GOVERNORS

Introduction :-

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. A little consideration will show, that when the load  increases, the configuration of the governor changes and a valve is moved to increase the supply of the working fluid ; conversely, when the load decreases, the engine speed increases and the governor decreases the supply of working Fluid.

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. 18.1. These balls are known as goveror 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 arms are connected by the links to a sleeve, which is keyed to the spindle. This sleeve re-volves 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 down-ward 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 de-creases when the sleeve rises and increases when it falls.

 When the load on the engine increases, the en-gine 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 down-wards. The downward movement of the sleeve oper-ates 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. In this case, 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 in-crease of centrifugal force on the balls. Thus the balls move outwards and the sleeve rises upwards. This up-ward movement of the sleeve reduces the supply of the working fluid and hence the speed is decreased. In this case, the power output is reduced.

*          The controlling force is provided either by the action of gravity as in Watt governor or by a spring as in case of Hartnell governor. 

Note : When the balls rotate at uniform speed, controlling force is equal to the centrifugal force and they balance each other.