Why do you have two pumps ?
I don't see the use of using one PLC, never mind two, but if it suits you then why not.
I guess you are using two plc's one for each pump circuit ?
I think maybe you should write some pseudo code to show what is happening in your system along with a simple flow...
To return to the original post, I would like to say that I bought 6 double sockets Mk1 LightwaveRF and every one failed.
The problem is the internal PSU for the control circuit has components that cannot take the strain over a long period. LightwaveRF said they would repair them for free, so...