Short Answer:

A Porter governor is a type of centrifugal governor that is an improved version of the Watt governor. It includes a central load (dead weight) on the sleeve to increase the controlling force and stability. This added load makes the governor more sensitive and suitable for moderately high-speed engines.

The Porter governor works on the principle of centrifugal force, where rotating balls move outward with increasing engine speed, lifting the sleeve to control the fuel supply. It maintains a nearly constant speed by automatically adjusting the engine’s fuel or steam input according to load variations.

Detailed Explanation:

Porter Governor

A Porter governor is a modified and improved version of the Watt governor, designed to overcome its limitations. The Watt governor is suitable only for low-speed engines because it cannot develop enough controlling force to handle large variations in load. To increase the sensitivity and stability, the Porter governor includes a heavy central load (dead weight) on the sleeve. This additional weight increases the downward force on the sleeve, resulting in better speed control even at higher speeds.

The Porter governor works on the principle of centrifugal force. When the engine speed increases, the centrifugal force on the rotating balls causes them to move outward, raising the sleeve. This movement partially closes the throttle valve, reducing the fuel or steam supply and thus slowing down the engine. Conversely, when the speed decreases, the balls move inward, the sleeve moves downward, the throttle opens wider, and the speed increases again. This automatic adjustment keeps the engine speed nearly constant.

Construction of Porter Governor

The main components of the Porter governor are:

1. Spindle:
   It is a vertical shaft driven by the engine using bevel gears. The spindle rotates at a speed proportional to the engine speed.
2. Balls (Fly Balls):
   Two equal masses or balls are attached to the ends of the arms. These balls rotate about the spindle and experience centrifugal force.
3. Arms:
   The arms connect the balls to the spindle and the sleeve. There are two pairs of arms—upper and lower. The upper arms are connected to the spindle at a pivot point, and the lower arms are connected to the sleeve.
4. Sleeve:
   The sleeve is a movable collar that slides up and down on the spindle. It is connected to the throttle valve mechanism that regulates the fuel or steam supply.
5. Dead Weight (Central Load):
   A heavy central weight is mounted on the sleeve. This weight increases the controlling force and improves the stability of the governor.

Working of Porter Governor

The working of a Porter governor is similar to that of a Watt governor but with greater sensitivity due to the added dead weight.

• When Engine Speed Increases:
  As the engine speed rises, the spindle rotates faster, increasing the centrifugal force on the balls. The balls move outward, raising the sleeve along the spindle. This upward motion reduces the opening of the throttle valve, which decreases the fuel or steam supply to the engine. Consequently, the engine speed decreases to its mean value.
• When Engine Speed Decreases:
  If the engine load increases, the speed falls, reducing the centrifugal force. The balls move inward due to the effect of gravity and the central load, causing the sleeve to move downward. This movement increases the throttle opening, allowing more fuel or steam to enter, which increases the speed again to the desired value.

This continuous balancing action maintains a nearly uniform speed.

Height of Porter Governor

The height (h) of a Porter governor is the vertical distance between the center of the governor balls and the point where the upper arms intersect the spindle axis. The relationship between the height and the speed is given by:

where,

•  = height of the governor (m)
•  = speed of governor (rpm)
•  = weight of each ball (N)
•  = central load (N)
•  = acceleration due to gravity

This equation shows that the height depends on both the speed and the ratio of the ball weight to the central load. A larger dead weight decreases the height, allowing the governor to operate efficiently at higher speeds.

Advantages of Porter Governor

1. More stable and sensitive than the Watt governor.
2. Suitable for moderately high-speed engines.
3. Can handle larger load variations.
4. Provides smoother and more accurate speed control.

Disadvantages of Porter Governor

1. Slightly more complex and heavier than Watt governor.
2. Friction between the sleeve and spindle may reduce accuracy.
3. Not suitable for very high-speed engines.
4. Maintenance is slightly more difficult due to the additional central load.

Applications of Porter Governor

• Used in medium-speed stationary steam engines.
• Suitable for engines where moderate speed regulation is needed.
• Found in early mechanical power plants and steam locomotives.

Conclusion:

The Porter governor is an important centrifugal governor used to maintain constant engine speed by adjusting the fuel or steam input automatically. It is an improved form of the Watt governor, with a central load on the sleeve that provides greater stability and sensitivity. The Porter governor is ideal for medium-speed engines where accurate and smooth control is required. Its design paved the way for more advanced governors like the Proell and Hartnell types used in modern engines.