of the motor should be greater than that of the pump – the selection was wrong! In practical applications, the pump does not achieve the power specified by the manufacturer – is such a requirement really necessary?!
Once the power of the pump is determined, the corresponding motor power selected should have a margin factor of 1.2 or 1.5 added to it
The nameplate of a pump usually indicates the shaft power corresponding to its highest efficiency point; the power of the motor must be greater than the pump’s shaft power, generally by a factor of 1.2 or more, otherwise the motor will be overloaded.
Generally, the power of the motor should be greater than that of the pump; otherwise, the motor will experience overcurrent or the pump’s operating point will be far from its rated operating point, resulting in lower efficiency of the pump.
When determining the motor power, it is essential to take into account a safety factor based on the shaft power of the pump, in order to prevent the motor from being overloaded. The general rule is that motor power = shaft power × safety factor. When the shaft power is ≤ 18.5 KW, the safety factor is set at 1.25; when 18.5 KW < shaft power ≤ 55 KW, the safety factor is 1.15; and when the shaft power is > 55 KW, the safety factor is 1.10. In addition, when the motor is used at an altitude of over 1000 M, or in an environment with a temperature exceeding 40°C and a relative humidity of over 95%, there are corresponding correction factors, which can be found in the relevant standards. Last edited by Hunter on 2009-3-4 16:51]
The situation described by the original poster is something that is encountered frequently in actual work. Some centrifugal pumps, as finished products, have their performance characteristics standardized into series; each type of pump has fixed parameters, which are based on clean water at normal temperature – and of course, the shaft power is also included in these parameters. This situation occurs when the pump’s nameplate specifications are based on parameters for clean water at normal temperatures, but the medium being transported actually has a lower specific gravity (such as aromatic compounds, liquefied gases, etc.). The standard approach is to calculate the parameters based on the characteristics of the medium and write them on the nameplate, so as to avoid any misunderstandings.
The power rating on the new pump’s nameplate is 22KW, and the motor’s power is also 22KW. Is this appropriate? If it operates at its maximum flow rate, will the motor trip?
There should be no problem; we choose options in this way for many cases, and it has never caused any issues.
Refer to this post: http://bbs.hcbbs.com/viewthread.php?tid=406084&page=1#pid2168316
They all have the same rated power, no problem!
1 From the perspective of selection principles, it can at least be said to be not very appropriate. 2 There are two coefficients to consider between the pump shaft power and the minimum power required of the driving motor: 2.1 Transmission efficiency 2.2 Safety factor. 3 If direct drive is used, the transmission efficiency is 1； The safety factor should be at least 1.1. Therefore, the motor power should be greater than the shaft pump power by 4. However, for certain configurations, such as when the selected pump capacity is higher than the maximum required level, or when transporting fluids with low density and thus the pump already has sufficient headroom, the aforementioned selection can also be acceptable
Generally, the power of the motor should be greater than the shaft power, usually 1.2 to 1.5 times the shaft power
What are the operating conditions of the pumped medium? Compared to water, does the power increase or decrease at the same flow rate? The power indicated on the nameplate is a value for operation at 20 degrees Celsius, and it differs from the actual value. If the density of the medium being transported is greater than that of water, it is certainly not appropriate.
No problem; under normal circumstances, it won’t exceed the rated power
What everyone is saying makes sense. However, now the authorities have come to inspect and say that the nameplate does not meet the standards, but I think the label shouldn’t be changed arbitrarily! In some cases, the shaft power of the pump is even greater than the power of the motor
It does seem that there is indeed something wrong with the nameplate； The motor power must be greater than the power at the output shaft, which in turn must be greater than the actual power of the pump