K1 is first to come on, which is pump #2
R is pump #1
K2 is pump #3
K1, R, then when level raises above X, only R runs.
Then if pressure drops K2 and R run.
The only time K1 comes back on is if the system is shut off unless F comes from another contact upstream.
Actually the way I read this diagram is:
R = Relay used for flip-flop to sequence the 2 pumps.
K1 = Pump #1
K2 = Pump #2
When K1 gets energized it seals itself in and allows R coil to be energized at the same time.
When pressure switch opens K1 seal-in is broken and pump stops.
When pressure switch closes again, R is now energized so circuit will not flow to K1, this time and will flow to energize K2 coil which will seal itself in and de-engergize R coil at the same time.
When pressure switch opens it will break the seal-in for K2 and pump will stop.
The next time pressure switch closes R is not energized so we start all over again with K1 energizing and running pump # 1.
Just quickly off the top of my head you could add the 3rd pump in much the same way by adding another holding relay and working this into the process using 2 relays and 3 pump contactors.
It might even be simpler than that but I would need to sit down and work it out to be sure.
OP you say you can use single line or Ladder.
Is this to be hard wired or are you going to use this control through a PLC?
And if you are going to use PLC, what brand and model?
If I get some time later I can put a electrical scematic drawing together for 3 pumps for you.
But if you are doing this through a plc then just writting the ladder would save some time.
Edit: I got wrapped up in your drawing here and then went back and read your first post.
A couple of questions have come to mind now.
1) Are you wanting to run more than one pump at the same time???? (Because your drawing does not reflect this.)
2) If you do want to run more than one pump at a time to maintain a certain constant pressure, then you will need multiple pressure switches or a combination of pressure switches and timers OR an analog pressure switch and do the entire control through a PLC.
3) If you want to change the run sequence of the pumps as you say in post 1 then PLC is the way to go for sure.
4) You will also want to add logic so that if a pump Overload is tripped or a breaker is off on one pump the run logic will be passed off to the next pump in the scheduled sequence.
Please provide more detail as to what you actually have now and what it is you want to achieve as and end result and what equipment and method you plan to use to achieve this result.
BCS
