Centrifugal pumps cannot extract the last bit of liquid from a tank truck
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Hello, the operation in our factory is intermittent, and the same pump is used for different raw materials. The tank truck carrying the raw material is connected via a hose; after passing through a section of straight pipe, the liquid is pumped into the plant using a centrifugal pump. The problem is that every time there are the last few dozen liters of liquid in the tank truck, the centrifugal pump shuts down automatically due to low current levels. It is presumed that the pump has suffered from air locking, and when it is restarted, there isn’t enough liquid to pump those last few dozen liters of raw material into the plant. The solution now is to install a branch pipe on the main pipe; at the end of each process, those dozens of liters of raw material are drawn out using the branch pipe and poured into a waste liquid tank. Due to the high level of contamination in the raw material, the cost of treating this waste liquid is very high. Therefore, it is necessary to use the pump to extract as much liquid as possible from the tank truck. I studied different temperatures, different materials, and different flow rates, and found no pattern at all. I thought that liquids with higher viscosity might leave more residue, but I discovered that for the same liquid, under the same temperature and flow rate, the amount of waste fluid produced could range from a few liters to over a hundred liters. So I wanted to keep the pump running as long as possible; I manually reduced the pump’s minimum protection current. Eventually, the pump started operating abnormally and the outlet pressure increased sharply, so I stopped the pump manually. In the end, about 20 liters of the material remained un pumped up. The lobe pumps in the factory perform much better, enabling the tank trucks to be emptied quite effectively. I wonder if anyone has encountered a similar situation. Without replacing the pump, do you have any suggestions to improve this issue? Thank you
See if it’s possible to seal the tank and supply nitrogen or compressed air; in that way, pressure alone can be used to push the liquid through, without the need for a pump. Another option is to consider modifying the system by using a high-flow metering pump – such pumps aren’t expensive; domestic ones cost around 30,000 yuan. If that still doesn’t work, then use a small sealed container to hold the excess liquid, connect an outlet at the bottom of the container, and use air or nitrogen to push the liquid through.
Using gas pressure won’t work; the storage tank may not be a pressure vessel, and controlling gas pressure is also rather complicated； It is recommended to use a pneumatic diaphragm pump to extract the last remaining amount of material; this pump can draw out both the material and water together, achieving a fairly clean extraction process. A bypass line can be installed alongside the outlet pipe of the tank, connected to the piping of the pneumatic diaphragm pump.
Thank you to the two people above. I’m sorry for forgetting to mention it – the tank truck is already under pressure, at around 0.5 bar, due to nitrogen sealing. The pump is used to transfer the material into another tank truck for top-up; that other tank truck is the actual storage tank for the material, and a lobe pump is used to transfer the material into the process system. I’ve drawn a simple diagram below. The pump on the left is a lobe pump, while the one on the right is a centrifugal pump. My feeling is that it is precisely because the tank truck is under pressure that, at the last moment, when only about 100 liters of liquid remain at the bottom of the tank, the liquid becomes unstable and cannot fill the entire pipeline; this allows gas to enter the centrifugal pump, resulting in gas lock. Does the 3rd floor mean we need to replace the pump? I personally also think that positive displacement pumps are much better than centrifugal pumps in this regard. . . But the price is also high. . . .
Dozens of liters – actually, that’s very little. You could try making a parking platform that lowers the rear of the car and raises the front, allowing the fuel to be drawn off in one go without stopping along the way.
5# TF123 Hey. . . Parking platforms are available, and the rear of the vehicle is always slightly lower than the front. . . If you draw liquid all at once, it’s impossible to draw it out completely; the pump always stops due to too low a current level
Is there really no other solution besides replacing the pump? . . .
Replace it with a pump of proper displacement, one with strong self-priming capability, such as a pneumatic diaphragm pump, cam pump, screw pump, or peristaltic pump.
It’s impossible to use a centrifugal pump without any residue remaining. Because centrifugal pumps cannot be emptied.
Try removing the protection for low current
The correct answer is already given above. When a problem arises, one needs to think carefully about whether it’s necessary to replace the pump or not. 1. Why is there so much material stored? 2. What’s the problem with the pump? Once these two problems are solved, just do what needs to be done; it doesn’t matter whether there are other solutions or not