a switchbox for monitoring the position of a manual quarter - turn valve has a housing mountable to the valve to be monitored / controlled . a handle - driven shaft extends through the housing , with one end of the shaft couplable to the valve stem such that movement of the shaft moves the valve stem . one or more shaft position sensor switches interact with a cam on the shaft to signal shaft position and / or provide control signals . a plate coupled to the shaft articulates within a recess on the surface of the switchbox to limit motion of the valve to an operable range , such as between full on and full off . the switchbox has a pair of lock tabs with lock apertures . a lock aperture in the plate is alignable with the lock tab apertures to receive a pin or padlock for locking the valve in a selected position . a potentiometer can be utilized in place of a switch as a shaft position sensor . the switchbox may be used with an original or new handle and may feature detents to allow a range of valve settings .