Slurry pump head calculation
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The design details are as follows: a vertical submersible slurry pump is selected; the tank depth is 4 meters below the reference level. The pump outlet leads to the tank after traveling a horizontal distance of about 30 meters. The inlet is at a height of 3 meters, while the tank itself is 16 meters high and has a diameter of 16 meters. During normal production, the tank is filled with liquid; it has an overflow port on top, and the pressure is below 2 KPa. The raw material is pig manure slurry with a concentration of 8%. We designed the system for a head of 30 meters, but in practice the pump was unable to move the fluid after starting. After ruling out various possible causes, it was determined that the resistance inside the tank was too high, resulting in insufficient head. I communicated with the supplier, and their technical staff said that the resistance that needs to be overcome for feeding at the bottom of the tank is different from that for feeding at the top of the tank. I’m not quite sure about this; could someone experienced give me some guidance? Does the resistance not come from the potential difference of the slurry? It is related to the height of the can, is it also related to the diameter? May I ask what size should be chosen in practice to ensure normal feeding?
Hello, the original poster. I work in the pump industry, and I’ll give you a brief analysis of the situation you described. Based on your operating conditions, the inlet elevation is at 3 meters; the pump isn’t installed at the top of the tank, and there’s less than 2 kilograms of pressure inside the tank. In other words, the pressure at the outlet of the pump needs to be greater than 2 kilograms. Starting from the pump’s outlet, the pool is 4 meters deep and 30 meters wide; the inlet is at a height of 3 meters. Such a piping setup requires at least 3 to 4 right-angle bends. After making these calculations and adding some extra margin, a head of around 35 meters is needed. Logically, a pump designed with a 30-meter head should be sufficient, which means that the actual head provided by the pump you purchase will not reach 30 meters. Personal suggestion: If there is no need to replace the pump, install the inlet to the tank at the top of the tank.
Thank you. The pump manufacturer believes that feeding occurs at the bottom of the tank; once the tank is full of liquid, the resistance increases and the pump stops pumping. Isn’t it still necessary to overcome the resistance due to pipe elevation when placing the feed at the top of the tank? Is this different from the resistance inside the tank? Is there energy loss due to the increase in tank diameter after material enters from the bottom?
You’re welcome. Of course, it’s different: if the feed is placed at the top of the tank and rises another 13 meters, the pressure exerted is around 1.3 kilograms; if it enters the tank at a height of 3 meters, the pressure to be borne is nearly 2 kilograms. The principle is very simple; you should understand it if you think about it.
I have a question: why is there a pressure of 2 kilograms inside the tank?
You’ve confused me. Why is the pressure only 1.3 kilograms when feeding along the pipeline, but 2 kilograms when feeding from the bottom? Where did you get this 1.3 kilograms from? If feeding from the bottom, then where does this 2 kilograms come from? Based on my understanding, if feeding along the pipeline, there is also the friction associated with an additional 16 meters of vertical pipeline to overcome, so the resistance should be greater.
I think the 2 kilograms he mentioned probably refers to this: the pump is installed at the bottom of the pool, which is 4 meters deep; the feed inlet is 3 meters above the pool level, and the total height of the tank is 16 meters, so together they amount to 20 meters. I think, given the conditions mentioned by the original poster, it’s fine to choose a head of 30m. However, I would like to ask: what was the outlet pressure of the pump specified in the data sheet at that time? If the pump pressure is 3 barg, there’s no problem. Generally, it involves conducting hydraulic calculations to determine the head pressure, and then providing the supplier with flow rate data. It is recommended to check again whether the motor of the pump is suitable, to verify the pump’s data sheet and flow/head curves, and also to ensure that the smallest possible impeller has been selected.
Could the poster provide a simple diagram? From what I understand, the pump inlet is currently located in the middle to lower part of the tank; in terms of resistance, there is a difference between inflowing from the bottom and from the top. If what you mean is to enter from the bottom now, and if we were to change that to entering from the top, I think the hydrostatic pressure would remain the same, but the resistance would need to be calculated separately
Thank you for the discussion. I conducted experiments on site, and it seems that the outlet pressure of the pump is insufficient – it’s less than 1.5 kilograms per square centimeter. It’s impossible for such pressure to reach the tank. I wonder which presents more resistance: feeding from the bottom of the tank or from the top. Feel free to share your opinions; I think feeding from the top of the tank creates more resistance
The manufacturer will come to the site to handle it; there is no other solution for now. Additionally, we are considering whether it might be a problem with the raw materials, and we plan to install a filtering screen before the material enters the pump.