Tom Jenkins
Lifetime Supporting Member
Incorrect Tom, pumps produce pressure, and if there is a route for the fluid, you will get a flow.
Did you not read the example I quoted, where the pressure can be, and is being, controlled to this day, even though there is no flow.
If you pump contaminated fluid through a filter, and control the pressure to a setpoint, you will come to a time when there is no flow through the filter, but the control PID maintains the desired pressure. Obviously at this point, the filter is useless, as it is not filtering anything. So usually a low flow setpoint kicks the filter into a backwash cycle.
What you are describing is called dead heading the pump. (Assuming that it is a centrifugal and not a positive displacement pump.) https://techblog.ctgclean.com/2012/03/pumps-pump-performance-curves/
The dead head pressure will vary with speed, like everything else on the performance curve. It is generally a very bad idea to dead head for extended periods of time. The pump will heat up and the result is damage to the pump. You get the same effect if you close a valve at the pump discharge connection. The pressure will rise to the dead head pressure, and no further. (See the link above.)
I suspect that in your system either there was a bypass or relief valve to provide a flow path or the low flow shut off kicked in before you hit dead head pressure.
Obviously, the assumption in my example was the flow would be within the safe operating range. My presumption was that the OP wanted to keep his operation within the safe flow range of the pump.
Again, in your example, the system resistance to flow is what is producing the pressure. The system curve becomes a vertical line because the resistance to flow is infinite. The intersection of that system curve and the pump curve would be at zero flow and the dead head pressure. However, no centrifugal pump manufacturer will provide a curve showing that because the pump self-destructs.
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