I am trying to trouble shoot a water model that is having some issues with pumps cycling on/off. I have isolated the problem to the pressure controls. The pumps are single speed pumps so they cannot be set to adjust speed to achieve the necessary pressure. Is there a way to add a dead range to the pressure controls to moderate the pump cycling in the model? The real-life controls have a dead range on the pressure switches and the system does not cycle as often as the model.
Thanks-
Kevin,
You'd have to add those controls to the pump. If you provided examples of what you currently have for controls and what you're looking to add, someone should be able to provide you with a detailed answer.
Regards,
Mark
I am not sure what you mean by "dead range" - can you explain? In general, you can certainly use pressure as a control condition, and I assume you have already tried this. The problem with pressure-based controls is that you can run into a situation where the act of turning on the pump can instantly cause the pressure to exceed the control that turns it back off, which then immediately causes the pressure to exceed the control to turn the pump back on, and so forth.
In the very least, you'll want to set up the pressure controls so that the above does not happen, by setting the on and off pressure values beyond the pressure that will immediately occur, if possible. However you may not necessarily be able to predict what the pressure will be immediately after the pump turns on and turns off, as it may depend on other factors. If the range is set too wide, the controls may never trigger.
As Mark mentioned, having an example of the exact logic that the real-life pumps follow would be helpful.
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.
Deadrange is a setting on a pressure switch that prevents the switch from triggering when the pressure goes back and forth over a small range. It is intended to minimize the situation you describe. I appreciate the input. I wish I could just abandon the pressure controls and/or add VFDs to the pumps, but I am dealing with a system run by an operator that is unable/unwilling to invest the money/effort to completely overhaul their system and I'm trying to come up with a scheme that they can use to make their system work with what they have.
You need to have a gap between the on and off pressures.
For example
If (P>90 Then Off
If (P<81) Then On
This means that if 81 < P < 90, the pump will stay at whatever setting it has been at and won't keep switching.
I have added the information from this conversation to the following Wiki article: Troubleshooting Controls in WaterCAD and WaterGEMS