Governor Experiment — Watt, Porter, Proell and Hartnell Governor Procedure and Observations

The governor experiment is one of the most important practicals in the Theory of Machines laboratory. Governors are speed-control devices used in engines and turbines to maintain a constant speed under varying load conditions. This guide covers the complete procedure, observations, and calculations for the four main types of governors: Watt, Porter, Proell, and Hartnell.

Aim of the Experiment

To study the working of different types of governors — Watt, Porter, Proell, and Hartnell — and to plot the characteristic curves (radius of rotation vs. speed) for each governor type.

Theory

What is a Governor?

A governor is a device that automatically controls the speed of an engine by regulating the fuel supply according to the load. When the load on the engine decreases, the engine tends to speed up; the governor detects this and reduces the fuel supply to bring the speed back to the set value. Conversely, when the load increases, the governor opens the fuel supply.

Classification of Governors

• Centrifugal governors: Watt, Porter, Proell — use centrifugal force of rotating balls
• Inertia governors: Respond to rate of change of speed
• Spring-loaded governors: Hartnell — use spring force to control ball position

Watt Governor

The simplest form of centrifugal governor. Two fly balls are connected to the spindle by arms. As speed increases, centrifugal force moves the balls outward, raising the sleeve which throttles the fuel supply.

Formula for equilibrium speed:

N² = 895/h (where h = height of governor in metres, N = speed in rpm)

The Watt governor has poor isochronism — it has a wide range of speed variation for a small change in load. This is its main limitation.

Porter Governor

An improved version of the Watt governor with a central load (dead weight) added to the sleeve. The central load increases the controlling force, making the governor more sensitive.

Formula: N² = 895(m + M)/mh (where m = mass of ball, M = mass of sleeve/central load)

Proell Governor

Similar to the Porter governor, but the balls are placed at the extension of the lower arms (beyond the pivot). This gives the Proell governor higher sensitivity than the Porter governor for the same speed range.

Hartnell Governor

A spring-loaded governor in which the controlling force is provided by a central coil spring. Two bell-crank levers carry the balls on their horizontal arms. The spring connects the vertical arms to the sleeve.

Stiffness of spring: s = (Fc2 – Fc1) × a / (b × (x2 – x1))

where Fc = centrifugal force, a = horizontal arm length, b = vertical arm length, x = lift of sleeve

Apparatus Required

• Governor apparatus (motorised, variable speed) with Watt, Porter, Proell, and Hartnell attachments
• Tachometer (contact or non-contact optical)
• Steel rule / Vernier caliper (for measuring radius of rotation)
• Weights (for Porter and Proell governor central load)
• Speed controller unit

Procedure

1. Set up the Watt governor on the motorised spindle. Ensure all connections are tight and the balls are at their lowest position.
2. Switch on the motor and gradually increase speed using the speed control knob.
3. Note the speed (N in rpm) using the tachometer and the corresponding radius of rotation (r in mm) of the fly balls at 5–6 different speed settings.
4. Record observations in the table below.
5. Reduce speed to zero and change the governor to Porter type by adding the central sleeve load.
6. Repeat the speed variation and observation procedure.
7. Repeat for Proell and Hartnell governors with their respective configurations.
8. For the Hartnell governor, note the initial and final spring compression for each speed setting.

Observation Table

Calculations

For Watt Governor

Theoretical speed: N_th = √(895/h) rpm
Percentage error = (N_actual – N_theoretical)/N_theoretical × 100%

Coefficient of Insensitiveness

CI = (N₂ – N₁)/N_mean × 100%
(where N₁ = speed when sleeve begins to rise, N₂ = speed when sleeve begins to fall)

For Hartnell Governor — Spring Stiffness

s = 2(Fc2 – Fc1) × a / (b × x)
where Fc = mω²r, a = horizontal bell-crank arm, b = vertical bell-crank arm, x = sleeve lift

Result and Discussion

Plot the characteristic curve (radius of rotation vs. speed in rpm) for each governor on the same graph. Observations to note:

• The Watt governor has the lowest controlling force and widest speed range for a given radius change
• The Porter governor is more sensitive than Watt due to the central dead load
• The Proell governor gives the highest radius for a given speed — it is the most sensitive
• The Hartnell governor maintains nearly constant speed across its operating range (closest to isochronous)

Precautions

• Do not exceed the rated speed of the governor apparatus
• Ensure the governor spindle is vertical before starting
• Take tachometer readings when the speed has stabilised
• Keep hands and clothing away from rotating parts

Viva Questions

1. What is the difference between a governor and a flywheel?
2. What is isochronous governor? Which of the four types is closest to isochronous?
3. Define coefficient of insensitiveness. What causes it?
4. Why does the Proell governor have higher sensitivity than the Porter governor?
5. What is the effect of friction on governor performance?
6. Define equilibrium speed, mean speed, and range of speed of a governor.
7. What is the purpose of the central load in the Porter governor?

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