Here is some pictures about 2 pumps control with plc ..include real program .
This picture has shown ..Testing by program before
installation at the real place.
This project was written by me with SFC (Sequencecial fungtion chart)
and the program that I have post is a real program.
Here is more picture with control valve & pressure sw.
Almost input & output signal of PLC has cross check..
for example output No.1 control the Contactor Pump No.1 ..
bring Aux. contact (Contactor Pump No.1 ) to be another input of PLC..
After start Pump No.1
check pressure Sw. for 30 sec...if the presure not reach to set point
or no pressure then stop Pump1 and start Pump No.2
If you use program Gx Devellopper version 8 , you will know the process from the program that I have post.