The Porter governor is a modification of a Watt’s governor, with central load attached to the sleeve as shown in Fig. 5.3 (a). The load moves up and down the central spindle. This additional downward force increases the speed of revolution required to enable the balls to rise to any predetermined level. Consider the forces acting on one-half of the governor as shown in Fig. 6.3 (b).

**Fig. 5.3.**

Let m = Mass of each ball in kg,

w = Weight of each ball in newtons = m.g, M = Mass of the central load in kg,

W = Weight of the central load in newtons = M.g,

r = Radius of rotation in metres, h = Height of governor in metres , N = Speed of the balls in r.p.m .,

T1 = Force in the arm in newtons,

T2 = Force in the link in newtons,

Though there are several ways of determining the relation between the height of the governor (h) and the angular speed of the balls (ω), yet the following two methods are important from the subject point of view :

**1.**** **Method of resolution of forces ; and

**2.**** **Instantaneous centre method.

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