Machine Dynamics Multiple Choice Questions on “Porter Governor”.
1. Sensitiveness of the governor is defined as the ratio of the
a) mean speed to the maximum equilibrium speed
b) mean speed to the minimum equilibrium speed
c) difference of the maximum and minimum equilibrium speeds to the mean speed
d) sum of the maximum and minimum equilibrium speeds to the mean speed
Answer: c
Clarification: The sensitiveness is defined as the ratio of the difference between the maximum and minimum equilibrium speeds to the mean equilibrium speed.
2. A governor is said to be stable, if the
a) radius of rotation of balls increases as the equilibrium speed decreases
b) radius of rotation of balls decreases as the equilibrium speed decreases
c) radius of rotation of balls increases as the equilibrium speed increases
d) radius of rotation of balls decreases as the equilibrium speed increases
Answer: c
Clarification: 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.
3. When the radius of rotation of balls ______________ as the equilibrium speed increases, the governor is said to be unstable.
a) remains constant
b) decreases
c) increases
d) none of the mentioned
Answer: b
Clarification: A governor is said to be unstable, if the radius of rotation decreases as the speed increases.
4. A governor is said to be isochronous when range of speed is zero for all radii of rotation of the balls within the working range, neglecting friction.
a) True
b) False
Answer: a
Clarification: A governor is said to be isochronous when the equilibrium speed is constant (i.e. range of speed is zero) for all radii of rotation of the balls within the working range, neglecting friction. The isochronism is the stage of infinite sensitivity.
5. A Porter governor can not be isochronous.
a) True
b) False
Answer: a
Clarification: None
6. In a Hartnell governor, if a spring of greater stiffness is used, then the governor will be
a) less sensitive
b) more sensitive
c) unaffected of sensitivity
d) isochronous
Answer: a
Clarification: In general, the greater the lift of the sleeve corresponding to a given fractional change in speed, the greater is the sensitiveness of the governor.
7. When the speed of the engine fluctuates continuously above and below the mean speed, the governor is said to be
a) stable
b) unstable
c) isochronous
d) hunt
Answer: d
Clarification: The isochronous governor is not of practical use because the sleeve will move to one of its extreme positions immediately the speed deviates from the isochronous speed.
8. A very sensitive governor will cause hunting.
a) True
b) False
Answer: a
Clarification: A governor is said to be hunt if the speed of the engine fluctuates continuously above and below the mean speed. This is caused by a too sensitive governor which changes the fuel supply by a large amount when a small change in the speed of rotation takes place.
9. For isochronous Hartnell governor
a) mg + S1 / mg + S2 = r1/r2
b) mg – S1 / mg – S2 = r2/r1
c) S1/S2 = r1/r2
d) S2/S1 = r1/r2
Answer: a
Clarification: None
10. Effort of a governor is the
a) mean force exerted at the sleeve for a given percentage change of speed
b) workdone at the sleeve for maximum equilibrium speed
c) mean force exerted at the sleeve for maximum equilibrium speed
d) none of the mentioned
Answer: a
Clarification: The effort of a governor is the mean force exerted at the sleeve for a given percentage change of speed (or lift of the sleeve).