Aim: To study the characteristics of different types of governors (Watt, Porter, Proell, Hartnell) and plot the equilibrium speed vs. radius of rotation curves.
Apparatus Required
- Governor Apparatus with variable-speed motor drive and interchangeable governor assemblies (Watt, Porter, Proell, Hartnell)
- Tachometer (non-contact, stroboscope or digital)
- Measuring scale (for sleeve lift measurement)
Theory
A governor automatically controls the speed of an engine by varying the fuel supply based on load fluctuations. Centrifugal governors (Watt, Porter, Proell) use the centrifugal force on rotating balls to control a throttle. As speed increases, the balls fly outward — the sleeve rises and reduces fuel supply. Spring-loaded governors (Hartnell) use a spring to control ball movement.
Key parameters: Radius of rotation (r) — distance of ball from spindle axis; Height of governor (h) — vertical distance from pivot to the ball plane; Equilibrium speed (N) — speed at which the governor is in equilibrium for a given radius.
For Watt governor: N² = 895/h (rpm), where h is in metres. For Porter governor: N² = 895(m+M)/mh.
Procedure
- Set up the Watt governor assembly on the apparatus. Start the motor at minimum speed.
- Increase speed gradually. At each stable equilibrium position, record the speed N (rpm) using the tachometer and the radius of rotation r (mm).
- Record 5–6 readings over the operating speed range.
- Replace with the Porter governor assembly. Repeat the procedure with the additional central load (sleeve mass M).
- If available, test the Proell and Hartnell governor assemblies similarly.
- Plot N (rpm) vs r (mm) for each governor type.
Observation Table (Watt Governor)
| Obs. No. | Speed N (rpm) | Radius r (mm) | Height h (mm) | Theoretical N (rpm) | % Error |
|---|---|---|---|---|---|
| 1 | — | — | — | — | — |
| 2 | — | — | — | — | — |
| 3 | — | — | — | — | — |
| 4 | — | — | — | — | — |
Frequently Asked Questions
What is the difference between a Watt governor and a Porter governor?
A Watt governor uses only the mass of the rotating balls to generate centrifugal force for speed control. A Porter governor adds a central sleeve load (mass M) that increases the centrifugal force required for equilibrium — making the Porter governor more sensitive and capable of operating at higher speeds than the Watt governor for the same ball radius.
What is the formula for the height of a Watt governor?
For a Watt governor: N² = 895/h, where N is the equilibrium speed in rpm and h is the height of the governor in metres (vertical distance from the pivot to the plane of the rotating balls). This shows that height decreases as speed increases.
What is isochronous governor?
An isochronous governor maintains the same equilibrium speed for all positions of the sleeve — the speed vs radius curve is a vertical line. In practice, perfect isochronism is difficult to achieve; real governors have a range of speeds over which the sleeve position changes (hunting may occur if too sensitive).
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