Two issues arising from a single engineering project
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Dear experts, I encountered two problems while using a centrifugal pump on site today; I would be grateful if you could offer your guidance. After connecting the centrifugal pump, I filled it with water and then started it, but it was unable to draw water. Later, I found that a section of the pipe used for filling the pump was above the water level, which prevented the tank from being filled completely. After lowering the pipe later, it was possible to pump water, but the flow rate was very low at first (as the outlet valve was not fully open). After 5 minutes, the flow rate increased while keeping the outlet valve open, and it became normal. I have two questions. 1. In the pumping stage, there is a section of pipe that is above the water level, which allows air to get inside; could this be the reason why pumping isn’t possible? 2. Once pumping does start, why is the flow rate low at first? Could it be due to air leaks in the pipes (the pipes are made by fastening stainless steel sections together, and leaks at the joints are inevitable)? I hope everyone can offer some advice!
Personally, I think it’s a problem with the bottom valve. There is air in the filling pump; the bottom valve is not sealed properly. The low initial water flow is due to the bottom valve not being fully open.
At the beginning of pumping, it is difficult to remove all the air; several exhaust cycles are required to avoid a low flow rate at the start
It happened to me once while debugging a fire pump: I emptied the air from the inlet pipeline (thinking it was done completely). A few minutes after the pump started running, the pressure at both the inlet and outlet suddenly dropped, the pump emitted a whistling sound, and the pump body immediately became hot. I stopped the pump right away; upon inspection, it turned out that the air hadn’t been fully removed from the inlet pipeline near the exhaust valve at the top of the pump. I then found the highest point in the inlet pipeline (at the pressure tap of the inlet filter’s differential pressure gauge) and removed the air there several times, which resolved the issue