Is the pipeline design reasonable?
Thread Content
Three circulating water pumps are used in parallel. The outlet pipeline is as shown in the figure. Due to working conditions, the required circulating water flow rate is not fixed each time, so the valve on the outlet pipeline in the picture needs to be adjusted each time. I am not a designer, and I still think this design is unreasonable, but I can’t explain the reason. There are also two pumps that are started at the same time. If the flow rate is the same, it will run normally. If the flow rate differs by more than 50 cubic feet, one pump will be very noisy. I suspect 1 pipeline problem 2 that part of the flow cannot be discharged, and vortex flow occurs in the pipeline, resulting in increased noise and vibration. I don’t know if this is correct or not. Friends who know more about it can discuss it together.
There is only a butterfly valve and a flow meter coming out of the pump, but there is no need
1. When pumps are operated in parallel, the ideal requirement is that each pump has the same characteristic curve. 2. Even if they have the same characteristic curve, the pipe resistance is different due to factors such as location and pipe fittings, which will cause differences in the operating points of each pump. As shown in the photo, the entry point of the main pipe is asymmetrical relative to the three pumps, which is the reason for the difference in pipe resistance. 3 If the flow rate of each pump is adjusted separately, the valve opening will be inconsistent, which will inevitably cause differences in pump operation. If the outlet valve of each pump is fully opened, adjusting the flow rate on the main pipe can alleviate the unevenness. 4. When two pumps are operated in parallel, as long as the difference in pipe resistance is not large, the difference in flow rate will not be too large. If there is a large flow difference, it means that the opening of the pump outlet valve is very different. As a result, the small flow pump is actually below the stable flow rate, and vibration is inevitable.
This should be a steep drop curve. I didn’t read the manual.
Hello, how do you understand the sentence that the small flow pump is below the stable flow rate? When two units are put into use in parallel, if the flow rate is 360 cubic meters, the two units run fairly smoothly. Later, due to the need to adjust the outlet valve again on site, one is 410 and the other is 360. Then it starts to make noise and vibration. Why does the unbalanced flow lead to increased vibration? Is it a large flow at the same time as a small flow?
The gentle curve is suitable for parallel operation. Have you observed the outlet pressure of each pump during parallel operation?
Under normal circumstances, the outlet pressure of the two pumps should be kept constant when used in parallel. Sometimes there will be a pressure deviation of 0.2mpa. However, if the pressure of the two pumps is kept constant when used in parallel, there will be a flow difference of 50 cubic feet between the two pumps, which will lead to increased vibration and noise.
Are you looking at the pressure gauge near the pump outlet?
This post was last edited by lupg on 2018-11-16 08:52 1. The "small flow pump" in the question refers to the smaller one of the two parallel running pumps in your description. "Small flow pump" here is not a special term. 2. The "stable flow" in the question refers to the flow range that does not produce obvious vibration. Stable flow sometimes also refers to thermal stability (not included in this topic). 3. Manufacturers generally provide curves showing the relationship between flow and head, power, and NPSH. In fact, there is also a relationship between flow and vibration. Too large or too small flow will cause increased vibration. Excessive flow is generally limited by current. In actual operation, it is a common phenomenon for small flow to cause increased vibration. Users need to have this concept and avoid entering the small flow area during operation.