A governor is a tool used to measure and control a machine’s velocity, such as an engine.

governor device
By Globbet – Own work by uploader, with permission from the Mill Meece Pumping Station Preservation Trust, CC BY-SA 3.0,

A classic instance is a centrifugal governor on a reciprocating steam engine, also known as the Watt or fly-ball governor, which utilizes the impact of inertial force on rotating weights powered by the machine output shaft to control its velocity by changing the input flow of steam.


  1. Air-crafts: An implementation is the use of Aircraft propellers for example. The governor senses RPM shaft, adjusting or controlling the blade angle to change the engine torque load. The RPM is therefore kept constant as the aircraft speeds up (as in a dive) or slows down (in climb).
Photo by Thgusstavo Santana

2.Small Engines: Small engines used to power lawn mowers, mobile generators and lawn and garden tractors are fitted with a governor to restrict fuel to the engine at a maximum safe speed when unloaded and to keep a fairly steady velocity despite modifications in charging. The engine velocity must be carefully regulated in the event of generator apps so that the generator’s output frequency remains fairly constant.

Typically, small engine governors are one of three kinds:


Airflow from the flywheel blower used to cool the air-cooled engine is detected by the governor system.

The typical structure involves an air vane installed in the blower housing of the engine and connected to the throttle shaft of the carburetor.

A spring pulls the throttle open and increases the flow of air from the blower forces the vane back against the spring as the engine gains velocity, partly closing the throttle.

Eventually, a balance point is reached and the engine runs at a fairly steady velocity. Pneumatic governors are easy to design and cheap to manufacture.


The engine-driven flyweight mechanism is connected to the throttle and operates in a fashion comparable to that of the pneumatic governor against a spring, leading in fundamentally the same procedure.

A centrifugal governor is more complicated than a pneumatic governor to design and generate.

The centrifugal structure, however, is more susceptible to modifications in velocity and is, therefore, better suited for motors with big load fluctuations.


The servo motor is connected to the throttle and regulated by an electronic module that measures engine velocity by counting the electrical pulses emitted by the ignition or magnetic pick-up system.

The frequency of these pulses differs directly with engine velocity, making it possible for the control module to apply proportional voltage to the servo to regulate engine velocity.

Because of their sensitivity and rapid response to changes in velocity, electronic governors are often attached to engine-driven generators intended to power computer hardware, as the output frequency of the generator must be kept within tight boundaries to prevent malfunction

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