How would you run this pump/valve setup?

Tark

Member
Join Date
Apr 2004
Posts
503
I’m wondering how someone else might set-up the control for this.

It’s a pump/valve set-up used for pumping water. The existing system is hardwired and operates as follows – Run pump, pump contactor is energized and solenoid on valve is energized allowing water pressure to slowly open the valve. Turn off pump, solenoid is de-energized allowing water pressure to slowly close the valve, once valve is closed the pump contactor is de-energized. The pump started has an HOA where this logic is used for both Hand and Auto. As a note, the valve has an internal check.

Problem with the existing system – If the limit switch on the valve goes out (fails to signal that the valve is closed), the pump will not turn off. If something gets stuck in the valve’s tubing preventing proper water pressure flow, the valve will not close, preventing the pump from turning off.

Solution to the problem – Run the valve’s limit switch to a PLC and have the PLC control the output for the valve’s solenoid and pump contactor. Control logic is the same as the hardwired set-up except a timer is used to set a maximum valve close time, if the valve fails to close within a certain amount of time, turn off the pump.

Required additions – The pump must be able to be operated using the HOA at the pump site and using an HOA in the HMI, this operation must use the pump/valve logic as stated above. There must be a way to run the pump in the event of a PLC failure, this operation does not need to use the pump/valve logic as stated above, it is acceptable to shut off the pump before the valve is fully closed.

How we automated the system – We hardwired the Physical HOA (located on the pump starter) directly to the PLC. We removed the hardwired pump/valve circuit and wired the valve solenoid and pump contactor to the PLC. We programmed the PLC to use (2) HOAs, one being the Physical HOA and one being the HMI HOA. The logic for the HOAs is – Both HOAs in Auto, pump will run as required; either HOA in Hand the pump will run as long as the other HOA is in either Hand or Auto; either HOA in Off pump won’t run. To enable the pump to be operated in the event of a PLC failure we added a Keyed HOA switch to the pump starter. Since this is for use in (emergency situations) the Keyed HOA is left in Auto. In this position, power is sent from the starter to the relays used by the PLC to energize the solenoid and pump contactor. When the Keyed HOA is placed in Hand power is send to the solenoid and pump contactor (hardwired).

So I’m wondering how other people have solved these problems? Or how have other people have automated this kind of pump/valve set-up.
 
Tark said:
How we automated the system – We hardwired the Physical HOA (located on the pump starter) directly to the PLC. We removed the hardwired pump/valve circuit and wired the valve solenoid and pump contactor to the PLC. We programmed the PLC to use (2) HOAs, one being the Physical HOA and one being the HMI HOA. The logic for the HOAs is – Both HOAs in Auto, pump will run as required; either HOA in Hand the pump will run as long as the other HOA is in either Hand or Auto; either HOA in Off pump won’t run. To enable the pump to be operated in the event of a PLC failure we added a Keyed HOA switch to the pump starter. Since this is for use in (emergency situations) the Keyed HOA is left in Auto. In this position, power is sent from the starter to the relays used by the PLC to energize the solenoid and pump contactor. When the Keyed HOA is placed in Hand power is send to the solenoid and pump contactor (hardwired).

We had to control a feed water control valve for a nuclear power plant. Sounds similar to your application. We did not have a key switch at all. We used an RVDT to determine valve position and zero speed (for faults). We did have 2 HOAs, 1 switch and 1 soft key on the Touch Panel. Our pump had a manual crank in the event of an emergency situation. But the logic you described for standard operation sounds exactly like we wrote ours.

1 or both in Auto - runs in auto
either in Off - doesn't run
 

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