[garyk]

Generally we wire our limit switches to read 1 when they are pressed (the limit is hit) and 0 otherwise. That way if the switch gets disconnected it reads as though it's pushed, and the mechanism won't move toward the limit. Your team has to decide whether you want the mechanism to still work with a disconnected switch (risking damage) or stop if the switch is disconnected, rendering the mechanism not fully operational. This kind of design consideration is called "risk management."

Digital Inputs are "pulled up" through a resistor to +5v and will read 1 when there's no connection. The pneumatic pressure switch is wired in this manner, a disconnected switch reads the same as at full pressure. Therefore, the pump won't run with a disconnected pressure switch.