Final answer:
A three position vacuum motor with vacuum applied to one port and the shaft retracting halfway is usually represented by a Positional Valve Diagram (PVD).
Step-by-step explanation:
When a three position vacuum motor only has vacuum applied to one port on the motor and the shaft retracts halfway, this is typically represented by a Positional Valve Diagram (PVD). In hydraulic or pneumatic systems, a PVD is used to graphically represent the positions and functions of a valve. The three positions of the motor reflect three different flow paths or states that the valve can regulate. The midpoint position, where the shaft retracts halfway, is indicative of the transitional state. This is important to understand in controls and automation, as it directly affects the performance of the system.
Answer: C. PV