Construction and Working Principles Of Hartnell Governors -Advantages Of Hartnell Governors
The function of a governor is to regulate the mean speed of an engine, when there are variations in the load e.g. when the load on an engine increases, its speed decreases, therefore it becomes necessary to increase the supply of working fluid. On the other hand, when the load on the engine decreases, its speed increases and thus less working fluid is required. The governor automatically controls the supply of working fluid to the engine with the varying load conditions and keeps the mean speed within certain limits.
It is a Spring loaded Governor . It has two bell crank levers carrying fly ball at one end and roller attached to other end, the function of spring is provide the counter force which acts against centrifugal force. The spring and shaft is enclosed inside a casing .The sleeve is pressed against the spring when the centrifugal force on the balls increases. Due to spring return nature this governor can be mounded in horizontal,inverted, (inclined) position.
Working of Hartnell Governors :
Hartnell governor is a spring controlled centrifugal governor, in which a spring controls the movement of the ball and hence the sleeve. Above fig shows a Hartnell governor. It consists of a frame /casing, in which a precompressed helical spring is housed. The casing and spring can rotate about the spindle axis. The spring applies a downward force on the sleeve through an adjustable collar. The spring force can be adjusted by a nut provided. Two bell crank levers are pivoted at O,O’ to the frame, each carrying a ball at one end a roller at another end. The roller fits into the grooves of the sleeve.
The sleeve moves up and down depending on the governor speed. When the speed of governor/ engine increase, the ball tends to fly outward from the axis of governor, but balls movement is constrained. The bell crank lever moves on pivot, roller end of lever lifts the sleeve upward against the spring force. This movement transferred to the throttle valve through the suitable mechanism, the result is a low fuel supply and decreasing speed.
When speed decreases the sleeve move downward, and throttle open to more fuel supply; which results in increasing speed.
Advantages of Hartnell governor
It can be operated at very high speed
Smaller in size
Very close regulation
Pre-compression can be adjusted to give required equilibrium speed.