Abstract: A control device processes or agricultural sprayer. A slip member biased by a retaining member and springs to an initial neutral position produces a signal by a sensor upon initiation or cessation of angular forces from rotation of a machine driven shaft. The signal is caused by movement of the slip member from friction produced by an impeller situated within the grease filled slip member. The impeller is coupled directly or indirectly to the machine driven shaft and rotates upon rotation of the shaft. Upon initiation of angular forces on the impeller, the signal produced may cause a valve on an agricultural sprayer to open and initiate spraying therefrom. Upon cessation of angular forces on the impeller, the valve may be closed to turn off the spraying.