Final answer:
The control lever manipulates the oil pressure to the propeller in a hydraulic system.
Step-by-step explanation:
In a hydraulic system, the lever that manipulates the oil pressure to the propeller is called the control lever.
When the control lever is moved, it adjusts the flow of oil to the propeller, thereby changing the oil pressure and controlling the speed and direction of the propeller.
For example, in an aircraft, the control lever in the cockpit allows the pilot to increase or decrease the oil pressure to adjust the RPM (revolutions per minute) of the propeller, which affects the thrust generated by the propeller.