What will happen if the outlet valve of a centrifugal water pump remains closed and keeps running?
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The last edit to this post was made by yxmqh on 2010-11-9 at 17:13. My colleague and I don’t agree on this: one thinks that after a few minutes, when the pressure rises to a certain level, the pump will stop working and the motor will burn out due to overload； Another view is that the pump will not stop rotating; perhaps within a dozen minutes, the pressure at the outlet will remain relatively high, albeit fairly stable. During this time, the energy from the pump is entirely transferred to the fluid, and the excessive temperature of the fluid can cause damage to the pump’s impeller or shafting.
It should be the latter. The fluid temperature is too high
If it’s a mechanical seal, it will be ruined in one or two minutes. In short, the one that is the weak point will be the first to fail.
Excessive operating time can cause the fluid inside the pump to vaporize due to rising temperatures, thereby damaging the mechanical seal.
Operating a centrifugal pump with the outlet valve completely closed will cause the temperature of the liquid medium being transported within the pump to rise, thereby damaging the mechanical seal.
This post was last edited by Kuju Kyouko on 2010-11-9 at 18:52; obviously, the latter analysis is the more correct one. Imagine if the pump outlet pipe extended vertically into the infinite heights of the sky; even if the pump outlet valve were fully open, the liquid would rise upward indefinitely. Wouldn’t the pressure stop increasing once it reached a certain height? Won’t the pressure stabilize at this point? To be honest, it’s possible that the motor will burn out before the mechanical seal is damaged. This is especially true for multi-stage centrifugal pumps, as the clearance between the rings inside the pump is very small; when the temperature of the liquid inside the pump rises, this clearance decreases, leading to jamming and ultimately causing the motor to overheat and burn out.
A look at the performance curve of the centrifugal pump shows that when the outlet valve is closed, there is no flow at the outlet, so the motor cannot be overloaded. It will only cause the temperature of the fluid inside the pump to rise higher and higher, resulting in dry friction damage to the mechanical seal due to a lack of water.
I agree with everyone’s analysis; the latter one is more correct. But nothing will get damaged; if the outlet valve doesn’t open, don’t apply pressure at the outlet, and the interlock will stop the machine immediately. Of course, nothing will get damaged, haha! ! !
As the original poster mentioned, different pumps will yield different results; if it’s a single-stage pump with a modest power rating, then no problems will occur. I’ve encountered situations where this method was used to eliminate pump cavitation. One thing is certain: when the outlet valve is closed, the pump’s power decreases, and the motor’s current will only drop, not rise. Therefore, it’s absolutely impossible for the motor to be damaged as a result of the outlet valve being closed
At this point, the pressure indicates the shut-off head, and the motor should not burn out. As time passes, the temperature of the medium will rise! ! !
Centrifugal pumps have a certain amount of leakage, so they will not become overloaded. However, positive displacement pumps are most vulnerable to pressure buildup, which can cause the motor to overload and burn out