【Daily Question: Pump Equipment】Weekly Summary April 14, 2019
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Monday (2019.4.8) https://bbs.hcbbs.com/thread-2658955-1-1.html 1. If there are through-going scratches on the flange sealing surface and the depth of these scratches is less than 0.5 mm, a gasket with high elasticity and greater thickness can be used; in principle, no further action is required and the component can continue to be used. (Incorrect) 2. The separation efficiency of a suspension separator (also known as a hydrocyclone) is influenced far more by the volume of the particles than by their specific gravity. (Incorrect) Tuesday (2019.4.9) https://bbs.hcbbs.com/thread-2664936-1-1.html 1. To perform a dynamic balance test on the rotor, when calculating the allowable residual unbalance value for dynamic balance, the speed specified in the formula should be the actual speed of the dynamic balancing machine. (Incorrect) 2. For parts that cannot be used properly after being installed in a rotated or reversed position, and for which such issues are not easily detectable, error-proof installation mechanisms should be provided. (Yes) Wednesday (2019.4.10) https://bbs.hcbbs.com/thread-2665790-1-1.html 1. According to **standard requirements, when a three-phase asynchronous motor leaves the factory, if the power supply phases A, B, and C are connected respectively to the motor’s terminals U, V, and W one by one, then when looking at the motor from its shaft end, the motor should rotate (clockwise) ； 2. In cases where the medium temperature exceeds 200 degrees Celsius, it is necessary to warm up the pump before starting it. The warming rate should generally be controlled at (no more than 30 degrees Celsius per hour; it can be higher depending on the actual conditions). Thursday (2019.4.11) https://bbs.hcbbs.com/thread-2666824-1-1.html In the operation of a centrifugal pump whose performance curve is monotonic, if the outlet back pressure increases, then, as long as the pump is operating within its normal range and all other conditions remain unchanged, the pump’s flow rate will decrease while its head will increase. Friday (2019.4.12) https://bbs.hcbbs.com/thread-2667518-1-1.html 1. When the outer diameter of the centrifugal pump impeller is too close to the partition in the pump body, it can easily cause the pump to experience significant vibration ； (Yes) 2. Diaphragm pumps can be turned upside down and still function properly. (Incorrect) Saturday (2019.4.13): https://bbs.hcbbs.com/thread-2668281-1-1.html According to API610, when the weight of the motor exceeds 225 kg, motor adjustment blocks should be installed on the pump base so that set screws can be used to adjust the motor’s position during coupling alignment; furthermore, the thread size of these set screws must be at least M12. Happy weekend!
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How should the rotational speed be determined during rotor dynamic balancing?
It is well known that there is a close relationship between the balancing speed of a dynamic balancer and the operating speed of the workpiece. However, there are various opinions regarding the exact nature of this relationship. Many people believe that the higher the testing speed of the balancer, the better the balancing effect on the workpiece, and the more effectively vibrations and noise can be eliminated； Some believe it is best for the actual operating speed of the workpiece rotor to be the same as the speed used during calibration ； For beginners who are just getting started in the field of dynamic balancing, as well as factory operators. How to master the use of dynamic balancing machines quickly and accurately, and how to properly select a dynamic balancer for testing rotational speeds, are issues of great concern to many manufacturing enterprises and their technical staff, as the balancing process is directly related to the company’s production and quality standards. Regarding how to choose a balancing machine and its rotational speed, experienced technical staff from Guangzhou Keheng Dynamic Balancing Machine Company have provided their insights for reference, which are summarized as follows: 1) Selection based on the weight of the workpiece. When products need to undergo dynamic balancing tests, it is first necessary to select an appropriate balancing machine by estimating the weight of the product. Heavier products should be tested using a balancing machine with rigid supports, as such machines offer greater stiffness, while lighter products can be tested using balancing machines with soft supports. 2) Depending on the type of balancing machine, the test speed is generally determined based on the type of machine used: if a soft-support dynamic balancing machine is used, the test speed should be higher than the rotor’s operating speed, as the signal detected by the sensor is proportional to the vibration displacement of the support. If a hard-support balancing machine is used, then the test speed should be lower than the rotor’s operating speed, since the signal detected by the sensor is proportional to the vibrating force of the support. However, for high-speed rotors rotating at tens of thousands of revolutions per minute, a speed of around 1/10 should be chosen. 3) Different test speeds are selected based on different diameters; generally, the test speed is determined according to the principle that the larger the product’s diameter, the lower the speed should be. However, for some individual products that have a very small diameter but a high degree of static imbalance, dynamic balance testing should be carried out at low speeds, because when the degree of imbalance is high, the higher the testing speed, the greater the centrifugal force resulting from the imbalance. It will cause the workpiece to jump on the support frame; in severe cases, it can cause harm to people and damage the dynamic balancing equipment. A low rotational speed should be used for dynamic balance testing. 4) Select an appropriate rotational speed based on the operating speed of the product. Once the right dynamic balancing machine is chosen, the higher the operating speed of the product, the higher the rotational speed required for the dynamic balancing test. (Except for products with high static imbalance, as explained earlier.) 5) The speed at which dynamic balancing is performed varies depending on the material and structure of the workpiece. Some special materials such as plastics, found in fans and blades, or rotors with plastic impellers, may operate at high speeds; however, in such cases dynamic balancing can only be carried out at low speeds, because high speeds combined with high imbalance levels can cause the workpiece to deform, thereby severely affecting the accuracy of the dynamic balancing test. In our facility, a speed of around 600 revolutions per minute is sufficient to detect the imbalance in almost all rotors, with ease achieving a precision level of G2.5