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Governor is the device used to control the speed in engines. It is observed that when load is applied on the engine, the speed tends to decrease which is known as rpm drop also, to compensate the speed, governor is used in all stationary or mobile engines which run on either single speed or variable speeds. In general, following are the two operating systems being used in engines governors.
· Hit and Miss system
· Throttle system
In hit and miss system, the frequency of cycles for fuel supply is controlled in the fuel system. Whereas, in throttle system, the frequency remains the same but the quantity of fuel is being controlled as per the engine requirements. Throttle system is the most commonly governing system being used in modern engines these days. The extent of throttle opening controls the fuel supply and hence the engine speed.
Although, the governor is used to maintain the constant engine speed, but still some variation in engine speed can be observed at no load and maximum load. This variation can be expressed in terms of Governor Regulation (%).
Governor Regulation = (S0 + S1) / 2(S0 – S1)* 100
Where, S0 = No Load speed
S1 = Maximum Load spped
The governors may be further classified as:
· Centrifugal/Mechanical governor
· Pneumatic governor
· Hydraulic governor
Mechanical governor
The centrifugal/mechanical governor is most commonly used governor in tractors. Two spring-loaded centrifugal weights are mounted on the governor shaft having sliding collar which further actuates the throttle and the fuel supply. As the engine speed increases, the weights fly apart with the centrifugal force against the spring tension to actuate fuel injection pump to reduce the amount of fuel delivered and hence decreases the engine speed. Similarly, the fuel supply is increased by the governor when the engine speed tends to decrease.
Pneumatic governor
A pneumatic governor consists of venturi unit and diaphragm unit which are connected by a vacuum pump. The venturi unit leads to the engine inlet manifold and the diaphragm unit is connected with the fuel injection pump. The position of the butterfly valve in the venturi unit is controlled by the accelerator pedal to control the amount of vacuum from the inlet manifold, to actuate the fuel pump through diaphragm unit and hence the amount of fuel injected.
Hydraulic governor
A hydraulic governor works on the principle of pressure change and receives the oil from the engine lubricating system which further act as controlling force to control the fuel supply and hence the engine speed. The loss of oil pressure cuts the supply of oil to the governor and cause the governor to shut down the engine.
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