Watt Governor:

This governor was utilized by James Watt in his steam engine. The spindle is driven through the output shaft of the prime mover. At the junction of the two arms the balls are mounted. The upper are linked to the spindle and lower arms are linked to the sleeve as illustrated in Figure (a).

                  (a)                                         (b)

                                               Watt Governor

We avoid mass of the sleeve, lower and upper arms for simplicity of analysis. We might avoid the friction also. This ball is subjected to the three forces that are centrifugal force (F_c), weight (m_g) and tension by upper arm (T). Taking moment around point O (intersection of arm and spindle axis), we obtain the following

                                                            F_C  h - m_g r = 0

 Since,                                                 F_C  = m_r ω²

                                                        m_r ω² h - m_g r = 0

                                                                 ω² = g/ h                                                  . . (12.1)

                                                                ω= 2π N/60

                              . . . (12.2)

here 'N' is in rpm.

Given figure shows a graph among height 'h' and speed 'N' in rpm. At high speed the modification in height h is extremely small that indicates that the sensitiveness of the governor is very weak at high speeds as flatness of the curve at higher speeds.