Hartnell Governor is spring loaded centrifugal governor. It contains an additional spring which is used to apply an additional force to the sleeve. This governor has a nut place at the top of the spring . This nut is used to adjust the force of the spring.
Hartnell Governor has a spindle which is connected the engine and rotates with the same speed as that of engine. This spindle is connected with two fly balls which rotates and experience centrifugal force when spindle rotates. These fly balls are connected to sleeve via a bell crank lever which translate side ways motions of balls to up-down motion of sleeve using rollers. The upper side of sleeve has a spring which restricts the upward movement of sleeve. This spring has a nut which is used to adjust the force of the spring. The sleeve is connected to throttle valve through a link mechanism which controls the fuel supply to the engine.
Working at low load :-
When the load on the engine decreases, the speed of the engine will increase suddenly and hence the spindle speed will also increases. With the spindle rotates the balls also starts rotating, then due to centrifugal force they are pulled outward. As the balls move outward, the sleeve moves upward as they are connected through bell crank lever. Bell crank lever change the angle of motion to 90 degrees.The sleeves are connected to the bell crank lever via roller.As the balls move outward, these roller takes the ball upward.As the sleeve move upwards the spring present above the sleeve gets compressed. This spring limits the movement of sleeve in upward directon. As the sleeve move upward, the throttle valve which connected to the sleeve through a link mechanism starts closing and the supply of working fuel throught the throttle valve gets reduces. As the fuel supply reduces, the speed of the engine also get reduced.
Working at high load :-
When the load on the engine increases, the speed of engine will decrease and requires more fuel to increase its speed. As the speed of the engine decreases, the rotational speed of spindle which is connected to the engine also gets decreased.Due to decrease in spindle speed, the speed of rotation of balls also decreases and the centrifugal force on the balls also decreases. So the balls comes closer to each other and since the sleeve is connected to the balls via a bell crank lever , so the sleeve comes down . The spring which is located above the sleeve also pushes the sleeve downward.
When the sleeve comes down, the throttle valve connected to the sleeve via a link mechanism starts opening and the supply of working fuel to the engine increases and hence the speed of engine is maintained.