Final answer:
A pressure sensor or pressure switch signals the microprocessor to activate the lead pump when system pressure falls below 60 psi, similar to how the human heart maintains blood pressure.
Step-by-step explanation:
The component in a Type III system that signals the microprocessor to turn on the lead pump when the system pressure drops below 60 pounds per square inch (psi) is likely a pressure sensor or pressure switch. This device monitors the system pressure and communicates with the microprocessor to activate the pump when necessary.
Such automated systems are found in applications where consistent pressure is crucial, such as in power brakes and heavy equipment like bulldozers. In a similar way, the human circulatory system maintains blood pressure through the action of the heart, with long-term deviations in pressure having significant medical implications, as discussed in the context of Fluid Dynamics and its biological and medical applications.