CODE Supply pressure Return to pump Propeller servo pressure Py FCU Arm Governor spring Hydraulic low pitch adjustment Carbon block Reset post Propeller speed control lever Minimum govenor adjustment Beta valve Pilot valve Engine oil CSU pump Beta rod Rearward movement Reset arm Beta valve lever Shut-off (lock pitch) solenoid valve Rearward movement Full fwd position Push-pull control Reversing cam Figure 7-52.  Beta mode reverse operation.  governor oil pressure into forces that act through the cams  to turn propeller blades. The pitch-changing mechanism of hydromatic propellers is  a mechanical-hydraulic system in which hydraulic forces  acting on a piston are transformed into mechanical twisting  forces acting on the blades. Linear movement of the piston  is converted to rotary motion by a cylindrical cam. A bevel  gear on the base of the cam mates with bevel gear segments  attached to the butt ends of the blades, thereby turning the  blades. This blade pitch-changing action can be understood  by studying the schematic in  Figure 7-56 . The centrifugal force acting on a rotating blade includes a  component force that tends to move the blade toward low  pitch. As shown in  Figure 7-56 , a second force, engine oil  pressure, is supplied to the outboard side of the propeller  piston to assist in moving the blade toward low pitch. 7-37 Principles of Operation Propeller governor oil, taken from the engine oil supply and  boosted i pressure by the engine-driven propeller governor,  is directed against the inboard side of the propeller piston. It  acts as the counterforce, which can move the blades toward  higher pitch. By metering this high-pressure oil to, or draining  it from, the inboard side of the propeller piston by means of  the  constant-speed control unit, the force toward high pitch  can balance and control the two forces toward low pitch. In  this way, the propeller blade angle is regulated to maintain  selected rpm. The basic propeller control forces acting on the Hamilton  Standard propeller are centrifugal twisting force and high  pressure oil from the governor. The centrifugal force acting  on each blade of a rotating propeller includes a component  force that results in a twisting moment about the blade center  line that tends, at all times, to move the blade toward low  pitch. Governor pump output oil is directed by the governor  to either side of the propeller piston. The oil on the side of 