On the performance testing of centrifugal pumps

If there is a certain difference between the actual operating speed of the centrifugal pump during testing and its rated speed, is it necessary to convert all the measured parameters based on the rated speed when compiling the test data? In my opinion, this conversion is essential; otherwise, it would be impossible to determine whether the parameters meet the requirements specified in the PO at the rated speed. If the actual performance does not meet the standard requirements, but the parameters after conversion based on speed do meet those requirements, or if the actual results satisfy the requirements while the converted results do not, can we consider the pump’s performance to be acceptable? In my opinion, the data from factory tests should be converted to the test conditions specified in PO in order to make a judgment. The method for this conversion should be one recognized by ISO 9906 or equivalent standards. If the transformed parameters meet the requirements, then the pump’s performance can be considered satisfactory. I don’t quite understand why factory testing can’t be carried out at the rated speed. Is it a very small pump factory? If there are indeed disputes, some large pump manufacturers can be engaged to conduct tests and confirm the situation. It’s better to clarify it when placing the order. A section in the API states: “Unless otherwise agreed, the test speed shall be within 3 % of the rated speed indicated on the pump data sheet (see example in Annex N). Test results shall be converted to anticipated results at the rated speed.” How should the part in red be understood? Personal understanding: Assuming your rated speed is 1000 RPM, while the actual measured speed is 970 RPM, then the data obtained at 970 RPM should be converted to values corresponding to 1000 RPM (so as to compare them with the values specified in the data sheet and determine whether the product meets the requirements or not).

Thank you for your reply. Actually, what I wanted to ask is the last point you mentioned: For example, if the required rated speed is 1000 revolutions per minute, but the actual speed of the motor supplied is 970 revolutions per minute, and the head at the rated flow rate is lower than the rated value and exceeds the allowable deviation range; yet if the values are adjusted to the rated speed, both the flow rate and the head fall within the allowable ranges, which would mean the product is qualified. However, in practice, after such a pump is installed and put into operation, the actual head it achieves will be the measured head, not the adjusted value, and it’s very likely that the requirements won’t be met. According to API standards, the actual speed must be within ±3% of the rated speed. Taking an extreme value of 910 revolutions per minute as the actual speed, the head will increase significantly when converted to the rated speed, resulting in a larger difference between the actual parameters and the adjusted parameters. Another scenario is when there is a larger difference between the actual rotation speed and the rated rotation speed; if the results obtained after conversion are satisfactory but the actual data are not, then the pump, which was purchased as a qualified product for use in a particular application, may not meet the design requirements. The rotation speeds (tested) I mentioned are all based on the supply motor, not the test motor. I can understand the use of test motors in such cases, as there is no better way, and comparison can only be done through this type of data conversion. But I can’t understand the situation regarding the supply motors. Because the physical object is just as it is; attempting to transform it requires multiple attempts, and this can also lead to incorrect judgments. These are my questions. Could you answer them again? Thank you!

I understand that the core of all your questions lies in one sentence: namely, “The rated speed we require is 1000 revolutions per minute, while the actual speed of the motor supplied is 970 revolutions per minute.” I’m not sure if your motor was supplied by the pump manufacturer. If it was supplied by the pump manufacturer, then there is a problem with the motor provided by the manufacturer. If the motor was not supplied by the pump manufacturer, then it does not meet the design requirements. However, as part of the pump’s factory testing, it cannot be assumed that there is a problem with the motor; these are two separate issues. For example, if you go to a clinic to see a doctor, the doctor will write you a prescription. But unfortunately, your condition wasn’t cured in the end (i.e., the performance tests did not meet the standards); it might be that there was an issue with the doctor’s prescription (the quality of the pump), or it could be a problem with the quality of the medication itself. If the clinic also sells drugs, then you hold the clinic accountable; but if the clinic is not responsible for the drugs, then the doctor can only assume that his drugs are fine.

This post was last edited by dodoren on 2015-12-23 at 15:06. There is a difference between the rated speed of a motor and its actual speed; both the motor and the pump are supplied by the manufacturer.

If both the motor and the pump are supplied by the manufacturer, then you don’t need to worry about the rated speed or the actual speed at all; you can simply use the motor actually purchased as specified in the order to measure the pump’s performance parameters.

Do you mean that if the motor is not supplied by the manufacturer, one simply needs to convert the actual test results to the rated speed specified in the purchase order and compare them; if the result falls within the acceptable error range, it is considered qualified, otherwise it is not. If the motor is supplied by the manufacturer itself, then the actual test results are compared directly with the parameters specified in the purchase order, and if they are within the error range, it is considered qualified, otherwise not. Is that what you mean? In the current situation, the motor supplied by the manufacturer shows a significant deviation from the standard values, exceeding the allowed error range; but when converted to the rated speed specified in the purchase order, the value falls within the acceptable error range. Is this considered qualified?

It is recommended that when providing users with the rated speed of the pump, you use the rated speed indicated on the nameplate provided by the motor manufacturer. That is, for a pump with a speed of level 2 as we usually refer to it, at 50HZ, we typically specify 2950RPM. However, the actual speed indicated on the motor’s nameplate provided by the motor manufacturer might be 2920RPM. I recommend using 2920RPM as the rated speed of the pump. Under normal circumstances, the actual speed of the motor should differ from the value on the nameplate by no more than 3%, which should help to avoid significant differences between the theoretical and actual speeds

Sorry, I just saw your post now. What you mean is that if the motor isn’t supplied by the manufacturer, one just needs to convert the actual test results to the rated speed specified in the purchase order and compare them; if it’s within the acceptable error range, it’s considered qualified, otherwise it’s not. That’s correct. If it is a motor supplied by the manufacturer itself, then compare it directly with the actual test results and the parameters specified in the purchase order; if it falls within the acceptable error range, it is considered qualified, otherwise it is not. Is that what it means? Yes, that’s right. The current situation is that the manufacturer supplies the motors themselves, and the actual measurement results show significant deviations that exceed the allowed error range. Yet when the rated speed specified in the purchase order is used for calculation, the results fall within the acceptable error range. Is this considered acceptable? In such cases, the pump can be deemed qualified, but the motor is not; the manufacturer needs to replace the motor and conduct further tests.