The circulating water doesn’t reach the fourth floor – what’s going on?
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This post was last edited by silentsheep on 2025-8-26 08:53. Dear experts, I would like to ask for advice regarding circulating water issues. The situation is as follows: A chemical processing plant has four floors, and an external circulating water supply system is installed on the first floor; the pump has a flow rate of 250 m3/h and a head of 50 m, with intelligent variable-frequency constant-pressure control. During debugging, it was found that: 1) Most of the equipment on the fourth floor (at a height of about 21 meters) did not receive water supply, while the equipment on floors 1–3 functioned normally. The system was set to a pump outlet pressure of 4.0 BAR, but after startup the pressure remained around 2.5 BAR and failed to increase ； 2) During testing, the high-point exhaust valve on the return water main on the fourth floor experienced negative pressure while drawing in air; however, after reducing the valve opening on the circulation return water main on the first floor, the exhaust valve stopped drawing in air and began to discharge water. I would like to ask everyone, what could be the reasons for this phenomenon, and how can it be resolved?
Reduce the valve until the pump outlet pressure reaches 5 kilograms
The circulating water system is short-circuited; the pressure drop across the equipment on floors 1–3 is low. Reduce the valves on these three floors, and set the valve on floor 1 to its minimum setting, and so on
This indicates that the fluid resistance in floors 1 to 3 is low (which results in a small pressure drop), and therefore water naturally flows toward areas with lower resistance, just as electric current flows toward areas with lower resistance. Try turning down the branch pipe valves for the circulating water on floors 1 to 3 slightly.
It should be an operational issue. First, close the pump outlet valve completely, then start the pump. When the pressure reaches its maximum value, gradually open the pump outlet valve while ensuring that the pressure remains above the rated value. Once the system is filled with water, the valves can be gradually opened fully, but the degree of opening must not cause the pump outlet pressure to drop below the rated value; the current level also needs to be kept within the specified range (higher current leads to higher flow rate and lower pressure). ). Additionally, exhaust is required at the end of the process until the process is filled with water. It is worth noting that when filling the system with water, it is necessary to exhaust air first, then close the valve, and continue to fill water and exhaust air towards the back, until water emerges from the end point. For reference.
This post was last edited by Zao Bao Ting Xiang on 2025-8-27 at 12:02. Everyone from Sichuan who commented above has explained things very clearly. 250 m3/h, 50 m – these are the capabilities of a single pump. What is the designed flow rate requirement for the entire pipeline? If the pipeline is not full, it will only cause a short circuit; the resistance in the pipes upstairs is too high, so it’s impossible for fluid to flow upward. Required: Determine the required flow rate of the pipeline; start several circulation pumps to ensure this flow rate while striving to increase the outlet pressure as much as possible.