Gary,
so are you well on the way? ... or do you still have questions? ...
obviously this is not a "student assignment" problem ... so I for one (and I'm sure that there are others) would be glad to give you whatever help you need with the code ... but right now, I'm not 100% sure that I know exactly what your system is supposed to do ...
my understanding so far:
you started out wanting to sequence three pumps ... so that only one pump would run at a time ... each pump would run for 900 seconds (15 minutes) ... and then shut off ... then the next pump in the sequence would turn on ... and run for 900 seconds ... then shut off ... then the next pump would turn on ... and run for 900 seconds ... then shut off ... and then back to the first pump ... and continue the sequence as before ...
BUT ...
any one of the pumps can be disabled by turning on any one of three inputs to the PLC ... if a pump is disabled, then the sequence skips that particular pump ... but it continues to sequence the remaining two pumps in the same "your-turn-my-turn-your-turn-my-turn" pattern ... I'm going out on a limb here, but I assume (gosh I hate that word) that if any TWO pumps are disabled at the same time, then the one remaining pump would simply stay on continuously ...
so how close am I? ...
now ... (looking at your latest posted program) all of a sudden we have three "vacuum" switches thrown into the mix ... and each switch has a different vacuum level assignment ... I'm assuming (and I still hate that word) that these are sensors that are used to determine the amount of existing vacuum and then turn on additional pumps if the vacuum is not low enough ... but I'm not sure about that ... and if all of the switches are satisfied, should all of the pumps turn off? ...
so far you've shown a great deal of enthusiasm ... not only for simply getting this thing to work ... but also for making the program turn out as “professional” as possible ... trust me, we LIKE to see that attitude ... and I for one (and there are many others here I’m sure) would like to help you achieve your goals ... but honestly we’re not 100% sure just what you’re trying to do ...
here’s a recommended plan of attack: instead of telling us what your PROGRAM is intended to do, try telling us what the MACHINE is supposed to do ... exactly how do the pumps need to cycle? ... do you sometimes need more than one pump at a time? ... exactly what do the vacuum switches do? ... etc. ... etc. ... once we’ve got some definite details like that to work with, then we can give you SPECIFIC answers and suggestions ... right now, all anyone can offer are generic “this is an example that might work” programs ... those SHOULD help you out ... but again, if you need more SPECIFIC answers, then we need more SPECIFIC details ...
we look forward to hearing from you again soon ... this is beginning to sound like a fun little exercise that is likely to be a lot more entertaining than some of the “traffic light” type programs that often turn up around here ...