automatic fill/drain tank

I'm new to PLC's and I'm working through an exercise to manually control filling and draining a tank which I completed but the automatic function has me stumped. I know the limits and can get the tank filled and drained to the levels but I can't figure out how to open and close the "valves" automatically when the certain levels are reached. I'm working on Rockwell software. Any help is greatly appreciated.

First welcome to the forum
Which PLC are you using?
Can you post a screen shot of your code?

May I suggest the following.

draw a sketch of your system.
sketch the level control limits and other devices in place. just a rough sketch.
1. Now, what do you want it to do? what were you asked to do?
Write it down on paper. these are the customer specs.
2. Write out what you want the system to do - forget the I/O locations,
just write down what you want the system to do.
3. go through what you just wrote and write in hi float switch, start pb, motor 1 starter, and so on. Don't worry about the I/o locations.
4. repeat step 3 again, this time, walk through the process as if you are the plc. think through each step in detail. Does it make sense?
5. assign addresses to your devices.
6. write the code.

it's going to be hard at first, but gets much easier in time.

regards,
james

Sooo...you have level switches on the tank for proper levels and you want to automate the use of the switches using valves for fill and drain?

Some good reading...(learning)

http://www.plcs.net/chapters/example10.htm

The whole series..

http://www.plcs.net/contents.shtml

http://accautomation.ca/plc-programming-example-process-mixer/

The above post may help you out.
Regards,