Regarding metering pumps and canned motors
Thread Content
I’ve encountered the following issues recently and hope experts can discuss them: 1. The outlet pressure of the shielded pump has decreased by about 1.5 kilograms, with the normal value being around 15.5 kilograms. With other conditions such as inlet pressure remaining unchanged and no apparent abnormalities visible on the surface, why is the pump’s flow rate still sufficient and operating normally? 2. The outlet pressure of the metering pump is determined by the outlet resistance; with other conditions such as those of the process equipment remaining unchanged, the outlet pressure is about 1 kilogram lower than usual, while the flow rate remains normal. The backup pump was started, but the pressure remains the same as usual. Why is that? 3. The outlet pressure of the metering pump is normal, but there is no flow at all. There are no abnormalities in the pump temperature, etc. Why is that?
1. The outlet pressure of a centrifugal pump is also related to the characteristics of your piping system; the backpressure in the system affects the outlet pressure. 2. The outlet pressure of the metering pump is determined by the back pressure; changes in back pressure result in changes in outlet pressure. If the pipelines for the two pumps are different, the outlet pressures may also differ. There could also be a problem with the pressure gauge, but as long as it functions properly, that’s fine. 3. If your outlet pressure is normal, it’s impossible for there to be no flow over an extended period of time. In theory, the pressure built up in a positive displacement pump can become infinite. Could there be a problem with the flow meter, or has your stroke adjustment been set to zero?
When the back pressure at the outlet of a centrifugal pump is low, the outlet flow rate increases. If the pressure drop is large enough, the flow rate rises too much, which increases the current flowing through the motor and can damage it. A metering pump is a positive-displacement pump; under normal conditions, as long as the outlet pressure remains within the specified range, the outlet flow rate remains essentially constant.
Reply to 3# yuchenchf: Could you explain it in more detail? Thank you!
What type of metering pump is yours? Mechanical diaphragm type? Plunger type? Hydraulic diaphragm type? If the diaphragm is damaged, there can be internal or external leaks, and in such cases, no flow will occur. Contacting the manufacturer is the best solution.
Learn a bit about metering pumps and shielded pumps
1. It’s possible that there is a slight blockage at the pump inlet, resulting in low pressure at that location; however, this won’t cause the pump to run out of fluid； So the flow rate is sufficient, but the pressure is slightly low ； 2. The metering pump is determined by its back pressure; is a slightly lower pressure due to a reduced back pressure? ； It’s impossible for the back pressure to be the same; the backup pump has a pressure 1 kilogram higher than that of the pump in use. This leads me to believe that there is something wrong with your pressure gauge, or that the resistance in the outlet pipe of the backup pump is greater than that of the pump in use. 3. Is the flow meter bypass turned on? I can think of nothing else. Personal opinion: wait for experts
Regarding the second question raised by the original poster: the outlet pressure of the metering pump is determined by the outlet resistance; with all process equipment and other conditions remaining unchanged, the outlet pressure is about 1 kilogram lower than usual, while the flow rate remains normal. The backup pump was started, but the pressure remains the same as usual. Why is that? ） ______It is possible that the common pump pressure relief valve is loose, which has caused the outlet pressure to drop by 1 kilogram. If the outlet pressure is higher, the 1-kilogram difference represents a small error, so the flow rate will remain normal. If the outlet pressure is not high, a pressure of 1 kilogram results in a large pressure difference, and as a result the flow rate will not be normal.