Introduction To Governors
Function Of Governor :
- The function of the 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.
- The Governor mechanism is used 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.
- Figure shows an illustrative sketch of a governor along with linkages which regulates the supply to the engine. The governor shaft is rotated by the engine.
- If the load on the engine increases the engine speed tends to reduce, as a result of which governor balls move inwards. This causes the sleeve to move downwards and this movement is transmitted to the valve through linkages to increase the opening and, thereby, to increase the supply.
- On the other hand, a reduction in the load increases engine speed. As a result of which the governor balls try to fly outwards. This causes an upward movement of the sleeve and it reduces the supply.
- Thus, the energy input (fuel supply in IC engines, steam in steam turbines, water in hydraulic turbines) is adjusted to the new load on the engine. Thus the governor senses the change in speed and then regulates the supply.
- Due to this type of action it is a simple example of a mechanical feedback control system which senses the output and regulates input accordingly.
CLASSIFICATION OF GOVERNORS
2. Inertia governor.
2. Loaded type
(ii) Proell governor
(ii) Hartung governor
(iii) Wilson–Hartnell governor
(iv) Pickering governor
- These governors work on the principle of centrifugal action. They have two balls that rotate along with the sleeve. As the centrifugal forcer is directly proportional to the radius of rotation of the mass, therefore, when the speed of a device increases, the balls rotate at a larger radius.
- As a result of it, the sleeve slides upwards on the spindle and with the help of a lever, the throttle is closed to the required extent.
- With the decrease in speed, the balls rotate at a smaller radius of rotation, compelling the sleeve to move down on the spindle. The downward movement of the sleeve opens the throttle to the required extent to admit more fuel into the prime movers. By this process, the speed of the prime mover and in turn that of the driven device is maintained constant.
Inertia and Flywheel Governors
Types of Centrifugal Governors
- In the gravity-loaded governors, a central load is attached to the sleeve, which slides on the spindle.
- There is a force of friction between the loaded sleeve and the spindle. The frictional force acts downwards when the sleeve moves up and acts upwards when the sleeve moves down. Thus, the height of the governor increases or decreases from the normal value.
Watts GovernorWhen the load on the engine decreases, the speed of the engine and then the angular velocity of the governor spindle increase. The centrifugal force on the ball increase; that tends balls move outward and sleeve move upward. The upward movement of the sleeve actuates a mechanism that operates the throttle valve at the end of ―bell crank lever to decrease the fuel supply. The power output is reduced.
When the speed of the engine decreases as the load on the engine increase, the centrifugal force decreases. The result is that the inward movement fly-balls and downward movement of the sleeve. The movement causes a wide opening of the throttle valve. The increase in the fuel supply also increases engine speed.
Terms Used in Governors
Performance of Governors :
- For maintaining a constant speed of rotation, the movement of the sleeve of the governor should be as large as possible and the corresponding change of equilibrium speed as small as possible.
- The bigger the displacement of the sleeve for a given fractional change of speed, the more sensitive is the governor. Sensitiveness is more correctly defined as the ratio of the difference between the maximum and minimum equilibrium speeds to the mean equilibrium speed.
- A too sensitive governor changes the fuel supply by a large amount when a small change in the speed of rotation takes place. This causes wide fluctuations in the engine speed, resulting in the hunting of the governor.
Nmin = minimum equilibrium speed
Nmean = mean equilibrium speed
- A governor is said to be stable when for each speed within the working range, there is only one radius of the governor balls at which the governor is in equilibrium. For a stable governor, if the equilibrium speed increases, the radius of the governor balls must also increase.
- A governor is said to be isochronous, when the equilibrium speed is constant for all radii of rotation of the balls, within the working range. An isochronous governor will be infinitely sensitive.
- It is a condition in which the speed of the engine controlled by the governor fluctuates continuously above and below the mean speed. It is caused by a governor which is too sensitive.
5. Governor effort:
The effort of a governor is the force it can exert at the sleeve on the mechanism, which controls the supply of fuel to the engine. The mean force exerted during the given change of speed is termed as effort. Generally efforts are defined for 1% change of speed.
The power of a governor is defined as the work done at the sleeve for a given percentage change of speed.
Power = efforts X displacement of sleeve
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