Pump Controls not functioning as expected

[RossV]

I am troubleshooting why a pump is not remaining off. Three pumps are set to shut off when the level in a tank hits 113'. One of these pumps continues to turn on unexpectedly. This pump also has controls based on downstream pressure and a VFD setting. However, the results graphs don't make sense given these control points. During the shown time, the tank is full, so all pumps should be off, but pump 1 continues to cycle. Any ideas?
Capture.JPGcontrols.JPG

Also here is pump 2 and its controls which correctly shuts off:
pump2.jpgcontrols2.JPG

Thanks,
Ross

[Patrick Moore]

Ross,

It is difficult to say for sure without seeing the model or the run report, but in general, a VFD with PRessure based simple controls definitely can be an unstable creation.

Since you have simple controls based on a remote pressure for J-684 and potentially have a VSP pressure on discharge pressure it is difficult to say why the pump remains off without seeing what is happening at J-684 and verifying the VSP control setup.

The other potential oddity is your On rule says on if above 155 and and off if below 145 at J-684. This seems a bit unusual in that it is usually on for low pressure and off for high pressure, but you have it as on for high pressure and off for low pressure for one pump and on for below 155 and off for below 171 for the other pump.

With a VSP generally the HGL will remain constant as long as the pumps have enough capacity to handle the flow and so pressure based controls would generally not be applicable as the pressure would be expected to remain essentially constant at the control point and if you use additional parallel pumps will urn on the pumps as needed to maintain the discharge HGL or flow indicated.

I think your pump 1 control is backward and this causes your issues.

Can you review that control and then comment back?

Patrick Moore

I am troubleshooting why a pump is not remaining off. Three pumps are set to shut off when the level in a tank hits 113'. One of these pumps continues to turn on unexpectedly. This pump also has controls based on downstream pressure and a VFD setting. However, the results graphs don't make sense given these control points. During the shown time, the tank is full, so all pumps should be off, but pump 1 continues to cycle. Any ideas?
Capture.JPGcontrols.JPG

Also here is pump 2 and its controls which correctly shuts off:
pump2.jpgcontrols2.JPG

Thanks,
Ross

[RossV]

Hi Patrick, I tried to redo the controls to reflect how the pump station is set up but I'm still having issues. What is supposed to happen is Pump 1 should run to maintain 171psi discharge pressure. If this pump can't maintain this and pressure drops below 155psi, a second pump kicks on. If pressure still cannot be maintained and drops below 145, Pumps 1 and 2 kick off and the fire flow Pump 3 kicks on. Here is the model if you want to take a look: https://www.dropbox.com/s/9oni1f89hk...model.inp?dl=1

[Patrick Moore]

Ross, I emailed you directly and sent you what appears to be the solution. Your control for pump WEST-02 still had conflicting pressure rules closed if above 155 and open if below 155 and this was causing the instability. When I disabled the closed if above 155 rule the model ran with a green light.

so the problem is definitely with this specific simple control. Review to make sure it is set up properly and doesn't have conflicting statements and it should run ok.

Patrick Moore