Governors for Reversible Hydraulic Constant Speed Propellers

The P-9( )-( ) hydraulic propeller governor is a single acting governor developed for dual piston hydraulic variable pitch propellers equipped with reverse and feathering capability.

This governor works in combination with a dual pressure single acting propeller system. It is designed for oil pressure to decrease pitch (counterweighted propellers, only).
The governor is equipped with two relief valves. A low pressure relief valve is used for normal operation and a high pressure relief valve is used for reverse/beta range.

In low pressure operation the necessary increase in engine oil pressure is generated by a gear pump in the governor, which increases the servo oil pressure. Flyweights and a speeder spring move a pilot valve, allowing servo oil to flow to and from the piston in the propeller. In an "on speed" condition there is no oil flow.
A speed adjusting lever controlled via a cable link from the cockpit (as commonly used) changes the preload of the speeder spring. This results in an engine/propeller speed (RPM) change.

The high pressure mode is activated by a switch installed in the cockpit (preferrably connected to the throttle lever), which controls a magnetic beta valve, that is installed on the governor. In this condition the servo oil pressure is approximately doubled and the inner piston pushes the blades into full reverse position.
The propeller RPM is not controlled by the governor during high pressure mode, because the constant speed section is cut out. The negative thrust is produced just by increasing or decreasing the throttle (RPM) comparable with a fixed pitch system.

After the electric signal has been turned off, the governor returns into normal pressure mode for regular constant speed operation.

The governor contains a gear pump, relief valves, pilot valve flyweights and the beta valve.

The flange type of the governor is built in accordance with the AND20010 standard. The magnetic valve is installed on the bottom of the governor. The electromagnet controls an hydraulic valve, which changes from low pressure to high pressure mode via an electric signal, which is produced by a switch installed inside the cockpit. If the high pressure mode is selected, the pilot valve is inoperative.

Governors for Hydraulic Constant Speed Propellers

Accumulator