ME Subjects – Concepts Simplified

Topics on Mechanical Engineering Courses

This content shows Simple View


FLYWHEEL AND GOVERNOR                 flywheel theory                  flywheel design


Sr. No. Flywheel Governor
1. Maintains constant speed but

the means is different from that

of Governor. Stores excess of rotational

energy from the power stroke and supply

back during non- power strokes of the cycle

Maintains constant speed but the means is different from that of Flywheel.
Controls mean speed of the engine under full/half/varying load conditions by regulating the supply of working fluid to the engine
2.  In this, there are energy variations but runs the crankshaft at constant speed in each stroke of the cycle   When load on the engine increases, speed decreases. It increases the flow of fuel to keep the constant mean speed
3.  Flywheel controls the speed for one cycle only  Governor maintains constant mean speed over a period of time.
4.  Flywheel is not required in all the prime movers (engines)   Governor is required in all the prime movers (engines)
5. It is a  heavy machine part It is a relatively light machine part
6. Has large moment of inertia Relatively small moment of inertia
7.  Rotating part Non- Rotating part
8.  Running charges are less  Running charges are high
9.  Angular speed increases while storing energy and decreases during supply back of energy  Runs at mean speed under all loads on the engine
10. Crankshaft runs at constant speed Load increases speed decreases and vice -varsa. But it controls the MEAN speed by controlling the flow of fuel in the engine
11. There are no valves attached with the flywheel  Valves are there and there opening is controlled by the centrifugal force on the balls attached
 12. Flywheel does not need any extra mechanism to supply back energy  Governor needs a piston /plunger mechanism
 13.  It absorbs energy from the high momentum generated in power stroke and engine running smooth in non power strokes   It controls the air supply to the carburetor and fuel supply to the engine
 14.  It is connected to the crank shaft and runs it at a constant speed   It is not connected to the crankshaft
 15.  It is an energy storing device and prevents the fluctuations of energy during each cycle of operation of the engine.  It is not an energy storing device.
 16.  It is a wheel and only its size may differ from one machine to another  There is a large variety of governors used in different prime movers
 17. Flywheel is a fairly rigid structure and undergoes no changes while in operation  A governor undergoes changes while in operation
 18.  Short term energy storage  A long term speed controller as per load on the prime mover
 19.  Used in reciprocating steam and IC engines  Used in riveting machines to store energy from the motor and release the energy during the riveting operation Used in SI and CI engines
 20.  It cannot change the speed of the crankshaft   It is used to limit the speed.
21. Flywheel supply back energy as when required Power is supplied to the governor from the engine shaft
22. Energy stored in a flywheel is directly proportional to the square of its rotational speed There is no such relation



Keywords: Hunting-sticking-sensitiveness-performance

1. What is the meaning of a  governor in a machine?
Maintains a constant speed under changing power requirements over a longer interval of time by controlling supply of driving fluid / fuel in case of an engine / the supply of steam flow in case of a steam turbine,

2. What is hunting of a governor?

Hunting is alternate increase and decrease of speed as per load changes on the engine. If load increases, speed decreases. If the load decreases, speed increases. Hunting means governor is highly sensitive and immediately responds to the increase or decrease of load.

3. What is Sticking-failure of a governor?

When the governor does not respond to load changes on the engine i.e. speed do not change with change of load on the engine, the sticking failure has occurred. It may be due to wear of some parts of the governor.
4. What is meant by the controlling force in a governor?
It is the inward pull exerted on each ball of the governor under constant speed of rotation. It is equal and opposite to the outward centrifugal force acting on the governor.
5. How is the performance of a governor judged?
Following four parameters determines the quality of performance of a governor:
(i) Sensitiveness: governor responds immediately to load changes. Mathematically it is defined as the ratio of difference in maximum and minimum equilibrium speeds divided by the mean equilibrium speed.
Say maximum speed =100, minimum speed =50
Then sensitiveness = (100 – 50) / 75 = 0.67
(ii) Stability: if there is only one radius of the balls of the governor at which it is in equilibrium for entire range of speeds.
(iii) Governor effort: It is the mean force exerted by the governor on the sleeve which controls the supply of fuel to the engine in a given range of speed variation. Normally it is 1 % of the range of speed variation.
(iv) Governor power: It is the work done on the sleeve for a given % change of speed.
Mathematically Power = Effort x displacement of sleeve

1. What is a flywheel?
It is heavy wheel which stores excess ROTATIONAL energy during power stroke and releases during non working strokes such as exhaust, suction and compression strokes. Time duration of storage and release of excess rotational energy is small.

2. What is difference between a governor and a flywheel?

Sr. No. Flywheel Governor
1. Stores excess ROTATIONAL energy during power stroke and releases during non working strokes such as exhaust, suction and compression strokes. Maintains a constant speed by controlling supply of driving fluid / fuel in case of an engine / the supply of steam flow in case of a steam turbine
2. Heavy mechanical part  Light mechanical part
3. Stores and supply of excess rotational energy  Controls the supply of working fluid
4. Cheap as it reduces running expenses of the prime mover   Costly as there is a chance of more consumption of driving fluid in case of governor.
5. A flywheel controls the SPEED VARIATION caused by different strokes of the engine by storing and releasing excess rotational energy A governor maintains a CONSTANT SPEED during load variation on the engine.
6. Works over a shorter interval of time governors are used to regulate speed over a longer interval of time