I would like to ask, how the centrifugal pump operation is done through PLC in Auto - sequence mode in general.
Starting of Pump in Auto Sequence:
1) Whenever the pump has to be operated, the discharge valve needs to be in "shut" or "close" position.
2) After the Motor/pump has been started/accelerated to full speed, the discharge valve should start opening slowly to "open" position.
3) What happens if the discharge valve got struck in the middle position?
4) There is a timer which starts after the motor/pump has been given a start command. If the discharge valve got struck, the timer would get run out and stops the motor regardless of the discharge valve position.
Stopping of Pump in Auto Sequence:
1) First the discharge valve should be shut to give "Close" signal.
2) Again What happens if the discharge valve got struck in the middle position?
3) There is a timer which starts after the motor/pump has been given a stop command. If the discharge valve got struck, the timer would get run out and stops the motor regardless of discharge valve position.
I'm concerned because if the discharge valve got struck in the middle, the motor would be stopped/ started frequently which would affect the motor's life. Also how the discharge valve "Open torque switch" & "Close torque switch" be put into use in the ladder programming
Thank you for your insights!
Treat the valve and pump as individual items.
When an internal flag is set to open the valve, it opens.
You have a check timer to make sure it does so in a reasonable time, otherwise you set a fault flag.
Likewise for closing mindful the 'set to open' flag and fault flag are common to open and close sequences,
but you will have confirmed opened flag and confirmed closed flag.
Motor start/run command starts the motor provided the confirmed closed flag is raised.
The motor will continue to run provided - Motor start/run command remains raised and the valve is not at fault.
When the Motor start/run command is removed the motor continues to run and the open valve flag is removed.
The motor stops when the valve confirmed closed flag is raised.
If at any time either the valve fault flag or the motor fault flag is raised (you should have motor failed to start /
failed to stop fault flags) then the valve is set to close and motor to stop. These fault flags should have manual resets to prevent continued adverse operation.