Have a look at the top left of this excerpt:
The CTI PS4aT converts the single channel to up and down (two functions aren't used).
The two lines out of the CTI go through limit switches to break the circuit when the limit is reached(one has three in this case as the tipper is a three way unit).
These trigger a relay which handles the full current of the pump...
The relay is available from Scale Art.
Cheers,
Ap