Governors (Mechanism)

Introduction

Governors are automatic devices that regulate the speed of an engine by altering the rate of flow of its working fluid, that is, fuel. If the engine is loaded or if there is an increase in load, this would cause the speed of the engine  to decrease. The governor would react by operating the mechanism that operates the supply valve. This leads to an increase to fuel supply and thus increase in engine speed bringing the engine to its initial original speed. Hence, the function of a governor is to maintain the engine speed within certain limits irrespective of the load[1][2][3].

Types

Governors are classified thus:

  1. Inertia and flywheel governors: this is type of governor in which inertia predominates. This means it works with principle of resistance to motion. These types of governors are fitted to the crankshaft or flywheel. Their design and appearance differ from the centrifugal governors. They have balls arranged in such a way that the force of inertia alters their position when the shaft is accelerated or decelerated. Springs controls the amount of displacement of the balls and this in turn regulate the fuel supply. The inertia governor is very sensitive than the centrifugal governor however balancing the revolving parts is extremely difficult. This makes it less popular in engines.flywheel-governor
  2. Centrifugal governors: this can be further classified as (i) gravity controlled; this is the type of governor which gravity is the major force which balances the balls as they revolve (ii) Spring controlled governors are those in which springs balances the centrifugal force.

Centrifugal governors are more popular in engines because it easier to balance the weights. The following  important types centrifugal governors would be discussed further, this include; watt governor, Porter governor, Proell governor and Hartnell governor[1].

(a) Watt Governor: This was invented by James Watt and used on the very types of steam engines. It works in engines designed for slow movements and it is not longer in use.

It consists of two arms which are hinged at the top of the spindle and two balls are attached on the other end. Two links are hinged with the arms and the other end hinged with the sleeve. The sleeve slides over the spindle. The rotation of the spindle is via bevel gears from the crankshaft. The revolution of the spindle causes the weights to spread out due to centrifugal force. This causes the sleeve to move upward. The movement of the sleeve is then transmitted by means of a lever which partly closes or opens the steam pipe and this in turn reduces or increases the supply of steam to the engine. Thus the speed of the engine is adjusted.

(b) Porter Governor

This comprises of two or more governor balls rotating about the axis of the governor shaft which is driven through suitable gears from the crankshaft. The balls are hinged to the upper and lower arms. The other end of the lower arm is attached to the sleeve which act as the central weight. If load is placed on the engines, the speed of the engine decreases, the balls would fly inwards and the sleeve moves downward and opens the fuel valve for more fuel to flow in and thus increase the speed of the engine. On the other hand, if load is removed from the engine, the speed of the engine increases and the balls would fly outwards, this in turn would cause the sleeve to move upward, thus reducing fuel flow until the speed of engine returns to its designed speed. The design speed of the engine is the speed when the outward inertia or centrifugal force is just balanced by the inward controlling force.

porter-governor

(c) Proell Governor

This is similar to the Porter governor. The balls are placed on an extension of the lower arms. For a given weight of ball, sleeve and height of governor, a Proell governor runs at a lower speed

proell-governor.

(d) Hartnell Governor

This governor operates by the use of springs. It has a case attached to the spindle. Inside the casing is a compressed spring that presses against the top of the casing and adjustable collars. The sleeve moves up and down in response to the speed of the governor. The balls are placed on the bell crank lever which is hinged to the lower end of the casing. Increase or decrease in speed of the governor causes the ball to fly outward or inward respectively.

Uses and Application

Used in petrol engines, diesel engines.

Reference

[1]R.K., Rajput. Thermal Engineering. Delhi : Laxmi Publications (P) LTD, 2009. 9788131805954.

[2] Governor (mechanics).” Microsoft® Student 2009 [DVD]. Redmond, WA: Microsoft Corporation, 2008.

[3] governor.” Encyclopædia Britannica. Encyclopaedia Britannica Student and Home Edition.  Chicago: Encyclopædia Britannica, 2010

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