Determination of rigid or flexible support for centrifugal pumps
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Section 4.3.2 on balance and vibration in GB/T 5656-2008/ISO 5199:2002 states: \"A rigid support is a type of support used when the lowest natural frequency ratio of the unit and its support system in the direction of measurement is at least 25% higher than the rotational frequency.\" Any other support is considered a flexible support. How should this sentence be understood: What are the minimum natural frequencies of the unit and the support system, and how can they be measured? In common centrifugal pumps, the pump and the motor share a single chassis; is grouting it to the ground provided with a rigid support? How should it be determined when installing on a steel structural frame? The rotation frequency should be the frequency of the motor used, right? For example, ordinary motors in China operate at 50Hz
This sentence means that if the lowest natural frequency of the unit and its support system in the direction of measurement is 25% or more higher than the rotational frequency, then a rigid support type is used. Conversely, it is a flexible support. The minimum natural frequency of the unit and support system refers to the vibration characteristics of the unit and support system during operation, and can be determined through vibration testing or simulation analysis. For the common configuration where a centrifugal pump and motor share a single chassis, if grouting is done to the ground level, and the lowest natural frequency of the unit and its support system in the direction of measurement is 25% or more higher than the rotational frequency, it can be considered that rigid support is being used. For centrifugal pumps installed on steel structural frames, it is necessary to make a judgment based on the specific circumstances. If the lowest natural frequency of the unit and support system in the measurement direction is 25% or more higher than the rotational frequency, rigid support shall be used ； If it is below this value, flexible support should be used. The rotation frequency should be the speed of the motor being used, not its frequency. For example, the rated voltage of ordinary motors in China is 380V, the frequency is 50Hz, and the speed is 1450rpm or 2900rpm. .
1. Almost any object in the real world has countless natural frequencies, among which the lowest one has the greatest impact when excited. Measurement is generally carried out by striking or using an exciter, followed by analysis with a vibration signal analyzer. Generally, as long as it is not equipped with springs or rubber shock absorbers, it can be considered a rigid support. Of course, improper design or installation may cause it to become flexible, but when it becomes flexible, it is in a faulty state. 2. The rotation frequency is the speed of the device divided by 60.