Overcurrent in the new centrifugal liquid oxygen pump and liquid nitrogen pump
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I would like to ask: During the full-backflow test of the new centrifugal liquid oxygen pump and liquid nitrogen pump, overcurrent occurs. The only way to reduce the current and increase the speed is by closing the backflow valve; when the backflow valve is closed to 26%, the pipeline vibration stops and the testing can proceed. It’s a Danfoss frequency converter, and the current displayed on the converter matches the value read by the clamp ammeter. Flow rate cannot be measured, and the product cannot be sent out. What could be the reasons for this overcurrent?
Questions should be comprehensive; one shouldn’t take shortcuts. Liquid oxygen pumps come in positive-displacement and centrifugal types. Which one do you want to ask about? For centrifugal pumps, it is sufficient to adjust the current at the pump outlet to remain within the rated range. The pump outlet valve should be closed slightly at startup. If it is piston-type (plunger-type), then it is necessary to check for any mechanical problems.
Yes, the title mentions a new centrifugal liquid oxygen pump; the outlet valves are fully closed while the return valves are fully open
Bro, is the description for that item unclear? For the first time that the pump is started, it’s clear that it’s a centrifugal pump. During the full-backflow test, the outlet valve must be completely closed; backflow is used for regulation. With the outlet valve fully closed, the backflow valve is opened to start the pump, after which the frequency is increased to raise the speed. At 2200 revolutions per minute, a certain current level is reached (the designed speed is 2985 rpm). After that, the backflow valve can only be gradually closed to reduce the flow rate, thereby reducing the load and the current, while increasing the speed to raise the pressure. When the backflow valve is closed to 26%, vibrations occur in the pipeline; for safety reasons, the pump is stopped.
This post was last edited by CHANGBAISHI on 2019-8-29 08:00. Oh, I’m sorry; I didn’t see the topic. Apologies! Never. Your procedure should be to open the return valve fully and start the pump; the current should then be at its maximum. But with your variable-frequency motor, the current increases as the speed increases. If a high current is present, the reflux should be reduced. Gradually increase the pressure to the design pressure; at this point, a backflow valve and speed control are required. When the pressure approaches the design value, it is necessary to switch on the outlet valve and close the circulation valve. It is possible that during adjustment, the changes in speed, pressure, and current were overlooked.
It’s okay. No aspect such as speed, pressure, or current is overlooked; the pump is started with the return valve set at its maximum position. After starting, the frequency is gradually increased to raise the speed. When the current becomes too high, the return valve is adjusted to reduce the current, after which the speed is increased again. This approach should work fine. Vibration occurs when the return valve is set to 26%, and at that point the pressure has not yet reached the designed value
If that’s the case, the pressure gauge should be checked. This is likely a process involving compression within a large air separation unit; two pumps should be installed, so it’s necessary to see how the other pump is performing. It is possible to determine whether there is a problem with the machinery. For example, if water vapor has frozen in the bearing seal packing, try heating it again. There is another key issue: the pump has a filter at its inlet, which needs to be cleaned once at the beginning of use.
Bro, all the possibilities that could be ruled out easily have already been ruled out
The key to this pump technology lies in sealing. If both pumps are in this condition, then the equipment supplier needs to step in and resolve the issue.