Hi there,
We have a system at a water treatment plant where large raw water tanks feed into the plant that's all on the same level. At high tank level water can gravity flow through with additional throttling and at about 50% tank level it will need to be pumped. I was hoping to get some advice on the controller setup for this system.
The delivery setup is storage tanks - pump - flow control valve - plant
The intent would be that the valve tends open, and once opened, pump starts up with the valve throttling back to give a smooth transition at pump minimum speed.
In other applications have done this setup off a single PI controller with 0-50% on the valve and 50-100% output on the pump. This gave a step change in output when the pump engages, although wasnt important in those cases like it is here.
Had considered trying it like a duty assist pump setup with valve on the controller and the pump open loop to startup, then position/speed match the two to the controller output. Although I think this would be feasible here, it'd mean a lot of the time the pump will be going against a throttled valve which is wasting power.
I wanted to see what suggestions others may have for controlling this system?
Only option I've come up with at the moment is using two sequential controllers.
Valve (PIv & SPv)
Pump (PIp & SPp)
Increasing
SPv > 85% start pump at 45% and lock speed PIp (SPv will drop as valve throttles)
SPv > 100% lock valve controller PIv, and unlock pump controller PIp
Decreasing
SPp < 40% lock pump controller PIp, and unlock valve controller PIv
SPv < 50% turn off pump
This setup feels a tad complicated and not too robust
Main risk I see with this is when I turn off the pump, the valve setpoint will jump up. Can calculate how far it'll probably go but still feels like may incidentally go past 85% sometimes and cause fluttering around the pump start up sequence.
If there's been a past Q&A on this in the forums I missed, apologies
Cheers,
We have a system at a water treatment plant where large raw water tanks feed into the plant that's all on the same level. At high tank level water can gravity flow through with additional throttling and at about 50% tank level it will need to be pumped. I was hoping to get some advice on the controller setup for this system.
The delivery setup is storage tanks - pump - flow control valve - plant
The intent would be that the valve tends open, and once opened, pump starts up with the valve throttling back to give a smooth transition at pump minimum speed.
In other applications have done this setup off a single PI controller with 0-50% on the valve and 50-100% output on the pump. This gave a step change in output when the pump engages, although wasnt important in those cases like it is here.
Had considered trying it like a duty assist pump setup with valve on the controller and the pump open loop to startup, then position/speed match the two to the controller output. Although I think this would be feasible here, it'd mean a lot of the time the pump will be going against a throttled valve which is wasting power.
I wanted to see what suggestions others may have for controlling this system?
Only option I've come up with at the moment is using two sequential controllers.
Valve (PIv & SPv)
Pump (PIp & SPp)
Increasing
SPv > 85% start pump at 45% and lock speed PIp (SPv will drop as valve throttles)
SPv > 100% lock valve controller PIv, and unlock pump controller PIp
Decreasing
SPp < 40% lock pump controller PIp, and unlock valve controller PIv
SPv < 50% turn off pump
This setup feels a tad complicated and not too robust
Main risk I see with this is when I turn off the pump, the valve setpoint will jump up. Can calculate how far it'll probably go but still feels like may incidentally go past 85% sometimes and cause fluttering around the pump start up sequence.
If there's been a past Q&A on this in the forums I missed, apologies
Cheers,