Pump system

[svarney 0]

I have a 3 pump system that i need to program. One pump needs to be running all the time. But if the system pressure drops below a setpoint a 2nd pump will come on. If we are still below pressure the 3rd pump will come on also. Note there are time delay between pump on triggers. If 3 pumps are running and our flow is below a given value we will turn off the 1st pump. Then when we are running 2 pumps and our flow is below a given value we will turn off the 2nd pump. Kind of a first on First off setup. Can this be done in straight ladder logic or do i need to use a sequencer or FIFO setup? My contactor does not want to use the sequencer or FIFO at all and I have to convince them that straight ladder logic will not be the solution. Any ideas? If so is there an example i can look at for this?

[jimdi4 2]

Can this be done in straight ladder logic or do i need to use a sequencer or FIFO setup? Make it as simple as possible....You already are on the right track by typing out the exact steps, logically. All you have to do now is put it in If, then, else statements and your done.... My contactor does not want to use the sequencer or FIFO at all and I have to convince them that straight ladder logic will not be the solution. ...but by reading the above, you already have chosen a solution, but aren't quite sure about your solution...

[finfin 0]

Sounds like straight ladder logic to me.

[svarney 0]

I may just not be seeing the forest among the trees. I will have to look over the old Symax Square D program again. Thanks for the assist.

[Mandar 0]

Sorry for getting in late , but I agree with finfin, straight ladder logic would help. Keeping it simple would be helpful in debugging in case of operational problems. The 3 pumps application can get a bit handfull if the logic written is not simple.....I speak from experience!!!

[ElecPneuGuy 1]

Simple is good, but keep in mind that most likely the customer would want to alternate the pumps so that the the main and backup pumps change everytime power is cycled. You could have a timer on each pump running whereas the pump with lowest time would be the main pump, then the pump with the second lower time would be the standby. As things get going, pumps will alternate.

[finfin 0]

Even if you change the pump priority every Monday, I would still keep it simple and do it within the ladder logic.

[OkiePC 14]

I haven't had the opportunity to use this construct, but why not use run timers? Always run the pumps based on demand just like you have it, but use retentive timers to record the pump "hours" and then you can even out the maintenance intervals by setting up simple compare logic to determine which pump to use next. Maybe you want to use one pump as back up until its hourmeter hits a certain target and then rotate it. Maybe you want to always start the pump with the least run hours and keep them all the same. The possibilities are endless. . .and the logic is ultra simple.

[slcman 9]

Like other member says, you may change the main pump periodicaly. I f you just use first on first off logic, pump #2 will never be a main pump.

[Taotaoba 0]

Edited 18 Dec 2007 by Taotaoba