The return flow rate of the centrifugal pump is too low
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Pump model: Sterling KS-10; pump parameters: head of 22 meters, flow rate of 6 tons per hour, power of 1.5 Kw, three-phase 380V connection, without variable frequency control. The system works as follows: the pump inlet is connected to the bottom of the water tank (pipe diameter 38 mm), while the pump outlet (pipe diameter 32 mm) is connected via a pipeline that is 400 meters long. The pipeline runs from the first floor to the second floor, at a height of about 7–8 meters, before returning to the top of the tank for water return (the valves along the pipeline are closed). The question now is: the flow rate of water returning to the top of the tank is only 1.7 tons per hour, and the pressure gauge at the pump outlet reads 2 bar with the pointer constantly swinging. Why is the flow rate of returning water so low? Is it because the pump is too small, or are there issues with the piping or something else? ? What are some ways to achieve a return flow of at least 3 tons per hour?
Fluctuations in outlet pressure indicate that the pump is not operating properly; issues such as vacuum conditions, faulty pressure gauges, or mechanical problems may be at fault. It is necessary to conduct an inspection and resolve these issues as soon as possible.
It’s quite likely; let’s check by blowing air out.
Check the pump’s rotation direction and whether it’s empty
I guess it’s due to excessive pipeline losses, as well as the height difference, which results in insufficient return water volume. The pump’s head can be increased (by selecting a different pump), or the diameters of the inlet and outlet pipes can be enlarged.
The pump’s inlet diameter is too small – the outlet is 32, while the inlet is 80 – which results in increased pressure. The head is 22, the pressure is low, and the situation resembles that of air in the system.
First, check the gauge – it’s fine. Check the pipelines – they’re also fine. Check the pump. Cavitation present? Operating with air present? ；
The answers given by those upstairs cannot be agreed with: high pipeline losses result in a low amount of water returning. The pump operates at a flow rate corresponding to an outlet pressure of 2 bar; higher resistance downstream leads to a low return pressure, and since the pump’s discharge flow rate is fixed, it cannot decrease.