What is Watt governor?

Short Answer:

A Watt governor is the simplest type of centrifugal governor used to control the speed of an engine by regulating the fuel supply. It works on the principle of centrifugal force acting on two rotating balls connected to the spindle through arms. When the engine speed increases, the balls move outward, lifting a sleeve that reduces the fuel supply, and when speed decreases, the balls move inward, increasing the fuel supply to maintain a constant speed.

It was invented by James Watt and is mainly used in low-speed steam engines. Though simple in design, it is not suitable for high-speed engines because of limited sensitivity.

Detailed Explanation:

Watt Governor

A Watt governor is one of the earliest and simplest types of centrifugal governors used to maintain a nearly constant speed of an engine under varying load conditions. It was invented by James Watt in the 18th century for use in steam engines. The main purpose of this governor is to automatically control the supply of working fluid (steam or fuel) so that the engine speed remains steady even when the load changes.

The Watt governor operates purely on the centrifugal force principle. As the engine shaft rotates, the balls attached to it also rotate. When the engine runs faster, the centrifugal force increases, causing the balls to move outward. This movement raises a central sleeve on the spindle, which reduces the fuel or steam supply to the engine. When the speed drops, the centrifugal force decreases, the balls move inward, the sleeve drops, and the fuel supply increases, thus balancing the speed.

Construction of Watt Governor

A Watt governor consists of the following main parts:

  1. Spindle (vertical shaft):
    A vertical spindle is driven by the engine through bevel gears. It rotates at a speed proportional to the engine speed.
  2. Balls (fly balls):
    Two equal masses, called governor balls, are attached to the arms of the governor. These balls rotate around the spindle and experience centrifugal force.
  3. Arms:
    The arms connect the balls to the spindle and the sleeve. They transmit the movement of the balls to the sleeve.
  4. Sleeve:
    A movable sleeve is mounted on the spindle. It moves up and down depending on the position of the balls. The sleeve is connected to the throttle valve or fuel control mechanism.
  5. Links and collar:
    These are used to connect the sleeve and arms and help in transmitting the vertical movement to the control mechanism.

Working of Watt Governor

The working of a Watt governor is based on changes in engine speed, which affect the centrifugal force acting on the rotating balls.

  • When engine speed increases:
    As the speed of the engine increases, the centrifugal force on the balls also increases. This force makes the balls move outward, lifting the arms and raising the sleeve upward along the spindle. The upward movement of the sleeve reduces the opening of the throttle valve, decreasing the fuel or steam supply to the engine. This reduction in supply causes the engine speed to decrease to its normal value.
  • When engine speed decreases:
    If the load on the engine increases, the speed decreases, reducing the centrifugal force acting on the balls. The balls move inward, lowering the arms and the sleeve. The downward movement of the sleeve increases the throttle opening, allowing more fuel or steam to enter. The engine speed increases again until it returns to the desired mean speed.

This automatic adjustment of the fuel supply helps maintain a nearly constant engine speed despite load variations.

Height of Watt Governor

The height (h) of a Watt governor is the vertical distance between the point of rotation of the arms on the spindle and the center of the balls. The height is related to the speed of rotation by the following equation:

where,

  •  = height in meters
  •  = speed in revolutions per minute (rpm)

This equation shows that the height of the governor decreases with an increase in engine speed.

Advantages of Watt Governor

  1. Simple in design and easy to construct.
  2. Works automatically without external power.
  3. Reliable and durable for low-speed applications.
  4. Provides smooth and stable control of engine speed.

Disadvantages of Watt Governor

  1. Suitable only for low-speed engines (below 200 rpm).
  2. Large in size and occupies more space.
  3. Not very sensitive to small speed changes.
  4. The controlling force is limited, reducing its effectiveness for high-speed engines.

Applications of Watt Governor

  • Used in early steam engines.
  • Found in small stationary engines and educational demonstration models.
  • Used for understanding the basic principle of centrifugal control mechanisms.
Conclusion:

The Watt governor is the most basic and classic type of centrifugal governor that operates on the principle of centrifugal force. It was the first mechanical device designed to control engine speed automatically by adjusting the fuel or steam supply. Although it is simple and reliable, its application is limited to low-speed engines because of low sensitivity and large size. Despite its limitations, it laid the foundation for more advanced governor designs like Porter, Proell, and Hartnell governors used in modern engines.