8. Figure shown
represents a schematic
diagram of a Porter
governor. Each fly ball
weighs 16.1 lb and the
central weight D is 40 lb.
Determine the rotational
speed in rpm about the
vertical axis AD at which
the weight D begins to
Given : BP = BD = 250 mm ; m = 5 kg ; M = 30 kg ; r1 = 150 mm ; r2 = 200 mm
Minimum and maximum speed of the governor
The minimum and maximum position of the governor is shown in Fig. 1 (a) and (b) respectively. N1 = Minimum speed when r1 = BG = 150 mm,
and N2 = Maximum speed when r2 = BG = 200 mm.
To find Speed range of the governor
Referring Fig. 1 (a), height of the governor,
Referring fig. 1 (b) height of the governor,
Speed range when friction at the sleeve is equivalent of 20 N of load (i.e. when F = 20 N). When the sleeve moves downwards, the friction force (F) acts upwards and the minimum speed is given by
We also know that when the sleeve moves upwards, the frictional force (F) acts downwards and the maximum speed is given by
Speed range of the governor = N2 – N1= 210 – 172 = 38 rpm.