Showing posts with label governor uses. Show all posts
Showing posts with label governor uses. Show all posts

Monday 18 November 2013

Stability of Governors

A governor is said to be stable when for every speed within the working range there is a definite configuration i.e. there is only one radius of rotation of the governor balls at which the governor is in equilibrium.
For a stable governor, if the equilibrium speed increases, the radius of governor balls must also increase. 
 
 
 

Inertia Governors

This works on a different principle. The governor balls are arranged so that the inertia forces caused by angular acceleration or retardation of the governor shaft tend to alter their positions. The amount of the displacement of the balls is controlled by springs and
the governor mechanism to alter the supply of energ y to the engine. 
 
The advantage of this type of governor is that the positions of the balls are affected by
the rate of change of speed of the governor shaft.Consequently, a more rapid response
to a change of load is obtained, since the action of the governor is due to acceleration
and not to a finite change of speed. The advantageis offset, however, by the practical
difficulty of arranging for a complete balance of the revolving parts of the governor. For
this reason centrifugal governors are much more frequently used. 
 
 
 
Inertia Governors
 
 
 

Centrifugal Governors

The centrifugal governors are based on the balancing of centrifugal force on the rotating balls by an equal and opposite radial force, known as the controlling force* .It consists of two balls of equal mass, which are attached to the arms as shown in Fig . These balls are known as governor balls or fly balls.The balls revolve with a spindle, which is driven by the engine through bevel gears. The upper ends of the arms are pivoted to the spindle, so that the balls may rise up or fall down as they revolve about the vertical axis. The sleeve revolves with the spindle; but can slide up and down. The balls and the sleeve rises when the spindle speed increases, and falls when the speed decreases. In order to limit the travel of the sleeve in upward and downward directions, two stops S,S are provided on the spindle.

The sleeve is connected by a bell crank lever to a throttle valve. The supply of the working fluid decreases when the sleeve rises and increaseswhen it falls. When the load on the engine increases, the engine and the governor speed decreases. This results in the decrease of centrifugal force on the balls. Hence the balls move inwards and the sleeve moves downwards. The downward movement of the sleeve operates a throttle valve at the other end of the bell crank lever to increase the supply of working fluid and thus the engine speed is increased.

Hence, the extra power output is provided to balance the increased load. When the load on the engine decreases, the engine and the governor speed increases, which results in the increase of centrifugal force on the balls. Thus the balls move outwards and the sleeve rises upwards. This upward movement of the sleeve reduces the supply of the working fluid and hence the speed is decreased. Hence, the power output is reduced.



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Other Topics

Types of Governors

Governors

Flywheel which minimizes fluctuations of speed with
in the cycle but it cannot minimize fluctuations due to load variation. This means flyw
heel does not exercise any control over mean speed of the engine. To minimize fluctuat
ions in the mean speed which may occur due to load variation, governor is used. The
governor has no influence over cyclic speed fluctuations but it controls the mean speed o
ver a long period during which load on the engine may vary. 
 
The function of governor is to increase the supply of working fluid going to the prime- mover when the load on the prime-mover increases and to decrease the supply when the load decreases so as to keep the speed of the prime-mover almost constant at different loads.
 
Example: 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 hence less working fluid is required.
When there is change in load, variation in speed also takes place then governor operates a regulatory control and adjusts the fuel supply to maintain the mean speed nearly constant. Therefore, the governor automatically regulates through linkages, the energy supply to the engine as demanded by variation of load so that the engine speed is maintained nearly constant. 
 
 
 
 
 
 
 

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