Strange well pump wiring
It's a perfectly normal 240V circuit. There's no need for the neutral, since nothing in the circuit requires 120V.

It must have been installed before safety grounds became mandatory; in a modern installation, you'd also have a green wire connecting the cases of all the elements (disconnect, pressure switch, pump) together, tied back to the ground at the main panel. If all of the wiring is in metallic conduit, the conduit may be meeting that requirement. Personally, I tend not to trust the electrical continuity of conduit.