Insufficient terminal pressure
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I have a boiler circulation system here; two centrifugal pumps are connected in parallel, with an outlet pressure of 0.45 MPa. By the time the water reaches the point of use, the pressure drops to 0.15 MPa. The vertical distance is only about 10.5 meters Could the experts please explain this?
1. Pressure loss due to height； 2. Pressure due to pipeline resistance losses ； 3. Measurement error of the pressure gauge; all of the above can lead to a large pressure difference
In this situation, the outlet valve should be gradually opened while ensuring that the pump outlet pressure is met. When the pressure drops to the design pressure, that’s sufficient. Wait until the system behind the pump is filled to the highest point; at that point the pump pressure will increase. Continue to gradually open the outlet valve, and if the pressure decreases at that point, then that is the maximum flow rate. If the flow rate is too high, it can also cause the pump to stop due to an excessively high current. This issue is an operational one.
Do you mean the head of the pump we’re using is not enough? The main pipeline splits into two branches via a tee; one branch has a longer pipeline, and the pressure at its end is only 0.15 MPa, while the other branch has a shorter pipeline, and the pressure at its end is sufficient
According to Bernoulli’s equation, the pressure at the outlet is 0.45 MPa; after reaching a height of 10.5 m, it should still be 0.35 MPa. The gauge readings are fine, but I’m not sure if the pipe resistance losses could be that high
The head specified on the nameplate of the pump we selected is 37.5 m, and the outlet pressure meets the requirements. However, it was unexpected that the pressure drop at the point of use would be so high, only 0.15 MPa; the piping layout is indeed a bit complicated!
There is a large discrepancy between the theoretical calculated values and the actual operational values
As long as the head and flow rate are within the specified range, the phenomenon you described will not occur. I’m not sure about the location of your measurement points; it would be best to create a simple process for easier discussion.
Here’s how it is on my end: it’s a boiler circulation system. The hot water coming out of the boiler passes through two pumps connected in parallel; the head of these pumps is 37.5 m, and their flow rate is 138 m3/h. The pressure gauge at the pump outlets shows 0.45 MPa, but once the water reaches the end points via the pipes, the pressure drops to 0.15 MPa. The vertical height from the pump outlets to the points where the water is used is approximately 10.5 m! How do I go through the small process? :lol
It seems that there is still an issue with your measurement points; it’s not clear whether the flow rate is equal to or less than the pump’s designed value. If it is greater than the design value, it is an operational issue that should be controlled using valves.