The centrifugal pump cannot discharge water due to pressure buildup
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Hello, experts. I have a question I’d like to ask everyone here. Thank you! There is a set of parallel horizontal centrifugal pumps in the factory, each with a power of 45 kW and a head of approximately 80 m. Rated current 80A. Install a vacuum water lift tank to draw water from the pool, with a suction height of about 2 meters. Currently, there are pumps of the same model operating in parallel, all at line frequency. One of them works properly, with a water pressure of around 7.6 bar and a measured current of about 70 A. The other unit experienced pressure buildup, with the water flow from the pump being blocked at the check valve located at the pump head’s outlet; the pump head and the water intake tank became very hot, but the system was not emptied of water. The current is about 40A. It seems to me that the water pressure is too low, so it isn’t sufficient to push open the check valve; however, the water pressure measured at the outlet of the pump is around 7.5 bar. When the small valve is opened, the flow of water becomes very rapid. This indicates that the pump is capable of pumping water, but it gets stuck at the check valve – it’s as if the outlet valve of the pump is closed while it’s still running. Additionally, the pump under pressure has been fitted with brand new impellers and mechanical seals, allowing it to operate properly when running alone; the water pressure is around 7.4 bar, and the current level has not been measured. Please give me some advice. Thank you
Is it possible that the check valve at the pump outlet is stuck and cannot open?
“Additionally, the pump under pressure has been fitted with brand new impellers and mechanical seals, allowing it to operate properly when running alone; the water pressure is around 7.4 bar, and the current level has not been measured. ”You didn’t make that clear – after replacing the impellers and mechanical seals, were both pumps started at the same time? Are there any other questions? Since the unit operates normally after the replacement, it indicates that the issue is not with the check valve but rather a mechanical problem with the pump itself.
The check valve is probably broken; try replacing it with a new one
Here, only Mr. K has carefully analyzed every word said by the poster; each pump works fine when operated individually, but when they are connected in parallel, one of the pumps experiences pressure buildup. This is a typical issue caused by competition for flow rate – pumps that can draw enough fluid operate normally, while those that cannot do so have problems They are all power-frequency pumps; they cannot draw a sufficient volume of fluid, as the kinetic energy is converted into heat energy. That’s why, as the original poster mentioned, the pump heats up due to pressure buildup. Solution: Gradually reduce the outlet size of the pump that was working normally, so that the other pump can draw a relatively larger volume of fluid; then see how it works (For reference only!) ）
I have to understand that it’s a system load issue. It is recommended to start one pump first, preferably the pump with the problem, using the rated current as a reference, and adjust the current to be within the rated range. Then start another pump,,,。 Both pumps have their own outlet valves to control the flow rate. If pressure buildup occurs, the outlet valve of the pump that is not experiencing such buildup can be closed. The key lies in coordinating the adjustments of the two pumps; it is necessary to use the current readings from the outlet valves to make the adjustments. It’s worth a try.
The outlet check valve is stuck, check it.
The pipeline can be modified； Go our own ways
If it works fine when used alone, the issue is likely arising when two pumps are used in parallel, with one pump not receiving enough feed. It is recommended to have each pump operate independently, or to increase the diameter of the feed pipes to ensure sufficient feed.